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CLINICAL ARTICLE
Since the introduction of pedicle screw xation in
spine surgery, loosening and pull-out of pedicle
screws have become well-known problems. In many
patients, especially those with osteoporosis, pedicle screw
anchoring may be problematic,23,55 and several efforts to
cope with this challenge have failed. Increasing screw
length and diameter leads to an improved screw-bone in-
terface in nonosteoporotic vertebrae but not in osteoporot-
ic vertebrae;6 and increased screw diameter, in particular,
increases the risk of pedicle rupture.23 Bicortical anchor-
ing leads to enhanced pullout force but may also increase
the risk of vascular or visceral injuries.2
Augmentation of pedicle screws with bone cement
was described as early as 1975 and increases the pedicle-
screw interface and pullout strength in osteoporotic verte-
brae.8,19,42,43 It allows pedicle screw xat ion in patients with
preoperatively known risk for screw loosening. Various
types of cement and techniques of application have been
described,42 but all of them involve the risk of cement leak-
age into the venous system or along fracture gaps around
the vertebrae. Cement leakage rates are reported in the lit-
erature of 13% to 17%.3,10, 25, 31,35 Indeed, pulmonary cement
embolism may occur.1
The aim of the present study was to identify cement
ABBREVIATIONS ASIA = American Spinal Injury Association; PMMA = polymethylmethacrylate; VAS = visual analog scale.
SUBMITTED May 4, 2015. ACCEPTED October 30, 2015.
INCLUDE WHEN CITING Published online March 4, 2016; DOI: 10.3171/2015.10.SPINE15511.
Cement leakage in pedicle screw augmentation: a
prospective analysis of 98 patients and 474 augmented
pedicle screws
Jan U. Mueller, MD,1 Joerg Baldauf, MD,1 Sascha Marx, MD,1 Michael Kirsch, MD,2
Henry W. S. Schroeder, MD, PhD,1 and Dirk T. Pillich, MD1
1Department of Neurosurgery, University Medicine Greifswald, 2Department of Radiology and Neuroradiology,
University Medicine Greifswald, Germany
OBJECTIVE Loosening and pull-out of pedicle screws are well-known problems in pedicle screw xation surgery. Aug-
mentation of pedicle screws with bone cement, rst described as early as 1975, increases the pedicle-screw interface
and pullout force in osteoporotic vertebrae. The aim of the present study was to identify cement leakage and pulmonary
embolism rates in a large prospective single-center series of pedicle screw augmentations.
METHODS All patients who underwent cement-augmented pedicle screw placement between May 2006 and October
2010 at the authors’ institution were included in this prospective cohort study. Perivertebral cement leakage and pul-
monary cement embolism were evaluated with a CT scan of the area of operation and with a radiograph of the chest,
respectively.
RESULTS A total of 98 patients underwent placement of cement-augmented pedicle screws; 474 augmented screws
were inserted in 237 vertebrae. No symptomatic perivertebral cement leakage or symptomatic pulmonary cement em-
bolism was observed, but asymptomatic perivertebral cement leakage was seen in 88 patients (93.6%) and in 165 aug-
mented vertebrae (73.3%). Cement leakage most often occurred in the perivertebral venous system. Clinically asympto-
matic pulmonary cement embolism was found in 4 patients (4.1%).
CONCLUSIONS Perivertebral cement leakage often occurs in pedicle screw augmentation, but in most cases, it is
clinically asymptomatic. Cement augmentation should be performed under continuous uoroscopy to avoid high-volume
leakage. Alternative strategies, such as use of expandable screws, should be examined in more detail for patients at high
risk of screw loosening.
http://thejns.org/doi/abs/10.3171/2015.10.SPINE15511
KEY WORDS pedicle screw; cement augmentation; cement leakage; technique
©AANS, 2016 J Neurosurg Spine March 4, 2016 1
J. U. Mueller et al.
J Neurosurg Spine March 4, 20162
leakage and pulmonary embolism rates in a large prospec-
tive monocentric series of pedicle screw augmentations.
We hypothesize that the actual leakage rate is higher than
the rates that have been reported in the literature.
