Biomechanical analysis of medial collateral ligament reconstruction grafts of the elbow.

BACKGROUND: There are no biomechanical studies evaluating different tendon grafts for elbow medial collateral ligament reconstruction. HYPOTHESIS: Using a larger tendon for the graft will yield greater resistance to valgus load for medial collateral ligament docking technique reconstructions. The type of graft used for a medial collateral ligament docking technique reconstruction will have a significant effect on the resistance to valgus loads. STUDY DESIGN: Controlled laboratory study. METHODS: Cadaveric elbows from male donors were cyclically loaded to 3 and 5 mm elongation, both intact and after a docking technique medial collateral ligament reconstruction using palmaris longus, gracilis, semitendinosus, and patellar tendon grafts. RESULTS: There was no significant difference in load to 3 or 5 mm elongation, number of cycles to failure, or stiffness between any tendon graft studied. Every tendon graft reconstruction tested was significantly weaker and less stiff than was the native medial collateral ligament. CONCLUSION: There appears to be no biomechanical advantage to be gained by using a larger tendon graft instead of a palmaris longus graft. CLINICAL RELEVANCE: The most readily available graft source with the lowest morbidity (often the palmaris longus tendon) should be used for medial collateral ligament reconstruction.

Radiographic assessment and quantitative motion analysis of the cervical spine after serial sectioning of the anterior ligamentous structures.

STUDY DESIGN: Cadaveric study of a diagnostic test for cervical spine instability. OBJECTIVE: Determine if flexion-extension (FE) radiographs can be used to detect incremental damage to anterior cervical structures. SUMMARY OF BACKGROUND DATA: Prior studies have shown that damage to cervical structures can alter motion between vertebrae, and FE radiographs are sometimes used to detect this damage. However, no study has determined if FE radiographs are sensitive and specific for acute injury. METHODS: FE radiographs were taken of the intact neck and after each incremental increase in damage to the anterior structures. Intervertebral motion was quantified using previously validated methods. The sensitivity and specificity of intervertebral motion measurements were assessed. RESULTS: Motion within the intact spines was within normal ranges. Although intervertebral rotation changed significantly after certain anterior structures were damaged, rotation frequently remained within normal ranges, even after extensive damage. A center of rotation that was posterior to the 95% confidence interval for normal motion was 100% sensitive and specific for damage to the anterior structures of the spine. CONCLUSIONS: The results suggest that extensive damage to the anterior cervical spine could be missed if instability assessment was based on intervertebral rotation or displacements measured from FE radiographs. In contrast, a center of rotation that was located posterior to normal was both sensitive and specific for damage to anterior structures.

Reduction in head and intervertebral motion provided by 7 contemporary cervical orthoses in 45 individuals.

STUDY DESIGN: Biomechanical evaluation of cervical orthoses. OBJECTIVE: To provide data to help clinicians select an orthosis for immobilization of the adult cervical spine. SUMMARY OF BACKGROUND DATA: There are limited data on the effectiveness of cervical orthoses at restricting intervertebral motion, and many of the commonly used, contemporary braces have not been evaluated. Additionally, no data exist comparing the effectiveness of braces in the supine versus the upright position. New technology is available to measure intervertebral motion with greater accuracy. METHODS: Overall range of motion of the head in 3 planes as well as intervertebral motion in the sagittal plane were measured in 45 healthy adult volunteers while wearing 7 cervical orthoses. Subject-reported comfort of each brace was also recorded. RESULTS: All braces significantly reduced intervertebral motion. Effectiveness and comfort varied between braces. In general, orthoses could be grouped as cervical braces or cervicothoracic braces. The latter was consistently better at limiting motion, with some differences within these groups as well. CONCLUSION: These data will help to guide the clinician in selecting the appropriate cervical orthosis for their adult patient based on comfort, morphologic considerations, and degree of immobilization required.

Intervertebral motion after incremental damage to the posterior structures of the cervical spine.

STUDY DESIGN: Compare intervertebral motion after incremental damage to posterior cervical structures in whole cadavers to motion in asymptomatic subjects. OBJECTIVE: Determine if damage to the posterior structures of the cervical spine can be detected by quantitative analysis of flexion-extension radiographs. SUMMARY OF BACKGROUND DATA: Simulated damage to the posterior structures of the cervical spine can change intervertebral motion, if intervertebral motion before damage is known. It is not known if intervertebral motion measured from flexion-extension radiographs can be used to detect damage to the posterior structures if motion before damage is not known. METHODS: Incremental injury to posterior ligaments and facet joints was simulated in 12 whole cadavers. Intervertebral motion was measured from flexion-extension images using validated and clinically applicable software. Measurements were compared to previously published measurements for asymptomatic subjects. RESULTS: Extensive damage could be simulated in all the cervical spines without intervertebral motion exceeding the 95% confidence limits for asymptomatic subjects. After sectioning all posterior ligaments, destroying both facet joints, and then sectioning the posterior longitudinal ligaments, intervertebral motion exceeded the 95% confidence intervals in 69% of the cadavers. Intervertebral shear decreased with incremental damage to posterior structures. CONCLUSIONS: Radiographic assessment of the cervical spine may not be sufficient to exclude even extensive damage to the posterior structures of the cervical spine.

