Cervical spinal arthrodesis is the standard of care for the treatment of spinal diseases induced neck pain. However, adjacent segment disease (ASD) is the primary postoperative complication, which draws great concerns. At present, controversy still exists for the etiology of ASD. Knowledge of cervical spinal loading pattern after cervical spinal arthrodesis is proposed to be the key to answer these questions. Musculoskeletal (MSK) multi-body dynamics (MBD) models have an opportunity to obtain spinal loading that is very difficult to directly measure in vivo. In present study, a previously validated cervical spine MSK MBD model was developed for simulating cervical spine after single-level anterior arthrodesis at C5-C6 disc level. In this cervical spine model, postoperative sagittal alignment and spine rhythms of each disc level, different from normal healthy subject, were both taken into account. Moreover, the biomechanical properties of facet joints of adjacent levels after anterior arthrodesis were modified according to the experimental results. Dynamic full range of motion (ROM) flexion/extension simulation was performed, where the motion data after arthrodesis was derived from published in-vivo kinematic observations. Meanwhile, the full ROM flexion/extension of normal subject was also simulated by the generic cervical spine model for comparative purpose. The intervertebral compressive and shear forces and loading-sharing distribution (the proportions of intervertebral compressive and shear force and facet joint force) at adjacent levels (C3-C4, C4-C5 and C6-C7 disc levels) were then predicted. By comparison, arthrodesis led to a significant increase of adjacent intervertebral compressive force during the head extension movement. Postoperative intervertebral compressive forces at adjacent levels increased by approximate 20% at the later stage of the head extension movement. However, there was no obvious alteration in adjacent intervertebral compressive force, during the head flexion movement. For the intervertebral shear forces in the anterior-posterior direction, no significant differences were found between the arthrodesis subject and normal subject, during the head flexion/extension movement. Meanwhile, cervical spinal loading-sharing distribution after anterior arthrodesis was altered compared with the normal subject's distribution, during the head extension movement. In the postoperative loading-sharing distribution, the percentage of intervertebral disc forces was further increased as the motion angle increased, compared with normal subject. In conclusion, cervical spinal loading after anterior arthrodesis was significantly increased at adjacent levels, during the head extension movement. Cervical spine musculoskeletal MBD model provides an attempt to comprehend postoperative ASD after anterior arthrodesis from a biomechanical perspective

Introduction. This research determines the feasibility of radiostereometric analysis (RSA) as a diagnostic tool for assessing fusion following spinal arthrodesis. Further, to estimate clinical thresholds for precision and accuracy of the proposed method in the cervical and lumbar spine. Methods. Two-level lumbo-sacral and three-level cervical posterior arthrodesis procedures were performed on an artificial spine model and a cadaveric spine (Figure 1). Using a spring-loaded inserter, RSA marker beads were placed within each of the L4-S1 and C3-C6 vertebrae, then analyzed for optimal bead distribution and detection. RSA imaging consisted of 12 double exams (24 exams) of the cervical and lumbar regions for both the Sawbones and cadaveric spine to assess precision of measurement under zero-displacement conditions, defined as the 95% confidence interval of error. Accuracy assessment was performed on the Sawbones model in which the middle vertebrae (L5 and C4-C5) were moved relative to the superior (L4 and C3) and inferior (S1 and C6) vertebrae by known, incremental displacements (Figure 2). RSA images were obtained at each displacement (Figure 3). Accuracy was defined as the mean difference between known and measured displacements. Results. Median RSA bead detection was 100% in cervical vertebrae and >75% in lumbar vertebrae in the artificial and cadaveric models. Translational RSA precision for both spine models was better than 0.25mm and 0.82mm for the lumbar and cervical regions, respectively. Rotational precision was better than 0.4° and 1.9° for the lumbar and cervical regions, respectively. RSA accuracy for the artificial spine overall demonstrated less than 0.11 mm translational bias (margin < ±0.02 mm) and less than 0.22° rotational bias (margin < ±0.15°). Discussion and Conclusion. This study demonstrates that RSA achieves sufficient precision and accuracy to detect intervertebral micromotion for the purpose of assessing arthrodesis. Well dispersed bead placement is critical to achieving sufficient accuracy and avoiding occlusion by metal hardware. The results of this work will aid in the development of a clinical study to assess arthrodesis in patients. For any figures or tables, please contact the authors directly

