Jeffrey M. Spivak

Results of the prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement versus circumferential fusion for the treatment of 1-level degenerative disc disease.

Study Design. A prospective, randomized, multicenter, Food and Drug Administration-regulated Investigational Device Exemption clinical trial. Objective. To evaluate the safety and effectiveness of the ProDisc®-L (Synthes Spine, West Chester, PA) lumbar total disc replacement compared to circumferential spinal fusion for the treatment of discogenic pain at 1 vertebral level between L3 and S1. Summary of Background Data. As part of the Investigational Device Exemption clinical trial, favorable single center results of lumbar total disc replacement with the ProDisc®-L have been reported previously. Methods. Two hundred eighty-six (286) patients were treated on protocol. Patients were evaluated before and after surgery, at 6 weeks, 3, 6, 12, 18, and 24 months. Evaluation at each visit included patient self-assessments, physical and neurologic examinations, and radiographic evaluation. Results. Safety of ProDisc®-L implantation was demonstrated with 0% major complications. At 24 months, 91.8% of investigational and 84.5% of control patients reported improvement in the Oswestry Low Back Pain Disability Questionnaire (Oswestry Disability Index [ODI]) from preoperative levels, and 77.2% of investigational and 64.8% of control patients met the ≥15% Oswestry Disability Index improvement criteria. Overall neurologic success in the investigational group was superior to the control group (91.2% investigational and 81.4% control; P = 0.0341). At 6 weeks and 3 months follow-up time points, the ProDisc®-L patients recorded SF-36 Health Survey scores significantly higher than the control group (P = 0.018, P = 0.0036, respectively). The visual analog scale pain assessment showed statistically significant improvement from preoperative levels regardless of treatment (P < 0.0001). Visual analog scale patient satisfaction at 24 months showed a statistically significant difference favoring investigational patients over the control group (P = 0.015). Radiographic range of motion was maintained within a normal functional range in 93.7% of investigational patients and averaged 7.7°. Conclusions. ProDisc®-L has been found to be safe and efficacious. In properly chosen patients, ProDisc®-L has been shown to be superior to circumferential fusion by multiple clinical criteria.

The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures.

STUDY DESIGN A biomechanical study comparing two materials for augmentation of osteoporotic vertebral bodies and vertebral bodies after compression fracture. OBJECTIVES To compare an injected, biodegradable calcium phosphate bone substitute with injected polymethylmethacrylate bone cement for strengthening osteoporotic vertebral bodies and improving the integrity of vertebral compression fractures. SUMMARY OF BACKGROUND DATA Injection of polymethylmethacrylate bone cement into fractured vertebral bodies has been used clinically. However, there is concern about thermal damage to the neural elements during polymerization of the polymethylmethacrylate bone cement as well as its negative effects on bone remodeling. Biodegradable calcium phosphate bone substitutes have been studied for enhancement of fixation in fractured vertebrae. METHODS Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: 1) injection into osteoporotic vertebrae: intact control (n = 8), calcium phosphate (n = 8), and polymethylmethacrylate bone cement (n = 8) groups. Each specimen then was loaded in anterior compression until failure; 2) injection into postfractured vertebrae: calcium phosphate (n = 8) and polymethylmethacrylate bone cement (n = 8) groups. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending. RESULTS For intact osteoporotic vertebrae, the average fracture strength was 527 +/- 43 N (stiffness, 84 +/- 11 N/mm), 1063 +/- 127 N (stiffness, 157 +/- 21 N/mm) for the group injected with calcium phosphate, and 1036 +/- 100 N (stiffness, 156 +/- 8 N/mm) for the group injected with polymethylmethacrylate bone cement. The fracture strength and stiffness in the calcium phosphate bone substitute group and those in the polymethylmethacrylate bone cement group were similar and significantly stronger than those in intact control group (P < 0.05). For the compression fracture study, anterior vertebral height was increased 58.5 +/- 4.6% in the group injected with calcium phosphate and 58.0 +/- 6.5% in the group injected with polymethylmethacrylate bone cement as compared with preinjection fracture heights. No significant difference between the two groups was found in anterior vertebral height, fracture strength, or stiffness. CONCLUSION This study demonstrated that the injection of a biodegradable calcium phosphate bone substitute to strengthen osteoporotic vertebral bodies or improve vertebral compression fractures might provide an alternative to the use of polymethylmethacrylate bone cement.

