Joshua D. Auerbach

Neurophysiological detection of impending spinal cord injury during scoliosis surgery.

BACKGROUND Despite the many reports attesting to the efficacy of intraoperative somatosensory evoked potential monitoring in reducing the prevalence of iatrogenic spinal cord injury during corrective scoliosis surgery, these afferent neurophysiological signals can provide only indirect evidence of injury to the motor tracts since they monitor posterior column function. Early reports on the use of transcranial electric motor evoked potentials to monitor the corticospinal motor tracts directly suggested that the method holds great promise for improving detection of emerging spinal cord injury. We sought to compare the efficacy of these two methods of monitoring to detect impending iatrogenic neural injury during scoliosis surgery. METHODS We reviewed the intraoperative neurophysiological monitoring records of 1121 consecutive patients (834 female and 287 male) with adolescent idiopathic scoliosis (mean age, 13.9 years) treated between 2000 and 2004 at four pediatric spine centers. The same group of experienced surgical neurophysiologists monitored spinal cord function in all patients with use of a standardized multimodality technique with the patient under total intravenous anesthesia. A relevant neurophysiological change (an alert) was defined as a reduction in amplitude (unilateral or bilateral) of at least 50% for somatosensory evoked potentials and at least 65% for transcranial electric motor evoked potentials compared with baseline. RESULTS Thirty-eight (3.4%) of the 1121 patients had recordings that met the criteria for a relevant signal change (i.e., an alert). Of those thirty-eight patients, seventeen showed suppression of the amplitude of transcranial electric motor evoked potentials in excess of 65% without any evidence of changes in somatosensory evoked potentials. In nine of the thirty-eight patients, the signal change was related to hypotension and was corrected with augmentation of the blood pressure. The remaining twenty-nine patients had an alert that was related directly to a surgical maneuver. Three alerts occurred following segmental vessel clamping, and the remaining twenty-six were related to posterior instrumentation and correction. Nine (35%) of these twenty-six patients with an instrumentation-related alert, or 0.8% of the cohort, awoke with a transient motor and/or sensory deficit. Seven of these nine patients presented solely with a motor deficit, which was detected by intraoperative monitoring of transcranial electric motor evoked potentials in all cases, and two patients had only sensory symptoms. Somatosensory evoked potential monitoring failed to identify a motor deficit in four of the seven patients with a confirmed motor deficit. Furthermore, when changes in somatosensory evoked potentials occurred, they lagged behind the changes in transcranial electric motor evoked potentials by an average of approximately five minutes. With an appropriate response to the alert, the motor or sensory deficit resolved in all nine patients within one to ninety days. CONCLUSIONS This study underscores the advantage of monitoring the spinal cord motor tracts directly by recording transcranial electric motor evoked potentials in addition to somatosensory evoked potentials. Transcranial electric motor evoked potentials are exquisitely sensitive to altered spinal cord blood flow due to either hypotension or a vascular insult. Moreover, changes in transcranial electric motor evoked potentials are detected earlier than are changes in somatosensory evoked potentials, thereby facilitating more rapid identification of impending spinal cord injury.

Assessment of Human Disc Degeneration and Proteoglycan Content Using T1ρ-weighted Magnetic Resonance Imaging

Study Design. T1&rgr; relaxation was quantified and correlated with intervertebral disc degeneration and proteoglycan content in cadaveric human lumbar spine tissue. Objective. To show the use of T1&rgr;-weighted magnetic resonance imaging (MRI) for the assessment of degeneration and proteoglycan content in the human intervertebral disc. Summary of Background Data. Loss of proteoglycan in the nucleus pulposus occurs during early degeneration. Conventional MRI techniques cannot detect these early changes in the extracellular matrix content of the disc. T1&rgr; MRI is sensitive to changes in proteoglycan content of articular cartilage and may, therefore, be sensitive to proteoglycan content in the intervertebral disc. Methods. Intact human cadaveric lumbar spines were imaged on a clinical MR scanner. Average T1&rgr; in the nucleus pulposus was calculated from quantitative T1&rgr; maps. After MRI, the spines were dissected, and proteoglycan content of the nucleus pulposus was measured. Finally, the stage of degeneration was graded using conventional T2 images. Results. T1&rgr; decreased linearly with increasing degeneration (r = −0.76, P < 0.01) and age (r = −0.76, P < 0.01). Biochemical analysis revealed a strong linear correlation between T1&rgr; and sulfated-glycosaminoglycan content. T1&rgr; was moderately correlated with water content. Conclusions. Results from this study suggest that T1&rgr; may provide a tool for the diagnosis of early degenerative changes in the disc. T1&rgr;-weighted MRI is a noninvasive technique that may provide higher dynamic range than T2 and does not require a high static field or exogenous contrast agents.

