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Measurement of Shift of the Cauda Equina in the Subarachnoid Space by Changing Position
Abstract
To perform spinal anesthesia, patients are usually placed in the lateral decubitus position with the knees drawn up to the stomach, the legs fully flexed, and the neck flexed to curve the back outward. Because the nerve roots of the cauda equina have considerable mobility in the subarachnoid space, the position of the cauda equina in the lateral decubitus position may be different from that in the supine position. However, the anatomic position of the cauda equina in the lateral decubitus position with fully flexed legs has not been carefully studied. In the present study, we geometrically measured the movement of the cauda equina in the subarachnoid space by changing positions, using magnetic resonance imaging (MRI).
After obtaining the approval of the hospital ethics committee and written informed consent, 12 healthy volunteers (age, 34 years [SD, 10 years]; height, 169 cm [SD, 9 cm]; weight, 65 kg [SD, 10 kg]) were studied with MRI, and their positions were changed as follows: the supine position, lateral decubitus position without fully flexed legs, and lateral decubitus position with fully flexed legs. The movement of the central point of the spinal cord and cauda equina by changing position was evaluated.
The spinal cord and cauda equina were observed in the gravity-dependent side of the subarachnoid space in each position. The movement to the gravity-dependent side by changing position from the supine to the lateral decubitus position was significant (mean [SD] in millimeters: T11/12, 0.7 [0.4]; T12/L1, 1.5 [0.9]; L1/L2, 3.0 [1.0]; L2/L3, 3.4 [1.0]; L3/L4, 2.7 [0.9]; L4/L5, 2.0 [0.9]; L5/S1, 1.2 [0.7]; S1/S2, 0.5 [0.2]). The most obvious shift was observed at the L2/3 intervertebral space. The fully flexed legs significantly moved the spinal cord and cauda equina to the ventral side of the subarachnoid space and created a free space in the dorsal side. The movement to the ventral side by the fully flexed legs was significant (mean [SD] in millimeters: T11/12, 2.2 [1.0]; T12/L1, 4.1 [1.5]; L1/L2, 6.1 [0.5]; L2/L3, 5.4 [0.9]; L3/L4, 5.1 [1.9]; L4/L5, 4.4 [1.1]; L5/S1, 5.0 [0.9]; and S1/S2, 2.6 [0.9]). The most obvious shift was observed at the L1/2 intervertebral space.
The present study using MRI showed dynamical movement of the spinal cord and cauda equina due to changing position. The most obvious movements by changing from supine to lateral decubitus position and fully flexed legs were observed at the L2/3 and L1/2 levels, respectively.
... 21 Anatomy studies about the medular cone has demonstrated that the cauda equina has a dinamic attitude that varies with the position assumed by the patient. 22,23 So, bending the column forward facilitates the introduction of the needle into the subarachnoid space in the lumbar segment not providing protection to the medulla. 22 The spinal medula and the cauda equina move inside the canal, depending on the gravity, when the patient assumes lateral decubitus, occurring it in all its extension, being it greater at L2-L3 with a mean movement of 3.4±1.0 ...
... mm. 23 In the inferior thoracic segment the deviation was of only 1.0 mm. 23 Forced flexion of the spine moves the spinal cord and cauda equina anteriorly (ventrally) while the forced flexion of the limbs provides the forward movement of the whole medula anteriorly. ...
... 23 In the inferior thoracic segment the deviation was of only 1.0 mm. 23 Forced flexion of the spine moves the spinal cord and cauda equina anteriorly (ventrally) while the forced flexion of the limbs provides the forward movement of the whole medula anteriorly. 23 ...
... The spinal cord and the cauda equina move, depending on the severity when the patient assumes the lateral decubitus position, occurring over its entire length, with the greatest magnitude between the L2-L3 spaces, with the measured distance of 3.4 ± 1.0 mm [11]. In the lower thoracic region, the deviation was less than 1.0 mm [11]. ...
... The spinal cord and the cauda equina move, depending on the severity when the patient assumes the lateral decubitus position, occurring over its entire length, with the greatest magnitude between the L2-L3 spaces, with the measured distance of 3.4 ± 1.0 mm [11]. In the lower thoracic region, the deviation was less than 1.0 mm [11]. Forced flexion of the spine dislocates the spinal cord and the cauda equina to the ventral side of the subarachnoid space. ...
