Darrel S. Brodke

Posterior lumbar interbody fusion. A biomechanical comparison, including a new threaded cage.

Study Design In vitro biomechanical testing was performed on eight lumbar calf spines. Objectives To compare the initial stiffness of a standard method of posterior lumbar interbody fusion using structural autograft with the same procedure using additional posterior instrumentation. These constructs also were compared to a new titanium implant. Summary of Background Data Posterior lumbar interbody fusion is gaining wide acceptance for the treatment of segmental spinal instability, spondylolisthesis, and discogenic pain. Many methods have been described, including use of autograft or allograft bone, in either structural or nonstructural form, with or without additional fixation. A new threaded titanium interbody implant has been designed to increase initial stability while allowing bony ingrowth for fusion. Methods Eight lumbar calf spines were subjected to axial compression, sagittal moments (flexion‐extension), and axial torque while displacement was measured. Stiffness was calculated from the load displacement curves, for each construct under each load pattern. Results The posterior lumbar interbody fusion by bone graft alone was the least stiff construct of all modes tested. In two of eight specimens the bone graft dislodged posteriorly into the canal during torsional testing. The titanium interbody implant was similar in stiffness to the bone graft posterior lumbar interbody fusion with posterior instrumentation group in all three modes. They were both significantly stiffer than the normal spine, the destabilized spine, and the posterior lumbar interbody fusion by bone graft alone (P < 0.05). Conclusions In this model, the posterior lumbar interbody fusion with bone graft alone had less initial stiffness than that of the intact spine. The addition of posterior instrumentation or interbody implants can increase initial stiffness significantly.

Efficacy and safety of surgical decompression in patients with cervical spondylotic myelopathy: results of the AOSpine North America prospective multi-center study.

BACKGROUND Cervical spondylotic myelopathy is the leading cause of spinal cord dysfunction worldwide. The objective of this study was to evaluate the impact of surgical decompression on functional, quality-of-life, and disability outcomes at one year after surgery in a large cohort of patients with this condition. METHODS Adult patients with symptomatic cervical spondylotic myelopathy and magnetic resonance imaging evidence of spinal cord compression were enrolled at twelve North American centers from 2005 to 2007. At enrollment, the myelopathy was categorized as mild (modified Japanese Orthopaedic Association [mJOA] score ≥ 15), moderate (mJOA = 12 to 14), or severe (mJOA < 12). Patients were followed prospectively for one year, at which point the outcomes of interest included the mJOA score, Nurick grade, Neck Disability Index (NDI), and Short Form-36 version 2 (SF-36v2). All outcomes at one year were compared with the preoperative values with use of univariate paired statistics. Outcomes were also compared among the severity classes with use of one-way analysis of variance. Finally, a multivariate analysis that adjusted for baseline differences among the severity groups was performed. Treatment-related complication data were collected and the overall complication rate was calculated. RESULTS Eighty-five (30.6%) of the 278 enrolled patients had mild cervical spondylotic myelopathy, 110 (39.6%) had moderate disease, and 83 (29.9%) had severe disease preoperatively. One-year follow-up data were available for 222 (85.4%) of 260 patients. There was a significant improvement from baseline to one year postoperatively (p < 0.05) in the mJOA score, Nurick grade, NDI score, and all SF-36v2 health dimensions (including the mental and physical health composite scores) except general health. With the exception of the change in the mJOA, the degree of improvement did not depend on the severity of the preoperative symptoms. These results remained unchanged after adjusting for relevant confounders in the multivariate analysis. Fifty-two patients experienced complications (prevalence, 18.7%), with no significant differences among the severity groups. CONCLUSIONS Surgical decompression for the treatment of cervical spondylotic myelopathy was associated with improvement in functional, disability-related, and quality-of-life outcomes at one year of follow-up for all disease severity categories. Furthermore, complication rates observed in the study were commensurate with those in previously reported cervical spondylotic myelopathy series.

