In Degenerative Spondylolisthesis, Unilateral Laminotomy for Bilateral Decompression Leads to Less Reoperations at 5 Years When Compared to Posterior Decompression With Instrumented Fusion: A Propensity-matched Retrospective Analysis.

STUDY DESIGN: Multicenter retrospective cohort study. OBJECTIVE: The aim of this study was to compare reoperation rates at 5-year follow-up of unilateral laminotomy for bilateral decompression (ULBD) versus posterior decompression with instrumented fusion (Fusion) for patients with low-grade degenerative spondylolisthesis (DS) with lumbar spinal stenosis (LSS) in a multicenter database. SUMMARY OF BACKGROUND DATA: Controversy exists regarding whether fusion should be used to augment decompression surgery in patients with LSS with DS. For years, the standard has been fusion with standard laminectomy to prevent postoperative instability. However, this strategy is not supported by Level 1 evidence. Instability and reoperations may be reduced or prevented using less invasive decompression techniques. METHODS: We identified 164 patients with DS and LSS who underwent ULBD between January 2007 and December 2011 in a multicenter database. These patients were propensity score-matched on age, sex, race, and smoking status with patients who underwent Fusion (n = 437). Each patient required a minimum of 5-year follow-up. The primary outcome was 5-year reoperation. Secondary outcome measures included postoperative complication rates, blood loss during surgery, and length of stay. Logistic regression models were used to estimate the odds ratio of the 5-year reoperation rate between the two surgical groups. RESULTS: The reoperation rate at 5-year follow-up was 10.4% in the ULBD group and 17.2% in the Fusion group. ULBD reoperations were more frequent at the index surgical level; Fusion reoperations were more common at an adjacent level. The two types of operations had similar postoperative complication rates, and both groups tended to have fusion reoperations. CONCLUSION: For patients with stable DS and LSS, ULBD is a viable, durable option compared to fusion with decreased blood loss and length stay, as well as a lower reoperation rate at 5-year follow-up. Further prospective studies are required to determine the optimal clinical scenario for ULBD in the setting of DS. LEVEL OF EVIDENCE: 3.

Does chronic kidney disease affect the mortality rate in patients undergoing spine surgery?

The number of patients with chronic kidney disease (CKD) and their life expectancy has been increasing. With time number of patients undergoing spine surgery has also been on a rise. This study we did a retrospective review of registry data to investigate the mortality rate of chronic kidney disease patients following spine surgery using a large, multi-center spine registry. 12,276 consecutive spine-fusion patients from January 2009 to December 2012 were included and mortality rates in patients with CKD compared to those with normal kidney function following spine surgery. Logistic regression was usedto evaluate risk of mortality following spine surgery. The average age of the cohort was 59 (SD=13.4). 53% were female. Patients who had stage 3, 4 or 5 CKD were older than non-CKD patients (mean=71,SD=9.2 vs. 59, SD=13.3). After adjusting for confounding variables, patients with stage 3 or 4 CKD had higher mortality rates than patients with normal kidney function (OR 1.78, 95% CI 1.3-2.45) Hemodialysis-dependent patients (stage 5 CKD) had even higher rates of mortality compared to patients with normal function (OR 4.18, 95% CI1.87-9.34). our findings suggest that spine surgery is associated with significantly higher mortality rates in patients with CKD compared to patients with normal kidney function. Understanding the additional morbidity and mortality of spine surgery in this medically complicated group of patients is imperative for accurate preoperative risk assessment.

An In Vitro Biomechanical Study Evaluating Cervical Extension Plates for Stabilizing Degenerated Adjacent Levels.