... Forced flexion of the spine dislocates the spinal cord and the cauda equina to the ventral side of the subarachnoid space. Forced flexion of the lower limbs causes deviation of the medullary nervous tissue from the lower thoracic region to the sacral region [11]. ...
... Importantly, in the context of this study, it has been shown previously that the LDP also allows for significant movement of the CM and nerve roots toward the dependent portion of the thecal sac (Takiguchi et al., 2004) (Fig. 1). Indeed, Takiguchi et al. (2009) demonstrated in patients who shift positions from supine to LDP (whether unflexed or in the fully flexed body/hips/knees posture) that the cauda equina moves toward the dependent portions of the thecal sac, most notably at L2-L3. When the LDP is augmented by a fully flexed posture, the additional ventral cauda equina movement is most evident at L1-L2 (Takiguchi et al., 2009). ...
... Indeed, Takiguchi et al. (2009) demonstrated in patients who shift positions from supine to LDP (whether unflexed or in the fully flexed body/hips/knees posture) that the cauda equina moves toward the dependent portions of the thecal sac, most notably at L2-L3. When the LDP is augmented by a fully flexed posture, the additional ventral cauda equina movement is most evident at L1-L2 (Takiguchi et al., 2009). The latter patient positioning also splays the lumbar spinous processes and the interlaminar spaces for better needle access to the thecal sac. ...
... Although current convention dictates performing LPs at L3-L4 or below to avoid injury to the CM, we hypothesized that a high LP might be safer than deemed in the past if we consider changes in location of the CM within the thecal sac when patients adopt the LDP. By first measuring the location of the CM within the thecal sac at the T12-L1, L1-L2, and L2-L3 positions using MR images obtained in the conventional supine position and then factoring in the theoretical gravity-dependent shifts of the CM at these three levels, as published by Takiguchi et al. (2009), here we demonstrate that high LPs at L1-L2 and L2-L3 performed in the LDP could be theoretically safer than considered hitherto. This new appreciation of the likely relative safety of high LPs is derived from our morphometric analyses combined with data from Takiguchi et al. (2009), showing theoretical gravity-dependent shifts of the CM and nerve roots in this particular position if adopted during the procedure. ...
A high lumbar puncture (LP) at L2–L3 or above is often necessary to consider on technical grounds, but complications of conus medullaris (CM) damage during high LP are potentially concerning. We hypothesized that a high LP might be safer than previously thought by accounting for movements of the CM upon patient positional changes. We retrospectively reviewed standard normal supine lumbar spine magnetic resonance imaging of 58 patients and used electronic calipers on axial images at the T12–L1, L1–L2, and L2–L3 disc levels to measure the transverse diameter of the CM relative to the size of the dorsal thecal sac space (DTSS) through which a spinal needle could be inserted. On 142 axial images, the means for CM diameters were 8.2, 6.0, and 2.9 mm at the three levels, respectively. We then used known literature mean CM displacement values in the legs flexed and unflexed lateral decubitus position (LDP) to factor in CM shifts to the dependent side. We found that at all three levels, the likely positional shift of the CM would be too small and insufficient to displace the entire CM out of the DTSS. However, if needle placement could be confined to the midsagittal plane, an LP in the unflexed LDP would theoretically be entirely safe at both L1–L2 and L2–L3, and almost so at L2–L3 in the legs flexed LDP. Thus, high LPs at L1–L2 and L2–L3 are in theory likely safer than considered previously, more so in the legs unflexed than in the flexed LDP. Clin. Anat. 32:618–629, 2019. © 2019 Wiley Periodicals, Inc.
... At the lower lumbar level, the position of cauda equina elements such as L4, L5, and sacral nerves are relatively definite (Fig. 3). Takiguchi et al. [24] reported the migration of the spinal cord and cauda equina from the T11-12 to the S1-2 disc level during position change in a study utilizing MRI. The maximum migration was observed at the L1-2 disc level, and the lower the cauda equina was located, the less the cauda equina moved during position change. ...