Perioperative and delayed complications associated with the surgical treatment of cervical spondylotic myelopathy based on 302 patients from the AOSpine North America Cervical Spondylotic Myelopathy Study

OBJECT Rates of complications associated with the surgical treatment of cervical spondylotic myelopathy (CSM) are not clear. Appreciating these risks is important for patient counseling and quality improvement. The authors sought to assess the rates of and risk factors associated with perioperative and delayed complications associated with the surgical treatment of CSM. METHODS Data from the AOSpine North America Cervical Spondylotic Myelopathy Study, a prospective, multicenter study, were analyzed. Outcomes data, including adverse events, were collected in a standardized manner and externally monitored. Rates of perioperative complications (within 30 days of surgery) and delayed complications (31 days to 2 years following surgery) were tabulated and stratified based on clinical factors. RESULTS The study enrolled 302 patients (mean age 57 years, range 29-86) years. Of 332 reported adverse events, 73 were classified as perioperative complications (25 major and 48 minor) in 47 patients (overall perioperative complication rate of 15.6%). The most common perioperative complications included minor cardiopulmonary events (3.0%), dysphagia (3.0%), and superficial wound infection (2.3%). Perioperative worsening of myelopathy was reported in 4 patients (1.3%). Based on 275 patients who completed 2 years of follow-up, there were 14 delayed complications (8 minor, 6 major) in 12 patients, for an overall delayed complication rate of 4.4%. Of patients treated with anterior-only (n = 176), posterior-only (n = 107), and combined anterior-posterior (n = 19) procedures, 11%, 19%, and 37%, respectively, had 1 or more perioperative complications. Compared with anterior-only approaches, posterior-only approaches had a higher rate of wound infection (0.6% vs 4.7%, p = 0.030). Dysphagia was more common with combined anterior-posterior procedures (21.1%) compared with anterior-only procedures (2.3%) or posterior-only procedures (0.9%) (p < 0.001). The incidence of C-5 radiculopathy was not associated with the surgical approach (p = 0.8). The occurrence of perioperative complications was associated with increased age (p = 0.006), combined anterior-posterior procedures (p = 0.016), increased operative time (p = 0.009), and increased operative blood loss (p = 0.005), but it was not associated with comorbidity score, body mass index, modified Japanese Orthopaedic Association score, smoking status, anterior-only versus posterior-only approach, or specific procedures. Multivariate analysis of factors associated with minor or major complications identified age (OR 1.029, 95% CI 1.002-1.057, p = 0.035) and operative time (OR 1.005, 95% CI 1.002-1.008, p = 0.001). Multivariate analysis of factors associated with major complications identified age (OR 1.054, 95% CI 1.015-1.094, p = 0.006) and combined anterior-posterior procedures (OR 5.297, 95% CI 1.626-17.256, p = 0.006). CONCLUSIONS For the surgical treatment of CSM, the vast majority of complications were treatable and without long-term impact. Multivariate factors associated with an increased risk of complications include greater age, increased operative time, and use of combined anterior-posterior procedures.

The evidence for intraoperative neurophysiological monitoring in spine surgery: Does it make a difference?

Objective. The objective of this article was to undertake a systematic review of the literature to determine whether IOM is able to sensitively and specifically detect intraoperative neurologic injury during spine surgery and to assess whether IOM results in improved outcomes for patients during these procedures. Summary and Background Data. Although relatively uncommon, perioperative neurologic injury, in particular spinal cord injury, is one of the most feared complications of spinal surgery. Intraoperative neuromonitoring (IOM) has been proposed as a method which could reduce perioperative neurologic complications after spine surgery. Methods. A systematic review of the English language literature was undertaken for articles published between 1990 and March 2009. MEDLINE, EMBASE, and Cochrane Collaborative Library databases were searched, as were the reference lists of published articles examining the use of IOM in spine surgery. Two independent reviewers assessed the level of evidence quality using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria, and disagreements were resolved by consensus. Results. A total of 103 articles were initially screened and 32 ultimately met the predetermined inclusion criteria. We determined that there is a high level of evidence that multimodal IOM is sensitive and specific for detecting intraoperative neurologic injury during spine surgery. There is a low level of evidence that IOM reduces the rate of new or worsened perioperative neurologic deficits. There is very low evidence that an intraoperative response to a neuromonitoring alert reduces the rate of perioperative neurologic deterioration. Conclusion. Based on strong evidence that multimodality intraoperative neuromonitoring (MIOM) is sensitive and specific for detecting intraoperative neurologic injury during spine surgery, it is recommended that the use of MIOM be considered in spine surgery where the spinal cord or nerve roots are deemed to be at risk, including procedures involving deformity correction and procedures that require the placement of instrumentation. There is a need to develop evidence-based protocols to deal with intraoperative changes in MIOM and to validate these prospectively.

