Joel A. Bauman

Anomalous fiber realignment during tensile loading of the rat facet capsular ligament identifies mechanically induced damage and physiological dysfunction

Many pathophysiological phenomena are associated with soft tissue loading that does not produce visible damage or tissue failure. As such, there is an unexplained disconnect between tissue injury and detectable structural damage during loading. This study investigated the collagen fiber kinematics of the rat facet capsular ligament to identify the onset of subfailure damage during tensile loading conditions that are known to induce pain. Quantitative polarized light imaging was used to determine the collagen fiber orientation in the capsular ligament (n=7) under tension, and an alignment vector correlation measurement was employed to identify local anomalous fiber realignment during loading. During the initial portion of loading when tissue stiffness was increasing, anomalous realignment was more likely to be detected than mechanical evidence of structural damage, and as a result, anomalous fiber realignment was identified significantly (p=0.004) before gross failure. The occurrence of anomalous fiber realignment was significantly associated (p=0.013) with a decrease in tangent stiffness during loading (ligament yield), suggesting this optical metric may be associated with a loss of structural integrity. The presence of localized anomalous realignment during subfailure loading in this tissue may explain the development of laxity, collagen fiber disorganization, and persistent pain previously reported for facet joint distractions comparable to that required for anomalous realignment. These optical data, together with the literature, suggest that mechanically induced tissue damage may occur in the absence of any macroscopic or mechanical evidence of failure and may produce local pathology and pain.

Subcutaneous heparin for prophylaxis of venous thromboembolism in deep brain stimulation surgery: evidence from a decision analysis.

OBJECTIVEThe addition of subcutaneous heparin (SQH) to mechanical prophylaxis for venous thromboembolism (VTE) involves a balance between the benefit of greater protection from VTE and the added risk of intracranial hemorrhage. There is evidence that the hemorrhage risk outweighs the benefits for patients undergoing craniotomy. We investigated the safety of SQH in patients undergoing deep brain stimulation (DBS) surgery. METHODSA retrospective analysis was performed of all patients with movement disorders (n = 254) undergoing DBS surgery at our institution from 2003 to 2007. Before September 2005, none of the patients undergoing DBS received SQH (non-SQH group) (n = 121). Thereafter, all patients were administered SQH perioperatively (SQH group) (n = 133). All patients wore graduated compression stockings and pneumatic compression boots postoperatively in bed. A postoperative brain magnetic resonance imaging scan was obtained on the day of surgery. RESULTSFive (3.8%) of 133 SQH patients and 1 (0.8%) of 121 non-SQH patients developed asymptomatic intracranial hemorrhage. None of the SQH patients developed clinically significant VTE, whereas 3 (2.5%) non-SQH patients developed VTE (1 deep venous thrombosis, 2 pulmonary embolisms). Using a decision-analysis model, we have shown that the use of SQH plus mechanical prophylaxis together yielded outcomes at least as good as mechanical prophylaxis alone. CONCLUSIONOur findings suggest that SQH for VTE prophylaxis in patients with movement disorders undergoing DBS surgery is safe. SQH protects against VTE in this patient population and merits further investigation.

ProDisc cervical arthroplasty does not alter facet joint contact pressure during lateral bending or axial torsion.

Study Design. A biomechanical study of facet joint pressure after total disc replacement using cadaveric human cervical spines during lateral bending and axial torsion. Objective. The goal was to measure the contact pressure in the facet joint in cadaveric human cervical spines subjected to physiologic lateral bending and axial torsion before and after implantation of a ProDisc-C implant. Summary of Background Data. Changes in facet biomechanics can damage the articular cartilage in the joint, potentially leading to degeneration and painful arthritis. Few cadaveric and computational studies have evaluated the changes in facet joint loading during spinal loading with an artificial disc implanted. Computational models have predicted that the design and placement of the implant influence facet joint loading, but limited cadaveric studies document changes in facet forces and pressures during nonsagittal bending after implantation of a ProDisc. As such, little is known about the local facet joint mechanics for these complicated loading scenarios in the cervical spine. Methods. Seven osteoligamentous C2–T1 cadaveric cervical spines were instrumented with a transducer to measure the C5–C6 facet pressure profiles during physiological lateral bending and axial torsion, before and after implantation of a ProDisc-C at that level. Rotations at that level and global cervical spine motions and loads were also quantified. Results. Global and segmental rotations were not altered by the disc implantation. Facet contact pressure increased after implantation during ipsilateral lateral bending and contralateral torsion, but that increase was not significant compared with the intact condition. Conclusion. Implantation of a ProDisc-C does not significantly modify the kinematics and facet pressure at the index level in cadaveric specimens during lateral bending and axial torsion. However, changes in facet contact pressures after disc arthroplasty may have long-term effects on spinal loading and cartilage degeneration and should be monitored in vivo.