Major Complications and Comparison Between 3-column Osteotomy Techniques in 105 Consecutive Spinal Deformity Procedures

Study Design. A retrospective review. Objective. To characterize the risk factors for the development of major complications in 3-column osteotomies and determine whether the presence of a major complication affects ultimate clinical outcomes. Summary of Background Data. Three-column spinal osteotomies, including pedicle subtraction osteotomy (PSO) and vertebral column resection (VCR), are common techniques to correct severe and/or rigid spinal deformities. Methods. Two hundred forty consecutive PSO (n = 156) and VCR (n = 84) procedures in 237 patients were performed at a single institution between 1995 and 2008. Of these, 105 patients (87 PSOs, 18 VCRs) had complete preoperative and minimum 2-year postoperative clinical outcomes data available for analysis. Using established criteria, we reported complications as major or minor and further stratified complications as surgical versus medical and permanent versus transient. Risk factors for complications and their effect on Scoliosis Research Society (SRS) clinical outcomes at baseline and at 2 years or more were assessed. Results. Major medical and surgical complications occurred at similar rates in both PSOs and VCRs (38%, 33 of 87 vs. 22%, 4 of 18; P = 0.28). Overall, 24.8% (26 of 105) experienced major surgical complications (3 permanent) and 15.2% (16 of 105) experienced major medical complications (4 permanent). Patients with PSO were older (53 vs. 29 yr; P < 0.001), had greater estimated blood loss (1867 vs. 1278 mL; P = 0.02), and showed a trend toward fewer fused levels (10.1 vs. 12.2; P = 0.06). Risk factors for major complications included preoperative sagittal imbalance of 40 mm or more (P = 0.01), age 60 years and older (P = 0.01), and the presence of 3 or more medical comorbidities (P = 0.04). Both groups improved significantly from baseline in SRS subscores; however, patients with PSO started off worse but improved more than VCRs in both the pain (+1.0 vs. +0.1; P < 0.001) and function (+0.6 vs. +0.2; P = 0.01) domains, with no differences in final satisfaction (4.1 vs. 4.3; P = 0.54). PSO and VCR patients with no complications had slightly higher satisfaction scores than patients with minor-only complications, major transient complications, and major permanent complications. There were no significant differences among the groups with respect to change in SRS subscores from baseline, and all complication groups improved significantly from baseline (P = 0.04). Conclusion. Major complications occurred in 35% of 3-column osteotomies and at similar rates for both PSO (38%) and VCR (22%) procedures. The presence of a major complication did not affect the ultimate clinical outcomes at 2 years or more.

Evaluation of spinal kinematics following lumbar total disc replacement and circumferential fusion using in vivo fluoroscopy.

Study Design. In vivo fluoroscopic analysis of lumbar spinal motion with total disc replacement (TDR), fusions, and controls. Objectives. Compare and contrast lumbar spinal motion profiles in TDR, circumferential fusion, and controls. Summary of Background Data. TDR has been shown to preserve motion and possibly prevent abnormal loading at the adjacent level. Although in vitro cadaveric studies have provided invaluable information, they are not capable of assessing the physiologic motion profile of the lumbar spine that is initiated and stabilized by in vivo trunk muscular contractions. Methods. Cross-sectional evaluation using high-frequency low-dose pulsated video fluoroscopy to evaluate lumbar spinal motion in subjects who underwent TDR (n = 8), circumferential fusion (n = 5), and controls (n = 4). Angulation and translation were recorded at 20 time points during the extension-flexion arc. Motion gradients, or slopes of the motion curves, were generated to allow for comparison of lumbar spinal motion profiles. Results. Circumferential fusions exhibited significantly steeper motion gradients at the proximal adjacent level compared with TDR during flexion. TDR had more physiologic motion profiles at the proximal adjacent level than fusions during flexion and extension. At operative levels L4/5 and L5/S1, TDR and controls exhibited similar motion profiles in flexion, while fusions exhibited significantly less motion. In extension, however, TDR had a steeper slope than controls at the L4/5 operative level. Between L3 and S1, the total range of motion accounted for by the L4/5 proximal adjacent level was 59% in 1-level fusions, 38% in 1-level TDR, and 29% in controls. While no control or TDR subjects underwent sagittal plane translation >3 mm during flexion-extension, 80% of fusions did (average 3.7 mm), most notably during the latter phase of extension. Conclusions. TDR produces physiologic lumbar spinal motion profiles in flexion and extension at the operative and proximal adjacent levels. Fusions, however, produced steeper motion gradients at the proximal adjacent level, while undergoing significantly greater sagittal plane translation during flexion-extension.

