Andrew T. Healy

Reoperation rates after anterior cervical discectomy and fusion versus posterior cervical foraminotomy: a propensity-matched analysis.

BACKGROUND CONTEXT Anterior cervical discectomy and fusion (ACDF) and posterior cervical foraminotomy (PCF) are both used to surgically treat patients with cervical radiculopathy and have been shown to have similar outcomes. Nonetheless, ACDF has become increasingly more commonplace compared with PCF, in part because of a pervasive belief that PCF has a higher incidence of required reoperations. PURPOSE To determine the reoperation rate at the index level of ACDF versus PCF 2 years postoperatively. STUDY DESIGN A retrospective case-control. PATIENT SAMPLE All patients that underwent ACDF and PCF for radiculopathy (excluding myelopathy indications) between January 2005 and December 2011. OUTCOME MEASURES Revision surgery within 2 years, at the index level, was recorded. METHODS Propensity score analysis between the ACDF and PCF groups was done, matching for age, gender, race, body mass index, tobacco use, median income and insurance status, primary surgeon, level of surgery, surgery duration, and length of hospital stay. RESULTS Seven hundred ninety patients met the inclusion/exclusion criteria, including 627 ACDF and 163 PCF. Before propensity matching, the PCF group was found to be significantly older and more likely to be male. After matching, there were no significant differences between groups for any baseline characteristics. Reoperation rate at the index level was 4.8% for the ACDF group and 6.4% for the PCF group (p=.7) within 2 years of the initial surgery. Using equivalence testing, based on an a priori null hypothesis that a clinically meaningful difference between the two groups would be ≥5%, we found that the absolute difference of 1.6% was significantly (p=.01) less than our hypothesized difference. CONCLUSIONS This study demonstrates that even after accounting for patient demographics, operative characteristics, and primary surgeon, there are no significant differences in 2-year reoperation rates at the index level between ACDF and PCF. The reoperation rates are statistically equivalent. Thus, spine surgeons can operate via the posterior approach without putting patients at increased risk for revision surgery at the index level.

Convection-enhanced drug delivery for gliomas

In spite of aggressive multi-modality treatments, patients diagnosed with anaplastic astrocytoma and glioblastoma continue to display poor median survival. The success of our current conventional and targeted chemotherapies are largely hindered by systemic- and neurotoxicity, as well as poor central nervous system (CNS) penetration. Interstitial drug administration via convection-enhanced delivery (CED) is an alternative that potentially overcomes systemic toxicities and CNS delivery issues by directly bypassing the blood–brain barrier (BBB). This novel approach not only allows for directed administration, but also allows for newer, tumor-selective agents, which would normally be excluded from the CNS due to molecular size alone. To date, randomized trials of CED therapy have yet to definitely show survival advantage as compared with todays standard of care, however, early studies appear to have been limited by “first generation” delivery techniques. Taking into consideration lessons learned from early trials along with decades of research, newer CED technologies and therapeutic agents are emerging, which are reviewed herein.

A Systematic Review of Lumbar Fusion Rates With and Without the Use of rhBMP-2.

Study Design. Systematic review. Objective. To evaluate literature comparing fusion rates in anterior lumbar interbody fusion (ALIF), posterior lumbar interbody/transforaminal lumbar interbody fusion (PLIF/TLIF), and posterolateral lumbar fusion (PLF) with and without recombinant human bone morphogenetic protein-2 (rhBMP-2). Summary of Background Data. rhBMP-2 is used for the FDA-approved indication of single-level ALIF with LT-Cage and off-label for PLIF/TLIF, and PLF. Due to recent controversies, it is essential to evaluate the literature for its effects on fusion rates to evaluate whether benefits outweigh potential complications. Methods. A Medline search was performed of clinical studies published between May 2000 and May 2012 comparing fusion rates after ALIF, PLIF/TLIF, and PLF surgery with versus without rhBMP-2. Only studies with a control arm were reviewed. Results. 16 studies were reviewed (1794 patients, 995 treated with rhBMP-2 and 799 without). 5 of 5 studies for PLIF/TLIF (including 301 of 301 patients), 1 of 4 for ALIF (including 279 of 589 patients), and 3 of 7 for PLF (including 272 of 904 patients) reported no significant improvement in fusion rates with rhBMP-2 compared with those without rhBMP-2 at longest follow-up investigated. Average fusion rate 24 months after surgery was 97.8% for ALIF (n = 316), 95.7% for PLIF/TLIF (n = 141), and 93.6% for PLF (n = 422) with rhBMP-2 and 88.2% (n = 228), 89.5% (n = 86), and 83.1% (n = 372) without rhBMP-2, for ALIF, PLIF/TLIF, and PLF, respectively. Odds ratio of fusion were calculated as 7.08 (95% CI: 1.54–32.7) in ALIF, 1.98 (95% CI: 0.39–10.1) in PLIF/TLIF, and 3.06 (95% CI: 1.61–5.80) in PLF with rhBMP-2 as compared with without rhBMP-2. Conclusion. Although numerous studies did not show statistically significant improvement in fusion rates with rhBMP-2 use, analysis of combined studies revealed significant improvement in fusion rate with rhBMP-2 in ALIF and PLF patients. Notably, even when pooling data from several studies, rhBMP-2 did not result in statistically significantly improved fusion rates in PLIF/TLIF. However, heterogeneity of rhBMP-2 dosing, surgical techniques, and quality of papers reviewed may limit the validity of conclusions drawn. Level of Evidence: 4