... In this case, the patient reported that he almost did not feel the difference in the change of the site and intensity of the stimulation by changing position. The little change of stimulation by position change may be associated with the low mobility of the cauda equina at the lower lumbar and sacral levels, as shown in the investigation of Takiguchi et al. [24] Although the spinal cord moves according to the patient's position, it is the most commonly used site of neurostimulation. Therefore, some mobility of the cauda equina, especially in the lower lumbar and sacral levels, may not be a contraindication to stimulation. ...
Phantom limb pain is a phenomenon in which patients experience pain in a part of the body that no longer exists. In several treatment modalities, spinal cord stimulation (SCS) has been introduced for the management of intractable post-amputation pain. A 46-year-old male patient complained of severe ankle and foot pain, following above-the-knee amputation surgery on the right side amputation surgery three years earlier. Despite undergoing treatment with multiple modalities for pain management involving numerous oral and intravenous medications, nerve blocks, and pulsed radiofrequency (RF) treatment, the effect duration was temporary and the decreases in the patient's pain score were not acceptable. Even the use of SCS did not provide completely satisfactory pain management. However, the trial lead positioning in the cauda equina was able to stimulate the site of the severe pain, and the patient's pain score was dramatically decreased. We report a case of successful pain management with spinal cauda equina stimulation following the failure of SCS in the treatment of intractable phantom limb pain.
... Our cases were studied in the supine position, whereas patients are usually in a lateral decubitus or sitting position for subarachnoid puncture. The effects of a change in posture on the position of the cauda equina have been studied using MRI 11 ; the lateral decubitus position with fully flexed legs creates a free zone in the posterior subarachnoid space 12,13 , with anterior displacement of the cauda equina, which may also be displaced to the dependent side 12,13 . These anatomical movements almost certainly increase the safety of low punctures in the lateral position, and the relative CSF and root volumes that we found may help contribute to a safe insertion approach. ...
... Our cases were studied in the supine position, whereas patients are usually in a lateral decubitus or sitting position for subarachnoid puncture. The effects of a change in posture on the position of the cauda equina have been studied using MRI 11 ; the lateral decubitus position with fully flexed legs creates a free zone in the posterior subarachnoid space 12,13 , with anterior displacement of the cauda equina, which may also be displaced to the dependent side 12,13 . These anatomical movements almost certainly increase the safety of low punctures in the lateral position, and the relative CSF and root volumes that we found may help contribute to a safe insertion approach. ...
Cerebrospinal fluid (CSF) and nerve root volumes within the lumbosacral dural sac were estimated at various vertebral levels, in an attempt to determine any possible relevance to the incidence of nerve root trauma during lumbar puncture or spinal anaesthesia. Magnetic resonance images from seven patients were studied. Volumes were calculated by semi-automatic threshold segmentation combined with manual editing of each slice. The mean dural sac volume from S1 to T12 was 42.8±5.8 ml and the mean CSF volume 34.3±5.1 ml with the mean root volume being 10.4±2.2 cm ³ . The mean CSF volume per vertebral segment ranged from 4.3±0.7 ml at L5, to 5.8±2.5 ml at L1, with high inter-individual variability. The mean root volume ranged from 0.6±0.1 cm ³ at L5 to 2.4±0.5 cm ³ at T12.
The conus medullaris was located at L1 in four of the five patients scanned at upper lumbar levels, and at the lower border of L2 in the other. Vulnerability to nerve root damage was expressed as the Vulnerability Index (%), being defined as the ratio of root volume to dural sac volume (CSF volume + root volume). The value ranged between 7 and 14% at L5, increasing rostrally to 30 to 43% at T12. Caution is obviously required in high punctures to avoid contact with the conus medullaris, but the cauda equina is also vulnerable to contact with more caudal punctures and had a Vulnerability Index of about 25% at L4, that increased rostrally.
... A good anaesthetic effect during caesarean section requires an anaesthetic level of at least T 6 , which is related to many factors, such as anaesthetic concentration, dose, injection speed and puncture space [19]. Takiguchi et al. [20] reported that the conus medullaris and cauda equina were signi cantly displaced in the direction of gravity inside the dural sac when a patient was lying on her side. That is, when a patient changes from the supine to lateral position, the cauda equina nerve moves in the direction of gravity, and this shift is most obvious at the L 2 − 3 level. ...