Methods
All patients treated with augmented pedicle screws
between May 2006 and October 2010 were included in
the present prospective study. Perivertebral cement leak-
age was evaluated with a CT scan of the area of opera-
tion performed within 72 hours postoperatively and was
categorized according to the classication of Yeom et al.54
Their study clearly pointed out the superiority of a CT
scan compared with a radiograph to evaluate cement leak-
age after vertebroplasty. Yeom and coauthors demonstrat-
ed that use of only anteroposterior and lateral radiographs
failed to identify the whole amount of cement leakage re-
lated to the spinal canal or neural foramina, respectively.
The evaluation for pulmonary cement embolism was done
with an anterior-posterior radiograph of the chest obtained
within 24 hours postoperatively. Even if the patients did
not complain of pulmonary problems, cement distribution
to the thorax was assessed. All radiological reports were
done by an experienced radiologist (K.M.). Additionally,
perioperative data were recorded, including the number of
vertebrae treated, operative complications, blood loss, and
duration of the operation (from incision to closure). Peri-
operative pain was evaluated with a visual analog scale.15
Neurological decits were classied with the American
Spinal Injury Association (ASIA) Impairment Scale. Re-
sults are given in absolute numbers and percentages. The
study was approved by the local ethics committee.
Operative Technique
All operations were performed under general anesthe-
sia. Patients were in a prone position on a carbon plate
due to the need for an intraoperative 3D scan (Siremobil
ISO-C3D, Siemens AG, Medical Solutions). All procedures
were performed using pedicle screws from the Tango
System (Ulrich GmbH & Co. KG) and polymethylmeth-
acrylate (PMMA) cement. The screw is fully cannulated
with 20 radial holes (hole diameter 1.2 mm) and an inner
diameter of 1.68 mm. The radial holes are all within the
distal third of the screw. Screw placement was performed
according to the technique described by Weinstein et al.51
The decision for augmentation was made by an experi-
enced surgeon after screw placement according to the
mechanical strength of the implanted pedicle screw. After
evaluation of correct screw position with the 3D scan and,
if required, screw revision, the cement application system
was xed on top of the screw. Under intermittent X-ray
uoroscopy 1.5 ml or 2 ml PMMA per pedicle screw was
administered in the thoracic or lumbar spine, respectively.
Injection was interrupted if cement leakage was observed.
The procedure was continued after curing of the PMMA.
PMMA preparation and application was done according
to the instructions given by the company. Therefore, the
phase duration of mixing powder and liquid was 30 sec-
onds, application device lling was also 30 seconds, and
the waiting period of 300 seconds had to be maintained
before use of the cement.
Four experienced spine surgeons performed the op-
erations. The technique does not require a steep learning
curve.
Results
Cement Leakage and Pulmonary Embolism Rate
In the study period, pedicle screw augmentation was
performed in 98 patients. A total of 474 augmented screws
were inserted in 237 vertebrae. For the evaluation of ce-
ment leakage rates, 4 patients (4.1%), 8 vertebrae (3.4%),
and 16 screws (3.4%) had to be excluded due to missing
postoperative CT scans. For the evaluation of pulmonary
embolism, all patients were eligible. No symptomatic per i-
vertebral cement leakage or a symptomatic pulmonary
cement embolism was observed. However, asymptomat-
ic perivertebral cement leakage was seen in 88 patients
(93.6%) and in 165 augmented vertebrae (73.3%). With
respect to the classication of perivertebral cement leak-
age according to Yeom at al.,54 leakage was seen through
the segmental veins, basivertebral vein, and fracture gaps
in the vertebral body in 139 (61.8%), 93 (41.3%), and 26
(11.6%) of vertebrae, respectively (Table 1). Leakage from
a single site was seen in 85 vertebrae (37.8%), and a com-
bination of 2 or 3 leakage sites per vertebra was seen in
75 (33.3%) and 5 (2.2%) vertebral bodies, respectively. No
inuence of the underlying pathology on the cement leak-
age rate was observed. Clinically asymptomatic pulmo-
nary cement embolism was found in 4 patients (4.1%)—1
with an osteoporotic fracture, 1 with degenerative instabil-
ity and 2 with pathological fractures (Table 1). No pulmo-
nary embolism or perivertebral cement leakage required
further treatment. Representative images demonstrating
perivertebral cement leakage and pulmonary cement em-
bolism are shown (Figs. 1 and 2).
