No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Biomechanical Analysis of an Interspinous Process Fixation Device with In Situ Shortening Capabilities: Does Spinous Process Compression Improve Segmental Stability?
Abstract
Study design:
In-vitro cadaveric biomechanical study STUDY OBJECTIVE: The objective of this study was to characterize the biomechanical implications of spinous process compression, via in-situ shortening of a next-generation interspinous process fixation (ISPF) device, in the context of segmental fusion.
Methods:
Seven lumbar cadaveric spines (L1-L4) were tested. Specimens were first tested in an intact state, followed by iterative instrumentation at L2/3 and subsequent testing. Order: 1) stand-alone ISPF (neutral height); 2) stand-alone ISPF (shortened in-situ from neutral height; 'shortened'); 3) lateral interbody cage ('LLIF')+ISPF (neutral); 4) LLIF+ISPF (shortened); 5) LLIF+unilateral pedicle screw fixation (PSF); 6) LLIF+bilateral PSF. A 7.5Nm moment was applied in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) via a kinematic test frame. Segmental range-of-motion (ROM) and lordosis were measured for all constructs. Comparative analysis was performed.
Results:
Statistically significant FE ROM reductions: all constructs vs. intact condition (p<0.01); LLIF+ISPF (neutral & shortened) vs. stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+USPF vs. ISPF (neutral) (p=0.049); BPSF vs. stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+BPSF vs. LLIF+UPSF (p<0.01). Significant LB ROM reductions: LLIF+ISPF (neutral & shortened) vs. intact condition & stand-alone ISPF (neutral) (p<0.01); LLIF+UPSF vs. intact condition & stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+BPSF vs. intact condition & all constructs (p<0.01). Significant AR ROM reductions: LLIF+ISPF (shortened) & LLIF+UPSF vs. intact condition & stand-alone ISPF (neutral) (p≤0.01); LLIF+BPSF vs. intact condition & all constructs (p≤0.04).
Conclusion:
In-situ shortening of an adjustable ISPF device may support increased segmental stabilization in comparison to static ISPF.
ResearchGate has not been able to resolve any citations for this publication.
OBJECTIVE
Lateral lumbar interbody fusion (LLIF) has emerged as a popular method for lumbar fusion. In this study the authors aimed to quantify the biomechanical stability of an interbody implant inserted using the LLIF approach with and without various supplemental fixation methods, including an interspinous plate (IP).
METHODS
Seven human cadaveric L2–5 specimens were tested intact and in 6 instrumented conditions. The interbody implant was intended to be used with supplemental fixation. In this study, however, the interbody was also tested without supplemental fixation for a relative comparison of these conditions. The instrumented conditions were as follows: 1) interbody implant without supplemental fixation (LLIF construct); and interbody implant with supplemental fixation performed using 2) unilateral pedicle screws (UPS) and rod (LLIF + UPS construct); 3) bilateral pedicle screws (BPS) and rods (LLIF + BPS construct); 4) lateral screws and lateral plate (LP) (LLIF + LP construct); 5) interbody LP and IP (LLIF + LP + IP construct); and 6) IP (LLIF + IP construct). Nondestructive, nonconstraining torque (7.5 Nm maximum) induced flexion, extension, lateral bending, and axial rotation, whereas 3D specimen range of motion (ROM) was determined optoelectronically.
RESULTS
The LLIF construct reduced ROM by 67% in flexion, 52% in extension, 51% in lateral bending, and 44% in axial rotation relative to intact specimens (p < 0.001). Adding BPS to the LLIF construct caused ROM to decrease by 91% in flexion, 82% in extension and lateral bending, and 74% in axial rotation compared with intact specimens (p < 0.001), providing the greatest stability among the constructs. Adding UPS to the LLIF construct imparted approximately one-half the stability provided by LLIF + BPS constructs, demonstrating significantly smaller ROM than the LLIF construct in all directions (flexion, p = 0.037; extension, p < 0.001; lateral bending, p = 0.012) except axial rotation (p = 0.07). Compared with the LLIF construct, the LLIF + LP had a significant reduction in lateral bending (p = 0.012), a moderate reduction in axial rotation (p = 0.18), and almost no benefit to stability in flexion-extension (p = 0.86). The LLIF + LP + IP construct provided stability comparable to that of the LLIF + BPS. The LLIF + IP construct provided a significant decrease in ROM compared with that of the LLIF construct alone in flexion and extension (p = 0.002), but not in lateral bending (p = 0.80) and axial rotation (p = 0.24). No significant difference was seen in flexion, extension, or axial rotation between LLIF + BPS and LLIF + IP constructs.
CONCLUSIONS
The LLIF construct that was tested significantly decreased ROM in all directions of loading, which indicated a measure of inherent stability. The LP significantly improved the stability of the LLIF construct in lateral bending only. Adding an IP device to the LLIF construct significantly improves stability in sagittal plane rotation. The LLIF + LP + IP construct demonstrated stability comparable to that of the gold standard 360° fixation (LLIF + BPS).
OBJECT
Insufficient biomechanical data exist from comparisons of the stability of expandable lateral cages with that of static transforaminal lumbar interbody fusion (TLIF) cages. The purpose of this biomechanical study was to compare the relative rigidity of L4–5 expandable lateral interbody constructs with or without additive pedicle screw fixation with that of L4–5 static TLIF cages in a novel cadaveric spondylolisthesis model.
METHODS
Eight human cadaver spines were used in this study. A spondylolisthesis model was created at the L4–5 level by creating 2 injuries. First, in each cadaver, a nucleotomy from 2 channels through the anterior side was created. Second, the cartilage of the facet joint was burred down to create a gap of 4 mm. Light-emitting-diode tracking markers were placed at L-3, L-4, L-5, and S-1. Specimens were tested in the following scenarios: intact model, bilateral pedicle screws, expandable lateral 18-mm-wide cage (alone, with unilateral pedicle screws [UPSs], and with bilateral pedicle screws [BPSs]), expandable lateral 22-mm-wide cage (alone, with UPSs, and with BPSs), and TLIF (alone, with UPSs, and with BPSs). Four of the spines were tested with the expandable lateral cages (18-mm cage followed by the 22-mm cage), and 4 of the spines were tested with the TLIF construct. All these constructs were tested in flexion-extension, axial rotation, and lateral bending.
RESULTS
The TLIF-alone construct was significantly less stable than the 18- and 22-mm-wide lateral lumbar interbody fusion (LLIF) constructs and the TLIF constructs with either UPSs or BPSs. The LLIF constructs alone were significantly less stable than the TLIF construct with BPSs. However, there was no significant difference between the 18-mm LLIF construct with UPSs and the TLIF construct with BPSs in any of the loading modes.
CONCLUSIONS
Expandable lateral cages with UPSs provide stability equivalent to that of a TLIF construct with BPSs in a degenerative spondylolisthesis model.
Purpose:
The minimally invasive transforaminal lumbar interbody fusion procedure with percutaneous pedicle screws was adopted in clinical practice, but the choice between a unilateral pedicle screw (UPS) or bilateral pedicle screw (BPS) fixation after lumbar fusion remains controversial. The purpose of the present retrospective study was to compare the clinical outcomes and radiological results of unilateral and bilateral pedicle screw fixations.
Methods:
The retrospective study recruited seventy-eight patients with a single-level pedicle screw fixation and lumbar interbody fusion at L4-L5 or L5-S1 from January 2010 to January 2013. The patients were treated with MIS TLIF with BPS fixation, and since May 2012, all patients were treated with UPS fixation. The perioperative outcomes including operative time, blood loss, hospital-stay length, and complication rates were accessed. Radiological outcomes regarding fusion were determined with the Bridwell grading system. Clinical outcomes were evaluated with the Oswestry Disability Index (ODI) and visual analog scale (VAS) during the mean follow-up of 2 years.
Results:
According to perioperative assessments, the operative time was significantly shorter for group UPS (84.7 ± 6.4 min) than for group BPS (103.6 ± 10.6 min; p < 0.0001), and similar results were found with regard to the mean blood loss (UPS, 96.3 ± 17.5; BPS, 137.4 ± 32.9, p < 0.0001). With regard to the hospital-stay period, though the UPS group seems shorter, there is no statistical significance (UPS, 10.0 ± 2.1; BPS, 10.4 ± 2.4, p = 0.428). There were four in the BPS group and six in the UPS group defined as unfused at 6 months pest-operative, but at 12 months post-surgery, all patients achieved solid fusion. Regarding clinical outcomes, the VAS and ODI scores were significantly lower in the UPS group than the BPS group at 7 days post-surgery, but there was no difference at 1 month post-surgery and during the later follow-up.
Conclusion:
There was no difference between the UPS and BPS flexion techniques about the clinical outcomes at 24 months post-surgery. However, because the UPS involves a shorter surgical time, less blood loss, faster pain relief, and faster functional recovery, UPS might be more suitable in performing single-segment pedicle screw fixation and lumbar interbody fusion.