Bow hunter's syndrome secondary to bilateral dynamic vertebral artery compression.

Bow hunters syndrome is a condition in which vertebrobasilar insufficiency is resultant from head rotation, clinically manifested by presyncopal sensation, syncope, dizziness, and nausea. It is usually diagnosed clinically, with supporting vascular imaging demonstrating an occluded or at the very least compromised unilateral vertebral artery, while the dominant vertebral artery remains patent in the neutral position. Dynamic imaging is utilized to confirm the rotational compression of the dominant vertebral artery. We present the rare case of a patient with typical Bow hunters symptoms, bilaterally patent vertebral arteries on neutral imaging, and bilateral compromise with head rotation. Our patient underwent posterior decompression of the culprit atlanto-axial transverse foramen and subaxial cervical fusion, with resolution of his symptoms. Our patient exemplifies the possibility of bilateral dynamic vertebral artery occlusion. We show that Bow hunters syndrome cannot be ruled out in the setting of bilaterally patent vertebral arteries on neutral imaging and that severe cervical spondylosis should impart further clinical suspicion of this unusual phenomenon.

Biomechanical analysis of the upper thoracic spine after decompressive procedures

BACKGROUND CONTEXT Decompressive procedures such as laminectomy, facetectomy, and costotransversectomy are routinely performed for various pathologies in the thoracic spine. The thoracic spine is unique, in part, because of the sternocostovertebral articulations that provide additional strength to the region relative to the cervical and lumbar spines. During decompressive surgeries, stability is compromised at a presently unknown point. PURPOSE To evaluate thoracic spinal stability after common surgical decompressive procedures in thoracic spines with intact sternocostovertebral articulations. STUDY DESIGN Biomechanical cadaveric study. METHODS Fresh-frozen human cadaveric spine specimens with intact rib cages, C7-L1 (n=9), were used. An industrial robot tested all spines in axial rotation (AR), lateral bending (LB), and flexion-extension (FE) by applying pure moments (±5 Nm). The specimens were first tested in their intact state and then tested after each of the following sequential surgical decompressive procedures at T4-T5 consisting of laminectomy; unilateral facetectomy; unilateral costotransversectomy, and subsequently instrumented fusion from T3-T7. RESULTS We found that in all three planes of motion, the sequential decompressive procedures caused no statistically significant change in motion between T3-T7 or T1-T12 when compared with intact. In comparing between intact and instrumented specimens, our study found that instrumentation reduced global range of motion (ROM) between T1-T12 by 16.3% (p=.001), 12% (p=.002), and 18.4% (p=.0004) for AR, FE, and LB, respectively. Age showed a negative correlation with motion in FE (r = -0.78, p=.01) and AR (r=-0.7, p=.04). CONCLUSIONS Thoracic spine stability was not significantly affected by sequential decompressive procedures in thoracic segments at the level of the true ribs in all three planes of motion in intact thoracic specimens. Age appeared to negatively correlate with ROM of the specimen. Our study suggests that thoracic spinal stability is maintained immediately after unilateral decompression at the level of the true ribs. These preliminary observations, however, do not depict the long-term sequelae of such procedures and warrant further investigation.

Predisposing Characteristics of Adjacent Segment Disease After Lumbar Fusion.

