Yu-Po Lee

Bone Morphogenetic Protein-2 (BMP-2) in the Treatment of Pyogenic Vertebral Osteomyelitis

Study Design. Retrospective case series. Objective. To present results of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in medically nonresponsive pyogenic vertebral osteomyelitis (PVO), treated by anterior/posterior debridement and instrumented fusion in the cervical, thoracic, and lumbosacral spine. Summary of Background Data. Surgical options for PVO vary, as do their outcomes, and can be complicated by recurrence, pseudarthrosis, and death. Although rhBMP-2 use in spinal fusion is increasing, its utility in PVO is unknown. Additionally, use in areas of infection is listed as a contraindication, although this is not supported by laboratory (animal) studies or clinical studies in long bones. Methods. Between 2003 and 2005, 14 patients who underwent circumferential fusion for PVO were included in this study. Average patient age was 54 years (range, 27–77 years). Eight (57%) patients had 3 or more vertebral bodies involved. Diagnostic studies included radiographs, CT, MRI, and markers of infection [(C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), white blood count (WBC)]. All patients underwent anterior fusion with rhBMP-2 inserted in structural allograft (11 patients) or titanium cylindrical cages (3 patients), followed by posterior instrumented fusion with autogenous iliac crest graft (8 occurring on the same day). Follow-up averaged 22 months (range, 11–30 months). All were studied with plain radiographs, including flexion-extension lateral films and fine cut CT scans with reconstruction. Pain ratings were recorded by visual analog scores (VAS). Results. Clinical resolution of infections, normalization of lab values, and bony fusion, based on dynamic radiographs and CT scans, were seen in all patients at latest follow-up. Staphylococcus aureus was the most frequently identified organism (8 patients). Four (29%) patients had positive blood cultures (all MRSA). Predisposing comorbidities were present in 12 patients. Six patients had epidural abscesses. Eight (57%) patients presented with neurologic deficits, ranging from paraparesis to quadriplegia. Complete recovery was seen in 7 (quadriplegia unchanged). At 1 year, mean VAS pain scores improved significantly (P < 0.05) from 7.9 (range, 3–10) to 2.8 (range, 0–6). Perioperative complications (non-BMP related) occurred in 2 patients. There were no surgically-related deaths. Conclusion. rhBMP-2 use, in combination with antibiotics and circumferential instrumented fusion, provides a safe and successful surgical treatment of medically nonresponsive PVO, with solid fusions obtained, good clinical results, and no adverse side effects from the BMP.

An evaluation of fracture stabilization comparing kyphoplasty and titanium mesh repair techniques for vertebral compression fractures: is bone cement necessary?

Study Design. In vitro biomechanical investigation using human cadaveric vertebral bodies. Objective. To evaluate differences in biomechanical stability of vertebral compression fractures (VCFs) repaired using an expandable titanium mesh implant, with and without cement, as compared with standard balloon kyphoplasty. Summary of Background Data. Vertebral augmentation, either in the form of vertebroplasty or kyphoplasty, is the treatment of choice for some VCFs. Polymethylmethacrylate, a common bone cement used in this procedure, has been shown to possibly cause injury to neural and vascular structures due to extravasation, embolization, and may be too rigid for an osteoporotic spine. Therefore, suitable alternatives for the treatment of VCFs have been sought. Methods. Individual vertebral bodies from 5 human cadaveric spines (from T4 to L5) were stripped of all soft tissues, and compressed at 25% of the intact height using methods previously described. Vertebral bodies were then randomly assigned to the following repair techniques: (1) conventional kyphoplasty, (2) titanium implant with cement, (3) titanium implant without cement. All vertebral bodies were then recompressed at 25% of the repaired height. Yield load, ultimate load, and stiffness were recorded and compared in these groups before and after treatment. Results. There were no differences in biomechanical data between intact groups, and between repaired groups. In all 3 treatment groups, yield load and ultimate load of repaired vertebrae were similar to that of intact vertebrae. However, the stiffness following repair was found to be statistically less than the stiffness of the intact vertebral body (P < 0.05 for all comparisons). Conclusion. Based on the biomechanical data, the titanium mesh implant with or without cement was similar to polymethylmethacrylate fixation by kyphoplasty in the treatment of VCFs. Avoiding the adverse effects caused by using cement may be the main advantage of the titanium mesh implant and warrants further study.