Patient Characteristics
The indications for pedicle screw augmentation were
TABLE 1. Route of cement leakage in numbers per vertebra and number of patients with lung embolism according to
the different indications for cement-augmented pedicle screw xation
Cement Leakage or Embolism
Indication
Osteoporotic Fracture Pathological Fracture Degenerative Instability Total
Segmental vein 31 9747
Basivertebral vein 42 14 460
Fracture gap 23 6 6 35
Lung embolism 1 2 1 4
Cement leakage in pedicle screw augmentation
J Neurosurg Spine March 4, 2016 3
unstable osteoporotic fractures in 68 patients (69.4%), path-
ological fractures due to bone metastases in 18 (18.4%),
and degenerative instability in 12 (12.2%). The patient
group included 64 men and 34 women, and the mean age
at surgery was 70.6 years (range 41–84 years). Patients with
osteoporotic fractures were older (mean age 72 years) than
patients with pathological fractures (mean age 64 years).
Augmented pedicle screws were inserted from T-2 to S-1,
with the most frequent levels being in the lumba r spine and
at the thoracolumbar junction (Fig. 3). Fixation was per-
formed at more levels in patients with pathological frac-
tures than in patients with osteoporotic fractures or degen-
erative instabilities. The operation was a primary surgery
in 83 cases (84.6%) and a revision surgery in 15 (15.4%).
Operative stabi lization with augmented pedicle screws was
the only procedure in 55 patients (56.1%). Secondary pro-
cedures were microsurgical decompression (performed in
26 cases [26.5%]) and intervertebral body fusion/vertebral
body reconstruction (performed in 17 cases [17.4%]). There
was no deterioration in the ASIA motor score in any pa-
tient, and an improvement of 1 or 2 levels was seen in 10
(10.2%) and 1 (1%) of the patients, respectively. The mean
visual analog scale (VAS) score improved from 7.4 points
at admission to 3.4 points at discharge. Detailed patient
characteristics are shown in Table 2.
Perioperative Complications
No clinical complication due to uncontrolled cement
leakage in the spinal canal or cement-induced pulmo-
nary embolism was observed. In 5 patients (5.1%), cement
application was stopped before the target volume was
reached due to obvious cement leakage under uorosco-
py control. Intraoperative screw revision due to medial or
lateral pedicle perforation occurred in 17 patients (17.3%)
and 19 screws (4%), respectively. In 3 patients (3.1%), in-
traoperative CSF leakage due to screw-related dura mater
injury was observed; in all 3 cases, the defect was repaired
with allogenic plastic reconstruction. In 2 patients (2%), a
cement-related blockade of the screw locking mechanism
occurred. However, the screws were replaced with screws
of the same caliber without problems. Major bleeding with
more than 1000 ml blood loss was observed in 9 patients
(9.2%), of whom 7 patients had pathological fractures, 1
patient had an osteoporotic fracture, and 1 patient was
undergoing multilevel instrumentation placement. In the
postoperative course, 2 patients (2%) suffered from asep-
tic epifascial seroma. Secondary wound closure could be
achieved after repetitive taps and treatment with continu-
ous vacuum therapy.
Discussion
Summary of Key Results
The present series of PMMA-augmented pedicle screw
placement in 98 patients reveals perivertebral cement
lea kage in 73.3% of analyzed vertebral bodies and asymp-
tomatic pulmonary embolism in 4% of evaluated patients.
Cement leakage most often occurred in the perivertebral
venous system, including the epidural veins via basiverte-
bral vein. However, no deterioration was seen in the post-
operative ASI A impairment scale scores, and no operative
cement removal was required.
FIG. 1. Postoperative CT scans illustrating leakage types according to the classification of Yeom. A: Type B, on the right side near
the neuroforamen, and Type S, a horizontal course in the spinal canal in the epidural plexus. B: Type C, via a cortical defect, and
Type S, via a basivertebral vein on the left side in the spinal canal in the epidural plexus. C: Type S, via a basivertebral vein in the
epidural plexus.
FIG. 2. Anteroposterior radiograph demonstrating a pulmonary cement
embolism on the left side (arrow).
J. U. Mueller et al.
J Neurosurg Spine March 4, 20164
Limitations
Although the present study reveals solid data in a pro-
spective design, some limitations need to be addressed.
First, the herein-investigated cement augmentation via
cannulated screws is not the only pedicle screw augmen-
tation technique. Cement can be applied in vertebroplasty
or kyphoplasty prior to screw insertion,4,27 but in these in-
stances, it is applied with less application pressure, and the
results of the present study should not be used for extrapo-
lation. Second, there are numerous different pedicle screw
types, varying in core diameter and size and number and
location of radial holes.42 The screw used in the present
study has about 20 radial holes in its distal third (hole
diameter 1.2 mm) and has a core diameter of 1.68 mm.