We present a novel, minimally invasive, navigation-guided approach for surgical treatment of degenerative spondylolisthesis (DS) that is a hybrid of the two most common techniques, posterior interbody fusion (PLIF) and transforaminal interbody fusion (TLIF). DS is an acquired condition with intersegmental instability of one or more lumbar motion segments. Seven patients with single level lumbar DS underwent lumbar arthrodesis utilizing the hybrid technique (HLIF) in our center. Using a standard unilateral midline approach a decompression and partial facetectomy on one side was performed, allowing for implantation of a specially designed interbody cage. Pedicle screws were placed using neuronavigation in a vertical vector on the side of the partial facetectomy and dorsolaterally (percutaneous) on the contralateral side. Patient and operative data, numeric rating scale (NRS) pain scores, core outcome measures index (COMI) and Oswestry disability index (ODI) were recorded preoperatively as well as 6 weeks, 3months, 6months and 1year after surgery. All patients completed the 1year follow-up. There was significant postoperative improvement of NRS, COMI and ODI scores at all postoperative follow-up time points (p<0.05). The radiological assessments of realignment showed a reduction of listhesis from an average of 21.04% (standard deviation [SD] 5.1) preoperatively to 9.14% (SD 4.0) postoperatively (p<0.001). The average blood loss was 492ml. Post-procedure CT scans demonstrated correct implant placement in all but one patient who required a revision of a single pedicle screw. HLIF allows thorough decompression as well as realignment and interbody fusion for patients with DS and may help reduce tissue trauma in comparison to other minimally invasive lumbar fusion techniques.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Application of minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is limited by long fluoroscopy time and a steep learning curve. Herein, MI-TLIF was modified using a trans-multifidus approach, assisted by microscope, termed MMI-TLIF, and the clinical outcomes of MMI-TLIF and open-TLIF were compared.
Forty-nine patients treated with MMI-TLIF were matched with 49 subjects who underwent open-TLIF. Patients were assessed using the North American Spine Society Score (NASS), Oswestry Disability Index (ODI), Short Form-36 (SF-36), and Visual Analogue Score (VAS) before surgery and during follow-up (6 months and 2 years). The four-type Bridwell anterior fusion grading system was used to evaluate fusion rates at 2 years.
The median fluoroscopic time did not differ significantly between the MMI-TLIF and open-TLIF groups. MMI-TLIF surgery took significantly longer than open-TLIF (91.3 vs. 82.5 min; P < 0.05). Meanwhile, MMI-TLIF patients lost significantly less blood than open-TLIF patients (75.3 vs. 215.2 ml; P < 0.05), and MMI-TLIF patients were hospitalized for less long than open-TLIF patients (3.7 vs. 6.9 days; P < 0.05) and reported less pain, faster ambulation, and lower morphine intake than open-TLIF patients (all P < 0.05). The NASS, ODI, VAS, and SF-36 scores were significantly improved 6 months and 2 years postsurgery in both groups, compared with preoperative values, and similar values were obtained for both groups. Finally, fusion rates were similar in MMI-TLIF and open-TLIF patients.
Overall, these findings strongly suggest the superiority of MMI-TLIF to open-TLIF. Therefore, MMI-TLIF could be a safe and effective alternative to MI-TLIF and open-TLIF.
Lumbar fusion has been found to be a clinically effective procedure in adult patients. The lateral transpsoas approach allows for direct visualization of the intervertebral space, significant support of the vertebral anterior column, while avoiding the complications associated with the posterior procedures. The aim of this study is to determine the fusion rate of inter body fusion using computed tomography in patients treated by extreme lateral intersomatic fusion (XLIF) technique.
All patients intervened by XLIF procedure between 2009 and 2013 by a single operating team at a single institution were recruited for this study. A clinical evaluation and a CT scan of the involved spinal segments were then performed with at least 1-year follow-up following the standard clinical practice in the center.
A total of 77 patients met inclusion criteria, of which 53 were available for review with a mean follow-up of 34.5 (12-62) months. A total of 68 (87.1 %) of the 78 operated levels were considered as completely fused, 8 (10.2 %) were considered as stable, probably fused, and 2 (2.6 %) of the operated levels were diagnosed as pseudarthrosis. When stratified by type of graft material complete fusion was obtained in 75 % of patients in which autograft was used to fill the cages, compared to 89 % of patients in which calcium triphosphate was used, and 83 % of patients in which Attrax™ was used.
Reports of XLIF fusion rate in the literature vary from 85 to 93 % at 1-year follow-up. Fusion rate in our series corroborates data from previous publications. The results of this series confirm that anterior inter body fusion by means of XLIF approach is a technique that achieves high fusion rate and satisfactory clinical outcomes.
Early interspinous process fixation constructs utilize rigid fixation plates with immobile spikes which increase the difficulty of device implantation when anatomic variations are encountered. Second generation systems have been designed with polyaxial properties with the goal of accommodating natural osseous anatomic variations to achieve optimal implant placement and fixation integrity. The purpose of this study was to evaluate clinical outcomes in patients treated with this device to supplement the biomechanical data from previous studies.
A retrospective, non-randomized, single-center chart review at or beyond the one year postoperative time point was conducted to collect preoperative and perioperative data on patients treated with a polyaxial intraspinous fixation system. A postoperative numerical pain rating scale and modified MacNab classification score were obtained from each patient in the cohort via phone survey.
A total of 53 patients were included in the study. Median hospital stay was 2 days (range 1-7 days). There were no reported perioperative blood transfusions or cases of radiographic fracture/migration of the device at the 6 week post-operative time point. There was a significant improvement in pain index score in the overall patient study group and a satisfactory (excellent or good) MacNab result was obtained in 48% of all patients. Patients with preoperative pain scores greater than 8/10 reported more pain improvement than patients with preoperative pain scores less than 5 (0 points, p = 0.96, n = 8). Patients with a BMI less than 30 had significantly better MacNab outcome classifications than patients with a BMI greater than 30.
The polyaxial interspinous fusion system produces significant clinical improvement when employed to treat patients with stenosis, herniated disc, or low grade spondylolisthesis. This device can be implanted with a low complication rate and short postoperative hospital admission time. Patients with high pre-operative pain score and BMI under 30 can be predictors of better clinical outcome and should be considered prior to implantation.
Purpose:
Purpose of this paper is to evaluate the primary stability of a new approach for facet fixation the so-called Facet Wedge (FW) in comparison with established posterior fixation techniques like pedicle screws (PS) and translaminar facet screws (TLS) with and without anterior cage interposition.
Methods:
Twenty-four monosegmental fresh frozen non-osteoporotic human motion segments (L2-L3 and L4-L5) were tested in a two-arm biomechanical study using a robot-based spine tester. Facet Wedge was compared with pedicle screws and translaminar screws as a stand-alone device and in combination with an anterior fusion cage.
Results:
Pedicle screws, FW and translaminar screws could stabilize an intact motion segment effectively. Facet Wedge was comparable to PS for lateral bending, extension and flexion and slightly superior for axial rotation. Facet Wedge showed a superior kinematic capacity compared to translaminar screws.
Conclusions:
Facet Wedge offers a novel posterior approach in achieving primary stability in lumbar spinal fixation. The results of the present study showed that the Facet Wedge has a comparable primary stability to pedicle screws and potential advantages over translaminar screws.
Background:
Transforaminal lumbar interbody fusion (TLIF) has been used in lumbar degenerative diseases. Some researchers have applied unilateral fixation in TLIF to reduce operational trauma without compromising the clinical outcome, but it is always suspected biomechanically unstable. The supplementary contralateral translaminar facet screw (cTLFS) seemed to be able to overcome the inherent drawbacks of unilateral pedicle screw (uPS) fixation theoretically. This study evaluates the safety, feasibility and efficacy of TLIF using uPS with cTLFS fixation in the treatment of lumbar degenerative diseases (LDD).
Materials and Methods:
50 patients (29 male) underwent the aforementioned surgical technique for their LDD between December 2009 and April 2012. The results were evaluated based on visual analogue scale (VAS) of the leg and back, Japanese Orthopedic Association (JOA) score and Oswestry Disability Index (ODI) were recorded. The radiographic examinations in form of X-ray, computed tomography (CT) or magnetic resonance imaging was done preoperatively and 1 week, 3 months, 6 months, 12 months and 24 months postoperatively. The student t-test was used for comparison between the preoperative values and postoperative counterparts. P < 0.05 was considered to be statistically significant.
Results:
Among 50 patients, 22 received one level fusion and 28 two level's, with corresponding operation time and estimated blood loss being approximately 90 min, 150 ml and 120 min, 200 ml, respectively. No severe complications happened perioperatively. The mean VAS (back, leg) scores dropped from (7.6, 7.5) preoperatively to (2.1, 0.6) at 12 months’ followup, ODI from 49.1 preoperatively to 5.6 and JOA score raised from 10.6 preoperatively to 28.5, all P < 0.001, suggesting of good clinical outcome. From the three-dimensional reconstructed CT, 62 out of 70 segments displayed solid fusion with fusion rate of 88.6% at 12 months postoperatively.
Conclusions:
TLIF using uPS fixation plus cTLFS fixation is a safe, feasible and effective technique in the treatment of one or two level lumbar degenerative diseases short termly.
Posterior lumbar interbody fusion (PLIF) and internal fixation are commonly performed for the treatment of lower back pain due to lumbar spinal degeneration. We have developed a novel interspinous fixation device, the interspinous fastener (ISF) for potential use in the surgical management of degenerative spinal disease. The aim of this study was to assess the in vitro biomechanical characteristics of calf lumbar spine specimens after ISF fixation with modified PLIF.