Spine surgeons survey on attitudes regarding osteoporosis and osteomalacia screening and treatment for fractures, fusion surgery, and pseudoarthrosis

COMMENTARY ON Dipaola CP, Bible JE, Biswas D, et al. Survey of spine surgeons on attitudes regarding osteoporosis and osteomalacia screening and treatment for fractures, fusion surgery, and pseudoarthrosis. Spine J 2009;9:537-44 (this issue).

Evaluation of hip flexion strength following lateral lumbar interbody fusion

BACKGROUND CONTEXT Lateral interbody fusion (LIF) is a minimally invasive procedure that is designed to achieve a solid interbody fusion while minimizing the damage to the surrounding soft tissue. Although short-term results have been promising, few data have been published to date regarding its risks and complication rate. PURPOSE The aim was to evaluate the extent of injury to the psoas muscle after the LIF procedure by measuring hip flexion strength. STUDY DESIGN A prospective case series was used in the study. METHOD Hip flexion strength was measured using a handheld digital dynamometer while the patient was seated on a chair; the examiner held the device against the patients attempt to flex the hip. Both sides were measured to compare the operated and nonoperated psoas muscles. Each side was measured three times and the average amount (in pounds) was recorded. Measurements were done before and after surgery on Day 2-3, at 2 weeks, 6 weeks, and at 3 and 6 months. RESULTS Thirty-three patients were recruited for this study. Mean preoperative hip flexion strength values were 20.7±3.47 lb and 21.3±4.31 lb for operated and nonoperated legs, respectively, with no significant difference (p=.85). With a mean of 11.2±2.24 lb postoperative measurements on Day 2, the operated side showed statistically significant reduction of strength (p=.0001). The nonoperated side was also weaker postoperatively, but not significantly (mean=19.12±1.74 lb; p=.097). From the first follow-up visit at 2 weeks, the values on the operated leg had returned to baseline values (20.6, p=.97) and were not significantly different from preoperative values on either side. DISCUSSION Hip flexion was weakened immediately after the LIF procedure, which may be attributed to psoas muscle injury during the procedure. However, this damage was temporary, with almost complete return to baseline values by 2 weeks.

A retrospective review of long anterior fusions to the sacrum

BACKGROUND CONTEXT In the setting of tumor, infection, or trauma, a corpectomy of the L5 vertebral body may be necessary. However, the space has an irregular trapezoidal shape, and the failure to account for this may lead to improper fitting of the titanium cages or the allograft struts when performing a reconstruction. PURPOSE The purpose of this study was to evaluate the failure rate of implants used to reconstruct the anterior lumbar spine when an L5 corpectomy has been performed. METHODS A retrospective review of the medical records and radiographs of 19 consecutive patients undergoing an L5 corpectomy and anterior spinal fusion was performed. The radiographs were reviewed for implant failure and successful fusions. RESULTS Cases included osteomyelitis (13), fractures (4), and tumor (2). Anterior reconstruction was performed with a straight cylindrical titanium cage in six cases, allograft in six cases, iliac crest bone graft (ICBG) in two cases, and cages with lordosis built into the cage or end plates in five cases. In the six straight cylindrical titanium cages, four cases had displaced anteriorly, necessitating revision surgery. In the other two cases, both had poor fixation to the sacrum and developed nonunions. In the six reconstructed with allograft, all three fibular struts developed nonunions. In the three reconstructed with humeral or femoral allograft, all patients formed a solid fusion. In the patients reconstructed with ICBG, one formed a nonunion, whereas the other one formed a solid fusion. In the cages with lordosis built into the cage or end plates, all five developed solid fusions. CONCLUSIONS A corpectomy of L5 resulting in an irregular trapezoidal shape must be accounted for when performing the reconstruction. Use of straight cylindrical cages or allograft with small footprints may lead to an increased rate of failure. When performing the reconstruction, adding approximately 20° to 30° of lordosis to the construct may create a better fit and increase stability and result in an improved fusion rate. If using allograft, using a larger graft with greater end plate contact may also improve fusion rates.

Biomechanical evaluation of transfacet screw fixation for stabilization of multilevel cervical corpectomies.