The purpose of this research was to determine the feasibility of radiostereometric analysis (RSA) as a diagnostic tool for assessing non-union following spinal arthrodesis procedures. Further, to estimate clinical thresholds for precision and accuracy of the proposed method in the cervical and lumbar spine. A three-level lumbo-sacral and a four-level cervical posterior arthrodesis procedures were performed on an artificial spine model (Sawbones, WA). Using a spring loaded inserter (RSA Biomedical, Sweden), eight to ten RSA markers were placed within each of the L4 and L5 segments in the spinous process (L4 only), lamina, transverse processes, posterior and anterior (down the pedicle) wall of the vertebral body. Eight to ten markers were placed within the proximal sacrum (S1) at the medial and lateral crests, tuberosity, and within the sacral canal wall. Four to eight RSA markers were placed into the C3-C6 lateral masses. Titanium screws and rods were applied to the spinal segments. Identical procedures were then performed on a cadaveric spine using similar bead placement and hardware. RSA imaging consisted of 12 double exams (24 exams) of the cervical and lumbar regions for both the Sawbones and cadaveric spine to assess precision of measurement under zero-displacement conditions. The most distal vertebrae were considered the datum against which the movement of all other vertebrae was compared. The artificial spine was then dismantled for accuracy assessment in which the middle vertebrae (L5 and C4-C5) were moved relative to the superior (L4 and C3) and inferior (S1 and C6) vertebrae by known, incremental displacements on an imaging phantom device. Displacements occurred along the superior-inferior, anterior-posterior, and flexion-extension (rotational) axes of motion. RSA images were obtained at each displacement. Image analysis was performed using model-based software (RSACore v3.41, Leiden, Netherlands) to visualize implanted RSA beads in 3-D space. Precision was defined as the 95% confidence interval of error in measuring zero-displacement. Accuracy was defined as the mean difference (with 95% confidence interval) between the known and measured displacement. The rate of RSA bead detection was high with 5–8 implanted beads being visible in both the lumbar and cervical regions of the artificial and cadaveric spines. Translational RSA precision for both spines was better than 0.25 mm and 0.82 mm for the lumbar and cervical regions, respectively. Rotational precision was better than 0.40° and 1.9° for the lumbar and cervical regions, respectively. RSA accuracy for the artificial spine overall demonstrated less than 0.11 mm translational bias (margin < ±0.02 mm) and less than 0.22° rotational bias (margin < ±0.15°). This study demonstrates that RSA achieves sufficient precision and accuracy to detect intervertebral micromotion for the purpose of assessing arthrodesis. Well dispersed RSA bead placement is critical to achieving sufficient accuracy as well as avoiding occlusion by metal hardware. Cervical bead implantation is particularly sensitive to bead clustering due to small vertebrae size and proximity to critical structures. The results of this work will aid in the development of a clinical study to assess arthrodesis in patients

Purpose. Bone morphogenic protein (BMP-2) is used in spinal arthrodesis to induce bone growth. Studies have demonstrated that it achieves similar fusion rates compared to iliac crest bone graft when used in instrumented fusions. Our study aims at evaluating the requirement for instrumentation in one and two-level spinal arthrodeses when BMP-2 is used in conjunction with local bone to achieve fusion. Method. 50 patients were recruited and randomized to instrumented versus non-instrumented spinal arthrodesis. BMP-2 with local autologous bone was used in all patients. Patients are evaluated at 3-months, 6-months, 12-months, and 24-months postoperatively with questionnaires to assess clinical outcome (ODI, VAS and SF-36), and PA and lateral x-rays of the spine to assess radiographic fusion (Lenke score). At 24 months, a thin-cut (1mm) CT scan was performed. Results. Two-year data is available on 40 patients. There were no statistically significant differences between the two groups based on the clinical outcomes measured. The ODI 22.55.1 for the instrumented group vs. 13.733.57 for the non-instrumented group (p=0.2)). The VAS for the instrumented group was 2.110.61 vs. 1.530.61 for the non-instrumented group (p=0.49). The SF-36 (physical) was 62.316.71 for the instrumented group vs 54.665.43 for the study group (p=0.8). The operating time was 105.85.91 minutes for the instrumented group versus 88.63.61 minutes for the non-instrumented group (p=0.01). Blood loss was 339.139.38 cc for the instrumented group vs 273.133.8 cc for the non-instrumented group (p=0.1). Preliminary radiographic analysis showed similar fusion rates for the two groups. Two-year follow-up on all patients will be completed by February 2010. Final clinical and radiographic data analysis will be presented at the meeting. Conclusion. BMP-2 and local bone graft demonstrated functionally equivalent clinical outcomes when used with or without instrumentation in lumbar spinal fusions while offering potential reduction in operative time and blood loss

Subjects. A prospective study of 127 patients who underwent posterior spinal arthrodesis and segmental spinal instrumentation with iliac crest bone graft for correction of adolescent idiopathic scoliosis. Patients were divided according to their Cobb angle into two groups. Group 1 (n= 78) with a Cobb angle > 70° who underwent an additional concave rib osteotomy (CRO) and group 2 (n= 49) with a Cobb angle < 70° who did not (NCRO). All patients received a pulmonary rehabilitation programme post-operatively. Vital capacity (VC) and peak expiratory flow rate (PEF) were measured pre-operatively, at 3 months and 12 months post-operatively. Summary of background data. Concave rib osteotomy technique is used for giving more mobility and flexibility of the spine during correction especially in rigid and severe curves. Only a few studies in the literature have looked at the effect of concave rib osteotomy on pulmonary function. Results. ∗Curve correction: the mean Cobb angles at the pre-operative and final follow-up for group 1 (CRO) were 82.2° and 10.9° respectively (87% correction). In group 2 (NCRO), the mean Cobb angle was 62.77% pre-operatively and 6.9% at the final follow-up (89% correction achieved). ∗Pulmonary function: Pre-operative: there was no significant difference between the 2 groups. 3 Months post-operative: the mean VC was 40.4% in group 1 and 48.05% in group 2 (p=0.05). The mean PEF was 27.38 % in group 1and 34.1% in group 2 (p = 0.02). 12 Months post-operative: the mean VC in group 1 was 102.4% versus 103.5% in group 2 (p = 0.43). The mean PEF in group 1 was 76.2% versus 73.5% in group 2 (p = 0.32). Conclusions. Concave Rib Osteotomy technique has a definite effect on the pulmonary function in the early post-operative period. However, this difference resolves with time and both groups had a similar outcome a year post-operatively