Management of strut graft failure in anterior cervical spine surgery

A Cadaver-Based Biomechanical Evaluation of a Novel Posterior Approach to Sacroiliac Joint Fusion: Analysis of the Fixation and Center of the Instantaneous Axis of Rotation

Purpose

The purpose of this study was to assess the stabilizing effect of a posterior joint fixation technique using a novel cortical allograft implant in unilateral and bilateral fixation constructs. We hypothesize that fixation would reduce the joint's range of motion during flexion-extension, axial rotation, and lateral bending loads. We also hypothesize that fixation would shift the center of the instantaneous axis of rotation during the predominant flexion-extension motions towards the implant's location, and that this shift would be correlated with the reduction in flexion-extension range of motion.

Materials and Methods

Six cadaveric sacroiliac joint specimens were tested under intact, unilateral fixation, and bilateral fixation conditions. The total range of motion (ROM) of the sacroiliac joint in flexion-extension, lateral bending, and axial rotation were evaluated by an optical tracking system, in a multidirectional flexibility pure moment model, between ± 7.5 Nm applied moment loads. The centers of the instantaneous axis of rotation (cIAR) of the sacroiliac joint were evaluated during flexion-extension loading. A correlation analysis was performed between the ROM reduction in flexion-extension upon implantation and shift of the cIAR to the graft implantation site.

Results

Unilateral and bilateral fixations generated sacroiliac joint ROM reductions in flexion-extension, lateral bending, and axial rotation motions. Fixation shifted the cIAR to the graft implantation site. Reduction in the total range of motion had a moderate correlation with the shift of the cIAR.

Conclusion

Our novel posterior approach presents a multifaceted mechanism for stabilizing the joint: first, by the reduction of the total range of motion in all planes of motion; second, by shifting the centers of the instantaneous axis of rotation towards the implant's location in the predominant plane of motion, ensuring little to no motion at the implantation site, thus promoting fusion in this region.

Spontaneous oral extrusion of an acrylic vertebral reconstruction 12 years after a vertebrectomy for a Ewing's sarcoma of the cervical spine: a case report

INTRODUCTION

Primary Ewing sarcoma of the cervical spine is rare, particularly in children population. The surgical management remains a challenge to associate the best oncological resection and to prevent spinal deformity. The situation is complicated owing to paucity of adapted instrumentation and their possible interactions with the growing bone.

CLINICAL PRESENTATION

We described the case of a young 19-year-old woman admitted for an oral extrusion of a bone polymethyl methacrylate (PMMA) allograft 12 years after a C4 circumferential vertebrectomy for primary Ewing's sarcoma. The vertebral anterior reconstruction was slowly repulsed by the growing spine giving way to an autologous bone without kyphosis deformation.

CONCLUSION

Bone reconstruction remains a challenge after extensive oncological resection particularly in cervical spine of children. Anterior and posterior instrumentation must be associated. The growing spine is not a good host for PMMA allograft and autograft seems to be preferred for anterior column fusion. In spite of the good oncological results, the authors raise the long-term issue of PMMA for vertebral reconstruction in young patients. With a long follow-up, they showed that posterior rigid fixation might prevent the cervical kyphosis.

Segmental anterior decompression and fusion for multilevel ossification of the posterior longitudinal ligament

The purpose of this study was to evaluate the outcome of segmental anterior decompression and fusion for multilevel ossification of the posterior longitudinal ligament. Data were collected from 23 patients with multilevel ossification of the posterior longitudinal ligament. Average operative time and blood loss were 121 minutes and 201.6 mL, respectively. The Nurick score significantly decreased from 2.7±0.9 preoperatively to 1.8±0.9 at last follow-up (P<.01). The preoperative Japanese Orthopaedic Association score was 8.2, which significantly increased to 13.8 points at last follow-up (P<.01), with an improvement rate of 64.5%. The operation also significantly increased cervical lordosis (P<.01) from 7.7° preoperatively to 13.3° postoperatively. The fusion rate was 95.7% at 6 months postoperatively, and 100% at 12 months postoperatively. The loss of cervical lordosis and height of fusion segments were 1.2° and 0.9 mm at last follow-up, respectively. No hardware complications occurred. Cerebrospinal fluid leakage occurred in 2 patients, and hematoma occurred in 1 patient who needed an emergency operation. Segmental anterior decompression and fusion was generally effective and safe in the treatment of multilevel ossification of the posterior longitudinal ligament if indications were well controlled.