STUDY DESIGN: To evaluate the biomechanical stability of 2 extender plates in a human cervical cadaveric model. OBJECTIVES: To evaluate 2 extender plates, placed adjacent to initially implanted plates and to compare their biomechanical stability with traditional techniques. SUMMARY OF BACKGROUND DATA: Traditionally, adjacent level degeneration is surgically treated by removing the previously implanted plate and extending the instrumentation to the new degenerated level. The exposure needed to remove the previously implanted plate may be extensive. To overcome these complications, cervical extension plates, which add-on to the initially implanted plate, were developed. MATERIALS AND METHODS: Fourteen fresh-frozen human cadaver cervical spines (C2-C7) were divided into 2 groups of 7 for a series of constructs to be tested. In group 1, an extender plate, which attaches to its own primary plate, was tested. In group 2, a universal extender plate, which can be placed adjacent to any previously implanted plate, was tested. The specimens prepared were mounted on a 6-degree-of-freedom spine simulator and were sequentially tested in the following order: (1) intact; (2) single-level plate; (3) single-level plate with extender plates; and (4) 2-level plate. An unconstrained pure moment of ±1.5 N m was used in flexion-extension, lateral bending, and axial rotation. RESULTS: All instrumented constructs significantly reduced the range of motion compared with the intact condition. In both the groups, single-level plates with adjacent extender plates demonstrated stability comparable to their respective 2-level plates in all loading modes. CONCLUSIONS: Extender plates give surgeons the opportunity to treat adjacent levels without removing the primary implants, which may reduce the overall risk of damage to vital neurovascular structures. From this cadaveric biomechanical model, both types of extender plates prove to be viable options for treating adjacent level degeneration.

A comparative biomechanical study of a novel integrated plate spacer for stabilization of cervical spine: an in vitro human cadaveric model.

BACKGROUND: Integrated plate-spacer may provide adequate construct stability while potentially lowering operative time, decreasing complications, and providing less mechanical obstruction. The purpose of the current study was to compare the biomechanical stability of an anatomically profiled 2-screw integrated plate-spacer to a traditional spacer only and to a spacer and anterior cervical plate construct. In addition, the biomechanical stability of 2-screw integrated plate-spacer was compared to a commercially available 4-screw integrated plate-spacer. METHODS: Two groups, each of nine cervical cadaver spines (C2-C7), were tested under pure moments of 1.5Nm. Range of motion was recorded at C5-C6 in all loading conditions (flexion, extension, lateral bending, and axial rotation) for the following constructs: 1) Intact; 2) 2-screw or 4-screw integrated plate-spacer; 3) spacer and anterior cervical plate; and 4) spacer only. FINDINGS: All fusion constructs significantly reduced motion compared to the intact condition. Within the instrumented constructs, spacer and anterior cervical plate, 2-screw and 4-screw integrated plate-spacer resulted in reduced motion compared to the spacer only construct. No significant differences were found in motion between any of the instrumented conditions in any of the loading conditions. INTERPRETATION: The application of integrated plate-spacer for anterior cervical discectomy and fusion is based on several factors including surgical ease-of-use, biomechanical characteristics, and surgeon preference. The study suggests that integrated plate-spacer provide biomechanical stability comparable to traditional spacer and plate constructs in the cervical spine. Clinical studies on integrated plate spacer devices are necessary to understand the performance of these devices in vivo.

The biomechanical effect of transverse connectors use in a pre- and postlaminectomy model of the posterior cervical spine: an in vitro cadaveric study.

STUDY DESIGN: An in vitro biomechanical study investigating the effect of transverse connectors on posterior cervical stabilization system in a laminectomy model. OBJECTIVE: To evaluate the optimal design, number, and location of the transverse connectors in stabilizing long segment posterior instrumentation in the cervical spine. SUMMARY OF BACKGROUND DATA: In the cervical spine, lateral mass screw (LMS) fixation is used for providing stability after decompression. Transverse connectors have been used to augment segmental posterior instrumentation. However, in the cervical region the optimal design, number, and the location of transverse connectors is not known. METHODS: Seven fresh human cervicothoracic cadaveric spines (C2-T1) were tested by applying ±1.5 Nm moments in flexion (F), extension (E), lateral bending (LB), and axial rotation (AR). After testing the intact condition, LMS/rods were placed and then were tested with two different transverse connectors (top-loading connector [TL] and the head-to-head [HH] connector) in multiple levels, pre- and postlaminectomy (PL). RESULTS: LMS significantly reduced segmental motion by 77.2% in F, 75.6% in E, 86.6% in LB, and 86.1% in AR prelaminectomy and by 75.4% in F, 76% in E, 80.6% in LB, and 76.4% in AR postlaminectomy compared to intact (P < 0.05). Only in AR, PL constructs with HH connectors at C3 & C7, TL connectors at C4-C5 & C5-C6, and at C3-C4 & C6-C7 significantly reduced the range of motion by 12.9%, 11.9%, and 11.9%, respectively, compared to PL LMS (P < 0.05). No statistical significance was observed between TL connector and HH connector in all loading directions. CONCLUSION: The biomechanical advantage of transverse connectors is significant in AR, when using two connectors at the proximal and distal ends, compared to one connector. In a clinical setting, this data may guide surgeons on transverse connector configurations to consider during posterior cervical instrumentation.