CERVICAL SPINE INJURIES IN PATIENTS 65 AND OLDER

Study Design. This study was a retrospective database review of patients with cervical injuries admitted to a regional spinal cord injury center over a 9‐year period. Objectives. Patients <40 and ≥65 were analyzed separately to determine differences in etiology, neurologic findings, mortality, and neurologic recovery. Summary of Background Data. Previous studies of cervical injuries in older patients have found a high percentage of falling as an etiology, a high incidence of injuries to C2, and a high mortality rate with spinal cord injury (SCI). Methods. Three databases containing information on all SCI patients, SCI patients with 1‐2 year follow‐up, and neurogically intact spinal injury patients were reviewed retrospectively. Results. A higher percentage of older patients had cervical injuries, and this group did not show the typical male predominance seen in young patients (4:1 vs. 1:1). Neurologic deficits were more common in the younger age group. In the older patients, falls were a much more common etiology, and upper cervical injuries, especially odontoid fractures, predominated. Cervical spondylosis and stenosis were more common in the older patients, and the mortality with associated SCI was 60 times higher than in younger patients. Younger patients more commonly had complete neurologic injuries, but had more early functional motor return in incomplete lesions. The older patients did show late functional return in incomplete deficits. Conclusions. Cervical spine injury commonly occurs with relatively minor trauma in patients ≥65, with a mortality rate of approximately 26% with associated SCI. Return of functional motor recovery is delayed in older patients with incomplete deficits, but can be expected. C2 injuries, especially odontoid fractures, must be ruled out in older patients with neck pain after even a minor injury.

ProDisc-C and anterior cervical discectomy and fusion as surgical treatment for single-level cervical symptomatic degenerative disc disease: five-year results of a Food and Drug Administration study.

Study Design. Randomized controlled trial. Objective. Analyze the clinical outcomes at 5 years comparing cervical total disc replacement (TDR) with ProDisc-C (Synthes Spine USA Products; LLC, West Chester, PA) with anterior cervical discectomy and fusion (ACDF). Summary of Background Data. Previous reports of 2- and 4-year results have shown that ProDisc-C, a TDR for surgical treatment of patients experiencing single-level symptomatic cervical disc disease between C3 and C7, is safe and effective. Methods. Two hundred nine patients (103 ProDisc-C and 106 ACDF) from 13 sites were randomized and treated. Results including neck disability index, visual analog scale (VAS) neck and arm pain, Short Form-36 (SF-36), neurological examination, device success, adverse event occurrence, and VAS patient satisfaction were analyzed. Results. Demographics were similar between the 2 patient groups (ProDisc-C: 42.1 ± 8.4 yr, 44.7% males; ACDF: 43.5 ± 7.1 yr, 46.2% males). Rates of follow-up at 2 years were 98.1% ProDisc-C and 94.8% ACDF, and at 5 years 72.7% ProDisc-C and 63.5% ACDF. For all clinical outcomes for both groups, there was a statistically and clinically significant improvement at 2 and 5 years compared with baseline. At 5 years, ProDisc-C patients had statistically significantly less neck pain intensity and frequency. Both groups scored high VAS satisfaction scores at 5 years, with ProDisc-C 86.56 and ACDF 82.74. There were no reports of device failures or implant migration with ProDisc-C. The ProDisc-C patients maintained motion at their index level. At 5 years, the ProDisc-C patients had a statistically significantly lower rate of reoperation compared with ACDF patients (2.9% vs. 11.3%). Conclusion. Five-year results show that TDR with ProDisc-C is a safe and effective treatment of single-level symptomatic cervical disc disease. Clinical outcomes were comparable with ACDF. ProDisc-C patients maintained motion at the index level and had significantly less neck pain intensity and frequency as well as a lower probability of secondary surgery.

An anatomic evaluation of L5 nerve stretch in spondylolisthesis reduction.