Study Design Cadaveric biomechanical investigation. Objectives To test the feasibility of transfacet screws as a minimally invasive posterior fixation device for the cervical spine by comparing the biomechanical stability of transfacet screws to lateral mass screws and rods in a multilevel cervical corpectomy model. Summary of Background Data Minimally invasive surgery (MIS) of the spine has gained increasing acceptance and popularity. However, a minimally invasive means of instrumenting the posterior cervical spine has yet to be discovered. Posterior transfacet screws have been described as a means of posterior fixation. In addition, they have the potential of being placed percutaneously through stab incisions. However, validation of transfacet screws in an unstable cervical model in which posterior instrumentation may be necessary has not been carried out till date. Methods Sixteen cadaveric cervical spines were randomized to transfacet or lateral mass instrumentation groups. The spines were tested in the following conditions: (a) intact, (b) after multilevel corpectomies with strut graft placement with stand-alone posterior fixation, and (c) with an additional anterior plate over the strut graft. Corpectomy site loading was measured with a custom-designed strut graft. Data were collected for spinal stiffness, range of motion, and strut graft loading, and was analyzed using 2-way analysis of variance (P<0.05). Results Stand-alone transfacet screw fixation was found to provide inferior spinal stability and resulted in increased spinal motion and graft loading compared with the other constructs (P<0.05 for all). Conclusions It is unclear what kind of mechanical stiffness is necessary to stabilize the cervical spine and obtain solid fusion. However, decreased stability and increased graft loading suggest that transfacet screws may not be the ideal method of posterior fixation to supplement multilevel anterior cervical corpectomies and fusions despite their potential as a minimally invasive method for posterior cervical instrumentation.

Vasculopathy, Ischemia, and the Lateral Lumbar Interbody Fusion Surgery: Report of Three Cases.

Multi-modal neurophysiologic monitoring consisting of triggered and spontaneous electromyography and transcranial motor-evoked potentials may detect and prevent both acute and slow developing mechanical and vascular nerve injuries in lateral lumbar interbody fusion (LLIF) surgery. In case report 1, a marked reduction in the transcranial motor-evoked potentials on the operative side alerted to a 28% decrease in mean arterial blood pressure in a 54-year-old woman during an L3-4, L4-5 LLIF. After hemodynamic stability was regained, transcranial motor-evoked potentials returned to baseline and the patient suffered no postoperative complications. In case report 2, a peroneal nerve train-of-four stimulation threshold of 95 mA portended the potential for a triggered electromyography false negative in a 70-year-old woman with type 2 diabetes, peripheral neuropathy, and body mass index of 30.7 kg/m undergoing an L3-4, L4-5 LLIF. Higher triggered electromyography threshold values were applied to this patients relatively quiescent triggered electromyography and the patient suffered no postoperative complications. In case report 3, the loss of right quadriceps motor-evoked potentials detected a retractor related nerve injury in a 59-year-old man undergoing an L4-5 LLIF. The surgery was aborted, but the patient suffered persistent postoperative right leg paresthesia and weakness. These reports highlight the sensitivity of peripheral nerve elements to ischemia (particularly in the presence of vascular risk factors) during the LLIF procedure and the need for dynamic multi-modal intraoperative monitoring.

Management of Sacroiliac Joint Dysfunction

S acroiliac (SI) joint pain is a difficult problem that is increasingly recognized for its contribution to chronic pain. In specific circumstances, it may present independently. However, in many scenarios, the SI joint represents one of the many factors contributing to the onset of axial back pain and its various referral patterns. Despite this, there remains no clear solution for SI joint-mediated pain. Low back pain remains a significant burden on the healthcare system and is the source of approximately 12 million physician office visits per year in the United States. It is among the leading causes of disability, accounting for expenditures in excess of

Altered bioreactivity and limited osteoconductivity of calcium sulfate-based bone cements in the osteoporotic rat spine

50 billion every year.1,2 Surgical management of back pain may involve fusion. Although nearly 1 million spinal fusions are performed annually, outcomes measures have demonstrated success rates anywhere from 35% to 89%.3,4 Therefore, it can be concluded that the etiology of back pain is complex and often multifactorial. Studies have shown that SI pathology may present in association with or contribute directly to the cause of back pain in greater than 30% of cases.4-7 Despite this, the SI joint is often overlooked as a contributing source of back pain. Maintaining an understanding of the anatomy, biomechanics, and clinical presentation of SI joint-mediated pain may allow the physician greater understanding regarding the constellation of symptoms that manifest as low back pain. This may further allow for more critical diagnostic capacity and help to develop an appropriate and more efficient treatment algorithm.