Can preoperative radiographic parameters be used to predict fusion in non-instrumented posterolateral fusion for degenerative spondylolisthesis?

STUDY DESIGN: Prospective cohort. OBJECTIVE: To determine whether preoperative radiographic parameters (translation, angular motion, and lateral disc height) can predict fusion status in patients with degenerative spondylolisthesis who underwent a single-level decompression and non-instrumented posterolateral fusion using autogenous iliac crest bone graft. SUMMARY OF BACKGROUND DATA: Non-instrumented posterolateral fusion is sometimes considered in patients with degenerative spondylolisthesis who do not have radiographic evidence of instability. No previous study has attempted to determine whether preoperative radiographic parameters can be used to predict successful fusion. METHODS: A prospective, randomized, controlled, multicenter clinical study was previously conducted to compare the outcomes of osteogenic protein 1 (BMP-7) putty to autogenous iliac crest bone graft for single-level non-instrumented posterolateral fusion for the treatment of symptomatic degenerative spondylolisthesis with spinal stenosis. A total of 90 patients who were randomized to the autograft group formed the basis of this study, 67 of whom had data on the 3 radiographic parameters. Preoperative and postoperative radiographs were evaluated by 2 independent observers. The spine was determined to be fused if there was presence of continuous bone bridging between the transverse processes, an angulation of ≤5°, and a translational movement of ≤3 mm on flexion/extension radiographs of the affected level. RESULTS: Forty-two (63%) of the 67 patients had a radiographic fusion. The mean preoperative translation in this group was 1.87 mm (range, 0.3-7.35 mm), the angular motion was 4.44° (range, 0.1°-12.1°), and the lateral disc height was 8.74 mm (range, 0.2-15.34 mm). Twenty-five (37%) of the 67 patients had a radiographic pseudarthrosis. The mean preoperative translation in the pseudarthrosis group was 1.20 mm (range, 0-3.55 mm), the angular motion was 4.66° (range, 1.1°-12.95°), and the lateral disc space height was 8.10 mm (range, 1.98-13.315 mm). There was no significant difference in these 3 parameters between the fusion and the pseudarthrosis group. CONCLUSION: These results indicate that preoperative radiographic parameters that may indicate the absence of gross instability in degenerative spondylolisthesis are not reliable in predicting radiographic fusion in a single-level non-instrumented fusion.

Analysis of in vivo corrosion of 316L stainless steel posterior thoracolumbar plate systems: a retrieval study.

STUDY DESIGN: One hundred eighteen patients retrieved 316L stainless steel thoracolumbar plates, of 3 different designs, used for fusion in 60 patients were examined for evidence of corrosion. A medical record review and statistical analysis were also carried out. OBJECTIVE: This study aims to identify types of corrosion and examine preferential metal ion release and the possibility of statistical correlation to clinical effects. SUMMARY OF BACKGROUND DATA: Earlier studies have found that stainless steel spine devices showed evidence of mild-to-severe corrosion; fretting and crevice corrosion were the most commonly reported types. Studies have also shown the toxicity of metal ions released from stainless steel corrosion and how the ions may adversely affect bone formation and/or induce granulomatous foreign body responses. METHODS: The retrieved plates were visually inspected and graded based on the degree of corrosion. The plates were then analyzed with optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. A retrospective medical record review was performed and statistical analysis was carried out to determine any correlations between experimental findings and patient data. RESULTS: More than 70% of the plates exhibited some degree of corrosion. Both fretting and crevice corrosion mechanisms were observed, primarily at the screw plate interface. Energy dispersive x-ray spectroscopy analysis indicated reductions in nickel content in corroded areas, suggestive of nickel ion release to the surrounding biological environment. The incidence and severity of corrosion was significantly correlated with the design of the implant. CONCLUSIONS: Stainless steel thoracolumbar plates show a high incidence of corrosion, with statistical dependence on device design.

