Construct stability of an instrumented 2-level cervical corpectomy model following fatigue testing: biomechanical comparison of circumferential antero-posterior instrumentation versus a novel anterior-only transpedicular screw-plate fixation technique.

INTRODUCTION: A high rate of complications in multilevel cervical surgery with corpectomies and anterior-only screw-and-plate stabilization is reported. A 360°-instrumentation improves construct stiffness and fusion rates, but adds the morbidity of a second approach. A novel ATS-technique (technique that used anterior transpedicular screw placement) was recently described, yet no study to date has analyzed its performance after fatigue loading. Accordingly, the authors performed an analysis of construct stiffness after fatigue testing of a cervical 2-level corpectomy model reconstructed using a novel anterior transpedicular screw-and-plate technique (ATS-group) in comparison to standard antero-posterior instrumentation (360°-group). MATERIALS AND METHODS: Twelve fresh-frozen human cervical spines were mounted on a spine motion tester to analyze restriction of ROM under loading (1.5 Nm) in flexion-extension (FE), axial rotation (AR), and lateral bending (LB). Testing was performed in the intact state, and after instrumentation of a 2-level corpectomy C4 + C5 using a cage and the constructs of ATS- and 360°-group, after 1,000 cycles, and after 2,000 cycles of fatigue testing. In the ATS-group (n = 6), instrumentation was achieved using a customized C3-C6 ATS-plate system. In the 360°-group (n = 6), instrumentation consisted of a standard anterior screw-and-plate system with a posterior instrumentation using C3-C6 lateral mass screws. Motion data were assessed as degrees and further processed as normalized values after standardization to the intact ROM state. RESULTS: Specimen age and BMD were not significantly different between the ATS- and 360°-groups. After instrumentation and 2,000 cycles of testing, no specimen exhibited a ROM greater than in the intact state. No specimen exhibited catastrophic construct failure after 2,000 cycles. Construct stiffness in the 360°-group was significantly increased compared to the ATS-group for all loading conditions, except for FE-testing after instrumentation. After 2,000 cycles, restriction of ROM under loading in FE was 39.8 ± 30% in the ATS-group vs. 2.8 ± 2.3% in the 360°-group, in AR 60.4 ± 25.8 vs 15 ± 11%, and in LB 40 ± 23.4 vs 3.9 ± 1.2%. Differences were significant (p < 0.05). CONCLUSION: 360°-instrumentation resembles the biomechanical standard of reference for stabilization of 2-level corpectomies. An ATS-construct was also shown to confer high construct stiffness, significantly reducing the percentage ROM beyond that of an intact specimen after 2,000 cycles. This type of instrumentation might be a clinical valuable and biomechanically sound adjunct to multilevel anterior surgical procedures.

Selective thoracic fusion in AIS curves: the definition of target outcomes improves the prediction of spontaneous lumbar curve correction (SLCC).

INTRODUCTION: The decision of when to use selective thoracic fusion (STF) and the prediction of spontaneous lumbar curve correction (SLCC) remain difficult. Using a novel methodological approach, the authors yielded for a better prediction of SLCC and analyzed the efficacy of anterior scoliosis correction and fusion (ASF). METHODS: A retrospective analysis of 273 patients treated with ASF for STF was performed. In total, 87 % of the patients showed a Lenke 1 curve pattern. The lumbar curve modifier was classified as A in 66 % of the patients, B in 21 % of the patients and C in 13 % of the patients. The fusion length averaged 6.7 levels. The analysis included an assessment of radiographic deformity and correction, surgery characteristics, complications and revisions and clinical outcomes to improve the prediction of SLCC. Patients with a Type A-L, Type B or Type C modifier were stratified into a target follow-up lumbar curve (LC) category of ≤20° or >20°. Linear regression analyses were performed to assess the accuracy of predicting LC magnitude, and a multivariate logistic regression model was built using the following preoperative (preop) predictors: main thoracic curve (MTC), LC, MTC-bending and LC-bending. The output variable indicated whether a patient had an LC >20° at follow-up. A variable selection algorithm was applied to identify significant predictors. Two thresholds (cut-offs) were applied to the test sample to create high positive and negative prediction values. The data from 33 additional patients were gathered prospectively to create an independent test sample to learn how the model performed with independent data as a test of the generalizability of the model. RESULTS: The average patient age was 17 years, and the average follow-up period was 33 months. The MTC was 53.1° ± 10.2° preoperatively, 29.8° ± 10.5° with bending and was 25.4° ± 9.7° at follow-up (p < 0.01). The LC was 35.7° ± 7.5° preoperatively, 8.9° ± 5.8° with bending, and 21.8° ± 7.0° at follow-up (p < 0.01). After applying a variable selection algorithm, the preop LC [p < 0.02, odds ratio (OR) = 1.09] and preop LC-bending (p < 0.009, OR = 1.14) remained in the model as significant predictors. The performance of the linear regression model was tested in an independent test sample, and the difference between the observed and predicted values was only 1° ± 4.5°. Based on the test sample, the lower threshold was set to 25 %, and the upper threshold was set to 75 %. Patients with prediction values of 25-75 % were identified by the model, but by definition of the model, no prediction was made. In the test sample, 87 % of the patients were correctly classified as having an LC ≤20° at follow-up, and 84 % of the patients were correctly classified as having an LC >20°. The model test in the independent test sample revealed that 100 % of the patients were correctly classified as having an LC ≤20°, and 86 % of the patients were correctly classified as having an LC >20°. CONCLUSION: After analyzing a sufficiently large sample of 273 patients who underwent ASF for STF, significant predictors for SLCC were established and reported according to the surgical outcomes. Application of the prediction models can aid surgeons in the decision-making process regarding when to perform STF. Our results indicate that with stratification of outcomes into target curves (e.g., an LC <20°), future benchmarks for STF might be more conclusive.

Surgical outcomes of scoliosis surgery in Marfan syndrome.