Intervertebral motion between flexion and extension in asymptomatic individuals.

STUDY DESIGN: Measure and analyze variation in intervertebral motion in asymptomatic subjects. OBJECTIVES: Gain further insight into intervertebral motion during flexion and extension in asymptomatic individuals, identify factors that contribute to variation in motion, and establish a quantitative database using a clinically practical imaging tool. SUMMARY OF BACKGROUND DATA: Several authors have reported on normal values for intervertebral motion during flexion and extension of the cervical spine. However, the sources of the wide variations in intervertebral motion are poorly understood. METHODS: Fluoroscopic images of the cervical spine in maximum flexion and extension were analyzed for 140 asymptomatic volunteers using a validated and clinically applicable image analysis system. Several independent variables were analyzed for their contribution to variation in motion. The dependent variables studied included sagittal plane rotation and translation, and displacements between vertebrae measured at the anterior and posterior aspects of each motion segment. RESULTS: There was considerable variation in measured intervertebral motion. Intervertebral level and total gross rotation between C2 and C6 significantly affected all measures of intervertebral motion. The intervertebral motion measures were all interrelated. After adjusting for differences in gross motion between C2 and C6, intervertebral levels and the three displacement measures could be used to explain almost 90% of the variation in sagittal plane intervertebral rotations. In addition, the data suggest that currently accepted clinical guidelines for shear should be raised at all levels except C6-C7. CONCLUSIONS: A database describing intervertebral motion in asymptomatic subjects representing both sexes and a wide age range was established that should aid in interpreting intervertebral motion in patients. Evaluating various aspects of intervertebral motion may improve the clinical efficacy of radiographic flexion-extension studies of the cervical spine.

Biomechanical evaluation of relationship of screw pullout strength, insertional torque, and bone mineral density in the cervical spine.

BACKGROUND: Understanding of implant failure mechanisms is important in the successful utilization of anterior cervical plates. Many variables influence screw purchase, including the quality of the bone. The purpose of this study was to assess the relationship of screw pullout and screw insertional torque across a wide range of bone mineral densities (BMDs). METHODS: A total of 54 cervical vertebrae in 12 cervical spines were evaluated for BMD using dual-energy x-ray absorptiometry scanning. Actual and perceived peak torques of 3.5-mm anterior cervical screws were determined at each level followed by screw pullout strength testing. RESULTS: A high correlation was observed between screw pullout strength and BMD. However, there was a low correlation of peak insertional torque to pullout strength. CONCLUSION: These findings suggest the quality of the bone is more instrumental in the success or failure of anterior cervical screws than is the insertional torque with which the screws are placed.

Changes in segmental intervertebral motion adjacent to cervical arthrodesis: a prospective study.

STUDY DESIGN: Prospective, observational. OBJECTIVES: Quantify the changes in intervertebral motion adjacent to cervical arthrodesis over time. SUMMARY OF BACKGROUND DATA: One of the frequently acknowledged sequelae following anterior cervical fusion is the development of adjacent segment disease. It has been argued that a spine fusion transfers stress to adjacent levels and results in increased compensatory motion. However, there are conflicting reports as to whether this actually occurs, and most of these are in vitro or retrospective clinical studies. METHODS: Patients undergoing anterior cervical discectomy and fusion underwent a preoperative dynamic fluoroscopic study, followed by imaging at regular intervals after surgery. Imaging data were analyzed by a validated software system. Relative motion between adjacent vertebrae was then calculated, and changes in motion cephalad to the fusion followed over time. RESULTS: Twenty-one patients were analyzed. Mean follow-up was 13 months (10-22 months). Intervertebral motion adjacent to the fusion changed by more than 4 degrees in 4 of the 21 patients. However, on average, there was no difference between preoperative and postoperative motion for shear, flexion-extension, or vertical displacement at the anterior or posterior disc space. CONCLUSIONS: Although there was some individual variation, at a mean of 13 months following surgery, there was no significant change in the average junctional intervertebral motion. If fusion is going to affect adjacent motion, it appears that this does not consistently occur in the first 1 to 2 years following surgery. Additionally, there was no observable relationship between motion and development of degenerative changes during this time.

Coracoclavicular ligament reconstruction using the lateral half of the conjoined tendon.

To preserve the coracoacromial (CA) ligament, we have used the lateral half of the conjoined tendon as an autograft source to replace the coracoclavicular (CC) ligament. The purpose of this study is to compare the ultimate tensile strength of the lateral 12 mm of the conjoined tendon with that of the CA ligament and the CC ligament. Eight paired cadaveric male shoulders were tested to tensile failure with a custom pneumatic testing apparatus. Although the lateral 12 mm of the conjoined tendon was stronger than the CA ligament, this difference was not statistically significant (P =.37). However, the intact CC ligament (621 +/- 209 N) was approximately 250% stronger than either the lateral 12 mm of the conjoined tendon (265 +/- 79 N, P <.001) or the CA ligament (246 +/- 69 N, P <.001). We believe that the lateral half of the conjoined tendon is a viable alternative autograft source for reconstruction of the CC ligament in cases of symptomatic acromioclavicular joint dislocation. Though not as strong as the native CC ligaments, the conjoined tendon is slightly stronger than the commonly used CA ligament.