Contact pressure in the facet joint during sagittal bending of the cadaveric cervical spine.

The facet joint contributes to the normal biomechanical function of the spine by transmitting loads and limiting motions via articular contact. However, little is known about the contact pressure response for this joint. Such information can provide a quantitative measure of the facet joints local environment. The objective of this study was to measure facet pressure during physiologic bending in the cervical spine, using a joint capsule-sparing technique. Flexion and extension bending moments were applied to six human cadaveric cervical spines. Global motions (C2-T1) were defined using infra-red cameras to track markers on each vertebra. Contact pressure in the C5-C6 facet was also measured using a tip-mounted pressure transducer inserted into the joint space through a hole in the postero-inferior region of the C5 lateral mass. Facet contact pressure increased by 67.6 ± 26.9 kPa under a 2.4 Nm extension moment and decreased by 10.3 ± 9.7 kPa under a 2.7 Nm flexion moment. The mean rotation of the overall cervical specimen motion segments was 9.6 ± 0.8° and was 1.6 ± 0.7° for the C5-C6 joint, respectively, for extension. The change in pressure during extension was linearly related to both the change in moment (51.4 ± 42.6 kPa/Nm) and the change in C5-C6 angle (18.0 ± 108.9 kPa/deg). Contact pressure in the inferior region of the cervical facet joint increases during extension as the articular surfaces come in contact, and decreases in flexion as the joint opens, similar to reports in the lumbar spine despite the difference in facet orientation in those spinal regions. Joint contact pressure is linearly related to both sagittal moment and spinal rotation. Cartilage degeneration and the presence of meniscoids may account for the variation in the pressure profiles measured during physiologic sagittal bending. This study shows that cervical facet contact pressure can be directly measured with minimal disruption to the joint and is the first to provide local pressure values for the cervical joint in a cadaveric model.

Facet joint contact pressure is not significantly affected by ProDisc cervical disc arthroplasty in sagittal bending: a single-level cadaveric study

BACKGROUND CONTEXT Total disc arthroplasty is a motion-preserving spinal procedure that has been investigated for its impact on spinal motions and adjacent-level degeneration. However, the effects of disc arthroplasty on facet joint biomechanics remain undefined despite the critical role of these posterior elements on guiding and limiting spinal motion. PURPOSE The goal was to measure the pressure in the facet joint in cadaveric human cervical spines subjected to sagittal bending before and after implantation of the ProDisc-C (Synthes Spine Company, L.P, West Chester, PA, USA). STUDY DESIGN A biomechanical study was performed using cadaveric human cervical spines during sagittal bending in the intact and implanted conditions. METHODS Seven C2-T1 osteoligamentous cadaveric cervical spines were instrumented with a transducer to measure the C5-C6 facet pressure profiles during physiological sagittal bending, before and after implantation of a ProDisc-C at that level. Rotations of the index segment and global cervical spine were also quantified. RESULTS The mean C5-C6 range of motion significantly increased (p=.009) from 9.6°±5.1° in the intact condition to 16.2°±3.6° after implantation. However, despite such changes in rotation, there was no significant difference in the facet contact pressure during extension between the intact (64±30 kPa) and implanted (44±55 kPa) conditions. Similarly, there was no difference in facet pressure developed during flexion. CONCLUSIONS Although implantation of a ProDisc-C arthroplasty device at the C5-C6 level increases angular rotations, it does not significantly alter the local facet pressure at the index level in flexion or extension. Using a technique that preserves the capsular ligament, this study provides the first direct measurement of cervical facet pressure in a disc arthroplasty condition.