Background: Patients who undergo spinal anaesthesia combined with epidural block during caesarean section often have prolonged dyskinesia and leg numbness after the operation. This study explored whether small-dose and low-concentration local anaesthetics can meet the needs of surgery while helping relieve motor blocks earlier, reduce discomfort during leg numbness, and promote early maternal activity to provide additional options for women undergoing caesarean section.
Methods: One hundred and twenty patients who underwent elective caesarean section were randomly divided into three groups according to the local anaesthetic concentration: 0.6%, 0.5%, and 0.4% ropivacaine. In all the groups, the puncture point, total dose and injection speed were the same, and an epidural catheter was inserted. Additionally, 2% lidocaine was added to the epidural catheter when the effect of spinal anaesthesia decreased during the operation. The primary outcome was the duration of lidocaine supplementation. Other secondary outcomes were the onset time, duration, highest sensory and motor block levels, use of additional epidural drugs, vital signs, adverse reactions, satisfaction and so on.
Results: The sensory and motor block levels decreased faster and were shorter in the 0.4% ropivacaine group than in the other two groups, but additional epidural drugs were needed. Intraoperative circulation was more stable. There were no significant differences in adverse reactions or satisfaction among the groups.
Conclusions: A small dose of 0.4% ropivacaine can meet the needs of surgery during combined spinal-epidural anaesthesia for caesarean section, and parturients can recover lower limb sensation and motor function faster after surgery; however, it is necessary to determine the operation time and administer epidural drugs in a timely manner.
Trial registration: ChiCTR-2000030968 (Chictr.org.cn); registered on 20/03/2020.
... The sitting position makes it easy to perform the TSA procedure because this position provides sufficient space for the needle to enter the subarachnoid space in the thoracic region. [2][3][4][5] Ultrasound is now routinely used to determine the correct thoracic level and it is strongly recommended. [6,7] Even using ultrasound in addition to the injection level, the depth of the needle can also be monitored so that spinal cord injury does not occur. ...
Introduction: Laparoscopy is mostly performed under general anesthesia (GA) but laparoscopy using anesthesia such as thoracic spinal anesthesia (TSA) is mostly performed by some anesthesiologists and it is very useful when compared to GA. Method: This paper presents a case report of the use of TSA in healthy pediatric patients who administered anesthesia with TSA in the T10-T11 interspace, using 1 ml of hyperbaric Bupivacaine 5 mg/ml mixed with: 1 ml of Levobupivacaine isobaric 5 mg/ml, Fentanyl 50 μg, Ketamine 10 mg and Dexmedetomidine 10 μg mixed in 1 syringe. Results: During procedure, hemodynamically stable, no nausea, vomiting, or discomfort. Postoperative recovery process was very smooth, hemodynamically stable, no pain was reported or PDPH (Post Dural Puncture Headache) even though we used a 26G spinal needle. The use of TSA is considered very practical and more economical even though it is still carried out very carefully. Conclusion: This is only one single case report. TSA can be a better choice compare with general anesthesia. Stable hemodynamic during laparoscope and TSA can avoid systemic effect of general anesthesia like cognitive affect after general anesthesia, longer for recovery from anesthesia, nausea, vomiting, poor control pain and high cost.
... ISSCs were reported on the right side of the body 3 times more often than on the left side. The cauda equina, including the sensory nerve fibers, moves dynamically in the subarachnoid space with changes in body position (19). The cauda equina is, therefore, shifted to the left side (the floor side) of the subarachnoid space by gravity when a patient is placed in the left lateral decubitus position. ...
Background:
Predicting the spread of anesthesia after intrathecal injection of plain local anesthetics is challenging owing to both patient and anesthesiologist-related factors.
Objectives:
This study aimed to examine the initial patient-reported sensory changes during intrathecal injections and used multi-level analyses to examine the relationships between these changes and other major factors affecting the spread of anesthesia.