Biomimetic calcium phosphate coatings as bone morphogenetic protein delivery systems in spinal fusion.

BACKGROUND CONTEXT: Use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to enhance spinal fusion rates. Case reports of soft-tissue swelling, ectopic bone formation, and osteolysis have recently surfaced. It is hypothesized that incorporation of rhBMP-2 within a calcium phosphate (CaP) coating may help to localize delivery and mitigate these complications. PURPOSE: To compare the characteristics of posterolateral fusion between rabbits receiving rhBMP-2 delivered via physical adsorption to a collagen sponge or rhBMP-2 incorporated within the physical structure of a CaP coating on a collagen sponge. STUDY DESIGN/SETTING: New Zealand white rabbit model of posterolateral lumbar fusion at L5-L6. METHODS: Eighteen (18) New Zealand white rabbits underwent posterolateral spinal fusion at L5-L6. Rabbits received bilateral collagen sponges that were either coated with CaP (n=3), coated with CaP and dipped in rhBMP-2 (n=3), coated with a hybrid CaP-rhBMP-2 film (n=6), or coated with a hybrid CaP-rhBMP-2 film and dipped in rhBMP-2 (n=6). Animals were followed weekly with radiographs and were sacrificed at 6 weeks. Fusion masses were further characterized by manual palpation, computed tomography, and histology. RESULTS: Radiographic evaluation showed that animals in Group 3 (incorporated BMP) fused at 4 weeks, whereas animals in Group 2 (adsorbed BMP) and Group 4 (incorporated and adsorbed BMP) fused by 6 weeks. Animals that received rhBMP-2 physically adsorbed to the collagen sponge showed extension of the fusion mass beyond the L5-L6 level in 56% of cases and bone resorption in 78%. Histology of fusion masses showed mature bone formation in animals belonging to Groups 2, 3, and 4 and extensive osteoclast recruitment in animals belonging to Groups 2 and 4. CONCLUSIONS: Delivery of rhBMP-2 via incorporation within CaP coatings results in increased rates of radiographic fusion. The burst release profile of rhBMP-2 adsorbed to surfaces, although effective in achieving fusion, may result in increased osteoclast recruitment.

Bilateral femoral artery ischemia detected by multimodality neuromonitoring during posterior scoliosis surgery: a case report.

STUDY DESIGN: Case report. OBJECTIVE: To report a case of a bilateral femoral artery ischemia detected by neuromonitoring during posterior scoliosis surgery and to review relevant literature regarding this rare complication. SUMMARY OF BACKGROUND DATA: Lower extremity ischemia is a potentially devastating risk of posterior spinal surgery. Ischemia can be a result of thrombotic occlusion or vascular compression during patient positioning. Multimodality neuromonitoring, increasingly used to prevent neurologic injury, can also detect hypoperfusion to the extremities. To date, there have been no reports of bilateral lower extremity ischemia detected by multimodality neuromonitoring during posterior spine surgery. METHODS: A 15-year-old boy with adolescent idiopathic scoliosis underwent posterior spinal fusion with instrumentation. Intraoperative changes in somatosensory-evoked potentials and motor-evoked potentials were noted 1 hour into the case, before instrumentation or the reduction maneuver. After trouble shooting methods did not localize a technical cause for the changes, the patient's lower extremities were noted to be hypoperfused and pulseless. RESULTS: The patients was repositioned and lower extremity perfused improved. Palpable distal pulses were detected. Neuromonitoring signals returned to baseline and the surgery completed. The patient had no postoperative neurologic or vascular deficits. CONCLUSION: Lower extremity ischemia secondary to prone positioning is a rare risk of posterior spinal surgery. This is the first case report of this potentially devastating, but preventable complication detected by multimodality neuromonitoring.