Comparison of intra-articular lidocaine and intravenous sedation for reduction of shoulder dislocations a randomized, prospective study

Background: Acute anterior glenohumeral dislocations have been commonly treated with closed reduction and the use of intravenous sedation. Recently, the use of intra-articular lidocaine has been advocated as an alternative to sedation, since intravenous access and patient monitoring are not required. The purpose of this study was to evaluate the value of local anesthesia compared with that of the commonly used intravenous sedation during the performance of a standardized reduction technique.Methods: In a prospective, randomized study, skeletally mature patients with an isolated glenohumeral joint dislocation and no associated fracture were randomized to receive either intravenous sedation or intra-articular lidocaine to facilitate reduction of the dislocation. Reduction was performed with the modified Stimson method. The two groups were compared with regard to the rate of successful reduction, pain as rated on a visual analog scale, time required for the reduction, time from the reduction until discharge from the emergency department, and cost.Results: Thirty patients were enrolled in the study. Five (two in the lidocaine group and three in the sedation group) required scapular manipulation in addition to the Stimson technique to reduce the dislocation. The lidocaine group spent significantly less time in the emergency department (average time, seventy-five minutes compared with 185 minutes in the sedation group, p < 0.01). There was no significant difference between the two groups with regard to pain (p = 0.37), success of the Stimson technique (p = 1.00), or time required to reduce the shoulder (p = 0.42). The cost of the intravenous sedation was

Total Disc Replacement Positioning Affects Facet Contact Forces and Vertebral Body Strains

97.64 per patient compared with

Thoracic pedicle screw instrumentation: the learning curve and evolution in technique in the treatment of adolescent idiopathic scoliosis.

0.52 for use of the intra-articular lidocaine.Conclusions: Use of intra-articular lidocaine to facilitate reduction with the Stimson technique is a safe and effective method for treating acute shoulder dislocations in an emergency room setting. Intra-articular lidocaine requires less money, time, and nursing resources than does intravenous sedation to facilitate reduction with the Stimson technique.

Sagittal Cervical Alignment After Cervical Disc Arthroplasty and Anterior Cervical Discectomy and Fusion : Results of a Prospective, Randomized, Controlled Trial

Study Design. A validated nonlinear three-dimensional finite element (FE) model of a single lumbar motion segment (L3-L4) was used to evaluate the effects of total disc replacement (TDR). The model was implanted with a fixed-bearing TDR (ProDisc-L) at 2 surgically relevant positions and exercised about the 3 anatomic axes. Facet forces, range of motion (RoM), and vertebral body strains were evaluated. Objective. The objective of the current study was to evaluate how TDR implantation and positioning affects facet joint forces and vertebral body strains. We hypothesized that facet contact forces (FCFs) would increase with TDR to compensate for the loss of periprosthetic load-bearing structures, and that vertebral body strains would increase in the region around the metallic footplates. Summary of Background Data. TDR has the potential to replace fusion as the gold standard for the treatment of painful degenerative disc disease. However, complications after TDR include index level facet arthrosis and implant subsidence. Alterations in facet and vertebral body loading after TDR and their dependence on implant positioning are not fully understood. Methods. An FEM of L3-L4 was created and validated using RoM, disc pressure, and bony strains from previously published data. A TDR was incorporated into the L3-L4 spine model. All models were subjected to a compressive follower load of 500 N and moments of 7.5 Nm about the 3 anatomic axes. Results. Overall RoM and FCFs tended to increase with TDR. FCFs increased by an order of magnitude during flexion. Posterior placement of the device resulted in an unloading of the facets during extension. Areas of strain maxima were observed in the anterior portion of the vertebral body during flexion after TDR. The area of initial bone resorption signal under the metal footplate was greater when the device was anteriorly placed. Conclusion. The current study predicted a decrease in segmental rotational stiffness resulting from TDR. This resulted from the removal of load bearing soft tissue structures, and caused increased loading in the facets. Additionally, vertebral body strains were generally higher after TDR, and tended to increase with decreased rotational stiffness. Posterior placement of the device provided a more physiologic load transfer to the vertebral body.