Methods:
The participants were 120 consecutive patients with the American Society of Anesthesiologists status I and II, who were scheduled for open repair of inguinal hernias under spinal anesthesia. Lumbar puncture was performed at the midline of the L3 - L4 vertebrae and 3 mL of 0.5% isobaric bupivacaine was administered at 0.25 mL/s. The onset, dermatome, and side of the initial subjective sensory changes (ISSCs) were assessed by patient report. The extent of sensory loss to ice and pinprick stimuli, the degree of motor block in lower extremities, blood pressure, and heart rate were examined at 5-minutes intervals for 20 minutes after intrathecal injection.
Results:
All patients reported ISSCs after 9 (4, 18) seconds [median (minimum, maximum)] of the intrathecal injection onset. In 66.7% of the patients, ISSCs occurred in the L1 - L5 dermatomes. Three patients experienced pain during the early intraoperative period, and described ISSCs in the sacral dermatome. Height, mean blood pressure, and ISSCs were significantly correlated with sensory loss. Faster onset, lower dermatome, and floor-side of ISSCs predicted a narrower area of sensory loss, with dermatome as the most important indicator.
Conclusions:
Our findings demonstrate that ISSC, primarily based on dermatome, is a significant predictor for spinal anesthesia spread.
... The normal rhythm of the spinal cord is maintained by pulsations of cerebrospinal fluid (CSF) flow, which in turn is maintained by the transmitted cardiac pulsations. Exploiting the physiological movements of the spinal cord, Takiguchi and colleagues tried to measure the shift of the spinal cord in various positions (supine, prone, and lateral) but could not measure the accurate distances in prone position due to motion and pulsation artifact [22]. Winklhofer et al., measured the distance from the vertebral body to anterior border of spinal cord (oscillatory distance) and found that the measurements differed significantly between the scans conducted during breath-holding, normal breathing, and forced breathing. ...
Background
Dynamic magnetic resonance imaging (MRI)-based criteria for diagnosing magnitude of tethered cord syndrome (TCS) in occult spinal dysraphism are proposed.
Methods
In this prospective, case-control design study, MRI lumbosacral spine was performed in 51 subjects [pilot group (n = 10) without TCS (for defining radiological parameters), control group (n = 10) without TCS (for baseline assessment), and study group (n = 31) with spinal dysraphism (thick filum terminale [n = 12], lumbar/lumbosacral meningomyelocoele [n = 6], and lipomyelomeningocoele [n = 13])]. The parameters compared in control and study groups included oscillatory frequency (OF), difference in ratio, in supine/prone position, of distance between posterior margin of vertebral body and anterior margin of spinal cord (oscillatory distance [OD]), with canal diameter, at the level of conus as well as superior border of contiguous two vertebrae above that level; delta bending angle (ΔBA), difference, in supine/prone position, of angle between longitudinal axis of conus and that of lower spinal cord; and sagittal and axial root angles, subtended between exiting ventral nerve roots and longitudinal axis of cord. An outcome assessment at follow-up was also done.
Results
In the study group (cord tethered), significantly less movement at the level of conus (OF0, p = 0.013) and one level above (OF1, p = 0.03) and significant difference in ΔBA (p = 0.0) were observed in supine and prone positions, compared to controls. Ventral nerve root stretching resulted in sagittal/axial root angle changes. Median OF (0.04) in the lipomyelomeningocoele group was significantly less than that in control group (0.23). Median OF was also lesser in patients with thick filum terminale or meningomyelocele. Difference in median sagittal and axial root angles among the study and control groups was statistically significant (p = 0.00).
Conclusion
New dynamic MRI-based parameters to establish the presence and magnitude of TCS have been defined. OF measured the extent of loss of translational cord displacement in supine and prone positions; ΔBA defined the relative angulation of conus with lower spinal cord, and sagittal and axial root angles represented ventral nerve root stretching. The difference in OF or ΔBA was minimum in the group with thick filum terminale and progressively increased in the groups with lipomyelomeningocele and meningomyelocele.
... Cette étude montre que la rotation homolatérale ou controlatérale peut diminuer le confl it in vitro. Une préférence directionnelle est retrouvée dans 70 % des cas (n = 2 368 patients, 5 études) [20], mais il existe un amalgame trompeur entre les cervicales et les lombaires dans cet article. ...
