John Sherman

Somatosensory evoked potential spinal cord monitoring reduces neurologic deficits after scoliosis surgery: results of a large multicenter survey

Neurologic deficits were compared to somatosensory evoked potential (SEP) spinal cord monitoring in a survey of spinal orthopedic surgeons. Experienced SEP spinal cord monitoring teams had fewer than one-half as many neurologic deficits per 100 cases compared to teams with relatively little monitoring experience. Experienced SEP monitoring teams also had fewer neurologic deficits than were seen in previous surveys of this group. Definite neurologic deficits, despite stable SEPs (false negative monitoring), occurred during surgery in only 0.063% of patients. Factors independently associated with fewer neurologic deficits also included the surgeons years of experience in orthopedic surgery and the use of the wake-up test. Other technical survey results are also presented here. These results confirm the clinical efficacy of experienced SEP spinal cord monitoring for prevention of neurologic deficits during spinal surgery such as for scoliosis.

Pathophysiology of spinal cord injury. Recovery after immediate and delayed decompression

We evaluated the effect of the timing of decompression of the spinal cord after compression of 50 per cent of the diameter of the spinal cord at the fourth lumbar level in thirty purebred dogs. The dogs were divided into five groups of six dogs each on the basis of the duration of the compression. Decompression was performed immediately (Group I), one hour (Group II), six hours (Group III), twenty-four hours (Group IV), or one week (Group V) after the compression. Monitoring of somatosensory evoked potentials, daily neurological examinations, and histological and electron microscopic studies at the time of the autopsy were performed for all of the dogs. Initially, all of the dogs were paraplegic after the compression of the spinal cord. The dogs that had immediate decompression or decompression after one hour of compression recovered the ability to walk (grades 4 and 5, according to Tarlovs system) as well as control of the bowel and bladder, and the somatosensory evoked potentials improved an average of 85 and 72 per cent, respectively. However, when compression lasted six hours or more, there was no neurological recovery and there was progressive necrosis of the spinal cord. Somatosensory evoked potentials improved 29 per cent in Group III, 26 per cent in Group IV, and 10 per cent in Group V. The percentage of recovery of the somatosensory evoked potentials by six weeks after the decompression was significantly related to the duration of the compression (p < 0.0008).

Spinal Cord Monitoring: Results of the Scoliosis Research Society and the European Spinal Deformity Society Survey

The Scoliosis Research Society (SRS) and the European Spinal Deformity Society (ESDS) membership was surveyed regarding the use of intraoperative monitoring of somatosensory evoked potentials in spinal surgery. A total of 242 people responded, with 188 using intraoperative monitoring. A second survey was distributed detailing the technical aspects of monitoring, of which 71 were returned. A total of 342 neurologic deficits were reported to have occurred with monitoring in place. Two hundred forty-six (72%) were accurately detected, and 96 (28%) were not detected by sensory cord evoked potentials (SCEP). There were 1,003 false-positive cases reported. The incidence of false-negative cases was related to those not monitoring both latency and amplitude, to using fewer recording electrodes, and with those surgeons doing more kyphosis corrections.

Four-year follow-up results of lumbar spine arthrodesis using the Bagby and Kuslich lumbar fusion cage.

Study Design. This was a prospective multicenter clinical trial of a lumbar interbody fusion cage with a minimum of 4 years’ follow-up. Objectives. To determine whether the early positive clinical results in fusions with lumbar cages, such as the Bagby and Kuslich (BAK) cage, are maintained beyond 2 years. Summary of Background Data. Threaded cages have been used increasingly for the treatment of symptomatic degenerative intervertebral disc disease. Concerns about the long-term clinical outcomes of this procedure have been posed, particularly regarding bony fusion viability, revision rates, potential adjacent level disease, and late complications. Methods. The study cohort was a 196-patient subset from a prospective investigational device exemption. In addition to early postoperative examinations, these patients were examined biannually with a minimum of 4 years’ follow-up. Patient outcome was assessed by a 6-point scale that evaluated pain relief, and functional improvement was determined by changes in activities of daily living. Fusion rates and return to work were determined. Complications and secondary operations were reported and categorized as non–device related or device related. Results. The patient cohort with 4-year follow-up represented 25.6% of the original study population eligible at that time. Overall, the largest percentage of pain relief and functional improvements occurred by 3 months, and these improvements were maintained at each follow-up. Overall fusion rate was 91.7% and 95.1% at 2 and 4 years, respectively. In this cohort, 39.5% of patients were working or were able to work within 3 months of surgery. After 4 years, 62.7% of patients were gainfully employed or able to work. The late-occurring complication rate in this cohort was 13.8% (27/196). Complications necessitating a second operation occurred in 8.7% (17/196), whereas reoperations that were deemed device related were performed in 3.1% (6/196). Conclusions. This study indicates that the early positive benefits of interbody fusion cage procedures are maintained through 4 years with acceptably low morbidity.

