High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
BACKGROUND: High tibial osteotomy is a well-established method for the treatment of symptomatic medial unicompartmental cartilage degeneration. While the findings of several outcome studies have led to the widely practiced postoperative goal alignment of 8 degrees to 10 degrees of valgus, there exists no literature to account for patient-specific measurements such as body weight, baseline geometry, and medial chondral defect size. Furthermore, there is a lack of literature to support the ideal goal alignment when using high tibial osteotomy to unload isolated chondral defects. PURPOSE: To identify a relationship between these patient-specific factors and the ideal postoperative alignment. STUDY DESIGN: Controlled laboratory study. METHODS: High tibial osteotomy was performed on 8 human cadaveric knees and was fixed with a dynamic external fixator. The fixator was used to vary the tibiofemoral alignment from 12 degrees valgus to 10 degrees varus. At each alignment, force, contact area, and pressure distribution were recorded. This pattern was repeated for a range of applied loads (0.8-1.8 x ideal body weight) and across a range of medial chondral defect sizes (10-20 cm). RESULTS: As tibiofemoral alignment was shifted from varus to valgus alignment, we found a decrease in medial contact pressure (P < .001) and a decrease in medial contact area (P < .001). For all defect sizes, all contact pressure within the medial compartment was shifted to the lateral compartment at between 6 degrees and 10 degrees of valgus. Contact pressure was found to concentrate around the defect rims for all defect sizes. CONCLUSION: We show that regardless of condylar width, baseline tibiofemoral alignment, body weight, or chondral defect size, all specimens demonstrated complete unloading of the medial compartment at between 6 degrees and 10 degrees of valgus, which favors cartilage repair at these alignments. In addition, regarding the use of high tibial osteotomy for unloading isolated chondral defects, we find that contact pressure is approximately equally distributed between the medial and lateral compartments for alignments of 0 degrees to 4 degrees of valgus. CLINICAL RELEVANCE: This loading situation most closely approximates physiologic loading and therefore represents an ideal outcome for patients with isolated chondral defects. Reduction in stress concentration around chondral defects has been found to favor cartilage repair.
Mina, C; Garrett, WE; Pietrobon, R; Glisson, R; Higgins, L
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