Study Design. Lumbosacral spondylolisthesis was simulated using four embalmed human spines, and the path of the L5 nerve was studied. Objectives. To quantify the change in length of the L5 nerve root associated with reduction of spondylolisthesis, correction of slip angle, and changing disc height. Summary of Background Data. Stretch injury to the lumbar nerves remains a complication of spondylolisthesis reduction. To date, no anatomic studies have been performed to quantify this effect of reduction on the lumbar nerves. Methods. The L5 vertebral body and the sacrum of four embalmed human spines were constrained in an adjustable jig, and the length of a simulated nerve was determined for various position variables‐sagittal translation (0‐100% slip), slip angle (‐40° to +20°), and disc height (5 or 10 mm). Two standard points of reference were chosen to represent fixed points along the path of the L5 nerve. An inelastic cord was used to measure the path length between these points as L5 was reduced from 100% to 0% slip. Testing was performed using a 5‐mm and a 10‐mm disc height. The effect of varying slip angle alone was also studied. Results. The effect of spondylolisthesis reduction and slip angle correction on nerve length varied depending on the location of L5 with respect to the sacrum. There was an increasing effect of partial reduction on nerve length as L5 approached full reduction. Initially, little strain was produced in the L5 nerve as L5 was reduced in higher grade slips. However, as L5 approached full reduction, the strain per increment of reduction increased rapidly. On average, the mean nerve strain was 4.0% for the first 50% of reduction and 10.0% for the second half of reduction. Increasing lordosis relaxed the nerve in high‐grade slips and stretched the nerve in fully reduced slips. At 100% slip, the mean nerve excursion decreased 5.1 mm (nerve slackening) when L5 was rotated from +20° to ‐40°. At 0% slip, the mean nerve excursion increased 3.1 mm (nerve stretch). Increasing disc height directly stretched the L5 nerve. However, given a larger disc height, the strain on the nerve per increment of reduction was less than for the smaller height. Conclusion. The findings suggest that the risk of stretch injury to the L5 nerve with reduction of a high‐grade spondylolisthesis is not linear; with 71% of the total L5 nerve strain occurring during the second half of reduction, partial reduction may be a significantly safer treatment approach for high‐grade spondylolisthesis than complete reduction. Correction of lumbosacral kyphosis in high‐grade spondylolisthesis may be protective of the L5 nerve.

The Effect of Locking Fixation Screws on the Stability of Anterior Cervical Plating

STUDY DESIGN Current anterior cervical plate systems were tested with locked and unlocked fixation screws and with unicortical and bicortical fixation screws to determine fixation rigidity and pull-off strengths. OBJECTIVES To evaluate the effects of screw-plate locking and screw length on fixation strength and stability of anterior cervical plates. SUMMARY OF BACKGROUND DATA New plate systems provide for rigid locking of the screw-plate interface, theoretically increasing construct rigidity, allowing unicortical fixation, and preventing screw back-out. There are few data on the effects of locking screws on the stability of anterior cervical plating. METHODS Eighty fresh lamb vertebrae (C3-T1) were used. Test systems included: Cervical Spine Locking Plate (CSLP; Synthes, Paoli, PA, Orion plate (Sofamor-Danek, Memphis, TN), and Acroplate (AcroMed, Cleveland, OH). The CSLP and Orion plates were tested with fixation screws, locked and unlocked, and the AcroMed plate with unicortical and bicortical screw purchase. Biomechanical testing of the screw-plate constructs was performed to determine the initial bone-plate rigidity and pull-off strength. A 2.5-Nm cyclic bending moment was then applied to additional constructs for 10(5) cycles, and these constructs retested. RESULTS Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading (P < 0.05). After cycling, the rigidity of all unlocked unicortical constructs decreased significantly (P < 0.05). There was no significant difference in pull-off strengths between the CSLP, the Orion, and the unicortical AcroMed plate. However, all had significantly less pull-off strength than the AcroMed plate with bicortical screws. A negative correlation was observed between initial pull-off strength and sagittal vertebral body diameter. CONCLUSIONS Locking screws significantly increased the rigidity of the tested screw-plate systems initially and after cyclic loading. Because pull-off strength was affected by the vertebral body diameter, use of longer unicortical screws may be clinically beneficial in the patient with larger cervical vertebrae.

Demineralized Bone Matrix: Enhancement of Spinal Fusion

A study was conducted to determine the ability of demineralized bone matrix gel to act as an osteoconductive/osteoinductive materiaI to enhance cenine spinal fusion. Seven dogs underwent posterior spinal fusion, Four-level fusions were performed with one of four procedures at each level: decortication alone, with gel added, with autograft, or with both gal and autograft. Dogs were killed at 6 weeks ano early histologic response was studied. At untreated control sites, little bone formation was evident. Gel-filled sitas showed abundant osteoid, with 60% of deminerallized particles fused to or surrounded by new bone. Sites filled with autograft had more new bone, but there was more osteoid at gal-treated sites. Autograft augmented with gel showed the most vigorous response with extensive bridging between demineralized particles, host bone, autograft, and new bone. Significantly less autograft was needed to induce a similar amount of now bone formation when gel was added. Use of the gal as an autograft extender may improve the chance for successful spinal fusion.