STUDY DESIGN: Retrospective review of a case series. OBJECTIVE: To present the radiologic and surgical characteristics of scoliosis treatment in patients with Marfan syndrome (MFS). SUMMARY OF BACKGROUND DATA: The treatment of scoliosis in MFS has been reported to pose unique challenges. However, the information on surgical outcomes is sparse. In clinical practice, surgery for scoliosis in MFS is reported to confer higher perioperative risks and instrumentation-related complications compared with adolescent idiopathic scoliosis because of atypical and rigid curve patterns and the underlying desmogenic disorder. METHODS: Database research identified 26 MFS patients treated surgically during 7 years at a single spine center. Three patients presented with previous failed surgeries and were excluded. The medical records, charts, and radiographs of 23 patients were analyzed focusing on curve characteristics, surgical outcomes including complications, and curve correction using modern third-generation hybrid or pedicle screw systems, and the behavior of junctional segments and compensatory curves. RESULTS: The sample included 18 female and 5 male patients with an average age of 18.2±9.2 years (13-52 y) at index surgery and 21.2±9.2 years (14-53 y) at follow-up, averaging 35.8±23.5 months (6-95 mo). According to the Lenke classification, 30% presented as type 1, 9% as type 2, 22% as type 3, 9% as type 4, 17% as type 5, and 13% of patients as type 6. Seventy-four percent of patients had a type C lumbar modifier. In total, 48% of patients underwent a posterior spinal fusion (PSF). Thirty percent had instrumented anterior spinal fusion (AISF), whereas 22% had a combined anterior release and staged PSF. Ninety-one percent of patients achieved solid fusion; there was 1 asymptomatic nonunion and 1 recalcitrant nonunion. Add-on phenomena were identified in 13% of patients (n=3) treated with AISF, indicating staged PSF once. In total, complications were encountered in 30% of patients, indicating redo surgery in 17% of patients. The cause for revision included nonunion (2x), liquor leakage (1x), and wound infection at the iliac crest (1x). We judged the outcome as excellent/good if the patient had no major redo surgery and was very satisfied/satisfied. Overall, excellent/good outcome was noted in 78% of the patients. Blood loss averaged 659 mL in AISF and 1748 mL in PSF. The surgical time was 193 minutes in AISF and 229 minutes in PSF. Preoperative, postoperative, and follow-up Cobb T4-T12 was 13, 13, and 16 degrees, respectively; the mean thoracic curves measured 66 (23-106), 36 (0-58), and 38 degrees (0-58), respectively. Lumbar curves measured 63 (23-110), 27 (0-80), and 24 degrees (0-68), respectively. Coronal plumb line measured 2.2, 2.6, and 1.2 cm, respectively, indicating good trunk balance in most patients. The flexibility rates of thoracic curves and lumbar curves were 38% and 47%, respectively. Thoracic curve correction in PSF and combined anterior release/PSF was 44%, and in AISF, it reached 57%. CONCLUSIONS: The current study highlights the potential pitfalls in scoliosis surgery for patients with MFS. Surgery was performed using third-generation pedicle screw-based and hook-based systems for PSF and second-generation and third-generation implants for AISF. We illustrated that the treatment of scoliosis in MFS, taking into account the individual challenges of the underlying desmogenic disorder, can be performed with a moderately increased risk for surgical complications compared with adolescent idiopathic scoliosis.

Non-instrumented correction of cervicothoracic kyphosis in ankylosing spondylitis: a critical analysis on the results of open-wedge osteotomy C7-T1 with gradual Halo-Thoracic-Cast based correction.

INTRODUCTION: With progression of cervicothoracic kyphosis (CTK), ankylosing spondylitis (AS) patients suffer functional disability. Surgical correction still poses neurologic risks, while evidence of an ideal technique preventing its complications is weak. MATERIALS AND METHODS: We report our results with non-instrumented correction in perspective of a review of literature, serving as an important historical control. Database review identified 18 AS patients with CTK correction. After application of a Halo-Thoracic-Cast (HTC) patients underwent posterior non-instrumented open-wedge osteotomy at C7/T1 and osteotomy closure by threaded HTC-rod adjustments. Postoperative gradual HTC correction was continued for 2-4 weeks. Patients were invited for follow-up and medical charts were reviewed for demographics, surgical details, complications and outcomes. The patients' preoperative, postoperative, before HTC removal and follow-up photographs were analyzed for the Chin-Brow-Vertical-Angle (CBVA), radiographs for the CTK angle. RESULTS: Patients' age was 50 ± 11 years, follow-up was 37 ± 47 months and CBVA correction was 25° ± 9° (p < 0.000001). The final radiographic correction at follow-up was 20° ± 11° (p = 0.00002). At the latest follow-up, three patients judged their outcome as excellent, nine good, three moderate and one poor. Upon invitation, seven patients appeared with follow-up averaging 87 months. Neck-pain disability index was 8 ± 14 %. Two patients died, three were lost, one had revision elsewhere and five just had a routine follow-up. Six patients sustained a minor and ten a major complication. Revisions were indicated in five patients including infection, C8-radiculopathy and neurologic events by translation at the osteotomy. A total of 44 % of patients showed translation at the osteotomy indicating acute surgery with instrumentation twice after osteotomy closure, three patients had a revision posterior decompression and instrumented fusion for sequels related to translation. CONCLUSION: With the non-instrumented HTC-based technique, average CBVA correction of 25° was achieved and all patients were ambulatory at follow-up. However, regarding translation at the osteotomy, loss of correction, morbidity of the HTC and lack of control at the osteotomy instrumentation-based correction and instrumented fusion seem to be preferable.

In vivo analysis of cervical kinematics after implantation of a minimally constrained cervical artificial disc replacement.

INTRODUCTION: To better understand cervical kinematics following cervical disc replacement (CDR), the in vivo behavior of a minimally constrained CDR was assessed. METHODS: Radiographic analysis of 19 patients undergoing a 1-level CDR from C4-5 to C6-7 (DISCOVER, Depuy-Spine, USA) was performed. Neutral-lateral and flexion-extension radiographs obtained at preop, postop and late follow-up were analyzed for segmental angle and global angle (GA C2-7). Flexion-extension range of motion was analyzed using validated quantitative motion analysis software (QMA®, Medical Metrics, USA). The FSU motion parameters measured at the index and adjacent levels were angular range of motion (ROM), translation and center of rotation (COR). Translation and COR were normalized to the AP dimension of the inferior endplate of the caudal vertebra. All motion parameters, including COR, were compared with normative reference data. RESULTS: The average patient age was 43.5 ± 7.3 years. The mean follow-up was 15.3 ± 7.2 months. C2-7 ROM was 35.9° ± 15.7° at preop and 45.4° ± 13.6° at follow-up (∆p < .01). Based on the QMA at follow-up, angular ROM at the CDR level measured 9.8° ± 5.9° and translation was 10.1 ± 7.8 %. Individuals with higher ROM at the CDR level had increased translation at that level (p < .001, r = 0.97), increased translation and ROM at the supra-adjacent level (p < .001, r = .8; p = .005, r = .6). There was a strong interrelation between angular ROM and translation at the supra-adjacent level (p < .001, r = .9) and caudal-adjacent level (p < .001, r = .9). The location of the COR at the CDR- and supra-adjacent levels was significantly different for the COR-X (p < .001). Notably, the COR-Y at the CDR level was significantly correlated with the extent of CDR-level translation (p = .02, r = .6). Shell angle, which may be influenced by implant size and positioning had no impact on angular ROM but was correlated with COR-X (p = .05, r = -.6) and COR-Y (p = .04, r = -.5). CONCLUSION: The COR is an important parameter for assessing the ability of non-constrained CDRs to replicate the normal kinematics of a FSU. CDR size and location, both of which can impact shell angle, may influence the amount of translation by affecting the location of the COR. Future research is needed to show how much translation is beneficial concerning clinical outcomes and facet loading.