Long-term follow-up of cervical radiographic sagittal spinal alignment after 1- and 2-level cervical corpectomy for the treatment of spondylosis of the subaxial cervical spine causing radiculomyelopathy or myelopathy: a retrospective study

Object

Few data exist regarding long-term outcomes after cervical corpectomy for spondylotic cervical myelopathy and radiculomyelopathy. In this retrospective review, long-term radiographic outcomes are reported for 130 patients after 1- or 2-level cervical corpectomy for spondylotic myelopathy or radiculomyelopathy.

Methods

Electronic medical records including clinical data and radiographic images during a 15-year period (1993–2008) were reviewed at the Cincinnati Department of Veterans Affairs Medical Center. All patients underwent radiographic follow-up for at least 12 months (range 12–156, mean 45 ± 39.3 months), as well as clinical follow-up performed by neurosurgery staff for a mean of 29.3 ± 39.6 months (range 4–156 months). Clinical parameters at surgery and last examination included the Chiles modified Japanese Orthopaedic Association (mJOA) Myelopathy Scale. Measurements included cervical spine sagittal alignment on lateral radiographs preoperatively and postoperatively, focal Cobb angles at operated levels, and C2–7 regional alignment. Statistical analysis included the Student t-test and chi-square test. Perioperative complications and additional surgery in the cervical spine were recorded.

Results

The mJOA scores improved from a mean of 11.91 ± 2.4 preoperatively to 14.9 ± 2.33 postoperatively. The mean sagittal lordosis of the C2–7 spine increased from −16.2° ± 9.2° preoperatively to −18.5° ± 11.9° at last follow-up. Focal Cobb angles averaged a slight kyphotic angulation of 4.1° ± 2.3° at latest radiographic follow-up; of note, 7 patients (5.4%), all who had cylindrical titanium mesh cages (CTMCs), showed severe kyphotic angulation (+8.4° ± 2.4°). Patients with preoperative myelopathy showed clinical improvement at follow-up. The fusion rate was 96.2%; 3 of the 5 patients with radiographic evidence of nonfusion were smokers. Patients with postoperative kyphosis had significantly more chronic neck pain (visual analog scale score >4 lasting more than 6 months) and visits related to pain (p <0.01). Those with CTMCs had higher rates of postoperative kyphosis, chronic neck pain, and visits related to pain, irrespective of the number of levels fused (p <001). At latest follow-up, although a kyphotic increase occurred in the focal cervical sagittal Cobb angles, lordosis increased in C2–7 sagittal Gore angles. Two patients (1.5%) underwent revision of the implanted graft and/or hardware, and 5 patients (3.8%) had another procedure for adjacent-level pathologies 1–9 years later (mean 4.4 ± 2.7 years).

Conclusions

Long-term follow-up data in our veteran population support cervical corpectomy as an effective, long-lasting treatment for spondylotic myelopathy of the cervical spine. Use of CTMCs without end caps was associated with statistically significant increased postoperative kyphotic angulation and chronic pain. Despite an increase in focal kyphosis over time, regional cervical sagittal lordotic alignment had increased at the latest follow-up. Further investigation will include the association of chronic neck pain and postoperative kyphosis, and high fusion rates among a veteran population of heavy smokers.

Expansive open-door laminoplasty and selective anterior cervical decompression and fusion for treatment of multilevel cervical spondylotic myelopathy

OBJECTIVE

To evaluate the clinical results of combined expansive open-door laminoplasty by splitting of spinous processes and selective anterior cervical decompression and fusion in treatment of multilevel severe cervical spondylotic myelopathy (CSM).

METHODS

Twenty-eight patients (16 men and 12 women) underwent one-stage combined expansive open-door laminoplasty and selective anterior decompression and fusion for severe CSM; the average patient age was 51.3 years (range, 32-63 years). Clinical results were assessed by Japanese Orthopaedic Association (JOA) scores, number of finger grip and releases (G and R) in ten seconds, hand-grip strength, visual analog scale (VAS) of axial pain, and C2-C7 angle.