Dynamic Cervical Plates: Biomechanical Evaluation of Load Sharing and Stiffness

Study Design. An in vitro biomechanical study using a simulated cervical corpectomy model to compare the load-sharing properties and stiffnesses of two static and two dynamic cervical plates. Objectives. To evaluate the load-sharing properties of the instrumentation with a full-length graft and with 10% graft subsidence and to measure the stiffness of the instrumentation systems about the axes of flexion–extension, lateral bending, and axial torsion under these same conditions. Summary of Background Data. No published reports comparing conventional and dynamic cervical plates exist. Methods. Six specimens of each of the four plate types were mounted on ultra-high molecular weight polyethylene-simulated vertebral bodies. A custom four-axis spine simulator applied pure flexion–extension, lateral bending, and axial torsion moments under a constant 50 N axial compressive load. Load sharing was calculated through a range of applied axial loads up to 120 N. The stiffness of each construct was calculated in response to ±2.5 Nm moments about each axis of rotation with a full-length graft, a 10% shortened graft, and no graft. ANOVA and Fisher’s post hoc test were used to determine statistical significance (alpha ≤ 0.05). Results. The two locked cervical plates (CSLP and Orion) and the ABC dynamic plate were similar in flexion–extension, lateral bending, and torsional stiffness. The DOC dynamic plate was consistently less stiff. The Orion plate load shared significantly less than the other three plates with a full graft. Both the ABC and the DOC plates were able to load share with a shortened graft, whereas the conventional plates were not. Conclusions. All plates tested effectively load share with a full-length graft, whereas the two dynamic cervical plates tested load share more effectively than the locked plates with simulated graft subsidence. The effect of dynamization on stiffness is dependent on plate design.

Minimally Invasive Spine Surgery

Paul C. McAfee, MD, MBA, Frank M. Phillips, MD, Gunnar Andersson, MD, PhD, Asokumar Buvenenadran, MD, Choll W. Kim, MD, Carl Lauryssen, MD, Robert E. Isaacs, MD, Jim A. Youssef, MD, Darrel S. Brodke, MD, Andrew Cappuccino, MD, Behrooz A. Akbarnia, MD, Gregory M. Mundis, MD, William D. Smith, MD, Juan S. Uribe, MD, Steve Garfin, MD, R. Todd Allen, MD, William Blake Rodgers, MD, Luiz Pimenta, MD, PhD, and William Taylor, MD

Biomechanical Analysis and Review of Lateral Lumbar Fusion Constructs

Study Design. Biomechanical study and the review of literature on lumbar interbody fusion constructs. Objective. To demonstrate the comparative stabilizing effects of lateral interbody fusion with various supplemental internal fixation options. Summary of Background Data. Lumbar interbody fusion procedures are regularly performed using anterior, posterior, and more recently, lateral approaches. The biomechanical profile of each is determined by the extent of resection of local supportive structures, implant size and orientation, and the type of supplemental internal fixation used. Methods. Pure moment flexibility testing was performed using a custom-built 6 degree-of-freedom system to apply a moment of ±7.5 Nm in each motion plane, while motion segment kinematics were evaluated using an optoelectronic motion system. Constructs tested included the intact spine, stand-alone extreme lateral interbody implant, interbody implant with lateral plate, unilateral and bilateral pedicle screw fixation. These results were evaluated against those from literature-reported biomechanical studies of other lumbar interbody constructs. Results. All conditions demonstrated a statistically significant reduction in range of motion (ROM) as a percentage of intact. In flexion-extension, ROM was 31.6% stand-alone, 32.5% lateral fixation, and 20.4% and 13.0% unilateral and bilateral pedicle screw fixation, respectively. In lateral bending, the trend was similar with greater reduction with lateral fixation than in flexion-extension; ROM was 32.5% stand-alone, 15.9% lateral fixation, and 21.6% and 14.4% unilateral and bilateral pedicle screw fixation. ROM was greatest in axial rotation; 69.4% stand-alone, 53.4% lateral fixation, and 51.3% and 41.7% unilateral and bilateral pedicle screw fixation, respectively. Conclusion. The extreme lateral interbody construct provided the largest stand-alone reduction in ROM compared with literature-reported ALIF and TLIF constructs. Supplemental bilateral pedicle screw-based fixation provided the overall greatest reduction in ROM, similar among all interbody approach techniques. Lateral fixation and unilateral pedicle screw fixation provided intermediate reductions in ROM. Clinically, surgeons may evaluate these comparative results to choose fixation options commensurate with the stability requirements of individual patients.