Comparison of revision strategies for failed C2-posterior cervical pedicle screws: a biomechanical study.

STUDY PURPOSE: With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs. MATERIALS AND METHODS: Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion accuracy was verified by fluoroscopy. C2 vertebrae were potted and fixed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with 4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%). RESULTS: The POR of primary 3.5-mm CPSs was 1,140.5 ± 539.6 N for Group-1 and 1,007.7 ± 362.5 N for Group-2; the difference was not significant. In the revision setting, the POR in Group-1 was 705.8 ± 449.1 N, representing a reduction of 38.1 ± 32.9 % compared with that of primary screw fixation. For Group-2, the POR was 875.3 ± 367.9 N, representing a reduction of 13.1 ± 23.4 %. A statistical analysis showed a significantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a significantly reduced POR for both revision strategies compared with primary fixation (p < 0.001/p = 0.001), the loss of POR (in %) in Group-1 was significantly higher compared with the loss in Group-2 (p = 0.04). CONCLUSIONS: Using a larger-diameter screw combined with the application of a pedicle bone-plastic, the POR can be significantly increased compared with the use of only an increased screw diameter.

The impact of halo-gravity traction on curve rigidity and pulmonary function in the treatment of severe and rigid scoliosis and kyphoscoliosis: a clinical study and narrative review of the literature.

INTRODUCTION: The treatment of rigid and severe scoliosis and kyphoscoliosis is a surgical challenge. Presurgical halo-gravity traction (HGT) achieves an increase in curve flexibility, a reduction in neurologic risks through gradual traction on a chronically tethered cord and an improvement in preoperative pulmonary function. However, little is known with respect to the ideal indications for HGT, its appropriate duration, or its efficacy in the treatment of rigid deformities. MATERIALS AND METHODS: To investigate the use of HGT in severe deformities, we performed a retrospective review of 45 patients who had severe and rigid scoliosis or kyphoscoliosis. The analysis focused on the impact of HGT on curve flexibility, pulmonary function tests (PFTs), complications and surgical outcomes in a single spine centre. RESULTS: PFTs were used to assess the predicted forced vital capacity (FVC%). The mean age of the sample was 24±14 years. 39 patients had rigid kyphoscoliosis, and 6 had scoliosis. The mean apical rotation was 3.6°±1.4°, according to the Nash and Moe grading system. The curve apices were mainly in the thoracic spine. HGT was used preoperatively in all the patients. The mean preoperative scoliosis was 106.1°±34.5°, and the mean kyphosis was 90.7°±29.7°. The instrumentation used included hybrids and pedicle screw-based constructs. In 18 patients (40%), a posterior concave thoracoplasty was performed. Preoperative PFT data were obtained for all the patients, and 24 patients had ≥3 assessments during the HGT. The difference between the first and the final PFTs during the HGT averaged 7.0±8.2% (p<.001). Concerning the evolution of pulmonary function, 30 patients had complete data sets, with the final PFT performed, on average, 24 months after the index surgery. The mean preoperative FVC% in these patients was 47.2±18%, and the FVC% at follow-up was 44.5±17% (a difference that did not reach statistical significance). The preoperative FVC% was highly predictive of the follow-up FVC% and the response during HGT. The mean flexibility of the scoliosis curve during HGT was only 14.8±11.4%, which was not significantly different from the flexibility measures achieved on bending radiographs or Cotrel traction radiographs. In rigid curves, the Cobb angle difference between the first and final radiographs during HGT was only 8°±9° for scoliosis and 7°±12° for kyphosis. Concerning surgical outcomes, 13 patients (28.9%) experienced minor and 15 (33.3%) experienced major complications. No permanent neurologic deficits or deaths occurred. Additional surgery was indicated in 12 patients (26.7%), including 7 rib-hump resections. At the final evaluation, 69% of the patients had improved coronal balance, and at a mean follow-up of 33±23.3 months, 39 patients (86.7%) were either satisfied or very satisfied with the overall outcome. CONCLUSION: The improvement of pulmonary function and the restoration of sagittal and coronal balance are the main goals in the treatment of severe and rigid scoliosis and kyphoscoliosis. A review of the literature showed that HGT is a useful tool for selected patients. Preoperative HGT is indicated in severe curves with moderate to severe pulmonary compromise. HGT should not be expected to significantly improve severe curves without a prior anterior and/or posterior release. The data presented in this study can be used in future studies to compare the surgical and pulmonary outcomes of severe and rigid deformities.

Efficacy of anterior odontoid screw fixation in the elderly patient: a CT-based biometrical analysis of odontoid fractures.