1991 Volvo Award in Experimental Studies: Cauda Equina Syndrome: Neurologic Recovery Following Immediate, Early, or Late Decompression

An animal model of cauda equina syndrome was developed. Neurologic recovery was analyzed following immediate, early, and delayed decompression. Five experimental groups, each containing six dogs, were studied. Compression of the cauda equina was performed in all 30 dogs following an L6-7 laminectomy. The cauda equina was constricted by 75% in each group. The first group was constricted and immediately decompressed. The remaining groups were constricted for 1 hour, 6 hours, 24 hours, and 1 week, respectively, before being decompressed. Somatosensory evoked potentials were performed before and after surgery, before and immediately after decompression, and 6 weeks following decompression. Daily neurologic exams using the Tarlov grading scale were performed. At 6 weeks postdecompression, all dogs were killed, and the neural elements analyzed histologically. Following compression, all 30 dogs had significant lower extremity weakness, tail paralysis, and urinary incontinence. All dogs recovered significant motor function 6 weeks following decompression. The dogs with immediate decompression generally recovered neurologic function within 2-5 days. The dogs receiving 1-hour and 6-hour compression recovered within 5-7 days. The dogs receiving 24-hour compression remained paraparetic 5-7 days, with bladder dysfunction for 7-10 days and tail dysfunction persisting for 4 weeks. The dogs with compression for 1 week were paraparetic (Tarlov Grade 2 or 3) and incontinent during the duration of cauda equina compression. They recovered to walking by 1 week and Tarlov Grade 5 with bladder and tail control at the time of euthanasia. Immediately after compression, all five groups demonstrated at least 50% deterioration of the posterior tibial nerve evoked potential amplitudes. Six weeks after decompression, all five groups had a mean amplitude recovery of 20-30%. There were no statistical differences in recovery of somatosensory evoked potentials among the groups. Histologic analysis of the cauda equina in all groups demonstrated scattered wallerian degeneration and axonal regeneration. Areas of poor myelination, fibrosis, and macrophage activity were seen at the level of constriction. There were no significant differences in the histologic neuroanatomy of the five groups. It has been advocated that early decompression of cauda equina syndrome enhances neurologic recovery. This study does not support this premise. Although decompression allowed significant recovery in all 30 dogs, no significant differences were found in somatosensory evoked potentials, neurologic recovery, or histopathology in groups decompressed immediately, at 1 hour, 6 hours, 24 hours, or 1 week.

Economic impact of improving outcomes of lumbar discectomy

BACKGROUND Lumbar discectomy is usually a successful operation with a relatively low cost. Potential adjunctive procedures, such as repairing the anulus fibrosus or nucleus replacements, necessitate a cost-benefit analysis. PURPOSE This economic analysis was performed to understand the potential value of advanced implantable technologies designed to improve outcomes after discectomy. STUDY DESIGN/SETTING Using an insurance claims-based database, the economics of less-than-favorable outcomes after lumbar discectomy were studied. Estimates of improved clinical outcomes because of adjunctive surgical procedural items were modeled. PATIENT SAMPLE Using Current Procedural Terminology (CPT-4) codes and International Classification of Diseases, Clinical Modification procedure codes (ICD-9 CM), all lumbar discectomy patients were identified in a 6-month period from a large, 2002, commercially available claims-based data set representing 3.1 million insured lives. OUTCOME MEASURES Not applicable. METHODS Longitudinal data analysis from 3 years (2002-2004) of the database was performed for evidence of claims after the insureds discectomy (up to 18 months post) as a utilization estimate of surgical and medical treatment resultant of less-than-favorable outcomes. Incidence and cost of secondary operations, medical management, and complications were determined. Using these inputs, an economic model was generated to estimate the effect of improvement in discectomy outcomes. RESULTS Of the 494 patients who had a discectomy within a 6-month period, 137 (28%) had subsequent claims that suggested the outcome was less than favorable within 18 months. Patients whose insurance claims included codes for a second operation (n=52 patients with 56 operations; 11%) and patients being medically/nonsurgically managed (n=85, 17%) were studied. Average reimbursed charges incurred (2006 dollars) of repeated discectomy (80% of cases) was

Nucleus Replacement With the DASCOR Disc Arthroplasty Device: Interim Two-Year Efficacy and Safety Results From Two Prospective, Non-Randomized Multicenter European Studies

6,907 and for arthrodesis (20% of cases) was

Lumbar spinal stenosis secondary to calcium pyrophosphate crystal deposition (pseudogout)

24,375. Average additional medical treatment cost to diagnose or manage poor outcome requiring another surgery was

EEG and neuroimaging localization in partial epilepsy

3,365. Procedure-related complications within 40 days of surgery were evident in 15% of the group; with additional average cost to manage of

The Restoration of Lumbar Intervertebral Disc Load Distribution: A Comparison of Three Nucleus Replacement Technologies

3,939. CONCLUSIONS Substantial cost associated with poor discectomy outcomes is often overlooked or underappreciated. Surgical technologies that can improve outcomes of discectomy by 50% to 70% thus improving patient quality of life can be overall cost-neutral between