Clearance of the cervical spine in multitrauma patients: The role of advanced imaging

The cervical spine is injured in 3% of major trauma patients. Radiographic clearance for injury must be provided efficiently and accurately. There are numerous choices for clearance that are now in clinical practice: lateral radiograph only, 3-view or 5-view cervical-spine (c-spine) series, flexion-extension radiographs, computed tomography (CT) with multiplanar reformations, and magnetic resonance imaging (MRI). This article reviews the literature on methods of c-spine clearance, and emphasizes the pitfalls of each modality. Although lateral radiographs detect 60% to 80% of c-spine fractures, a significant number of fractures are not visible, even when three views of the spine are obtained. The sensitivity of plain radiographs can be improved by attention to several subtle features, which are discussed. Flexion-extension radiographs in the acute setting have an unacceptably high false-negative and false-positive rate. CT detects 97% to 100% of fractures, but its accuracy in detection of purely ligamentous injuries has not been documented. Furthermore, CT is limited in patients with severe degenerative disease. MRI is highly sensitive in the detection of ligamentous injury, but not all cases of injury may cause instability. MRI is also much less sensitive than CT to fractures of the posterior elements of the spine, and to injuries of the craniocervical junction. The causes of missed cervical spine injury and delayed instability are discussed and shown in this article. An algorithm for the use of advanced imaging is proposed.

Diagnosis and Management of Thoracolumbar Spine Fractures

The lack of robust clinical studies has contributed to controversy regarding optimal treatment for patients with injuries to the thoracolumbar spine. The transitional anatomy of the thoracolumbar spine makes it vulnerable to injury resulting from high-energy motor vehicle collisions and falls; osteoporosis is an underlying factor in most of the compression fractures identified in elderly patients. The formulation of a treatment plan for patients with injuries to the thoracolumbar spine depends on the presence and extent of neurologic injury and deformity and an estimate concerning spinal stability. Both nonsurgical and surgical treatment options are available to achieve the goals of preservation of neurologic function and restoration of spinal stability.

Early complications of surgical versus conservative treatment of isolated type II odontoid fractures in octogenarians: A retrospective cohort study

Study Design A retrospective cohort study of operative versus nonoperative treatment of isolated type II odontoid fractures in patients aged 80 years and more without neurologic deficit admitted to a level 1 spinal cord injury center between June 1985 and July 2006. Objective To assess the presentation and acute complications of operatively and nonoperatively managed type II odontoid fractures in the octogenarian population. Summary of Background Data Type II odontoid fractures are the most common cervical spine fracture in the elderly. Studies suggest acute in-hospital complication rates in type II odontoid fractures in the elderly exceed 50%. Few studies have examined the acute in-hospital outcomes of isolated type II odontoid fractures in the octogenarian population. Methods The medical records of 223 consecutive C2 fractures from June 1985 to July 2006 over the age of 80 years were reviewed retrospectively. Patients with associated cervical spine fractures were excluded. Eighty neurologically intact patients over age 80 were identified with isolated acute type II odontoid fractures. The charts were reviewed and mechanism of injury, comorbidities, date of injury, date of admission, date of discharge, radiology reports, discharge disposition, associated injuries, fracture management, type of surgical fixation (if any), and documented complications were abstracted. Results Thirty-two patients received operative treatment (10 anterior and 22 posterior) and 40 patients received nonsurgical treatment. Eight patients were excluded because the medical record could not be located. The mean age was 85.5±3.5 years in the surgical and 87.3±4.7 years in the nonsurgical group (P>0.05); mean length of acute hospital stay was 11.2±8.5 days in the nonsurgical and 22.8±28.3 days in the surgical group (P<0.05); mean comorbidity score was 2.3±1.2 in the nonsurgical and 2.0±1.0 in the surgical group (P>0.5); mean fracture displacement was 4.1±3.5 mm in the nonsurgical and 3.9±3.4 mm in the surgical group (P>0.5). Acute in-hospital mortality rate was 15% in the nonsurgical group and 12.5% in the surgical group (P>0.05). The percentage of patients experiencing at least one significant complication was higher in the operative group than the nonoperative group (62% vs. 35%, respectively, P<0.05). Conclusions Type II odontoid fractures in the octogenarian population are associated with substantial morbidity and mortality, irrespective of management method. Prospective studies are needed to better elucidate management strategies for this difficult clinical problem.