RESULTS

  There was no worsening of neurological symptoms due to cord injury, cerebrospinal fluid leakage, or wound infection. All cases completed one-year follow-up. The JOA scores, number of G and R in ten seconds, and hand-grip strength were all significantly improved (P < 0.05). Satisfactory decompression was shown by MRI or CT to have been achieved in all cases. The C2-C7 angle did not differ significantly from that found pre-operatively. The axial neck pain score was 2.0 ± 0.1 on VAS.

CONCLUSION

Combined expansive open-door laminoplasty by splitting of spinous processes and selective anterior decompression and fusion achieves complete spinal canal decompression with minimal morbidity; this strategy is effective in improving the surgical outcomes of CSM in one-year follow-up.

Anterior migration of spinal cord after cervical corpectomy

Posterior migration of spinal cord is a common complication of posterior cervical decompression, whereas anterior migration of spinal cord after anterior cervical decompression has not been reported previously. This report presents a case of anterior migration of spinal cord after cervical corpectomy. A 65-year-old male underwent a cervical corpectomy of the C4 and C5 for cervical spondylotic myelopathy. The postoperative MRI showed that spinal cord was decompressed. However, at 12 months postoperatively, the patient complained that improved gait aggravated again, and the MRI showed an anterior migration of the spinal cord at the level of the C4 and C5, and a compression of spinal cord at the level of caudal endplate of C3. Secondary surgery, laminaplasty of C3 and C4 was conducted. The postoperative MRI showed that the spinal canal increased at the C3 and C4 levels, and the spinal cord went through smoothly without sharp turning.

Biomechanical effects of anterior, posterior, and combined anterior-posterior instrumentation techniques on the stability of a multilevel cervical corpectomy construct: a finite element model analysis

BACKGROUND CONTEXT

Multilevel corpectomy, with or without anterior instrumentation, has been associated with both graft and anterior screw-plate complications. The addition of posterior instrumentation after anterior fixation has been shown to increase the overall stiffness of fused segments and decrease the likelihood of instrumentation failure. Little biomechanical information exists for providing guidance in the selection of an appropriate instrumentation technique after a multilevel cervical corpectomy. Clinical studies have also been inconclusive in choosing an optimum fixation strategy.

PURPOSE

To test the hypothesis that combined anterior-posterior fixation would lower the stresses on the bone-screw interfaces observed after an isolated anterior fixation and on the graft-end plate interfaces observed after an isolated posterior fixation.

STUDY DESIGN

A finite element (FE) analysis of a C4-C7 corpectomy fusion with three different fixation techniques: anterior, posterior, and combined anterior-posterior.

METHODS

A previously validated three-dimensional FE model of an intact C3-T1 segment was used. From this intact model, three additional instrumentation models were constructed using anterior (rigid screw-plate), posterior (rigid screw-rod), and combined anterior-posterior fixation techniques following a C4-C7 corpectomy fusion. Construct stability at the cephalad and caudal levels of the corpectomy was assessed.

RESULTS

Biomechanical comparisons between these instrumentation techniques show the least amount of construct motion in the combined anterior-posterior instrumentation model. The use of both anterior and posterior fixation shields the graft-end plate and screw-bone interfaces from peak stresses as compared with an isolated anterior or an isolated posterior fixation, thereby supporting the hypothesis of this study.

CONCLUSIONS

A combined fixation technique should be balanced against increased operating room time and surgery costs because of dual anterior and posterior fixation and the increased risk of long anterior plating, such as dysphasia, plate or screw dislodgement, or migration. Our study suggests that the use of posterior fixation, whether alone or in combination with anterior fixation, infers comparable stability. Further studies are warranted to identify whether the current findings are consistent with other biomechanical studies.

Screw angulation affects bone-screw stresses and bone graft load sharing in anterior cervical corpectomy fusion with a rigid screw-plate construct: a finite element model study

BACKGROUND CONTEXT

Anterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases.

PURPOSE

There has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4-C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct.

STUDY DESIGN

A finite element model of a two-level cervical corpectomy with static anterior cervical plate.