In the elderly population, reported union rates with anterior odontoid screw fixation (AOSF) for odontoid fracture (OF) treatment vary between 23 and 93% when using plain radiographs. However, recent research revealed poor interobserver reliability for fusion assessment using plain radiographs compared to CT scans. Therefore, union rates in patients aged ≥60 years treated with AOSF have to be revisited using CT scans and factors for non-union to be analysed. Prospectively gathered consecutively treated patients using AOSF for odontoid fracture with age ≥60 years were reviewed. Medical charts were assessed for demographics, clinical outcomes and complications. Patients' preoperative radiographs and CT scans were analysed to characterize fracture morphology and type, fracture displacement, presence of atlanto-dental osteoarthritis as well as a detailed morphometric assessment of fracture surfaces (in mm(2)). CT scans performed after a minimum of 3 months postoperatively were analysed for fracture union. Those patients not showing CT-based evidence of completely fused odontoid fracture were invited for radiographic follow-up at a minimum of 6 months follow-up. Follow-up CT-scan were studied for odontoid union as well as the number of screws used and the square surface of screws used for AOSF and the related corticocancellous osseous healing surface of the odontoid fragment (in %) were calculated. Patients were stratified whether they achieved osseous union or fibrous non-union. Patients with a non-union were subjected to flexion-extension lateral radiographs and the non-union defined as stable if no motion was detected. The sample included 13 male (72%) and 5 female (18%) patients. The interval from injury to AOSF was 4.1 ± 5.3 days (0-16 days). Age at injury was 78.1 ± 7.6 years (60-87 years) and follow-up was 75.7 ± 50.8 months (4.2-150.2 months). 10 patients had dislocated fractures, 14 had Type II and 4 "shallow" Type III fractures according to the Anderson classification, 2 had stable C1-ring fractures, 8 had displayed atlanto-dental osteoarthritis. Fracture square surface was 127.1 ± 50.9 mm(2) (56.3-215.9 mm(2)) and osseous healing surface was 84.0 ± 6.8% (67.6-91.1%). CT-based analysis revealed osseous union in 9 (50%) and non-union in 9 patients (50%). Union rates correlated with increased fracture surface (P = 0.02). Statistical analysis revealed a trend that the usage of two screws with AOSF correlates with increased fusion rates (P = 0.06). Stability at C1-2 was achieved in 89% of patients. CT scans are accepted as the standard of reference to assess osseous union. The current study offers an objective insight into the union rates of odontoid fractures treated with AOSF using CT scans in consecutive series of 18 patients ≥60 years. Literature serves evidence that elderly patients with unstable OF benefit from early surgical stabilization. However, although using AOSF for unstable OF yields segmental stability at C1-2 in a high number of patients as echoed in the current study, our analysis stressed that using follow-up CT scans in comparison to biplanar radiographs dramatically reduces osseous union rates compared to those previously reported for AOSF.

A biomechanical rationale for C1-ring osteosynthesis as treatment for displaced Jefferson burst fractures with incompetency of the transverse atlantal ligament.

Nonsurgical treatment of Jefferson burst fractures (JBF) confers increased rates of C1-2 malunion with potential for cranial settling and neurologic sequels. Hence, fusion C1-2 was recognized as the superior treatment for displaced JBF, but sacrifies C1-2 motion. Ruf et al. introduced the C1-ring osteosynthesis (C1-RO). First results were favorable, but C1-RO was not without criticism due to the lack of clinical and biomechanical data serving evidence that C1-RO is safe in displaced JBF with proven rupture of the transverse atlantal ligament (TAL). Therefore, our objectives were to perform a biomechanical analysis of C1-RO for the treatment of displaced Jefferson burst fractures (JBF) with incompetency of the TAL. Five specimens C0-2 were subjected to loading with posteroanterior force transmission in an electromechanical testing machine (ETM). With the TAL left intact, loads were applied posteriorly via the C1-RO ramping from 10 to 100 N. Atlantoaxial subluxation was measured radiographically in terms of the anterior antlantodental interval (AADI) with an image intensifier placed surrounding the ETM. Load-displacement data were also recorded by the ETM. After testing the TAL-intact state, the atlas was osteotomized yielding for a JBF, the TAL and left lateral joint capsule were cut and the C1-RO was accomplished. The C1-RO was subjected to cyclic loading, ramping from 20 to 100 N to simulate post-surgery in vivo loading. Afterwards incremental loading (10-100 N) was repeated with subsequent increase in loads until failure occurred. Small differences (1-1.5 mm) existed between the radiographic AADI under incremental loading (10-100 N) with the TAL-intact as compared to the TAL-disrupted state. Significant differences existed for the beginning of loading (10 N, P = 0.02). Under physiological loads, the increase in the AADI within the incremental steps (10-100 N) was not significantly different between TAL-disrupted and TAL-intact state. Analysis of failure load (FL) testing showed no significant differences among the radiologically assessed displacement data (AADI) and that of the ETM (P = 0.5). FL was Ø297.5 +/- 108.5 N (range 158.8-449.0 N). The related displacement assessed by the ETM was Ø5.8 +/- 2.8 mm (range 2.3-7.9). All specimens succeeded a FL >150 N, four of them >250 N and three of them >300 N. In the TAL-disrupted state loads up to 100 N were transferred to C1, but the radiographic AADI did not exceed 5 mm in any specimen. In conclusion, reconstruction after displaced JBF with TAL and one capsule disrupted using a C1-RO involves imparting an axial tensile force to lift C0 into proper alignment to the C1-2 complex. Simultaneous compressive forces on the C1-lateral masses and occipital condyles allow for the recreation of the functional C0-2 ligamentous tension band and height. We demonstrated that under physiological loads, the C1-RO restores sufficient stability at C1-2 preventing significant translation. C1-RO might be a valid alternative for the treatment of displaced JBF in comparison to fusion of C1-2.

Spinal surgery in patients with Parkinson's disease: experiences with the challenges posed by sagittal imbalance and the Parkinson's spine.

Only a few reports exist concerning biomechanical challenges spine surgeons face when treating Parkinson's disease (PD) patients with spinal deformity. We recognized patients suffering from spinal deformity aggravated by the burden of PD to stress the principles of sagittal balance in surgical treatment. Treatment of sagittal imbalance in PD is difficult due to brittle bone and (the neuromuscular disorder) with postural dysfunction. We performed a retrospective review of 23 PD patients treated surgically for spinal disorders. Mean ASA score was 2.3 (2-3). Outcome analysis included review of medical records focusing on failure characteristics, complications, and radiographic analysis of balance parameters to characterize special risk factors or precautions to be considered in PD patients. The sample included 15 female and 8 male PD patients with mean age of 66.3 years (57-76) at index surgery and 67.9 years (59-76) at follow-up. 10 patients (43.5%) presented with the sequels of failed previous surgery. 18 patients (78.3%) underwent multilevel fusion (C3 level) with 16 patients (69.6%) having fusion to S1, S2 or the Ilium. At a mean follow-up of 14.5 months (1-59) we noted medical complications in 7 patients (30.4%) and surgical complications in 12 patients (52.2%). C7-sagittal center vertical line was 12.2 cm (8-57) preoperatively, 6.9 cm postoperatively, and 7.6 cm at follow-up. Detailed analysis of radiographs, sagittal spinal, and spino-pelvic balance, stressed a positive C7 off-set of 10 cm on average in 25% of patients at follow-up requiring revision surgery in 4 of them. Statistical analysis revealed that patients with a postoperative or follow-up sagittal imbalance (C7-SVL >10 cm) had a significantly increased rate of revision done or scheduled (p = 0.03). Patients with revision surgery as index procedure also were found more likely to suffer postoperative or final sagittal imbalance (C7-SPL, 10 cm; p = 0.008). At all, 33% of patients had any early or late revision performed. Nevertheless, 78% of patients were satisfied or very satisfied with their clinical outcome, while 22% were either not satisfied or uncertain regarding their outcome. The surgical history of PD patients treated for spinal disorders and the reasons necessitating redo surgery for recalcitrant global sagittal imbalance in our sample stressed the mainstays of spinal surgery in Parkinson's: If spinal surgery is indicated, the reconstruction of spino-pelvic balance with focus on lumbar lordosis and global sagittal alignment is required.