High cement application pressure as well as low cement
viscosity are directly related to an increased cement leak-
age rate.27 According to the law of Hagen-Poiseuille, low-
er application pressure and applicability of cement with
a higher viscosity could be achieved by enlargement of
both radial holes and core diameter. Additionally, cement
leakage occurs most frequently in the most proximal ra-
dial holes.12 Screw design, therefore, might have an impact
on cement leakage rates, and results of the present study
cannot be extrapolated to all screw designs. However,
previous studies12,31 with rates of cement leakage varying
between 13% and 17% were based on the use of different
FIG. 3. Frequency of pedicle screw fixation according to ver tebral level. Results are given in absolute numbers of all treated
vertebral bodies. Th = thoracic.
TABLE 2. Demographic, operation-related, and clinical outcome data
Variable
Indication
Osteoporotic Fracture Pathological Fracture Degenerative Instability Total
Mean age (yrs) 72 64.4 70.4 70.6
Sex (no. of patients)
Female 47 10 960
Male 21 8338
Mean duration of op (mins) 158 192 224 174
Mean blood loss (ml) 324 1085 535 521
Change in ASIA score from preop to postop
(no. of patients)
Increased 6 4 1 11
Unchanged 52 14 11 77
Decreased 0 0 0 0
VAS score, mean
Preop 7.3 7.5 7.4 7.4
Postop 3.2 3.8 3.2 3.4
No. of augmented screws per patient 4.6 5.8 4.8 5
Cement leakage in pedicle screw augmentation
J Neurosurg Spine March 4, 2016 5
cannulated screws with fewer distal fenestrations than the
screws used in our study. Third, the pulmonary embolism
rate of 4% in the present series might be an underestimate
due to the low sensitivity of radiographs for detecting it.41
However, there is no indication for CT scans of the lung in
asymptomatic patients.
Cement Leakage in Pedicle Screw Augmentation is an
Underestimated Problem
Cement leakage during pedicle screw augmentation is
a well-known problem. However, reported leakage rates
of 0%,3 5.4%35 or 14%
10 differ greatly from our results.
Unfortunately, published data on leakage rates in pedicle
screw augmentation with a study group of a size similar
to ours are rare. The cement application, however, is com-
parable to its use in vertebroplasty and kyphoplasty,49 and
leakage rates might be comparable too. Cement leakage
rates in vertebroplasty and kyphoplasty are reported to be
bet ween 19. 3% 47 and 80%,
46 but they are usually above
40%.9,22,24,32,36,44,48,49 The reason for high leakage rates in
cadaver models might be the missing venous counter-pres-
sure,6 but this does not explain high leakage rates during
surgery. The amount of applied cement in the literature
varies between 1.8 ml and 2.9 ml per screw,18, 35 which is
comparable to the amount used in the present study. Bio-
mechanical capacity would not increase after raising the
application above 2.8 ml per screw.19 Furthermore, there
is a positive correlation between the applied cement vol-
ume and the likelihood of cement leakage.2 ,45 The cement
volume should be kept to the smallest volume needed
and should not exceed 2.8 ml per pedicle screw.17 High
application pressure, liquidity of the cement, and special
anatom ical features of the perivertebral venous system are
conducive to cement leakage.