METHODS

A three-dimensional finite element (FE) model of an intact C3-T1 segment was developed and validated. From this intact model, a fusion model (two-level [C5, C6] anterior corpectomy) was developed and validated. After corpectomy, allograft interbody fusion with a rigid anterior screw-plate construct was created from C4 to C7. Five additional FE models were developed from the fusion model corresponding to five different combinations of screw angulations within the vertebral bodies (C4, C7): (0 degrees, 0 degrees), (5 degrees, 5 degrees), (10 degrees, 10 degrees), (15 degrees, 15 degrees), and (15 degrees, 0 degrees). The fifth fusion model was termed as a hybrid fusion model.

RESULTS

The stability of a two-level corpectomy reconstruction is not dependent on the position of the screws. Despite the locked screw-plate interface, some degree of load sharing is transmitted to the graft. The load seen by the graft and the shear stress at the bone-screw junction is dependent on the angle of the screws with respect to the end plate. Higher stresses are seen at more divergent angles, particularly at the lower level of the construct.

CONCLUSION

This study suggests that screw divergence from the end plates not only increases load transmission to the graft but also predisposes the screws to higher shear forces after corpectomy reconstruction. In particular, the inferior screw demonstrated larger stress than the upper-level screws. In the proposed hybrid fusion model, lower stresses on the bone graft, end plates, and bone-screw interface were recorded, inferring lower construct failure (end-plate fractures and screw pullout) potential at the inferior construct end.

Anterior corpectomy approach for removal of a cervical intradural schwannoma

Spinal schwannomas are typically intradural-extramedullary neoplasms thought to arise from Schwann cells or their progenitors which occur proportionally throughout the spinal canal. They most typically arise from dorsal sensory rootlets and occupy a posterior-lateral location in the spinal canal. Thus, posterior surgical procedures have become the conventional method to remove these tumors providing adequate exposure in most cases. More anteriorly located tumors may be approached through a posterolateral direction with section of the dentate ligament and gentle rotation of the spinal cord. However, posterior and posterolateral approaches may be problematic for removing tumors located in the midline and ventral to the spinal cord.

Although the anterior approach has been applied widely to treat cervical spondylosis, it has rarely been used to remove intradural tumors. Here, we present a case of a ventral cervical spinal schwannoma removed through an anterior approach followed by spinal reconstruction.

Cervical anterior transpedicular screw fixation. Part I: Study on morphological feasibility, indications, and technical prerequisites

Multilevel cervical spine procedures can challenge the stability of current anterior cervical screw-and-plate systems, particularly in cases of severe three-column subaxial cervical spine injuries and multilevel plated reconstructions in osteoporotic bone. Supplemental posterior instrumentation is therefore recommended to increase primary construct rigidity and diminish early failure rates. The increasing number of successfully performed posterior cervical pedicle screw fixations have enabled more stable fixations, however most cervical pathologies are located anteriorly and preferably addressed by an anterior approach. To combine the advantages of the anterior approach with the superior biomechanical characteristics of cervical pedicle screw fixation, the authors developed a new concept of a cervical anterior transpedicular screw-and-plate system. An in vivo anatomical study was performed to explore the feasibility of anterior transpedicular screw fixation (ATPS) in the cervical spine. The morphological study was conducted based on 29 cervical spine CT scans from healthy patients and measurements were performed on the pedicle sizes, angulations, vertebral body depth, height and width at C2 to T1. Significant morphologic parameters for the new technique are discussed. These parameters include the sagittal and transverse intersection points of the pedicle axis with the anterior vertebral body wall, as well as the distances between sagittal intersection points from C2 to T1. On the basis of these results, standard spine models were reconstructed and used for the conceptual development of a preclinical release prototype of an anterior transpedicular screw-and-plate system. The morphological feasibility of the new technique is demonstrated, and its indications, biomechanical considerations, as well as surgical prerequisites are thoroughly discussed. In the future, the technique of cervical anterior transpedicular screw fixation might diminish the number of failures in the reconstruction of multilevel and three-column cervical spine instabilities, and avoid the need for supplemental posterior instrumentation.