The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping.

Clinical studies reported frequent failure with anterior instrumented multilevel cervical corpectomies. Hence, posterior augmentation was recommended but necessitates a second approach. Thus, an author group evaluated the feasibility, pull-out characteristics, and accuracy of anterior transpedicular screw (ATPS) fixation. Although first success with clinical application of ATPS has already been reported, no data exist on biomechanical characteristics of an ATPS-plate system enabling transpedicular end-level fixation in advanced instabilities. Therefore, we evaluated biomechanical qualities of an ATPS prototype C4-C7 for reduction of range of motion (ROM) and primary stability in a non-destructive setup among five constructs: anterior plate, posterior all-lateral mass screw construct, posterior construct with lateral mass screws C5 + C6 and end-level fixation using pedicle screws unilaterally or bilaterally, and a 360° construct. 12 human spines C3-T1 were divided into two groups. Four constructs were tested in group 1 and three in group 2; the ATPS prototypes were tested in both groups. Specimens were subjected to flexibility test in a spine motion tester at intact state and after 2-level corpectomy C5-C6 with subsequent reconstruction using a distractable cage and one of the osteosynthesis mentioned above. ROM in flexion-extension, axial rotation, and lateral bending was reported as normalized values. All instrumentations but the anterior plate showed significant reduction of ROM for all directions compared to the intact state. The 360° construct outperformed all others in terms of reducing ROM. While there were no significant differences between the 360° and posterior constructs in flexion-extension and lateral bending, the 360° constructs were significantly more stable in axial rotation. Concerning primary stability of ATPS prototypes, there were no significant differences compared to posterior-only constructs in flexion-extension and axial rotation. The 360° construct showed significant differences to the ATPS prototypes in flexion-extension, while no significant differences existed in axial rotation. But in lateral bending, the ATPS prototype and the anterior plate performed significantly worse than the posterior constructs. ATPS was shown to confer increased primary stability compared to the anterior plate in flexion-extension and axial rotation with the latter yielding significance. We showed that primary stability after 2-level corpectomy reconstruction using ATPS prototypes compared favorably to posterior systems and superior to anterior plates. From the biomechanical point, the 360° instrumentation was shown the most efficient for reconstruction of 2-level corpectomies. Further studies will elucidate whether fatigue testing will enhance the benefit of transpedicular anchorage with posterior constructs and ATPS.

In vitro study of accuracy of cervical pedicle screw insertion using an electronic conductivity device (ATPS part III).

Reconstruction of the highly unstable, anteriorly decompressed cervical spine poses biomechanical challenges to current stabilization strategies, including circumferential instrumented fusion, to prevent failure. To avoid secondary posterior surgery, particularly in the elderly population, while increasing primary construct rigidity of anterior-only reconstructions, the authors introduced the concept of anterior transpedicular screw (ATPS) fixation and plating. We demonstrated its morphological feasibility, its superior biomechanical pull-out characteristics compared with vertebral body screws and the accuracy of inserting ATPS using a manual fluoroscopically assisted technique. Although accuracy was high, showing non-critical breaches in the axial and sagittal plane in 78 and 96%, further research was indicated refining technique and increasing accuracy. In light of first clinical case series, the authors analyzed the impact of using an electronic conductivity device (ECD, PediGuard) on the accuracy of ATPS insertion. As there exist only experiences in thoracolumbar surgery the versatility of the ECD was also assessed for posterior cervical pedicle screw fixation (pCPS). 30 ATPS and 30 pCPS were inserted alternately into the C3-T1 vertebra of five fresh-frozen specimen. Fluoroscopic assistance was only used for the entry point selection, pedicle tract preparation was done using the ECD. Preoperative CT scans were assessed for sclerosis at the pedicle entrance or core, and vertebrae with dense pedicles were excluded. Pre- and postoperative reconstructed CT scans were analyzed for pedicle screw positions according to a previously established grading system. Statistical analysis revealed an astonishingly high accuracy for the ATPS group with no critical screw position (0%) in axial or sagittal plane. In the pCPS group, 88.9% of screws inserted showed non-critical screw position, while 11.1% showed critical pedicle perforations. The usage of an ECD for posterior and anterior pedicle screw tract preparation with the exclusion of dense cortical pedicles was shown to be a successful and clinically sound concept with high-accuracy rates for ATPS and pCPS. In concert with fluoroscopic guidance and pedicle axis views, application of an ECD and exclusion of dense cortical pedicles might increase comfort and safety with the clinical use of pCPS. In addition, we presented a reasonable laboratory setting for the clinical introduction of an ATPS-plate system.

C2-fractures: part II. A morphometrical analysis of computerized atlantoaxial motion, anatomical alignment and related clinical outcomes.

