Effect of open wedge high tibial osteotomy on the lateral compartment in sheep. Part I: Analysis of the lateral meniscus.

PURPOSE: To evaluate whether medial open wedge high tibial osteotomy (HTO) results in structural and biochemical changes in the lateral meniscus in adult sheep. METHODS: Three experimental groups with biplanar osteotomies of the right proximal tibiae were tested: (a) closing wedge HTO resulting in 4.5° of tibial varus, (b) open wedge HTO resulting in 4.5° of tibial valgus (standard correction) and (c) open wedge HTO resulting in 9.5° of valgus (overcorrection), each of which was compared to the contralateral knees with normal limb axes. After 6 months, the lateral menisci were macroscopically and microscopically evaluated. The proteoglycan and DNA contents of the red-red and white-white zones of the anterior, middle and posterior third were determined. RESULTS: Semiquantitative macroscopic and microscopic grading revealed no structural differences between groups. The red-red zone of the middle third of the lateral menisci of animals that underwent overcorrection exhibited a significant 0.7-fold decrease in mean DNA contents compared with the control knee without HTO (P = 0.012). Comparative estimation of the DNA and proteoglycan contents and proteoglycan/DNA ratios of all other parts and zones of the lateral menisci did not reveal significant differences between groups. CONCLUSION: Open wedge HTO does not lead to significant macroscopic and microscopic structural changes in the lateral meniscus after 6 months in vivo. Overcorrection significantly decreases the proliferative activity of the cells in the red-red zone of the middle third in the sheep model.