Ten lumbar spine (L3-L6) specimens from ten fresh calf cadavers (8-10 weeks of age) were used. Each specimen underwent sequential testing for each of the following four groups: no instrumentation (INTACT); interspinous fusion device fixation + PLIF (ISF); unilateral pedicle screw and titanium rod fixation + PLIF (UPS); bilateral pedicle screw and titanium rod fixation + PLIF (BPS). Outcome measures included angular range of motion (ROM) during unloaded and loaded (8 Nm) flexion, extension, left bending, right bending, left torsion and right torsion.
For all unloaded and loaded assessments, ROM was significantly higher in the INTACT group compared with all other groups (P < 0.05). Similarly, ROM was significantly higher in the UPS group (indicating decreased stability) compared with the ISF and BPS groups (P < 0.05). The only significant difference between the ISF and BPS groups was in the ROM with unloaded extension (higher in the BPS group, P = 0.006).
We found that ISF fixation with PLIF of the lower lumbar spine provided biomechanical stability that was equivalent to that associated with bilateral pedicle screw/rod fixation with PLIF. The ISF shows potential as an alternative means of fixation in the surgical management of degenerative spinal disease.
Object:
Through in vitro biomechanical testing, the authors compared the performance of a vertically expandable lateral lumbar interbody cage (EC) under two different torque-controlled expansions (1.5 and 3.0 Nm) and with respect to an equivalent lateral lumbar static cage (SC) with and without pedicle screw fixation.
Methods:
Eleven cadaveric human L2-3 segments were evaluated under the following conditions: 1) intact; 2) discectomy; 3) EC under 1.50 Nm of torque expansion (EC-1.5Nm); 4) EC under 3.00 Nm of torque expansion (EC-3.0Nm); 5) SC; and 6) SC with a bilateral pedicle screw system (SC+BPSS). Load-displacement behavior was evaluated for each condition using a combination of 100 N of axial preload and 7.5 Nm of torque in flexion and extension (FE), lateral bending (LB), and axial rotation (AR). Range of motion (ROM), neutral zone stiffness (NZS), and elastic zone stiffness (EZS) were statistically compared among conditions using post hoc Wilcoxon signed-rank comparisons after Friedman tests, with a significance level of 0.05. Additionally, any cage height difference between interbody devices was evaluated. When radiographic subsidence was observed, the specimen's data were not considered for the analysis.
Results:
The final cage height in the EC-1.5Nm condition (12.1 ± 0.9 mm) was smaller (p < 0.001) than that in the EC-3.0Nm (13.9 ± 1.1 mm) and SC (13.4 ± 0.8 mm) conditions. All instrumentation reduced (p < 0.01) ROM with respect to the injury and increased (p ≤ 0.01) NZS in flexion, extension, and LB as well as EZS in flexion, LB, and AR. When comparing the torque expansions, the EC-3.0Nm condition had smaller (p < 0.01) FE and AR ROM and greater (p ≤ 0.04) flexion NZS, extension EZS, and AR EZS. The SC condition performed equivalently (p ≥ 0.10) to both EC conditions in terms of ROM, NZS, and EZS, except for EZS in AR, in which a marginal (p = 0.05) difference was observed with respect to the EC-3.0Nm condition. The SC+BPSS was the most rigid construct in terms of ROM and stiffness, except for 1) LB ROM, in which it was comparable (p = 0.08) with that of the EC-1.5Nm condition; 2) AR NZS, in which it was comparable (p > 0.66, Friedman test) with that of all other constructs; and 3) AR EZS, in which it was comparable with that of the EC-1.5Nm (p = 0.56) and SC (p = 0.08) conditions.
Conclusions:
A 3.0-Nm torque expansion of a lateral interbody cage provides greater immediate stability in FE and AR than a 1.5-Nm torque expansion. Moreover, the expandable device provides stability comparable with that of an equivalent (in size, shape, and bone-interface material) SC. Specifically, the SC+BPSS construct was the most stable in FE motion. Even though an EC may seem a better option given the minimal tissue disruption during its implantation, there may be a greater chance of endplate collapse by over-distracting the disc space because of the minimal haptic feedback from the expansion.
Study Design Retrospective clinical study.
Objectives Recent biomechanical studies have shown no differences in stiffness or range of motion following minimally invasive (MIS) transforaminal lumbar interbody fusion (TLIF) between unilateral pedicle and contralateral facet screw (UPFS) and bilateral pedicle screw (BPS) constructs. No studies have compared these two constructs based upon clinical outcomes.
Methods Twenty-six consecutive patients who had single-level MIS TLIF were retrospectively reviewed. Outcome measures collected for patients with BPS were compared with those with UPFS.
Results No associations were found between construct and length of stay (p = 0.5), operative time (p = 0.2), or Odom's criteria (p = 0.7); 79% of patients in the UPFS group as compared with 71.5% in the BPS group had good or excellent outcomes. Mean follow-up was 17.7 months for the UPFS group and 20.2 months for the BPS group. There was one complication in each group, including a seroma in the BPS group and a revision operation in the UPFS group. Implant costs for the BPS group were 35% greater than the UPFS group.
Conclusions The present study is the first to demonstrate that patients undergoing MIS TLIF with BPS as compared with UPFS for single-level degenerative lumbar disease had similar clinical outcomes.
Object:
Lumbar interbody fusion is indicated in the treatment of degenerative conditions. Laterally inserted interbody cages significantly decrease range of motion (ROM) compared with other cages. Supplemental fixation options such as lateral plates or spinous process plates have been shown to provide stability and to reduce morbidity. The authors of the current study investigate the in vitro stability of the interbody cage with a combination of lateral and spinous process plate fixation and compare this method to the established bilateral pedicle screw fixation technique.
Methods:
Ten L1-5 specimens were evaluated using multidirectional nondestructive moments (± 7.5 N · m), with a custom 6 degrees-of-freedom spine simulator. Intervertebral motions (ROM) were measured optoelectronically. Each spine was evaluated under the following conditions at the L3-4 level: intact; interbody cage alone (stand-alone); cage supplemented with lateral plate; cage supplemented with ipsilateral pedicle screws; cage supplemented with bilateral pedicle screws; cage supplemented with spinous process plate; and cage supplemented with a combination of lateral plate and spinous process plate. Intervertebral rotations were calculated, and ROM data were normalized to the intact ROM data.
Results:
The stand-alone laterally inserted interbody cage significantly reduced ROM with respect to the intact state in flexion-extension (31.6% intact ROM, p < 0.001), lateral bending (32.5%, p < 0.001), and axial rotation (69.4%, p = 0.002). Compared with the stand-alone condition, addition of a lateral plate to the interbody cage did not significantly alter the ROM in flexion-extension (p = 0.904); however, it was significantly decreased in lateral bending and axial rotation (p < 0.001). The cage supplemented with a lateral plate was not statistically different from bilateral pedicle screws in lateral bending (p = 0.579). Supplemental fixation using a spinous process plate was not significantly different from bilateral pedicle screws in flexion-extension (p = 0.476). The combination of lateral plate and spinous process plate was not statistically different from the cage supplemented with bilateral pedicle screws in all the loading modes (p ≥ 0.365).
Conclusions:
A combination of lateral and spinous process plate fixation to supplement a laterally inserted interbody cage helps achieve rigidity in all motion planes similar to that achieved with bilateral pedicle screws.
Minimally invasive lumbar spine fusion surgery has gained popularity in recent years. Routinely, this technique requires bilateral parasagittal incisions for decompression, interbody fusion, and posterior instrumentation. The following study is a description of a new minimally invasive technique for one-level transforaminal lumbar interbody fusion (TLIF) using a unilateral parasagittal incision (Wiltse approach), with placement of pedicle screws and then a percutaneous transpedicular facet screw insertion on the contralateral side. The biomechanical stability of this posterior construct will be discussed while the efficacy and complications of this technique have been examined.
Forty patients underwent this new technique of one-level TLIF with posterior instrumentation using unilateral pedicle screw fixation supplemented with contralateral percutaneous transpedicular facet screw construct. Data regarding surgical time, estimated blood loss (EBL), hospital length of stay (LOS), and complications related to the posterior instrumentation are recorded.
The average surgical time of this new procedure was 124 minutes; average EBL was 140 cc; average hospital LOS was 3 days. Two patients developed new leg pain on the side where the facet screw had been placed. Both patients had the facet screw removed.
This novel technique of unilateral pedicle screw fixation combined with contralateral percutaneous transpedicular facet screw construct has further reduced the amount of normal tissue injury while maintaining the same biomechanical advantages of bilateral pedicle screw fixation. However, caution is needed during the placement of the percutaneous facet screw in order to avoid nerve root injury.
This study investigates the biomechanical stability of a large interbody spacer inserted by a lateral approach and compares the biomechanical differences with the more conventional transforaminal interbody fusion (TLIF), with and without supplemental pedicle screw (PS) fixation. Twenty-four L2-L3 functional spinal units (FSUs) were tested with three interbody cage options: (i) 18 mm XLIF cage, (ii) 26 mm XLIF cage, and (iii) 11 mm TLIF cage. Each spacer was tested without supplemental fixation, and with unilateral and bilateral PS fixation. Specimens were subjected to multidirectional nondestructive flexibility tests to 7.5 N·m. The range of motion (ROM) differences were first examined within the same group (per cage) using repeated-measures ANOVA, and then compared between cage groups. The 26 mm XLIF cage provided greater stability than the 18 mm XLIF cage with unilateral PS and 11 mm TLIF cage with bilateral PS. The 18 mm XLIF cage with unilateral PS provided greater stability than the 11 mm TLIF cage with bilateral PS. This study suggests that wider lateral spacers are biomechanically stable and offer the option to be used with less or even no supplemental fixation for interbody lumbar fusion.