Knowledge on the outcome of C2-fractures is founded on heterogenous samples with cross-sectional outcome assessment focusing on union rates, complications and technical concerns related to surgical treatment. Reproducible clinical and functional outcome assessments are scant. Validated generic and disease specific outcome measures were rarely applied. Therefore, the aim of the current study is to investigate the radiographic, functional and clinical outcome of a patient sample with C2-fractures. Out of a consecutive series of 121 patients with C2 fractures, 44 met strict inclusion criteria and 35 patients with C2-fractures treated either nonsurgically or surgically with motion-preserving techniques were surveyed. Outcome analysis included validated measures (SF-36, NPDI, CSOQ), and a functional CT-scanning protocol for the evaluation of C1-2 rotation and alignment. Mean follow-up was 64 months and mean age of patients was 52 years. Classification of C2-fractures at injury was performed using a detailed morphological description: 24 patients had odontoid fractures type II or III, 18 patients had fracture patterns involving the vertebral body and 11 included a dislocated or a burst lateral mass fracture. Thirty-one percent of patients were treated with a halo, 34% with a Philadelphia collar and 34% had anterior odontoid screw fixation. At follow-up mean atlantoaxial rotation in left and right head position was 20.2 degrees and 20.6 degrees, respectively. According to the classification system of posttreatment C2-alignment established by our group in part I of the C2-fracture study project, mean malunion score was 2.8 points. In 49% of patients the fractures healed in anatomical shape or with mild malalignment. In 51% fractures healed with moderate or severe malalignment. Self-rated outcome was excellent or good in 65% of patients and moderate or poor in 35%. The raw data of varying nuances allow for comparison in future benchmark studies and metaanalysis. Detailed investigation of C2-fracture morphology, posttreatment C2-alignment and atlantoaxial rotation allowed a unique outcome analysis that focused on the identification of risk factors for poor outcome and the interdependencies of outcome variables that should be addressed in studies on C2-fractures. We recognized that reduced rotation of C1-2 per se was not a concern for the patients. However, patients with worse clinical outcomes had reduced total neck rotation and rotation C1-2. In turn, C2-fractures, especially fractures affecting the lateral mass that healed with atlantoaxial deformity and malunion, had higher incidence of atlantoaxial degeneration and osteoarthritis. Patients with increased severity of C2-malunion and new onset atlantoaxial arthritis had worse clinical outcomes and significantly reduced rotation C1-2. The current study offers detailed insight into the radiographical, functional and clinical outcome of C2-fractures. It significantly adds to the understanding of C2-fractures.

Mid- to long-term outcome of instrumented anterior cervical fusion for subaxial injuries.

The management of patients with subaxial cervical injuries lacks consensus, particularly in regard to the decision which surgical approach or combination of approaches to use and which approach yields the best clinical outcome in the distinct injury. The trauma literature is replete with reports of surgical techniques, complications and gross outcome assessment in heterogeneous samples. However, data on functional and clinical outcome using validated outcome measures are scanty. Therefore, the authors performed a study on plated anterior cervical decompression and fusion for unstable subaxial injuries with focus on clinical outcome. For the purpose of a strongly homogenous subgroup of patients with subaxial injuries without spinal cord injuries, robust criteria were applied that were fulfilled by 28 patients out of an original series of 131 subaxial injuries. Twenty-six patients subjected to 1- and 2-level fusions without having spinal cord injury could be surveyed after a mean of 5.5 years (range 16-128 months). The cervical spine injury severity score averaged 9.6. Cross-sectional outcome assessment included validated outcome measures (Neck pain disability index, Cervical Spine Outcome Questionnaire, SF-36), the investigation of construct failure and successful surgical outcome were defined by strict criteria, the reconstruction and maintenance of local and total cervical lordosis, adjacent-segment degeneration and intervertebral motion, and the fusion-rate using an interobserver assessment. Self-rated clinical outcome was excellent or good in 81% of patients and moderate or poor in 19% that corresponded to the results of the validated outcome measures. Results of the NPDI averaged 12.4 +/- 12.7% (0-40). With the SF-36 mean physical and mental component summary scores were 47.0 +/- 9.8 (18.2-59.3) and 52.2 +/- 12.4 (14.6-75.3), respectively. Using merely non-constrained plates, construct failure was observed in 31% of cases and loss of local lordosis, expressed as a mean injury angle of 14 degrees, postoperative angle of -5.5 degrees and follow-up angle of -1 degree, was significant. However, total cervical lordosis was within the limits of normalcy (-24.3 degrees +/- 13.3) and fusion-rate was 88.5%. The progression of adjacent-level degeneration was shown to be significantly influenced by a decreased plate-to-disc-distance. Adjacent-level intervertebral motion was not altered due to the adjacent fusion, but reduced in the presence of advanced adjacent-level degeneration. Patients were more likely to maintain a high satisfaction level if they succeeded to maintain segmental lordosis (<0 degree), had a solid fusion, an increased plate-to-disc distance, and if they were judged to have a successful surgical outcome that included the absence of construct failure and reconstruction of lordosis within +/-1 SD of normalcy. Using validated outcome vehicles the interdependencies between radiographical, functional and clinical outcome parameters could be substantiated with statistically significant correlations. The use of validated outcome vehicles in a subgroup of patients with plated anterior cervical fusions for subaxial injuries is recommended. With future studies, it enables objective comparison of surgical techniques and related radiographical, functional and clinical outcome.

Study on accuracy and interobserver reliability of the assessment of odontoid fracture union using plain radiographs or CT scans.

In odontoid fracture research, outcome can be evaluated based on validated questionnaires, based on functional outcome in terms of atlantoaxial and total neck rotation, and based on the treatment-related union rate. Data on clinical and functional outcome are still sparse. In contrast, there is abundant information on union rates, although, frequently the rates differ widely. Odontoid union is the most frequently assessed outcome parameter and therefore it is imperative to investigate the interobserver reliability of fusion assessment using radiographs compared to CT scans. Our objective was to identify the diagnostic accuracy of plain radiographs in detecting union and nonunion after odontoid fractures and compare this to CT scans as the standard of reference. Complete sets of biplanar plain radiographs and CT scans of 21 patients treated for odontoid fractures were subjected to interobserver assessment of fusion. Image sets were presented to 18 international observers with a mean experience in fusion assessment of 10.7 years. Patients selected had complete radiographic follow-up at a mean of 63.3 +/- 53 months. Mean age of the patients at follow-up was 68.2 years. We calculated interobserver agreement of the diagnostic assessment using radiographs compared to using CT scans, as well as the sensitivity and specificity of the radiographic assessment. Agreement on the fusion status using radiographs compared to CT scans ranged between 62 and 90% depending on the observer. Concerning the assessment of non-union and fusion, the mean specificity was 62% and mean sensitivity was 77%. Statistical analysis revealed an agreement of 80-100% in 48% of cases only, between the biplanar radiographs and the reconstructed CT scans. In 50% of patients assessed there was an agreement of less than 80%. The mean sensitivity and specificity values indicate that radiographs are not a reliable measure to indicate odontoid fracture union or non-union. Regarding experience in years of all observers taking part in the study, there were no significant differences for specificity (P = 0.88) or sensitivity (P = 0.26). Further analysis revealed that if a non-union was judged present by an observer then, on average, each observer changed decision regarding the presence of a 'stable' or 'unstable non-union' in 4.2 of all the 21 cases (range 0-8 changes per observer). We investigated the interobserver reliability of the assessment of fusion in odontoid fractures using biplanar radiographs compared to CT scans. A sensitivity of 77% and a specificity of 62% for the radiographs resemble a substantial lack of agreement if different observers evaluate odontoid union. Biplanar radiographs are judged not a reliable measure to detect odontoid fracture union or non-union. The union rates of odontoid fractures have to be revisited and CT scans as the endpoint anchor in outcome studies of treatment related union rates are recommended.