In the French language literature, spinal anaesthesia (SA), epidural anaesthesia (EDA), and caudal anaesthesia (CA) are commonly grouped under the heading “anesthésies périmédullaires” (perispinal anaesthesia) or are still called “central nerve blocks”, compared to so-called “peripheral nerve blocks”. This definition leaves some doubt about the place of thoracic paravertebral (TPV) and lumbar plexus (LP) blocks: are they “proximal peripheral blocks” or “peripheral central blocks”? The English language literature combines spinal anaesthesia, epidural anaesthesia, and caudal anaesthesia under the label “central neuraxial blocks”, whilst TPV and LP blocks are combined under the term “perineuraxial blocks”. This very rightly promotes the concept of the close anatomical relationship between the thoracic paravertebral space and the neuraxis for TPV, and between the psoas compartment and the neuraxis for LP block. This relationship is confirmed by the functional consequences of these “perineuraxial” blocks: the commonplace and undesirable epidural spread of local anaesthetics observed during TPV and LP blocks. Perhaps in the French language literature, SA, EDA, and CA could be categorised under the term anesthésies médullaires (“spinal anaesthesia” with reference to central neuraxial blocks) and TPV block and LP block considered as anesthésies périmédullaires (“perispinal anaesthesia” with reference to perineuraxial blocks)? By analogy, the extremely low incidence of epidural spread during conduct of an interscalene block (ISB) leads us to classify it amongst peripheral nerve blocks. However, it could also be argued that ISB belongs under the heading “perineuraxial blocks” as the result of its injection site being so centrally located, and the proximity of the tissue planes which can lead to the direct injection or diffusion of local anaesthetic into the CSF. The rarity of this especially undesirable event is, without a doubt, due to the rigour with which ISB is practised: performed without ultrasound guidance (meticulous use of landmarks and safe axis of injection, depth of insertion limited by use of 25 mm needles etc.). The performance of TPV and LP blocks may suffer more from the lack of such precision as a result of their greater depth, their less common use and the fact that they are less well controlled (when compared to ISB).KeywordsCentral neuraxial anaesthesiaPerineuraxial anaesthesiaLumbar spineThoracic spineSpinal anaesthesiaEpidural anaesthesiaPre-proceduralReal time ultrasound guidanceParamedian sagittal obliquePosterior complexAnterior complexAcoustic window
Since the performance of the first thoracic spinal anaesthetic in early 1908 by Thomas Jonnesco in Romania, many anaesthetists have gained interest in this unorthodox neuraxial anaesthetic technique. The main rationale justifying its use is to prevent complications related to general anaesthesia in high-risk patient populations. There is, however, significant debate regarding this practice around the world. The main concerns are fear of iatrogenic injury to the spinal cord, cephalad spread of local anaesthetic causing a complete block, and haemodynamic instability owing to blockade of cardioaccelerator sympathetic fibres. The purpose of this narrative review is to appraise the literature critically regarding thoracic spinal anaesthesia and to synthesise the available information to provide a summary of evidence justifying its use in modern anaesthesia.
Spinal anesthesia can be affected by gaps in the ligamentum flavum that may confuse epidural needle placement; cause Quincke needle deformation if the vertebral bone is hit, expanding the dural sac hole and leading to cerebrospinal fluid (CSF) leakage and post-dural puncture headache; and variability in CSF volume, altering intrathecal drug dilution and anesthetic efficacy. Paramedian approaches with previously calculated optimal angles can be adopted, and CSF volumes may be estimated using threshold selection within the grayscale range following anatomical criteria. Angles can be determined by previously quantifying the skin-dural sac distance using ultrasound. Here, the relevant anatomical structures are illustrated (ligaments, the ligamentum flavum gap, vertebrae, meninges, cauda equina roots) using a freely available 3D PDF tool (http://hdl.handle.net/2445/55225), the additional inconvenience of variability in vertebra rotation is quantified, a free guide for optimizing spinal puncture is presented (http://hdl.handle.net/2445/179594), and the possibility of individualizing intrathecal drug dosages is discussed.