Lumbar spinal fusion is advancing with minimally invasive techniques, bone graft alternatives, and new implants. This has resulted in significant reductions of operative time, duration of hospitalization, and higher success in fusion rates. However, costs have increased as many new technologies are expensive. This study was carried out to investigate the clinical outcomes and fusion rates of a low implant load construct of unilateral pedicle screws and a translaminar screw in transforaminal lumbar interbody fusion (TLIF) which reduced the cost of the posterior implants by almost 50%. Nineteen consecutive patients who underwent single level TLIF with this construct were included in the study. Sixteen patients had a TLIF allograft interbody spacer placed, while in three a polyetheretherketone (PEEK) cage was used. Follow-up ranged from 15 to 54 months with a mean of 32 months. A clinical and radiographic evaluation was carried out preoperatively and at multiple time points following surgery. An overall improvement in Oswestry scores and visual analogue scales for leg and back pain (VAS) was observed. Three patients underwent revision surgery due to recurrence of back pain. All patients showed radiographic evidence of fusion from 9 to 26 months (mean 19) following surgery. This study suggests that unilateral pedicle screws and a contralateral translaminar screw are a cheaper and viable option for single level lumbar fusion.
Objectives:
This study sought to retrospectively compare three different posterior fixation techniques in transforaminal lumbar interbody fusion for two-level lumbar degenerative diseases.
Patients and methods:
This was a retrospective single-center study including 84 patients who underwent TLIF instrumented with unilateral pedicle screws (UPS), unilateral pedicle screws plus contra-lateral translaminar facet screws (UPSFS), or bilateral pedicle screws (BPS) between June 2008 and May 2012. These patients were divided into three groups: UPS (n=22), UPSFS (n=28) and BPS (n=34) group. Operative time, blood loss, length of hospital stay, hospital bill, fusion status and complications were recorded and analyzed statistically. Visual analog scale (VAS), Oswestry Disability Index (ODI), and Japanese Orthopaedic Association Scores (JOA) were used to assess the preoperative and postoperative pain and functional outcome. Sagittal aligment was evaluated by the segment lordosis (SL) and whole lumbar spine lordosis (LL).
Results:
The mean follow up duration was 46.2 (ranging from 36 to 60) months. A significant decrease occurred in operative time, blood loss and hospital bill in UPS and UPSFS group, compared with BPS group (p<0.05). The average postoperative VAS, ODI and JOA scores improved significantly in each group than the preoperative counterparts (p<0.05), however, there were no significant difference between groups at any follow-up time point (p>0.05). No statistically difference was detected regarding fusion rate and complication rate between groups (p>0.05), except the screw/rod failure rate (p<0.05). Radiographic analysis showed that the LLs in all these groups got improved (p<0.05) and the SLs maintained (p>0.05).
Conclusion:
UPS or UPSFS instrumented TLIF could achieve satisfactory mid-term clinical outcome comparable to BPS's, with less surgical time, less blood loss, and lower cost; UPS should be prudently performed for two-level cases in case of lower fusion rate, and cannulated screws should be replaced by stronger solid screws in UPSFS to reduce facet screw breakage.
This paper is to evaluate the efficacy and safety of transforaminal lumbar interbody fusion (TLIF) using unilateral pedicle screws along with contralateral translaminar facet joint screw (UPS+TFS) fixation in comparison with the method using bilateral pedicle screws fixation (BPS) in degenerative lumbar diseases.
Forty patients with single-level lumbar diseases were divided into two groups randomly. One group was treated by TLIF with BPS fixation while the other group was treated by the new technique with UPS+TFS fixation. The preoperative and postoperative ODI, JOA, VAPS scores, mean operation time, mean operation blood loss, fusion rate and complications were collected for comparison under two surgical methods. In terms of complications, only two cases of superficial infection in the BPS group and one case of urinary tract infection in the other group was found.
The mean operation time and blood loss was significantly less in UPS+TFS group than in BPS group. The preoperation and postoperative ODI, JOA and VAPS at the intervals of 6 weeks, 3, 6 months and 1 year between the BPS and UPS+TFS group showed no significant disparities. Only one patient in UPS+TFS group was not fused with pseudoarthrosis formation.
The clinical efficacy and safety of TLIF with UPS+TFS fixation were comparable to BPS fixation; however, the soft tissue injury and the corresponding operation cost were reduced with unilateral pedicle screw plus translaminar facet screw fixation.
Interbody fusion cages with integrated fixation components have become of interest due to their ability to provide enhanced post-operative stability and mitigate device migration. A recently approved anterior lumbar interbody fusion cage with integrated fixation anchors has yet to be compared in vitro to a standard polyetheretherketone cage when used in combination with an interspinous process clamp.
Twelve human cadaveric lumbar segments were implanted at L4-L5 with a Solus interbody cage (n=6) or standard polyetheretherketone cage (n=6) following Intact testing and discectomy. Each cage was subsequently evaluated in all primary modes of loading after supplementation with the following posterior constructs: interspinous process clamp, bilateral transfacet screws, unilateral transfacet screw with contralateral pedicle screws, and bilateral pedicle screws. Range of motion results were normalized to Intact, and a two-way mixed analysis of variance was utilized to detect statistical differences.
The Solus cage in combination with all posterior constructs provided significant fixation compared to Intact in all loading conditions. The polyetheretherketone cage also provided significant fixation when combined with all screw based treatments, however when used with the interspinous process clamp a significant reduction was not observed in lateral bending or axial torsion.
Interbody cages with integrated fixation components enhance post-operative stability within the intervertebral space, thus affording clinicians the potential to utilize less invasive methods of posterior stabilization when seeking circumferential fusion. Interspinous process clamps, in particular, may reduce peri-operative and post-operative comorbidities compared to screw based constructs. Further study is necessary to corroborate their effectiveness in vivo.
Copyright © 2015. Published by Elsevier Ltd.
The objective of the article was to: a) present results from a case cohort pilot study comparing stand-alone ALIF and TLIF and, b) review the literature on studies comparing the clinical outcome of stand-alone ALIF with posterior instrumentation including TLIF or PLIF, in patients with disabling low back pain resulting from degenerative disc disease. ALIF surgery has previously been linked with certain high risk complications and unfavorable long term fusion results. Newer studies suggest that stand-alone ALIF can possibly be advantageous compared to other types of posterior instrumented interbody fusion for a selected group of DDD patients. The methods and material consisted of a cohort pilot study of patients, with DDD treated with stand-alone ALIF or TLIF followed by a literature review conducted through a comprehensive PubMed database search of the English literature. Studies comparing stand-alone ALIF with posterior instrumented interbody fusion were selected and reviewed. Results from the pilot study, n=21, showed a reduced perioperative blood loss, shorter operative time and a trend towards better pain reduction and decreased use of opioid analgesics in patients undergoing stand-alone ALIF compared to posterior instrumented fusion with TLIF. The literature review included three studies, n=630. All three studies were retrospective cohort studies. The average patient follow-up was 2-years but with heterogeneous selected outcomes. Two of three articles documented significant advantages when using stand-alone ALIF on outcomes such as ODI, VAS, surgical time, blood loss and patient satisfaction. No study found stand-alone ALIF inferior in chosen outcomes including fusion. In conclusion the pilot study and the literature review, finds similar clinical outcomes and fusion rates after stand-alone ALIF and posterior interbody fusion. Stand-alone ALIF was associated with a shorter duration of surgery, less perioperative blood loss and a faster improvement post-operatively. Therefore stand-alone ALIF is a viable and important surgical option, which could be considered first choice as surgical treatment.
Copyright © 2015 Elsevier B.V. All rights reserved.
Minimally invasive transforaminal lumbar interbodyfusion (MI TLIF) is very popular in the United States.Two techniques are commonly used, based on either tubularor pedicle-screw-based retraction.
Sixty patients underwent MI TLIFbetween 2009 and 2012, using the tubular technique (43patients) or screw-based-retractor technique (17 patients).Perioperative parameters and 1-year outcomes were reviewed.
For the tubular technique, the average operative time,blood loss, and hospital stay were 189 min, 170 ml, and 3.37days, respectively. The visual analog scale (VAS) score improvedfrom 9.7 preoperatively to 2.6 at 1-year postoperatively. Therewere two incidental durotomies, none resulting in a CSF leak.There was one re-intervention for removal of a misplacedpedicle screw. For the screw-based-retractor technique, theaverage operative time, blood loss, and hospital stay were 223min, 257 ml, and 3.29 days, respectively. VAS improved from9.4 to 1.9. One patient who had an incidental durotomydeveloped a postoperative compressive hematoma with resultant cauda equina syndrome requiring re-intervention.There were no re-interventions for revision of instrumentation.Seven patients were lost at the 1-year visit. The fusion rateat 1-year was 100%.
Both techniques can be used with good results,but each technique offers distinct advantages and challengesthat can be tailored to individual patients.
Celsius.
Transforaminal lumbar interbody fusion with bilateral segmental pedicle screw fixation is a widely used and well-recognized technique that is performed to provide fixation and load-bearing capacity while restoring morphometric spine parameters and relieving symptoms in patients with degenerative disc disease. A supplemental interspinous process fixation plate (ISFP) as an adjunct to unilateral PS fixation allows for reduced invasiveness of this technique as compared to bilateral PS placement. The biomechanical comparison results have been previously reported, but the significance of these findings has not been studied in clinical settings.