Study Design. Retrospective Review. Objective. The aim of this study was to determine medical, radiographic, and surgical risk factors for the development of adjacent segment disease (ASD) after lumbar fusion. Summary of Background Data. ASD is a recognized outcome of spinal fusion that leads to increased costs and debilitating symptoms for patients. However, a comprehensive understanding of risk factors for the development of this surgical outcome does not exist. Methods. The medical records of patients who received their first lumbar fusion for any indication were retrospectively examined for preoperative medical comorbidities and medications, as well as surgical approach and perioperative complications. A blinded reviewer assessed radiographs for each patient to examine sagittal alignment after fusion. Multivariable logistic regression was used to model the risk of developing ASD on the basis of one or more predictors. Results. A total of 137 patients fit the inclusion criteria; 9% required a follow-up operation for degeneration at segments adjacent to the fusion. The ASD group had a mean follow-up of 21.1 months prior to revision surgery and an overall follow-up of 41.0 months. The average follow-up in the control group was 14.0 months. Statistically significant independent predictors of developing ASD included antidepressant use [odds ratio (OR) = 5.4], diagnosis of degenerative scoliosis (OR = 34.2), fusion of L4-S1 (OR = 56.5), having no decompressions adjacent to the fusion, and low sacral slope (OR = 0.9). No patient who developed ASD received a decompression adjacent to the fusion such that an OR could not be generated for this independent predictor. Conclusion. This study is the first to use a combination of medical, surgical, and postoperative sagittal balance as risk factors for the development of adjacent segment disease after lumbar fusion. The awareness of these risk factors may allow for better patient selection and surgical technique to decrease the probability of acquiring this adverse outcome. Level of Evidence: 4

A pilot study of the utility of a laboratory-based spinal fixation training program for neurosurgical residents

OBJECTIVE Pedicle and lateral mass screw placement is technically demanding due to complex 3D spinal anatomy that is not easily visualized. Neurosurgical and orthopedic surgery residents must be properly trained in such procedures, which can be associated with significant complications and associated morbidity. Current training in pedicle and lateral mass screw placement involves didactic teaching and supervised placement in the operating room. The objective of this study was to assess whether teaching residents to place pedicle and lateral mass screws using navigation software, combined with practice using cadaveric specimens and Sawbones models, would improve screw placement accuracy. METHODS This was a single-blinded, prospective, randomized pilot study with 8 junior neurosurgical residents and 2 senior medical students with prior neurosurgery exposure. Both the study group and the level of training-matched control group (each group with 4 level of training-matched residents and 1 senior medical student) were exposed to a standardized didactic education regarding spinal anatomy and screw placement techniques. The study group was exposed to an additional pilot program that included a training session using navigation software combined with cadaveric specimens and accessibility to Sawbones models. RESULTS A statistically significant reduction in overall surgical error was observed in the study group compared with the control group (p = 0.04). Analysis by spinal region demonstrated a significant reduction in surgical error in the thoracic and lumbar regions in the study group compared with controls (p = 0.02 and p = 0.04, respectively). The study group also was observed to place screws more optimally in the cervical, thoracic, and lumbar regions (p = 0.02, p = 0.04, and p = 0.04, respectively). CONCLUSIONS Surgical resident education in pedicle and lateral mass screw placement is a priority for training programs. This study demonstrated that compared with a didactic-only training model, using navigation simulation with cadavers and Sawbones models significantly reduced the number of screw placement errors in a laboratory setting.

Biomechanics of the lower thoracic spine after decompression and fusion: a cadaveric analysis

BACKGROUND CONTEXT Few studies have evaluated the extent of biomechanical destabilization of thoracic decompression on the upper and lower thoracic spine. The present study evaluates lower thoracic spinal stability after laminectomy, unilateral facetectomy, and unilateral costotransversectomy in thoracic spines with intact sternocostovertebral articulations. PURPOSE To assess the biomechanical impact of decompression and fixation procedures on lower thoracic spine stability. STUDY DESIGN Biomechanical cadaveric study. METHODS Sequential surgical decompression (laminectomy, unilateral facetectomy, unilateral costotransversectomy) and dorsal fixation were performed on the lower thoracic spine (T8-T9) of human cadaveric spine specimens with intact rib cages (n=10). An industrial robot was used to apply pure moments to simulate flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in the intact specimens and after decompression and fixation. Global range of motion (ROM) between T1-T12 and intrinsic ROM between T7-T11 were measured for each specimen. RESULTS The decompression procedures caused no statistically significant change in either global or intrinsic ROM compared with the intact state. Instrumentation, however, reduced global motion for AR (45° vs. 30°, p=.0001), FE (24° vs. 19°, p=.02), and LB (47° vs. 36°, p=.0001) and for intrinsic motion for AR (17° vs. 4°, p=.0001), FE (8° vs. 1°, p=.0001), and LB (12° vs. 1°, p=.0001). No significant differences were identified between decompression of the upper versus lower thoracic spine, with trends toward significantly greater ROM for AR and lower ROM for LB in the lower thoracic spine. CONCLUSIONS The lower thoracic spine was not destabilized by sequential unilateral decompression procedures. Addition of dorsal fixation increased segment rigidity at intrinsic levels and also reduced overall ROM of the lower thoracic spine to a greater extent than did fusing the upper thoracic spine (level of the true ribs). Despite the lack of true ribs, the lower thoracic spine was not significantly different compared with the upper thoracic spine in FE and LB after decompression, although there were trends toward significance for greater AR after decompression. In certain patients, instrumentation may not be needed after unilateral decompression of the lower thoracic spine; further validation and additional clinical studies are warranted.