The Perivertebral Venous System Fosters Cement
Leakage
Leakage reported in the present study occurred mostly
via segmental veins and basivertebral veins, which is in
agreement with data from the literature.11 Most cement
leakage during pedicle screw augmentation is along the
perivertebral venous system.11,19,5 4 The reduced pressure
of the venous system compared with the pressure of the
spongiosa that it surrounds and missing venous valves in
the internal and external anterior venous plexus are a rea-
sonable explanation.21 The position of the cement in the
vertebral body might have a major impact on the leakage
rate, since Kaso et al. demonstrated an enhanced cement
leakage in the spinal canal via basivertebral vein in a me-
dial needle position under vertebroplasty compared with
a lateral position.28 With respect to these data, a lateral
screw positioning could prevent dangerous cement leak-
age in the spinal canal. This technique, however, rst
described by Roy-Camille et al.,40 leads to an enhanced
violation rate of the upper facet joints compared with the
method of Weinstein et al., which is used in our depart-
ment.14, 51,52
Symptomatic Leakage is Rare
Cement leakage may cause neurological decits in sin-
gle cases.26 However, in the present series there was none
of the symptomatic cement lea kage repor ted in other stud-
ies.11,1 9,2 5,4 6 The rate of cement-associated lung embolism
was 4% in the present study. However, as in most cases,
it was clinically asymptomatic.1,29,38,39 Due to the low sen-
sitivity of conventional chest radiographs compared with
CT scans, a much higher asymptomatic embolism rate
must be assumed.30 Studies of the rate of pulmonary em-
bolism after percutaneous vertebroplasty have reported
substantially different rates depending on the detection
modality, with radiographs yielding a rate of 6.8%16 and
CT yielding a rate of 23%.13 Treatment of pulmonary ce-
ment embolism is recommended in symptomatic but not
asymptomatic cases. The treatment algorithm should fol-
low the guidelines for treatment of thrombotic pulmonary
embolism.33 Rev isi on of ceme nt-augmented pe dicle sc rews
can be done without hesitation, since it was practicable in
the present study as well as in reports from the literature.5,7
Has the Last Word Been Said in Cement Augmentation?
Cement leakage occurs frequently in pedicle screw
augmentation, but it is clinically asymptomatic in most
cases. Nevertheless, it is questionable to continue with
a basically harmful procedure without making attempts
at improvement. For instance, the indications for cement
augmentation might be made more objective. Intraop-
erative, pre-augmentation measurement of bone density
could be useful.37 Intraoperative osseous phlebography
after screw insertion and prior to cement augmentation
might be helpful to avoid cement leakage in larger verte-
bral veins;2 h owever, ph le bography is itsel f associat ed with
risks, including the risk of pedicle rupture, in addition to
increasing the overall duration of the operation. Careful
injection of cement under continuous uoroscopy and us-
ing the proper amount of cement might be more benecial.
New screw designs involving a cannulated screw with ra-
dial holes but a closed tip may reduce anterior leakage,20
but anterior leakage does not play a major role. One major
problem associated with PMMA is injury to neural tissue.
In addition to direct injury due to mechanical irritation,
thermal injury can result from the exothermic polymeriza-
tion process. For this reason cements have been developed
that do not generate heat during the hardening process.50
Bicortical anchoring of pedicle screws enhances the pull-
out strength in the same fashion as cement augmentation
while increasing the risk of vascular or visceral injuries.2
However, risk for vascular injuries might be minimal in
the sacral region. Therefore, cement augmentation in the
thoracic and lumbar spine and bicortical screw anchoring
without augmentation in the sacral spine might be a pos-
sible strategy.10 Encouraging results are reported for the
use of expandable pedicle screws, which have the same
biomechanical properties in osteoporotic bone without the
risk of cement leakage.13,34, 53
Conclusions
Perivertebral cement leakage often occurs in pedicle
screw augmentation (73.3%) but is usually clinically
asymptomatic. Cement augmentation should be performed
under continuous uoroscopy to avoid high-volume leak-
J. U. Mueller et al.
J Neurosurg Spine March 4, 20166
age. The indication for augmentation should be dened
with consideration of risks and benets for the patient. Al-
ternative strategies such as expandable screws should be
examined in more detail in patients at high risk for screw
loosening. Standard postoperative CT scans of the opera-
tion site or the chest may be avoided as long as there is no
symptomatic complication. In this way, radiation burden
and costs can be lowered.
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Disclosures
Jan U. Mueller is a consultant to Signus Medizintechnik GmbH
and Ulrich GmbH.
Author Contributions
Conception and design: Mueller, Baldauf, Pillich. Acquisition
of data: Mueller, Kirsch, Pillich. Analysis and interpretation of
data: Marx, Mueller, Baldauf, Kirsch, Pillich. Drafting the article:
Marx, Pillich. Critically revising the article: Marx, Mueller,
Baldauf, Schroeder. Reviewed submitted version of manuscript:
Marx, Schroeder. Approved the final version of the manuscript on
behalf of all authors: Marx. Study supervision: Mueller, Baldauf,
Schroeder.
Correspondence
Sascha Marx, Department of Neurosurgery, University of
Greifswald, Sauerbruchstraße, Greifswald 17475, Germany.
email: marxs@uni-greifswald.de.