A prospective cohort study with a supplemental retrospective chart review and radiographic analysis was performed. The patients were divided into two groups: surgeries that were performed using bilateral PS fixation (n=75) or unilateral PS fixation + ISFP (n=96). Lateral lumbar standing radiographs were used for pre- and postoperative foraminal height (FH), disc height (DH), segmental (SSA) and lumbar sagittal alignment (LSA) measurements. Standardized questionnaires were used to compare postoperative clinical outcomes.
The estimated blood loss, duration of procedure and the length of hospital stay were significantly lower for one- and two-level procedures in the unilateral PS + ISFP patient group. A statistically significant mean DH increase was observed in both groups. Regardless of this, a statistically significant FH loss was detected in the bilateral PS patient group (from 17.1 to 16.3 mm; 4.7% loss; P=0.04) compared to FH height loss in the unilateral PS + ISFP patient group that was not statistically significant (from 19.0 to 18.4 mm; 3.2% loss; P=0.1). The analysis of SSA, LSA, clinical outcomes and fusion rates did not demonstrate any statistically significant differences.
Significantly reduced surgical invasiveness was associated with unilateral PS + ISFP fixation, which represents the major advantage of this technique. Unilateral fixation was also associated with a slightly lower reduction in FH and was equally effective to bilateral PS fixation in regards to fusion rates, clinical and other radiographic outcomes studied.
Copyright © 2014 Elsevier Inc. All rights reserved.
Spinous process fixation (SPF) has gained attention as a less invasive option for lumbar fusion surgery. Minimally invasive techniques are of interest in an elderly population due to decreased surgical time and post-operative complications. Clinical outcomes and fusion rates have not been determined in a large cohort. Our objective was to describe significant predictors of visual analog scale (VAS), length of stay, blood loss, fusion rates, and complication rates for patients treated for degenerative lumbar spondolysis with ISP fixation with and without supplemental instrumentation. Charts were assessed for post-operative VAS vs. pre-operative VAS at: 1-3, >3-6, and >6-12 months. To control confounding variables, VAS scores were modeled as a repeated-measures linear-mixed-model. In a sub-cohort CT images were assessed for interspinous and interbody (IB) fusion. The images were reviewed by an independent radiologist to evaluate fusion status. Eighty-six SPF patients (91 levels, mean age 67 years) were identified. After determining the model, age and sex remained predictors of VAS. Adjusting for age and sex, patients saw a decrease of 3.6 VAS points from baseline to three months (95% CI: 2.9-4.4, p<0.0001) that was maintained over the six to 12 month follow-up period. A sub-cohort of 50 patients with CT scans were identified and assessed for ISP and IB fusion at a mean of 181 days postoperatively. Ninety-four percent of levels demonstrated ISP fusion. Sixty-one percent of solid ISP fusion patients also had an interbody cage, but this did not impact fusion rates. Eighty-six percent of these levels showed solid IB fusion (BSF-3). Of the four pseudoarthrosed levels, two had pedicle screw fixation, and two were IB and ISP fixation. Only two patients went on to re-exploration and explantation due to pain secondary to spinous process and/or lamina fracture. This elderly cohort treated with SPF demonstrated significant improvement in VAS with reliable fusion rates.
This investigation compares an interspinous fusion device with posterior pedicle screw system in a lateral lumbar interbody lumbar fusion.Methods
We biomechanically tested six cadaveric lumbar segments (L 1-L2) under an axial preload of 50 N and torque of 5 Nm in flexion-extension, lateral bending and axial rotation directions. We quantified range of motion, neutral zone/elastic zone stiffness in the following conditions: intact, lateral discectomy, lateral cage, cage with interspinous fusion, and cage with pedicle screws.FindingsA complete lateral discectomy and annulectomy increased motion in all directions compared to all other conditions. The lateral cage reduced motion in lateral bending and flexion/extension with respect to the intact and discectomy conditions, but had minimal effect on extension stiffness. Posterior instrumentation reduced motion, excluding interspinous augmentation in axial rotation with respect to the cage condition. Interspinous fusion significantly increased flexion and extension stiffness, while pedicle screws increased flexion/extension and lateral bending stiffness, with respect to the cage condition. Both posterior augmentations performed equivalently throughout the tests except in lateral bending stiffness where pedicle screws were stiffer in the neutral zone.InterpretationA lateral discectomy and annulectomy generates immediate instability in a spinal segment. Stand-alone lateral cages restore a limited amount of immediate stability, but posterior supplemental fixation provides additional stability. Both augmentations provide similar rigidity in a single level lateral fusion in-vitro model, but pedicle screws are more equipped for coronal stability. An interspinous fusion is a less invasive alternative than a pedicle screws and is potentially a conservative option for various interbody cage scenarios.
Stand-alone minimally invasive lateral transpsoas interbody fusion (MIS-LIF), without posterior instrumentation, is feasible because the technique does not necessitate the disruption of the stabilizing elements. The objectives of this study are to evaluate the efficacy and clinical outcomes of patients who underwent stand-alone lateral interbody fusion. A multicenter chart review was conducted to identify patients who underwent stand-alone MIS-LIF between 2008 and 2012. Patients were classified by spinal pathology (degenerative disc disease [DDD], spondylolisthesis [SL] and adult degenerative scoliosis [ADS]). Routine clinical follow-up was scheduled at 3, 6, and12months. Outcome measures included hospital length of stay, fusion rates, neurologic complications, integrity of construct and clinical outcome questionnaires (Visual Analog Scale [VAS] and Oswestry Disability Index [ODI]). A total of 59 patients met the inclusion criteria. The average age was 60years (range 31-86years). Spinal pathologies treated were DDD in 37 (63%), SL in four (7%) and ADS in 18 (30%) patients. Fusion rate was 93% of patients (95% of levels) at 12months. Two patients required re-operation. Mean hospital stay and follow-up were 3.3days (range 1-10) and 14.6months, respectively. The mean preoperative VAS and ODI were 69.1 and 51.8, respectively. VAS improved to 37.8 (p<0.0005). ODI improved to 31.8 (p<0.0005). Seventy percent of patients had grade 0 subsidence while 30% had grade I and grade II subsidence. Stand-alone MIS-LIF is viable option in a carefully selected patient population for both single and multilevel disease and shows significant improvement in health related quality of life.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Background context:
Lateral spacers (LSs) are the standard of care for a lateral lumbar interbody fusion. However, various types of fixation, such as bilateral pedicle screws (BPSs), unilateral pedicle screws (UPSs), bilateral facet screws (BFSs), and lateral plates (LPs) have been reported to increase the stability of LSs. The biomechanics of a novel lateral interbody implant, which is an interbody spacer with an integrated plate and two bone screws (lateral integrated plate-spacer [IPS-L]), has not been investigated yet.
Purpose:
To compare the biomechanical stability of IPS-L and LS with and without supplemental instrumentation.
Study design:
Human lumbar cadaveric study evaluating the biomechanical stability of an IPS-L.
Methods:
Each of the six (L2-L5) spines was sequentially tested in intact; IPS-L; IPS-L+UPS; IPS-L+BPS; IPS-L+BFS; LS+BFS; LS+UPS; LS+BPS; LS; and LS+LP, using a load-control protocol in which a ±8 Nm moment was applied, for three cycles each, in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Data results were obtained from the third cycle.
Results:
The IPS-L construct significantly reduced the range of motion (ROM) by 75% in FE, 70% in LB, and 57% in AR, compared with intact. Lateral integrated plate-spacer demonstrated similar biomechanical stability as LS+LP, and higher stability than the LS-alone construct, but the difference was not statistically significant.
Conclusions:
The IPS-L evaluated in the present study demonstrated equivalent biomechanical stability compared with standard lateral interbody fusion constructs. The addition of BPSs to the IPS-L showed significant reduction in ROM in FE, and the addition of BFSs showed significant reduction in ROM in FE and AR, compared with the integrated plate-spacer alone construct. The IPS-L with supplemental fixation may be a viable option for lateral interbody fusion. Long-term clinical studies are further required to confirm these results.
Study design:
In vitro cadaveric biomechanical study of lateral interbody cages and supplemental fixation in a degenerative spondylolisthesis (DS) model.
Objective:
To investigate changes in shear and flexion-extension stability of lateral interbody fusion constructs.
Summary of background data:
Instability associated with DS may increase postoperative treatment complications. Several groups have investigated DS in cadaveric spines. Extreme lateral interbody fusion (XLIF) cages with supplemental fixation have not previously been examined using a DS model.
Methods:
Seven human cadaveric L4-L5 motion segments were evaluated using flexion-extension moments to ±7.5 N·m and anterior-posterior (A-P) shear loading of 150 N with a static axial compressive load of 300 N. Conditions were: (1) intact segment, (2) DS simulation with facet resection and lateral discectomy, (3) standalone XLIF cage, (4) XLIF cage with (1) lateral plate, (2) lateral plate and unilateral pedicle screws contralateral to the plate (PS), (3) unilateral PS, (4) bilateral PS, (5) spinous process plate, and (6) lateral plate and spinous process plate. Flexion-extension range of motion (ROM) data were compared between conditions and with results from a previous study without DS simulation. A-P shear displacements were compared between conditions.