Long-term investigation of nonsurgical treatment for thoracolumbar and lumbar burst fractures: an outcome analysis in sight of spinopelvic balance.

The nonsurgical treatment of thoracolumbar (TLB) and lumbar burst (LB) fractures remains to be of interest, though it is not costly and avoids surgical risks. However, a subset of distinct burst fracture patterns tend to go with a suboptimal radiographic and clinical long-term outcome. Detailed fracture pattern and treatment-related results in terms of validated outcome measures are still lacking. In addition, there are controversial data on the impact of local posttraumatic kyphosis that is associated, in particular, with nonsurgical treatment. The assessment of global spinal balance following burst fractures has not been assesed, yet. Therefore, the current study intended to investigate the radiographical and clinical long-term outcome in neurologically intact patients with special focus on the impact of regional posttraumatic kyphosis, adjacent-level compensatoric mechanisms, and global spine balance on the clinical outcome. For the purpose of a homogenous sample, strong in- and exclusion criteria were applied that resulted in a final study sample of 21 patients with a mean follow-up of 9.5 years. Overall, clinical outcome evaluated by validated measures was diminished, with 62% showing a good or excellent outcome and 38% a moderate or poor outcome in terms of the Greenough Low Back Outcome Scale. Notably, vertebral comminution in terms of the load-sharing classification, posttraumatic kyphosis, and an overall decreased lumbopelvic lordosis showed a significant effect on clinical outcome. A global and segmental curve analysis of the spine T9 to S1 revealed significant alterations as compared to normals. But, the interdependence of spinopelvic parameters was not disrupted. The patients' spinal adaptability to compensate for the posttraumatic kyphotic deformity varied in the ranges dictated by pelvic geometry, in particular the pelvic incidence. The study substantiates the concept that surgical reconstruction and maintenance of a physiologically shaped spinal curve might be the appropriate treatment in the more severely crushed TLB and LB fractures.

Analysis of postoperative pain at the anterior iliac crest harvest site: a prospective study of the intraoperative local administration of ropivacaine.

STUDY DESIGN: This was a prospective randomized comparative study. PURPOSE: The aim of this study was to objectify donor site-related pain following anterior iliac crest graft harvesting, in patients who have undergone multilevel anterior cervical discectomy and fusion with plating (ACDFP); and to assess the effect of an intraoperative local single injection of ropivacaine on postoperative pain. OVERVIEW OF LITERATURE: Multilevel ACDFP can be associated with a high non-union rate. Autogenous iliac bone has been used to increase union rates, although a high incidence of donor site-related pain has been reported. METHODS: Forty consecutive patients who required 3-level or 4-level ACDFP were prospectively assessed for donor site-related pain. Pain levels were assessed daily for five days postoperative using the visual analog scale (VAS). Patients were randomly assigned to group A or B. In group A patients, 7-10 mL of ropivacaine (0.2%) was injected into the iliac crest after iliac crest graft harvesting. Morphine usage via patient controlled analgesia was calculated. At six months postoperative, patient complaints at the harvest site were documented. RESULTS: Patients were randomly assigned to group A or B. In group A, ropivacaine was locally administered at the site of the iliac crest graft harvest after fascia closure. In group B, no additional treatments were administered. The average patient age in group A was 56±7.6 years, whereas the average age of patients in group B was 52.6±10.4 years. Group A had an average of 0.6±0.7 previous surgeries per patient, whereas group B had an average of 0.8±1.0 previous surgeries per patient. The average number of levels fused in group A was 3.6±0.7, whereas the average number of levels fused in group B was 3.7±0.9 (all p>0.05). In group A, the mean ropivacaine volume administered was 8.4±1.5 mL. No patient complaints regarding chronic pain, were reported six months postoperatively. No complications were encountered from the harvest site, and all patients underwent successful 3-level and 4-level ACDFP. Statistical analysis showed significant differences for VAS on postoperative day 1 (p=0.004) and day 2 (p=0.005). CONCLUSIONS: VAS assessment showed overall moderate perioperative morbidity in terms of donor site-related pain, which was reduced by administering ropivacaine.

Comparison of Anteroposterior to Posterior-Only Correction of Scheuermann's Kyphosis: A Matched-Pair Radiographic Analysis of 92 Patients.

STUDY DESIGN: Retrospective radiographic benchmark study. OBJECTIVE: To evaluate the amount of instrumented correction obtained from a combined anterior/posterior (A/P) versus posterior-only (post-only) approach for Scheuermann's kyphosis. SUMMARY OF BACKGROUND DATA: An A/P approach was thought to optimize correction; however, instrumentation advances using pedicle screws allow treatment through an all-posterior approach. METHODS: A total of 166 Scheuermann's kyphosis patients were treated between 2 centers: 90 by combined A/P approach at 1 center and 76 by post-only at the second center. From the 166 patients, a matched cohort of 92 (46 from each) was established according to preoperative sagittal (±10°) and hyperextension (HE) Cobb (±10°) measurements and matched for age and gender. RESULTS: In the matched-pair group, average preoperative sagittal Cobb angles were 75.9° for the A/P group versus 78.8° for the post-only group (p = .2). The HE Cobb angles were similar (52.4° vs. 51.1°; p = .6). They showed similar corrections (33.7° vs. 30.6°; p = .3) and postoperative Cobb measurements (43.4° vs. 47.1°; p = .2) as well. The number of fusion levels was 9 in the A/P group and 12 in the post-only group; the difference yielded significance (p = .02). CONCLUSIONS: The A/P and post-only approaches averaged similar degrees of correction. The A/P patients were likely to correct more than their preoperative HE sagittal Cobb measurement, whereas the post-only group corrected close to their preoperative HE measurement. The number of fusion levels was larger with the post-only group.