Comparison of cobb angle measurement of scoliosis radiographs with preselected end vertebrae : Traditional versus digital acquisition

Study Design. Retrospective review. Objective. The purpose of this study is to evaluate the learning curve and associated evolution in surgical technique with thoracic pedicle screw instrumentation in adolescent idiopathic scoliosis (AIS). Summary of Background Data. Common treatment for AIS now includes posterior spinal fusion, using thoracic pedicle screws (TPS). It is critical to assess the efficacy, safety profile, and learning curve associated with this technique as its use becomes more widespread among inexperienced surgeons. Methods. Retrospective review of the senior author’s first 96 TPS cases for Lenke Type I AIS curves. Multiple regression techniques were used to discern whether increasing case number (CN) was associated with improved perioperative and 2-year minimum radiographic and clinical outcomes. The 96 cases were divided into 4 equal quartiles of 24 cases/group (i.e., Q1–Q4) and compared using analysis of variance measures. Results. A total of 1169 thoracic pedicle screws were placed in 96 patients. We found a significant correlation between CN and major curve correction at 2 years (P < 0.0001), inverse correlation between CN and length of stay (P = 0.02), and estimated blood loss (P = 0.03), but no differences in cell saver or complications. Univariate analysis revealed significant inverse correlations between increasing CN and transfusion rate (P = 0.02) and operative times (P = 0.0001). Total number of screws placed (Q1:9.4 vs. Q4:16.2, P < 0.0001) and number of screws/level (Q1:0.98 vs. Q4:1.64, P < 0.0001) increased linearly with increasing CN, whereas the average time for screw placement (Q1:24.2 vs. Q4:11.4 minutes, P < 0.0001) and ability to maintain T2–T12 kyphosis decreased (Q1:0.21 vs. Q4:−5.5 P = 0.02) with increasing CN. Conclusion. There is a significant learning curve associated with thoracic pedicle screw placement in AIS. We describe several technical steps that can be taken to increase the safety of screw placement at the beginning of the learning curve. Inexperienced surgeons should expect a gradual improvement over time in radiographic and clinical outcomes.

Segmental contribution toward total cervical range of motion: a comparison of cervical disc arthroplasty and fusion.

Study Design. Radiographic results of a multicenter, prospective randomized study comparing 1-level cervical total disc replacement (TDR-C) with anterior cervical discectomy and fusion (ACDF). Objective. To evaluate the effect on device-level lordosis, cranial and caudal adjacent level lordosis, and overall cervical sagittal alignment (C2–C6) after TDR-C or ACDF. Summary of Background Data. Cervical total disc replacement (TDR-C) has emerged as a promising alternative to ACDF in a select group of patients. The maintenance and/or improvement of sagittal balance is essential in preserving functionality after reconstructive spinal procedures. Recent studies have documented changes in spinal alignment after TDR-C, however, no studies have compared these changes to those noted in matched group of patients that have undergone ACDF. Methods. Radiographic data were obtained from the randomized group of a multicenter, randomized, prospective, controlled study comparing TDR-C (ProDisc-C, Synthes Spine, West Chester, PA) with ACDF in the treatment of 1-level cervical disc disease. Complete radiographic data were available for 89 TDR-C patients (average age: 42.2 years) and 91 ACDF patients (average age: 41.7 years). Cervical lordosis at the device level, cranial and caudal adjacent levels, and total cervical lordosis (C2–C6) were independently measured before surgery and 2 years after surgery using custom image stabilization software (Quantitative Motion Analysis, Medical Metrics, Inc, Houston, TX). Results. C5–C6 was the most common operative level (TDR-C: 54%; ACDF: 55%). At 2 years after surgery, the TDR-C group experienced statistically significant changes in lordosis of 3.0° (P < 0.001), 0.90° (P = 0.006), and −1.9° (P < 0.001) at the operative, cranial, and caudal adj-acent levels, respectively. ACDF experienced changes in lordosis of 4.2° (P < 0.001), 1.0° (P = 0.001), and −1.5° (P = 0.001), respectively. The between-group differences were significant at the operative level (P = 0.03) and the caudal adjacent level (P = 0.05). Total cervical lordosis increased in both TDR-C and ACDF by 3.1° and 3.8°, respectively (P = 0.49). Conclusion. In both TDR-C and ACDF, lordosis increased at the device-level, cranial adjacent level, and in total cervical lordosis, while lordosis decreased at the caudal adjacent level. Although ACDF facilitated a greater increase in device level lordosis (+1.25°) and less loss of lordosis at the caudal adjacent level compared with TDR-C (−0.39°), the clinical relevance of the small differences remain unknown.