Results:
Flexion-extension ROM after DS destabilization increased significantly by 181% of intact ROM. With the XLIF cage alone, ROM decreased to 77% of intact. All conditions were less stable than corresponding conditions with intact posterior elements except those including the spinous process plate. Under shear loading, A-P displacement with the XLIF cage alone increased by 2.2 times intact. Bilateral PS provided the largest reduction of A-P displacement, whereas the spinous process plate alone provided the least.
Conclusion:
This is the first in vitro shear load testing of XLIF cages with supplemental fixation in a cadaveric DS model. The variability in sagittal plane construct stability, including significantly increased flexion-extension ROM found with most fixation conditions including bilateral PS may explain some clinical treatment complications in DS with residual instability.
Level of evidence:
N/A.
Background Context
While multiple mechanisms of device attachment to the spinous processes exist, there is a paucity of data regarding lumbar spinous process morphology and peak failure loads.
Purpose
Using an in-vitro human cadaveric spine model, the primary objective of the current study was to compare the peak load and mechanisms of lumbar spinous process failure with variation in spinous process hole location and pullout direction. A secondary objective was to provide an in-depth characterization of spinous process morphology.
Study Design
Biomechanical and anatomical considerations in lumbar spinous process fixation using an in-vitro human cadaveric model.
Methods
A total of 12 intact lumbar spines were utilized in the current investigation. The vertebral segments (L1-L5) were randomly assigned to 1 of 5 treatment groups with variation in spinous process hole placement and pullout direction: 1) Central hole placement with superior pullout (n=10), 2) Central hole placement with inferior pullout (n=10), 3) Inferior hole placement with inferior pullout (n=10), 4) Superior hole placement with superior pullout (n=10) and 5) Intact spinous process with superior pullout (n=14). A 4mm diameter pin was placed through the hole followed by pullout testing using a material testing system (MTS). As well, the bone mineral density (BMD) (g/cm3) was measured for each segment. Data were quantified in terms of anatomic dimensions (mm), peak failure loads (Newtons) and fracture mechanisms, with linear regression analysis would identify relationships between anatomic and biomechanical data.
Results
Based on anatomic comparisons, there were significant differences between the anteroposterior and cephalocaudal dimensions of the L5 spinous process versus L1 through L4 (p<0.05). Statistical analysis of peak load at failure of the 4 reconstruction treatments and intact condition demonstrated no significant differences between treatments (range 350 to 500 Newtons) (p>0.05). However, a significant linear correlation was observed between peak failure load and anteroposterior and cephalocaudal dimensions (p<0.05). Correlation between BMD and peak spinous processes failure load was approaching statistical significance (p=0.08). 30/54 specimens failed via direct pullout (plow through), while 8/54 specimens demonstrated spinous process fracture. The remaining cases failed via plow through followed by fracture of the spinous process 16/54 (29%).
Conclutions
The current study demonstrated that variation in spinous process hole placement did not significantly influence failure load. However, there was a strong linear correlation between peak failure load and the anteroposterior and cephalocaudal anatomic dimensions. From a clinical standpoint, the findings of the current study indicate that attachment through the spinous process provides a viable alternative to attachment around the spinous processes. In addition, the anatomic dimensions of the lumbar spinous processes have a greater influence on biomechanical fixation than either hole location or bone mineral density.
Because degenerative spondylolithesis is prevalent in the elderly with associated osteoporosis, the rate of failure of pedicle screws is high; this leads to pseudoarthrosis and potentially requires reoperation. The burden of recurrent symptoms and reoperation is sufficiently significant to warrant prevention. We here describe a hybrid technique that involves a combination of a unilateral approach to bilateral decompression via a midline incision, transforaminal lumbar interbody fusion (TLIF), contralateral facet fusion, and percutaneously placed pedicle screws without compromising operative time and visualization. This approach is familiar to spine surgeons, adheres to the basic principles of minimally invasive spine surgery technique, minimizes dural and neural injury because of the unilateral TLIF approach, and provides a superior fusion construct because of facet fusion. In this procedure, patients with degenerative spondylolisthesis or scoliosis with moderate-severe canal/foraminal stenosis undergo a midline unilateral TLIF and contralateral facet fusion with closure of the midline incision. Percutaneous pedicle screws are inserted under stereotactic guidance with reduction of the deformity using a pedicle screws construct. Rods are inserted percutaneously to link the pedicle screws. Image intensification is used to confirmed satisfactory screw placement and reduction of the spondylolisthesis.
To investigate the feasibility of minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) using hybrid internal fixation of pedicle screws and a translaminar facet screw for recurrent lumbar disc herniation.
From January 2010 to December 2011, 16 recurrent lumbar disc herniation patients, 10 male and 6 female patients with an average age of 45 years (35-68 years) were treated with unilateral incision MIS-TLIF through working channel. After decompression, interbody fusion and fixation using unilateral pedicle screws, a translaminar facet screw was inserted from the same incision through spinous process and laminar to the other side facet joint. The results of perioperative parameters, radiographic images and clinical outcomes were assessed. The repeated measure analysis of variance was applied in the scores of visual analogue scale (VAS) and Oswestry disablity index (ODI).
All patients MIS-TLIF were accomplished under working channel including decompression, interbody fusion and hybrid fixation without any neural complication. The average operative time was (148 ± 75) minutes, the average operative blood loss was (186 ± 226) ml, the average postoperative ambulation time was (32 ± 15) hours, and the average hospitalization time was (6 ± 4) days. The average length of incision was (29 ± 4) mm, and the average length of translaminar facets screw was (52 ± 6) mm. The mean follow-up was 16.5 months with a range of 12-24 months. The postoperative X-ray and CT images showed good position of the hybrid internal fixation, and all facets screws penetrate through facets joint. The significant improvement could be found in back pain VAS, leg pain VAS and ODI scores between preoperative 1 day and postoperative follow-up at all time-points (back pain VAS:F = 52.845, P = 0.000;leg pain VAS:F = 113.480, P = 0.000;ODI:F = 36.665, P = 0.000).
Recurrent lumbar disc herniation could be treated with MIS-TLIF using hybrid fixation through unilateral incision, and the advantage including less invasion and quickly recovery.
Spinous process fixation (SPF) is presented as less invasive than pedicle screws. There has been little quantitative data to support this assertion, and "minimally invasive" has not been well defined in spine surgery. Length of stay (LOS) and blood loss (BL) were chosen as surrogate measures of "minimally invasive." A chart review was conducted on 192 lumbar fusion patients (374 levels). A backward-selection multiple-linear-regression was performed to determine what variables contribute to LOS and estimated blood loss (EBL). A logistic regression controlling for age and number of levels on complication rates was also performed. Number of levels with supplementary screw fixation (SSF) was significantly associated with LOS (p = 0.003). Controlling for number of surgical levels, LOS increased by 0.30 days (95% CI: 0.02-0.58) for each level with SSF. For each additional level including SSF, BL increases by 25.31 cc (95% CI: 3.50-47.12, p = 0.023). Interbody fusion increases blood loss by 68.16 cc (95% CI: 17.18-119.13, p = .009). For each additional level with SSF, odds of perioperative complications increase by OR = 2.34 (95% CI: 1.35-4.05). Long-term complications were not affected by instrumentation. LOS and BL are increased in patients with SSF vs. SPF only. Odds of perioperative complications are increased in patients with SSF relative to those treated with SPF alone.
Background context:
The lateral transpsoas approach to interbody fusion is gaining popularity because of its minimally invasive nature and resultant indirect neurologic decompression. The acute biomechanical stability of the lateral approach to interbody fusion is dependent on the type of supplemental internal fixation used. The two-hole lateral plate (LP) has been approved for clinical use for added stabilization after cage instrumentation. However, little biomechanical data exist comparing LP fixation with bilateral pedicle screw and rod (PSR) fixation.
Purpose:
To biomechanically compare the acute stabilizing effects of the two-hole LP and bilateral PSR fusion constructs in lumbar spines instrumented with a lateral cage at two contiguous levels.
Study design:
Biomechanical laboratory study of human cadaveric lumbar spines.
Methods:
Eighteen L1-S1 cadaveric lumbar spines were instrumented with lateral cages at L3-L4 and L4-L5 after intact kinematic analysis. Specimens (n=9 each) were allocated for supplemental instrumentation with either LP or PSR. Intact versus instrumented range of motion was evaluated for all specimens by applying pure moments (±7.5 Nm) in flexion/extension, lateral bending (LB) (left+right), and axial rotation (AR) (left+right). Instrumented spines were later subjected to 500 cycles of loading in all three planes, and interbody cage translations were quantified using a nonradiographic technique.
Results:
Lateral plate fixation significantly reduced ROM (p<.05) at both lumbar levels (flexion/extension: 49.5%; LB: 67.3%; AR: 48.2%) relative to the intact condition. Pedicle screw and rod fixation afforded the greatest ROM reductions (p<.05) relative to the intact condition (flexion/extension: 85.6%; LB: 91.4%; AR: 61.1%). On average, the largest interbody cage translations were measured in both fixation groups in the anterior-posterior direction during cyclic AR.
Conclusions:
Based on these biomechanical findings, PSR fixation maximizes stability after lateral interbody cage placement. The nonradiographic technique served to quantify migration of implanted hardware and may be implemented as an effective laboratory tool for surgeons and engineers to better understand mechanical behavior of spinal implants.