Marfan syndrome is a connective tissue disorder that may be complicated during pregnancy by aortic dissection. Caesarean section may be selected to avoid the haemodynamic challenges of vaginal birth. The common occurrence of dural ectasia in patients with Marfan syndrome is known to be associated with failed neuraxial anaesthesia. This report describes the administration of spinal anaesthesia to a woman with Marfan syndrome, and discusses why a hypobaric bupivacaine and opioid mixture, warmed to 37°C and injected intrathecally with the patient seated, produced successful surgical anaesthesia.
Introduction:
The classical recommendation for paramedian approaches is needle insertion 1-2cm paramedian and an angle of 10-15º medial-cephalad to the plane of the back, but contact with vertebrae is frequent.
Materials and methods:
A mathematical approach to individualizing punctures is proposed on the basis of skin-dural sac distance (d): Optimal angle ̴ inverse cosine [d/√(1+d^2)] and the distance covered by the needle ̴ √(1+d^2) for 1cm paramedian punctures. The inferred angles were compared to optimal angles leading to the central dorsal part of the dural sac from 1-2cm paramedian, measured by MRI in seven cases and in a short stature volunteer (1.58m, BMI 23.2), to study supine and fetal positions using both closed MR and ultrasound.
Results:
The average (d)decreased rostrally [6.8cm (L4-L5)-4.3cm (T11-T12)] while the mean optimal incidence angles increased [8.3º-16.5º (L4-L5) to 12.7º-24.1º (T11-T12) at 1-2cm paramedian, respectively] and coincided with the estimated angles with a correlation coefficient=0.98. In the volunteer, the optimal latero-medial angles increased from 14.4º-26.7º (L3-L4) to 17.1º-30.3º (T11-T12) for a (d)=3.7cm (L3-L4)-3.1cm (T11-T12) and increased ≤3.7º and ≤5.1º at 1 and 2 cm paramedian, respectively, in fetal positions in MR. Ultrasound yielded comparable figures. The range of possible angles for dural punctures is wider at 1cm paramedian in lower approaches in lateral decubitus [from 3.6º at T12L1 (12.2º-15.8º) to 9º at L3L4 (8.8º-18.7º)].
Conclusion:
The classically recommended angles of 10-15º differ from the optimal angles, particularly in small patients, suggesting the need for ultrasound guidance or for inferring angles prior to spinal anesthesia. This article is protected by copyright. All rights reserved.
We have designed, built, and tested an apparatus used for investigating the biomechanical response of a novel intradural spinal cord stimulator to the simulated physiological movement of the spinal cord within the thecal sac. In this apparatus, the rostral-caudal displacements of an anthropomorphic spinal cord surrogate can be controlled with a resolution of approximately 0.1% of a target value for up to 10(7) lateral movement cycles occurring at a repetition rate of 2 Hz. Using this system, we have been able to determine that the restoring force of the stimulator's suspension system works in concert with the frictional coupling between the electrode array and the surrogate to overcome the 0.42 μN inertial force associated with the lateral motion of the array. The result is a positional stability of the array on the surrogate (in air) of better than 0.2 mm over ∼500 000 movement cycles. Design modifications that might lead to improved physiological performance are discussed.
Abstract This study develops a means of delivering electrical stimuli directly to the pial surface of the spinal cord for treatment of intractable pain. This intradural implant must remain in direct contact with the cord as it moves within the spinal canal. Therefore, magnetic resonance imaging was used to measure the movement of the spinal cord between neutral and flexed-back positions in a series of volunteers (n = 16). Following flexion of the back, the mean change in the pedicle-to-spinal cord dorsal root entry zone distance at the T10-11 level was (8.5 ± 6.0) mm, i.e. a 71% variation in the range of rostral-caudal movement of the spinal cord across all patients. There will be a large spectrum of spinal cord strains associated with this observed range of rostral-caudal motions, thus calling for suitable axial compliance within the electrode bearing portion of the intradural implant.