4- and 5-level anterior fusions of the cervical spine: review of literature and clinical results

In the future, there will be an increased number of cervical revision surgeries, including 4- and more-levels. But, there is a paucity of literature concerning the geometrical and clinical outcome in these challenging reconstructions. To contribute to current knowledge, we want to share our experience with 4- and 5-level anterior cervical fusions in 26 cases in sight of a critical review of literature. At index procedure, almost 50% of our patients had previous cervical surgeries performed. Besides failed prior surgeries, indications included degenerative multilevel instability and spondylotic myelopathy with cervical kyphosis. An average of 4.1 levels was instrumented and fused using constrained (26.9%) and non-constrained (73.1%) screw-plate systems. At all, four patients had 3-level corpectomies, and three had additional posterior stabilization and fusion. Mean age of patients at index procedure was 54 years with a mean follow-up intervall of 30.9 months. Preoperative lordosis C2-7 was 6.5 degrees in average, which measured a mean of 15.6 degrees at last follow-up. Postoperative lordosis at fusion block was 14.4 degrees in average, and 13.6 degrees at last follow-up. In 34.6% of patients some kind of postoperative change in construct geometry was observed, but without any catastrophic construct failure. There were two delayed unions, but finally union rate was 100% without any need for the Halo device. Eleven patients (42.3%) showed an excellent outcome, twelve good (46.2%), one fair (3.8%), and two poor (7.7%). The study demonstrated that anterior-only instrumentations following segmental decompressions or use of the hybrid technique with discontinuous corpectomies can avoid the need for posterior supplemental surgery in 4- and 5-level surgeries. However, also the review of literature shows that decreased construct rigidity following more than 2-level corpectomies can demand 360 degrees instrumentation and fusion. Concerning construct rigidity and radiolographic course, constrained plates did better than non-constrained ones. The discussion of our results are accompanied by a detailed review of literature, shedding light on the biomechanical challenges in multilevel cervical procedures and suggests conclusions.

Successful treatment of cervical myelopathy with minimal morbidity by circumferential decompression and fusion

Circumferential cervical decompression and fusion (CCDF) is an important technique for treating patients with severe cervical myelopathy. While circumferential cervical decompression and fusion may provide improved spinal cord decompression and stability compared to unilateral techniques, it is commonly associated with increased morbidity and mortality. We performed a retrospective analysis of patients undergoing CCDF at the University of California, San Francisco (UCSF) between January 2003 and December 2004. We identified 53 patients and reviewed their medical records to determine the effectiveness of CCDF for improving myelopathy, pain, and neurological function. Degree of fusion, functional anatomic alignment, and stability were also assessed. Operative morbidity and mortality were measured. The most common causes of cervical myelopathy, instability, or deformity were degenerative disease (57%) and traumatic injury (34%). Approximately one-fifth of patients had a prior fusion performed elsewhere and presented with fusion failure or adjacent-level degeneration. Postoperatively, all patients had stable (22.6%) or improved (77.4%) Nurick grades. The average preoperative and postoperative Nurick grades were 2.1 +/- 1.9 and 0.4 +/- 0.9, respectively. Pain improved in 85% of patients. All patients had radiographic evidence of fusion at last follow-up. The most common complication was transient dysphagia. Our average clinical follow-up was 27.5 +/- 9.5 months. We present an extensive series of patients and demonstrate that cervical myelopathy can successfully be treated with CCDF with minimal operative morbidity. CCDF may provide more extensive decompression of the spinal cord and may be more structurally stable. Concerns regarding operation-associated morbidity should not strongly influence whether CCDF is performed.

Spinous process plate fixation as a salvage operation for failed anterior cervical fusion

✓The purpose of this retrospective review was to demonstrate the effectiveness of simple spinous process plate fixation as a salvage operation for failed anterior cervical fusion (ACF). In this technique, the spinous processes are securely sandwiched between a pair of plates with thorns, which are squeezed together by tightening screws that extend through the plates. The authors salvaged six failed ACFs (nonunion of bone graft, plate migration, or bone graft dislodgment) by conducting this fixation without bone grafting, or with an anterior or posterior local bone graft only. Anterior bone union was attained within 6 months in all cases. This technique is easy to perform and probably provides more mechanical strength than does conventional spinous process wiring, resulting in prompt fusion without the need for a new massive bone graft. This technique is a practical option in salvage operations for failed ACF.