Background:
Segmental fixation improves fusion rates and promotes patient mobility by controlling instability after lumbar surgery. Efforts to obtain stability using less invasive techniques have lead to the advent of new implants and constructs. A new interspinous fixation device (ISD) has been introduced as a minimally invasive method of stabilizing two adjacent interspinous processes by augmenting an interbody cage in transforaminal interbody fusion. The ISD is intended to replace the standard pedicle screw instrumentation used for posterior fixation.
Purpose:
The purpose of this study is to compare the rigidity of these implant systems when supplementing an interbody cage as used in transforaminal lumbar interbody fusion.
Study design:
An in vitro human cadaveric biomechanical study.
Methods:
Seven human cadaver spines (T12 to the sacrum) were mounted in a custom-designed testing apparatus, for biomechanical testing using a multiaxial robotic system. A comparison of segmental stiffness was carried out among five conditions: intact spine control; interbody spacer (IBS), alone; interbody cage with ISD; IBS, ISD, and unilateral pedicle screws (unilat); and IBS, with bilateral pedicle screws (bilat). An industrial robot (KUKA, GmbH, Augsburg, Germany) applied a pure moment (±5 Nm) in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) through an anchor to the T12 vertebral body. The relative vertebral motion was captured using an optoelectronic camera system (Optotrak; Northern Digital, Inc., Waterloo, Ontario, Canada). The load sensor and the camera were synchronized. Maximum rotation was measured at each level and compared with the intact control. Implant constructs were compared with the control and with each other. A statistical analysis was performed using analysis of variance.
Results:
A comparison between the intact spine and the IBS group showed no significant difference in the range of motion (ROM) in FE, LB, or AR for the operated level, L3-L4. After implantation of the ISD to augment the IBS, there was a significant decrease in the ROM of 74% in FE (p<.001) but no significant change in the ROM in LB and AR. The unilat construct significantly reduced the ROM by 77% compared with FE control (p<.001) and by 55% (p=.002) and 42% (p=.04) in LB and AR, respectively, compared with control. The bilat construct reduced the ROM in FE by 77% (p<.001), LB by 77% (p=.001), and AR by 65% (p=.001) when compared with the control spine. There was no statistically significant difference in the ROM in FE among the stand-alone ISD, unilat, and bilat constructs. However, in both LB and AR, the unilat and the bilat constructs were significantly stiffer (reduction in the ROM) than the ISD and the IBS combination. The ISD stability in LB and AR was not different from the intact control with no instrumentation at all. There was no statistical difference between the stability of the unilat and the bilat constructs in any direction. However, LB and AR in the unilat group produced a mean rotation of 3.83°±3.30° and 2.33°±1.33°, respectively, compared with the bilat construct that limited motion to 1.96°±1.46° and 1.39°±0.73°. There was a trend suggesting that the bilat construct was the most rigid construct.
Conclusions:
In FE, the ISD can provide lumbar stability comparable with Bilat instrumentation. It provides minimal rigidity in LB and AR when used alone to stabilize the segment after an IBS placement. The unilat and the more typical bilat screw constructs were shown to provide similar levels of stability in all directions after an IBS placement, though the bilat construct showed a trend toward improved stiffness overall.
Study design::
Cadaveric biomechanical study.
Objective::
To investigate the kinematic response of a stand-alone lateral lumbar interbody cage compared with supplemental posterior fixation with either facet or pedicle screws after lateral discectomy.
Summary of background data::
Lateral interbody fusion is a promising minimally invasive fixation technique for lumbar interbody arthrodesis. The biomechanical stability of stand-alone cage placement compared with supplemental posterior fixation with either facet or bilateral pedicle screws remains unclear.
Methods::
A 6-degree of freedom spine simulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral-bending, and axial-rotation were tested in the intact condition, followed by destabilization through a lateral discectomy at L2-L3 and L4-L5. Specimens were then reconstructed at both operative segments in the following sequence: (1) lateral interbody cage placement; (2) either Discovery facet screws or the Viper F2 system using a transfacet-pedicular trajectory randomized to L2-L3 or L4-L5; and (3) removal of facet screw fixation followed by placement of bilateral pedicle screw instrumentation. Acute range of motion (ROM) was quantified and analyzed.
Results::
All 4 reconstruction groups, including stand-alone interbody cage placement, bilateral Discovery facet screws, the Viper F2 system, and bilateral pedicle screw-rod stabilization, resulted in a significant decrease in acute ROM in all loading modes tested (P<0.05). There were no significant differences observed between the 4 instrumentation groups (P>0.05). Although not statistically significant, the Viper F2 system resulted in greatest reduction of acute ROM in both flexion-extension and axial rotation versus all other treatments (P>0.05).
Conclusions::
Stand-alone interbody cage placement results in a significant reduction in acute ROM at the operative segment in the absence of posterior supplemental fixation. If added fixation is desired, facet screw placement, including the Viper F2 facet screw system using an integrated compression washer and transfacet-pedicular trajectory, provides similar acute stability to the spinal segment compared with traditional bilateral pedicle screw fixation in the setting of lateral interbody cage deployment.
A human cadaveric biomechanical study of lumbar mobility before and after fusion and with or without supplemental instrumentation for 5 instrumentation configurations.
To determine the biomechanical differences between anterior lumbar interbody fusion (ALIF) and direct lateral interbody fusion (DLIF) with and without supplementary instrumentation.
Some prior studies have compared various surgical approaches using the same interbody device whereas others have investigated the stabilizing effect of supplemental instrumentation. No published studies have performed a side-by-side comparison of standard and minimally invasive techniques with and without supplemental instrumentation.
Eight human lumbosacral specimens (16 motion segments) were tested in each of the 5 following configurations: (1) intact, (2) with ALIF or DLIF cage, (3) with cage plus stabilizing plate, (4) with cage plus unilateral pedicle screw fixation (PSF), and (5) with cage plus bilateral PSF. Pure moments were applied to induce specimen flexion, extension, lateral bending, and axial rotation. Three-dimensional kinematic responses were measured and used to calculate range of motion, stiffness, and neutral zone.
Compared to the intact state, DLIF significantly reduced range of motion in flexion, extension, and lateral bending (P = 0.0117, P = 0.0015, P = 0.0031). Supplemental instrumentation significantly increased fused-specimen stiffness for both DLIF and ALIF groups. For the ALIF group, bilateral PSF increased stiffness relative to stand-alone cage by 455% in flexion and 317% in lateral bending (P = 0.0009 and P < 0.0001). The plate increased ALIF group stiffness by 211% in extension and 256% in axial rotation (P = 0.0467 and P = 0.0303). For the DLIF group, bilateral PSF increased stiffness by 350% in flexion and 222% in extension (P < 0.0001 and P = 0.0008). No differences were observed between ALIF and DLIF groups supplemented with bilateral PSF.
Our data support that the direct lateral approach, when supplemented with bilateral PSF, is a minimally invasive and biomechanically stable alternative to the open, anterior approach to lumbar spine fusion.
Biomechanical study and the review of literature on lumbar interbody fusion constructs.
To demonstrate the comparative stabilizing effects of lateral interbody fusion with various supplemental internal fixation options.
Lumbar interbody fusion procedures are regularly performed using anterior, posterior, and more recently, lateral approaches. The biomechanical profile of each is determined by the extent of resection of local supportive structures, implant size and orientation, and the type of supplemental internal fixation used.
Pure moment flexibility testing was performed using a custom-built 6 degree-of-freedom system to apply a moment of ±7.5 Nm in each motion plane, while motion segment kinematics were evaluated using an optoelectronic motion system. Constructs tested included the intact spine, stand-alone extreme lateral interbody implant, interbody implant with lateral plate, unilateral and bilateral pedicle screw fixation. These results were evaluated against those from literature-reported biomechanical studies of other lumbar interbody constructs.
All conditions demonstrated a statistically significant reduction in range of motion (ROM) as a percentage of intact. In flexion-extension, ROM was 31.6% stand-alone, 32.5% lateral fixation, and 20.4% and 13.0% unilateral and bilateral pedicle screw fixation, respectively. In lateral bending, the trend was similar with greater reduction with lateral fixation than in flexion-extension; ROM was 32.5% stand-alone, 15.9% lateral fixation, and 21.6% and 14.4% unilateral and bilateral pedicle screw fixation. ROM was greatest in axial rotation; 69.4% stand-alone, 53.4% lateral fixation, and 51.3% and 41.7% unilateral and bilateral pedicle screw fixation, respectively.
The extreme lateral interbody construct provided the largest stand-alone reduction in ROM compared with literature-reported ALIF and TLIF constructs. Supplemental bilateral pedicle screw-based fixation provided the overall greatest reduction in ROM, similar among all interbody approach techniques. Lateral fixation and unilateral pedicle screw fixation provided intermediate reductions in ROM. Clinically, surgeons may evaluate these comparative results to choose fixation options commensurate with the stability requirements of individual patients.
To study the stability offered by a clamping lumbar interspinous anchor (ISA) for transforaminal lumbar interbody fusion (TLIF).
Seven human cadaveric lumbosacral specimens were tested: 1) intact; 2) after placing ISA; 3) after TLIF with ISA; 4) with TLIF, ISA, and unilateral pedicle screws-rod; 5) with TLIF and unilateral pedicle screws-rod (ISA removed); and 6) with TLIF and bilateral pedicle screws-rods. Pure moments (7.5 Nm maximum) were applied in each plane to induce flexion-extension, axial rotation, and lateral bending while recording angular motion optoelectronically. Compression (400 N) was applied while upright foraminal height was measured.
