The influences of biomechanical factors on cartilage regeneration after high tibial osteotomy for knees with medial compartment osteoarthritis

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Abstract
Purpose: A high tibial osteotomy (HTO) is often performed on knees with medial compartment osteoarthritis. However, in varus knees with medial compartment osteoarthritis, degeneration of the articular cartilage tends to progress due to medial deviation of the mechanical axis. This can result in eburnated bone. A widening of the medial joint space has been observed after HTO with a proper correction as a result of decreased stress on the load-bearing cartilage in the medial compartment. Researchers have reported obtaining a repair of the articular cartilage with both eburnation and clinical improvement using HTO in patients showing a medial deviation of the mechanical axis. However, which factors influence cartilage regeneration remain unclear. The purpose of this study was to quantitatively evaluate the influence of cartilage regeneration after a high tibial osteotomy for knees with medial compartment osteoarthritis. Type of Study: Observational cohort study. Methods: The study involved 58 knees in 47 patients. A modified Noyes classification was used for arthroscopic grading. The patients underwent a second look arthroscopic evaluation of the articular cartilage 18 months after surgery. The articular cartilage was classified as no regenerative change (grade 1), white scattering with fibrocartilage (grade 2), partial coverage with fibrocartilage (grade 3), and even coverage with fibrocartilage (grade 4). The functional results were evaluated according to the Japanese Orthopedic Association score for osteoarthritic knees (JOA score), femorotibial angle (FTA), percentage of mechanical axis, and body mass index (BMI). Results: Partial or even coverage with fibrocartilage (grade 3 and 4) was achieved on 55% of the femorotibial joint surfaces. A repair with white scattering with fibrocartilage (grade 2) was achieved in 34%, and 3 knees showed no regenerative change (grade 1). At follow up, significant differences were seen between grade 4 and grade 1 in JOA score and percentage of mechanical axis. Conclusions: This study demonstrates the correlation between the visible improvement of the articular surface, the functional score, and the degree of correction obtained with a lateral closing wedge HTO.

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