Vertebral artery injury in cervical spine surgery: anatomical considerations, management, and preventive measures

BACKGROUND CONTEXT Vertebral artery (VA) injury can be a catastrophic iatrogenic complication of cervical spine surgery. Although the incidence is rare, it has serious consequences including fistulas, pseudoaneurysm, cerebral ischemia, and death. It is therefore imperative to be familiar with the anatomy and the instrumentation techniques when performing anterior or posterior cervical spine surgeries. PURPOSE To provide a review of VA injury during common anterior and posterior cervical spine procedures with an evaluation of the surgical anatomy, management, and prevention of this injury. STUDY DESIGN Comprehensive literature review. METHODS A systematic review of Medline for articles related to VA injury in cervical spine surgery was conducted up to and including journal articles published in 2007. The literature was then reviewed and summarized. RESULTS Overall, the risk of VA injury during cervical spine surgery is low. In anterior cervical procedures, lateral dissection puts the VA at the most risk, so sound anatomical knowledge and constant reference to the midline are mandatory during dissection. With the development and rise in popularity of posterior cervical stabilization and instrumentation, recognition of the dangers of posterior drilling and insertion of transarticular screws and pedicle screws is important. Anomalous vertebral anatomy increases the risk of injury and preoperative magnetic resonance imaging and/or computed tomography (CT) scans should be carefully reviewed. When the VA is injured, steps should be taken to control local bleeding. Permanent occlusion or ligation should only be attempted if it is known that the contralateral VA is capable of providing adequate collateral circulation. With the advent of endovascular repair, this treatment option can be considered when a VA injury is encountered. CONCLUSIONS VA injury during cervical spine surgery is a rare but serious complication. It can be prevented by careful review of preoperative imaging studies, having a sound anatomical knowledge and paying attention to surgical landmarks intraoperatively. When a VA injury occurs, prompt recognition and management are important.

Current Concepts Review - Degenerative Lumbar Spinal Stenosis*

Over the last ten years, the median age of the United States population has increased by 1.4 years, with more than two million additional people who are sixty-five years old or more91. As the population continues to age, more older people are maintaining an active lifestyle. Consequently, functional limitation and pain due to symptomatic degenerative disease of the spine is becoming more common. Lumbar spinal stenosis remains one of the most frequently encountered, clinically important degenerative spinal disorders in the aging population. Lumbar spinal stenosis is defined as a narrowing of the spinal canal that produces compression of the neural elements before their exit from the neural foramen3,84. The narrowing may be limited to a single motion segment (two adjacent vertebrae and the intervening intervertebral disc, facet joints, and supporting ligaments) or it may be more diffuse, spanning two motion segments or more. Lumbar spinal stenosis can be classified on the basis of either etiology or anatomy. The original etiological classification, described by Arnoldi et al., distinguishes congenital or developmental stenosis from acquired or degenerative spinal stenosis3. Congenital or developmental stenosis is due to either idiopathic narrowing of the spinal canal or developmental narrowing secondary to a bone dysplasia such as achondroplasia. Acquired or degenerative stenosis also may occur as a result of an underlying metabolic disorder such as Paget disease, a tumor, an infection, post-traumatic osteoarthrotic changes, or instability with spondylolisthesis following a previous operation. Anatomical classifications of lumbar spinal stenosis are used to identify specific areas of narrowing of the spinal canal and are particularly useful as guides for operative decompression. The anatomy of the spinal canal at each vertebral segment can be understood better by dividing the canal into a series of transverse regions (three levels from cephalad to …

Use of hydroxyapatite in spine surgery

Abstract. Hydroxyapatite- (HA-)based ceramics have been evaluated for a variety of applications in spinal surgery, utilizing in vivo animal models and human clinical series. In vivo animal studies have shown efficacy for these materials as a bone graft substitute in interbody fusions and as a bone graft extender or bioactive osteoinductive material carrier in posterolateral lumbar fusions. Clinically, HA ceramic has been shown to be effective as a bone graft extender in posterior spinal fusion surgery for childhood scoliosis, and as a structural bone graft substitute in anterior cervical spine fusions. As an osteoconductive material, it appears to function best as a bone graft extender or carrier for an osteoinductive bone growth factor rather than as a stand-alone bone graft substitute in nonstructural clinical applications. Injectable HA ceramics also hold promise as biocompatible and bioresorbable materials for use in spinal screw fixation strength augmentation and in minimally invasive vertebral body strength augmentation either following fracture or prophylactically in osteoporotic vertebrae.