Patellar tilt: the physical examination correlates with MR imaging.

Patella malalignment is a recognized cause of knee pain, tilt being one of its more common forms. Although patellar tilt has been described both on the physical examination and on computerized imaging, to date the correlation between the two has not been established. A strong correlation would strengthen the value of each. Moreover, in situations where tilt cannot be clinically assessed (e.g. obesity), CT or MR imaging could be an adequate substitute for the clinical determination of tilt. We propose to correlate the physical examination with the magnetic resonance examination by way of an MR Tilt Angle. This angle is measured in a manner similar to the assessment of tilt on the physical examination, in that a line is drawn across the medial and lateral borders of the patella and referenced off the posterior femoral condyles. Most tilt angles use the slope of the lateral facet as a measure of tilt. These tilt angles paradoxically diminish as patellar tilt increases, a potential source of confusion. In this study, we use an MRI tilt angle that increases in the same direction as the actual tilt, which is more intuitive. We examined 30 patients with tilt and 51 patients without tilt. Patients with significant tilt on the physical examination can be expected to have an MRI Tilt Angle that is 10 degrees or greater whereas an angle of less than 10 degrees is associated with the absence of significant tilt on the physical examination. This MRI Tilt Angle fills the need for an easy, objective, intuitive measure of tilt and is an excellent adjunct to the physical examination.

Thoracoscopic multilevel anterior instrumented fusion in a goat model.

STUDY DESIGN: A survival study in a caprine model for evaluation of a thoracoscopic anterior scoliosis instrumentation construct for fusion. OBJECTIVE: To compare the efficacy of performing multilevel anterior thoracoscopic "scoliosis" fusion with both allograft and autograft bone. SUMMARY OF BACKGROUND DATA: The use of minimally invasive thoracoscopic spinal surgery has been increasing. Until recently, instrumentation methods for correcting scoliosis entirely with a minimally invasive approach have not been available. Although multilevel thoracoscopic instrumentation and fusion now is in use clinically at some centers, reports of its effectiveness in an animal model are limited. METHODS: A thoracoscopically implanted multilevel screw-rod instrumentation construct was used in a goat survival model, with fusion quality evaluated 16 weeks after surgery. Autogenous iliac crest bone graft was compared with an allogenic bone graft substitute. The quality of fusion was evaluated both radiographically and biomechanically. RESULTS: Thoracoscopic insertion of a multilevel screw-rod construct was demonstrated to be technically feasible. However, with regard to the quality of fusion, only 47% of the disc space "fusion ratings" with the use of autogenous iliac crest graft were considered fully fused by computed tomography scan evaluation. This compares with no ratings of full fusion in the allograft demineralized bone group and only a single rating of full disc space fusion in the control group, which received no bone graft. Torsional range of motion was the smallest in the group receiving iliac crest bone graft and the greatest in the control animals that did not undergo bone grafting. CONCLUSIONS: The lack of complete fusion at 4 months in the autogenous iliac crest group emphasizes the importance of the discectomy and bone grafting technique. The use of demineralized bone allograft as a sole source of interbody fusion is not supported.