Impact of constrained dual-screw anchorage on holding strength and the resistance to cyclic loading in anterior spinal deformity surgery: a comparative biomechanical study.

STUDY DESIGN: Biomechanical in vitro laboratory study. OBJECTIVE: To compare the biomechanical performance of 3 fixation concepts used for anterior instrumented scoliosis correction and fusion (AISF). SUMMARY OF BACKGROUND DATA: AISF is an ideal estimate for selective fusion in adolescent idiopathic scoliosis. Correction is mediated using rods and screws anchored in the vertebral bodies. Application of large correction forces can promote early weakening of the implant-vertebra interfaces, with potential postoperative loss of correction, implant dislodgment, and nonunion. Therefore, improvement of screw-rod anchorage characteristics with AISF is valuable. METHODS: A total of 111 thoracolumbar vertebrae harvested from 7 human spines completed a testing protocol. Age of specimens was 62.9 ± 8.2 years. Vertebrae were potted in polymethylmethacrylate and instrumented using 3 different devices with identical screw length and unicortical fixation: single constrained screw fixation (SC fixation), nonconstrained dual-screw fixation (DNS fixation), and constrained dual-screw fixation (DC fixation) resembling a novel implant type. Mechanical testing of each implant-vertebra unit using cyclic loading and pullout tests were performed after stress tests were applied mimicking surgical maneuvers during AISF. Test order was as follows: (1) preload test 1 simulating screw-rod locking and cantilever forces; (2) preload test 2 simulating compression/distraction maneuver; (3) cyclic loading tests with implant-vertebra unit subjected to stepwise increased cyclic loading (maximum: 200 N) protocol with 1000 cycles at 2 Hz, tests were aborted if displacement greater than 2 mm occurred before reaching 1000 cycles; and (4) coaxial pullout tests at a pullout rate of 5 mm/min. With each test, the mode of failure, that is, shear versus fracture, was noted as well as the ultimate load to failure (N), number of implant-vertebra units surpassing 1000 cycles, and number of cycles and related loads applied. RESULTS: Thirty-three percent of vertebrae surpassed 1000 cycles, 38% in the SC group, 19% in the DNS group, and 43% in the DC group. The difference between the DC group and the DNS group yielded significance (P = 0.04). For vertebrae not surpassing 1000 cycles, the number of cycles at implant displacement greater than 2 mm in the SC group was 648.7 ± 280.2 cycles, in the DNS group was 478.8 ± 219.0 cycles, and in the DC group was 699.5 ± 150.6 cycles. Differences between the SC group and the DNS group were significant (P = 0.008) as between the DC group and the DNS group (P = 0.0009). Load to failure in the SC group was 444.3 ± 302 N, in the DNS group was 527.7 ± 273 N, and in the DC group was 664.4 ± 371.5 N. The DC group outperformed the other constructs. The difference between the SC group and the DNS group failed significance (P = 0.25), whereas there was a significant difference between the SC group and the DC group (P = 0.003). The DC group showed a strong trend toward increased load to failure compared with the DNS group but without significance (P = 0.067). Surpassing 1000 cycles had a significant impact on the maximum load to failure in the SC group (P = 0.0001) and in the DNS group (P = 0.01) but not in the DC group (P = 0.2), which had the highest number of vertebrae surpassing 1000 cycles. CONCLUSION: Constrained dual-screw fixation characteristics in modern AISF implants can improve resistance to cyclic loading and pullout forces. DC constructs bear the potential to reduce the mechanical shortcomings of AISF.

The impact of a distal expansion mechanism added to a standard pedicle screw on pullout resistance. A biomechanical study.

BACKGROUND CONTEXT: Spinal deformity surgery in elderly patients is associated with an increased risk of implant loosening due to failure at the screw-bone interface. Several techniques can be used to increase the screw anchorage characteristics. Cement-augmented screw fixation was shown to be the most efficient method; however, this technique is associated with a risk of complications related to vertebral cement deposition and leakage. Hence, there is a need to further elaborate the alternative screw augmenting techniques to reduce the indications for bone cement. PURPOSE: To analyze surgical alternatives to cement augmentation, the present study sought to quantify the impact of a distal expansion mechanism added to a standard pedicle screw on an axial pullout resistance. STUDY DESIGN: A biomechanical laboratory study on the uniaxial pullout resistance of a standard pedicle screw versus a customized pedicle screw with a distal expansion mechanism. METHODS: A total of 40 vertebrae from seven fresh-frozen human specimens were harvested and subjected to a computed tomography scanning and an analysis of the bone mineral density (BMD). The vertebrae were instrumented with a standard 6.0-mm pedicle screw and a modified 6.0-mm pedicle screw with a distal expansion mechanism added. The actual working length of both screws inside the vertebrae was identical. The distal expansion mechanism made up one-fifth of the shaft length. The accuracy of the screw insertion was assessed using biplanar radiographs and by inspection. Analysis of resistance to pullout was performed by a coaxial alignment of the pedicle screws and attachment to an electromechanical testing machine. The pullout rate was 5 mm/min, and the load-displacement curve was recorded until the force of the pullout resistance peaked. The peak load-to-failure was measured in Newtons and reported as the ultimate failure load. With each test, the mode of failure was noted and analyzed descriptively. RESULTS: A total of 17 vertebrae with matched pairs of standard and expansion pedicle screws were eligible for the final statistical analysis. The BMD of the vertebrae tested was 0.67±0.19 g/cm³. The screw length was 50 mm, and the actual working length of both screws was 40.3±4.2 mm. The ultimate failure load of the standard screw was 773.8±529.4 N and that of the expansion screw was 910.3±488.3 N. Statistical analysis revealed a strong trend toward an increased failure load with the expansion screw (p=.06). The mean increase of the ultimate failure load was 136.5±350.4 N. Abrupt vertebral fracture at the vertebral body-pedicle junction and the pedicle occurred seven times with the expansion screw and only five times with the standard screw (p=.16). CONCLUSIONS: Our study indicates that adding a distal expansion mechanism to a standard pedicle screw increases the failure load by one-fifth. Modern expansion screws might offer an intermediate solution for the augmentation of screw-rod constructs in osteoporotic bone while reducing the need for cement-augmented screws and avoiding the related risks.