Polyetheretherketone (PEEK) intervertebral cage as a cause of chronic systemic allergy: a case report.

BACKGROUND CONTEXT Polyetheretherketone (PEEK) is an organic polymer thermoplastic with strong mechanical and chemical resistance properties. It has been used in industry to fabricate items for demanding applications such as bearings, piston parts, compressor plate valves, and cable insulation. Since the early 1980s, polyetheretherketone polymers have been increasingly used in orthopedic and spinal surgery applications. Numerous studies and years of clinical experience have confirmed the biocompatibility of this material. PURPOSE The purpose of the study was to report a case of chronic systemic allergy after anterior cervical decompression and fusion (ACDF) and implantation of an intervertebral PEEK cage, with resolution of symptoms after removal of PEEK cage. STUDY DESIGN/SETTING This study is a case report with clinical evidence for allergy to PEEK. METHODS The methods involve clinical findings and review of current literature. RESULTS After ACDF and implantation of an intervertebral PEEK cage, the patient had developed an angioedema-like picture marked by severe redness, itching, swelling of his tongue, and skin thickening. A skin patch test was positive for PEEK. Removal of the implant resulted in the resolution of his allergy symptoms shortly after surgery. CONCLUSIONS Tissue reactions to PEEK are extremely rare. Herein, we present the first report of a chronic allergic response to interbody PEEK material.

Thoracic range of motion, stability, and correlation to imaging-determined degeneration

OBJECT The degenerative process of the spinal column results in instability followed by a progressive loss of segmental motion. Segmental degeneration is associated with intervertebral disc and facet changes, which can be quantified. Correlating this degeneration with clinical segmental motion has not been investigated in the thoracic spine. The authors sought to determine if imaging-determined degeneration would correlate with native range of motion (ROM) or the change in ROM after decompressive procedures, potentially guiding clinical decision making in the setting of spine trauma or following decompressive procedures in the thoracic spine. METHODS Multidirectional flexibility tests with image analysis were performed on thoracic cadaveric spines with intact ib cage. Specimens consisted of 19 fresh frozen human cadaveric spines, spanning C-7 to L-1. ROM was obtained for each specimen in axial rotation (AR), flexion-extension (FE), and lateral bending (LB) in the intact state and following laminectomy, unilateral facetectomy, and unilateral costotransversectomy performed at either T4-5 (in 9 specimens) or T8-9 (in 10 specimens). Image grading of segmental degeneration was performed utilizing 3D CT reconstructions. Imaging scores were obtained for disc space degeneration, which quantified osteophytes, narrowing, and endplate sclerosis, all contributing to the Lane disc summary score. Facet degeneration was quantified using the Weishaupt facet summary score, which included the scoring of facet osteophytes, narrowing, hypertrophy, subchondral erosions, and cysts. RESULTS The native ROM of specimens from T-1 to T-12 (n = 19) negatively correlated with age in AR (Pearsons r coefficient = -0.42, p = 0.070) and FE (r = -0.42, p = 0.076). When regional ROM (across 4 adjacent segments) was considered, the presence of disc osteophytes negatively correlated with FE (r = -0.69, p = 0.012), LB (r = -0.82, p = 0.001), and disc narrowing trended toward significance in AR (r = -0.49, p = 0.107). Facet characteristics, scored using multiple variables, showed minimal correlation to native ROM (r range from -0.45 to +0.19); however, facet degeneration scores at the surgical level revealed strong negative correlations with regional thoracic stability following decompressive procedures in AR and LB (Weishaupt facet summary score: r = -0.52 and r = -0.71; p = 0.084 and p = 0.010, respectively). Disc degeneration was not correlated (Lane disc summary score: r = -0.06, p = 0.861). CONCLUSIONS Advanced age was the most important determinant of decreasing native thoracic ROM, whereas imaging characteristics (T1-12) did not correlate with the native ROM of thoracic specimens with intact rib cages. Advanced facet degeneration at the surgical level did correlate to specimen stability following decompressive procedures, and is likely indicative of the terminal stages of segmental degeneration.