Failed epidural anaesthesia or analgesia is more frequent than generally recognized. We review the factors known to influence the success rate of epidural anaesthesia. Reasons for an inadequate epidural block include incorrect primary placement, secondary migration of a catheter after correct placement, and suboptimal dosing of local anaesthetic drugs. For catheter placement, the loss of resistance using saline has become the most widely used method. Patient positioning, the use of a midline or paramedian approach, and the method used for catheter fixation can all influence the success rate. When using equipotent doses, the difference in clinical effect between bupivacaine and the newer isoforms levobupivacaine and ropivacaine appears minimal. With continuous infusion, dose is the primary determinant of epidural anaesthesia quality, with volume and concentration playing a lesser role. Addition of adjuvants, especially opioids and epinephrine, may substantially increase the success rate of epidural analgesia. Adjuvant opioids may have a spinal or supraspinal action. The use of patient-controlled epidural analgesia with background infusion appears to be the best method for postoperative analgesia.
The goal of this study was to investigate,with magnetic resonance imaging, the human anatomic positions of the spinal canal (eg, spinal cord, thecal tissue) in various postures and identify possible implications from different patient positioning for neuraxial anesthetic practice.
Nine volunteers underwent magnetic resonance imaging in supine, laterally recumbent, and sitting (head-down) positions. Axial and sagittal slices of the thoracic and lumbar spine were measured for the relative distances between anatomic structures, including dura mater and spinal cord.
The posterior dura-spinal cord (midline) distance is on average greater than the anterior dura-spinal cord (midline) distance along the thoracic spinal column, irrespective of volunteer postures (P G 0.05).The separation of the dura mater and spinal cord is greatest posterior in the middle thoracic region compared with upper and lower thoracic levels for all postures of the volunteers (P G 0.05). By placing the patient in a head-down sitting posture (as commonly done in epidural and spinal anesthesia), the posterior separation of the dura mater and spinal cordis increased.
The spinal cord follows the straightest line through the imposed geometry of the spinal canal. Accordingly, there is relatively more posterior separation of the cord and surrounding thecal tissue at midthoracic levels in the apex of the thoracic kyphosis. Placing a patient in a position that accentuates the thoracic curvature of the spine (ie,sitting head-down) increases the posterior separation of the spinal cord and dural sheath at thoracic levels.
We investigated, with magnetic resonance imaging, the distance of the dura mater to the spinal cord in patients without spinal or medullar disease at the 2nd, 5th, and 10th thoracic segments.
Fifty patients in the supine position underwent magnetic resonance imaging. Medial sagittal slices of the 2nd, 5th, and 10th thoracic segments were measured for the relative distances using the 1.5-T superconducting system (Gyroscan Intera, Philips Medical Systems, Best, the Netherlands). In 10 patients, the angles relative to the tangent at the insertion point on the skin were measured.
The posterior dural-spinal cord distance is significantly greater at the midthoracic region (5th thoracic = 5.8 +/- 0.8 mm) than at the upper (2nd thoracic = 3.9 +/- 0.8 mm) and lower thoracic levels (10th thoracic = 4.1 +/- 1.0 mm) (P < 0.015). There were no differences between interspaces T2 and T10. There was no correlation between age and the measured distance between the dura mater and the spinal cord. The entry angle of the needle at T2 was 9.0 degrees +/- 2.5 degrees ; at T5, 45.0 degrees +/- 7.4 degrees ; and at T10, 9.5 degrees +/- 4.2 degrees .
This study demonstrated that there is greater depth of the posterior subarachnoid space at the T2, T5, and T10 levels. The greater distance was found at T5.
Leg manipulation has been postulated to affect spinal curvature and position of the cauda equina within the dural sac. However, no evidence of such mechanical effects has been shown in living subjects. We used magnetic resonance imaging to evaluate the mechanical effects of leg position on these 2 parameters.
Sagittal and axial magnetic resonance images of the lumbosacral vertebral canal were obtained in 5 healthy, female volunteers with the subject in the supine position with knees straight, knees slightly flexed, and knees fully flexed.
In the straight leg position, physiologic lumbar lordosis was evident in all subjects on midline sagittal slices, whereas lumbar lordosis disappeared in the fully flexed leg position. On the axial slices the cauda equina moved ventrally within the dural sac in all subjects in the fully flexed leg position. In 1 of the 5 subjects the cauda equina moved ventrally and also separated completely into right and left parts.
Our findings indicate that 2 potential factors, flattening of the lumbar lordosis and some added tension on the lumbosacral nerve roots, may contribute to postoperative back and leg aching after spinal anesthesia in the lithotomy position.
- Hirabayashi