Degenerative lumbar spondylolisthesis: trends in management.

Degenerative spondylolisthesis with spinal stenosis is common in elderly patients. When symptomatic, the resultant neurogenic claudication often leads to a diminished quality of life. A nonsurgical approach is an appropriate first step. Maximizing the chance of a solid arthrodesis improves the possibility of a successful long-term outcome. Treatment of this pathology has evolved over the past twenty years with the publication of numerous prospective randomized trials assessing the influence of fusion and instrumentation following decompression. Current prospective trials have evaluated the use of bone morphogenetic proteins as a substitute for autogenous bone graft. Recently, soft-tissue stabilization devices have been advocated as an alternative to fusion. Clinicians should critically evaluate these newer technologies and exercise caution regarding their use until controlled long-term trials are completed.

End organ effects of high-dose human equivalent methylprednisolone in a spinal cord injury rat model.

STUDY DESIGN: Interventional study. OBJECTIVE: To analyze the histologic effects of high-dose human equivalent methylprednisolone on the pulmonary, cardiac, intestinal, renal, hepatic, and splenic tissues in a spinal cord injury rat model. SUMMARY OF BACKGROUND DATA: There are numerous investigations of various medical interventions for the treatment of acute spinal cord trauma. Currently, the only generally accepted medical intervention in an acute spinal cord trauma is the intravenous administration of high doses of methylprednisolone. Although it has been nearly 2 decades since the first National Acute Spinal Cord Injury Study investigated the role high-dose steroids might play in the treatment of acute spinal cord trauma, controversy still exists regarding the efficacy of this treatment. To our knowledge, no study has examined the role of high-dose methylprednisolone in organ systems other than the spinal cord in an acute spinal cord injury model at the histologic level. This study attempts to characterize end organ histologic response to human dose equivalent (HDE) intravenous methylprednisolone administration in a rodent model of acute spinal cord injury. METHODS: A total of 48 Sprague-Dawley rats were divided equally into control and experimental groups. Each group was subdivided into 6 sets of 4 animals each, according to intervals after injury. Groups 1-6 consisted of animals euthanized at 0, 4, 8, 16, 24, and 48 hours after spinal cord injury. Paraplegia after lower thoracic laminectomy was achieved using a standardized Allen weight drop technique. Within 1 hour of injury, experimental animals were treated with HDE methylprednisolone, infused for 23 hours continuously. Liver, kidney, lung, intestine, spleen, and heart were harvested at variable intervals after injury and prepared for histologic examination. These slides were analyzed with microscopic staining techniques and compared in a blinded manner by a qualified pathologist. RESULTS: Of all the end organs analyzed, the spleens were most affected. Lymphocytic depletion was seen in as little as 4 hours after methylprednisolone infusion and continued until 48 hours. Pulmonary tissues variably showed interstitial congestion and eosinophilic alveolar collections. Intestinal mucosal tissues showed edema and autolyzed mucosa from 16 hours onwards. Cardiac, kidney, and hepatic tissue did not differ significantly from controls. CONCLUSIONS: Histologically, HDE methylprednisolone caused significant splenic lymphocytic depletion changes in as little as 4 hours. This trend of end organ lymphocytopenia continued to progress until 48 hours. Pulmonary eosinophilic infiltrates were seen from 8 until 24 hours. Intestinal mucosal edema and necrosis were seen in samples at 16 hours throughout 48 hours. This study was designed to evaluate end organ changes seen in an animal model of an acute spinal cord injury treated with HDE methylprednisolone. Study animals were infused with HDE methylprednisolone given according to the National Acute Spinal Cord Injury Study II protocol. The kidney, lung, cardiac, intestinal, splenic, and hepatic tissues from the aforementioned animals were then sectioned and analyzed using histologic staining techniques by a qualified pathologist.