All instrumentation reduced angular range of motion (ROM) significantly from normal. The loading modes in which the ISA limited ROM most effectively were flexion and extension, where the ROM allowed was equivalent to that of pedicle screws-rods (P > .08). The ISA was least effective in reducing lateral bending, with this mode reduced to 81% of normal. TLIF with unilateral pedicle screws-rod was the least stable configuration. Addition of the ISA to this construct significantly improved stability during flexion, extension, lateral bending, and axial rotation (P < .008). Constructs that included the ISA increased the foraminal height an average of 0.7 mm more than the other constructs (P < .05).
In cadaveric testing, the ISA limits flexion and extension equivalently to pedicle screws-rods. It also increases foraminal height. When used with TLIF, a construct of ISA or ISA plus unilateral pedicle screws-rod may offer an alternative to bilateral pedicle screws-rods for supplemental posterior fixation.
Osseoligamentous spinal specimens buckle under even a small vertical compressive force. To allow higher axial forces, a compressive follower load (FL) was suggested previously that approximates the curvature of the spine without inducing intervertebral rotation in both the frontal and the sagittal planes. In in vitro experiments and finite element analyses, the location of the FL path is subjected to estimation by the investigator. Such non-optimized FLs may induce bending and so far it is still unknown how this affects the results of the study and their comparability. A symmetrical finite element model of the lumbar spine was employed to simulate upright standing while applying a follower load. In analogy to in vitro experiments, the path of this FL was estimated seven times by different members of our institute's spine group. Additionally, an optimized FL path was determined and additional moments of +/-7.5Nm were applied to simulate flexion and extension. Application of the optimized 500N compressive FL causes only a marginal alteration of the curvature (cardan angle L1-S1 in sagittal plane <0.25 degrees). An individual estimation of the FL path, however, results in flexions of up to 10.0 degrees or extensions of up to 12.3 degrees. The resulting angles for the different non-optimized FL paths depend on the magnitude of the bending moment applied and whether a differential or an absolute measurement is taken. A preceding optimization of the location of the FL path would increase the comparability of different studies.
An interspinous anchor (ISA) provides fixation to the lumbar spine to facilitate fusion. The biomechanical stability provided by the Aspen ISA was studied in applications utilizing an anterior lumbar interbody fusion (ALIF) construct.
Seven human cadaveric L3-S1 specimens were tested in the following states: 1) intact; 2) after placing an ISA at L4-5; 3) after ALIF with an ISA; 4) after ALIF with an ISA and anterior screw/plate fixation system; 5) after removing the ISA (ALIF with plate only); 6) after removing the plate (ALIF only); and 7) after applying bilateral pedicle screws and rods. Pure moments (7.5 Nm maximum) were applied in flexion and extension, lateral bending, and axial rotation while recording angular motion optoelectronically. Changes in angulation as well as foraminal height were also measured.
All instrumentation variances except ALIF alone reduced angular range of motion (ROM) significantly from normal in all directions of loading. The ISA was most effective in limiting flexion and extension (25% of normal) and less effective in reducing lateral bending (71% of normal) and axial rotation (71% of normal). Overall, ALIF with an ISA provided stability that was statistically equivalent to ALIF with bilateral pedicle screws and rods. An ISA-augmented ALIF allowed less ROM than plate-augmented ALIF during flexion, extension, and lateral bending. Use of the ISA resulted in flexion at the index level, with a resultant increase in foraminal height. Compensatory extension at the adjacent levels prevented any significant change in overall sagittal balance.
When used with ALIF at L4-5, the ISA provides immediate rigid immobilization of the lumbar spine, allowing equivalent ROM to that of a pedicle screw/rod system, and smaller ROM than an anterior plate. When used with ALIF, the ISA may offer an alternative to anterior plate fixation or bilateral pedicle screw/rod constructs.
Quantitative data on the range of in vivo vertebral motion is critical to enhance our understanding of spinal pathology and to improve the current surgical treatment methods for spinal diseases. Little data have been reported on the range of lumbar vertebral motion during functional body activities. In this study, we measured in vivo 6 degrees-of-freedom (DOF) vertebral motion during unrestricted weightbearing functional body activities using a combined MR and dual fluoroscopic imaging technique. Eight asymptomatic living subjects were recruited and underwent MRI scans in order to create 3D vertebral models from L2 to L5 for each subject. The lumbar spine was then imaged using two fluoroscopes while the subject performed primary flexion-extension, left-right bending, and left-right twisting. The range of vertebral motion during each activity was determined through a previously described imaging-model matching technique at L2-3, L3-4, and L4-5 levels. Our data revealed that the upper vertebrae had a higher range of flexion than the lower vertebrae during flexion-extension of the body (L2-3, 5.4 +/- 3.8 degrees ; L3-4, 4.3 +/- 3.4 degrees ; L4-5, 1.9 +/- 1.1 degrees , respectively). During bending activity, the L4-5 had a higher (but not significant) range of left-right bending motion (4.7 +/- 2.4 degrees ) than both L2-3 (2.9 +/- 2.4 degrees ) and L3-4 (3.4 +/- 2.1 degrees ), while no statistical difference was observed in left-right twisting among the three vertebral levels (L2-3, 2.5 +/- 2.3 degrees ; L3-4, 2.4 +/- 2.6 degrees ; and L4-5, 2.9 +/- 2.1 degrees , respectively). Besides the primary rotations reported, coupled motions were quantified in all DOFs. The coupled translation in left-right and anterior-posterior directions, on average, reached greater than 1 mm, while in the proximal-distal direction this was less than 1 mm. Overall, each vertebral level responds differently to flexion-extension and left-right bending, but similarly to the left-right twisting. This data may provide new insight into the in vivo function of human spines and can be used as baseline data for investigation of pathological spine kinematics.
New implants and new surgical approaches should be tested in vitro for primary stability in standardized laboratory tests in order to decide the most appropriate approach before being accepted for clinical use. Due to the complex and still unknown loading of the spine in vivo a variety of different test loading conditions have been used, making comparison of the results from different groups almost impossible. This recommendation was developed in a series of workshops with research scientists, orthopedic and trauma surgeons, and research and development executives from spinal implant companies. The purpose was to agree on in vitro testing conditions that would allow results from various research groups to be compared. This paper describes the recommended loading methods, specimen conditions, and analysis parameters resulting from these workshops.
Mechanical testing of cadaveric lumbar spines and dual energy radiograph absorptiometry scanning were performed.
To devise a technique to measure the strength of lumbar spinous processes and to determine the bone mineral density of the vertebrae used.
The spinous process has been identified as the weakest part of the anatomy to which a flexible fixation device can be attached. It was unknown if the spinous processes could withstand the forces applied by the device.
A hook was fitted to the spinous process of 32 lumbar vertebrae. A custom-built rig was designed to secure a vertebra to a materials testing machine. A loop of cord was passed over a bar mounted on the crosshead of the machine and around the two bollards of the hook. As the crosshead was raised, a tension was applied to the cord. Each vertebra was tested to failure. The bone mineral density of each vertebra was then measured using dual energy radiograph absorptiometry.
Failure of the specimens occurred by failure of the spinous process, pedicles, or vertebral body. The logarithm (base 10) of the load (N) at which failure occurred was 2.53 +/- 0.3, which corresponded to a mean failure load of 339 N. The bone mineral density of each vertebral body varied between 0.263 and 0.997 g/cm2. A significant linear correlation was found between bone strength and bone mineral density (P < 0.0001).
Specimens with a bone mineral density in the range of 0.263-0.997 g/cm2 failed at a mean load of 339 N when the load was applied through the spinous process hook of a flexible fixation device.
The authors present the early clinical results obtained in patients who underwent SPIRE spinous process plate fixation following anterior lumbar interbody fusion (ALIF).
Between May 2003 and January 2005, 32 patients underwent titanium cage and bone morphogenetic protein-augmented ALIF and subsequent SPIRE (21 cases) or bilateral pedicle screw (BPS; 11 cases) fixation. Pedicle screws were implanted using either the open approach (three cases) or using a tubular retractor (eight cases). Patients' charts were reviewed for operative time, estimated blood loss (EBL), hospital length of stay (LOS), and evidence of pseudarthrosis or hardware failure. In SPIRE plate-treated patients, the median EBL (75 ml) was lower than in BPS-treated patients (open BPS [150 ml]; tubular BPS [125 ml]). The median operative time in SPIRE plate-treated patients was also shorter (164 minutes compared with 239 and 250 minutes in the open and tubular BPS, respectively). The median LOS was 3 days for both the SPIRE and tubular BPS groups, but 4 days in the open BPS group. There were no instances of major surgery-induced complication, pseudarthrosis, or hardware failure during mean follow-up periods of 5.5, 7.2, and 4.9 months in the SPIRE, open PS, and tubular BPS groups, respectively.
The SPIRE plate is easy to implant and is associated with minimal operative risk. Compared with BPS/rod constructs, SPIRE plate fixation leads to less EBL and shorter operative time, without an increase in the rate of pseudarthrosis. Hospital LOS was also shorter in SPIRE plate-treated patients, which is consistent with the goals of minimal access spinal technologies.
Modified Mini-Open Transforaminal Lumbar Interbody Fusion (MOTLIF): description of surgical technique and assessment of free-hand pedicle screw insertion
- Pakzaban