Pressure Measurement in the Cervical Spinal Facet Joint : Considerations for Maintaining Joint Anatomy and an Intact Capsule

Study Design. A novel noninvasive approach to measure facet joint pressure in the cervical spine was investigated using a tip-mounted transducer that can be inserted through a hole in the bony lateral mass. This technique is advantageous because it does not require resection of the joint capsule, but there are potential issues regarding its applicability that are addressed. Objective. The objective was to evaluate the effect of a tip-mounted pressure probes position and orientation on contact pressure measurements in biomechanical experiments. Summary of Background Data. Measurements of direct contact pressure in the facet joint of cadaveric spines have been obtained via pressure-sensitive films. However, that method requires the resection of the facet capsule, which can alter the overall joints mechanical behavior and can affect the measured contact pressures. Methods. Influence of position and orientation on probe measurements was evaluated in companion surrogate and cadaveric investigations. The probe was placed in the facet of an anatomic vertebral C4/5 surrogate undergoing sagittal bending moments. Pressure-sensitive paper was used to map contact regions in the joint of the surrogate and cadaveric cervical segments (n = 3) during extension. The probe also underwent uniaxial compression in cadaveric facets to evaluate the effect of orientation relative to the contact surface on the probe signal. Results. Although experimental and theoretical pressure profiles followed the same trends, measured maximum pressures were half of the theoretical ones. In the orientation study, maximum pressures were not different for probe orientations of 0° and 5°, but no signal was recorded at orientations greater than 15°. Conclusion. This approach to measure pressure was selected to provide a minimally-invasive method to quantify facet joint pressures during clinically relevant applications. Both the position and orientation of the probe are critical factors in monitoring local pressure profiles in this mobile synovial joint.

Biomechanical Comparison of Contact Pressure in the Cervical Facet Joint During Bending Using a Probe and Pressure-Sensitive Paper

Non-physiologic loading of the facet joint is a potential cause of facet joint pain in the cervical spine [1]. When the local biomechanical environment of the facet joint is altered, like with trauma or after surgery [2], the cartilaginous articular surfaces of the facets can also be damaged. Defining articular contact pressure can provide a metric of altered joint mechanics and the local mechanical environment of the cartilage in the facet joint. However, accessing the articular surface to make such measurements without altering the overall mechanics of the joint remains a substantial challenge.Copyright

Surgical Approaches for the Treatment of Thoracic Disk Herniation: Results of a Decision Analysis.

Study Design: A decision analysis. Objective: To perform a decision analysis utilizing postoperative complication data, in conjunction with health-related quality of life (HRQoL) utility scores, to rank order the average health utility associated with various surgical approaches used to treat symptomatic thoracic disk herniation (TDH). Summary of Background Data: Symptomatic TDH is an uncommon entity accounting for <1% of all symptomatic herniated disks. A variety of surgical approaches have been developed for its treatment, which may be classified into 4 major categories: open anterolateral transthoracic, minimally invasive anterolateral thoracoscopic, posterior, and lateral. These treatments have varying risk/benefit profiles, but there is still no set algorithm for choosing an approach in cases with multiple surgical options. Methods: We searched Medline, EMBASE, and the Cochrane Library for relevant articles on surgical approaches for TDHs published between 1990 and August 2014. Pooled complication data and HRQoL utility scores associated with each complication were evaluated using standard meta-analytic techniques to determine which surgical approach resulted in the highest average HRQoL. Results: Posterior surgical approaches resulted in the highest average HRQoL, followed by thoracoscopic, lateral, and finally open anterolateral transthoracic procedures. The higher average HRQoL associated with posterior approaches over all others was highly significant (P<0.001); conversely, the open anterolateral approach resulted in a lower average postoperative utility compared with all other approaches (P<0.001). Conclusions: The results of this decision analysis favor posterior over lateral approaches, and thoracoscopic over open anterolateral approaches for the treatment of symptomatic TDHs, which may guide surgeons in cases where multiple surgical options are feasible. Future studies, such as randomized clinical trials, are necessary to ascertain whether novel surgical strategies have risk/benefit profiles that ultimately supersede those of traditional approaches, and whether enough cases are encountered by the average surgeon to justify their adoption.