Relationship between Severity of Varus Osteoarthritis of the Knee and Contracture of Medial Structures.

Abstract

Knees with severe varus osteoarthritis can develop medial structure contracture. However, there is no report on the relationship between severity of varus deformity and contracture of the medial structure. We aimed to determine the threshold angle that could be corrected in proportion to the width of medial osteophyte removal and to examine correction differences between angles larger and smaller than the threshold angle in total knee arthroplasty. This study included 27 varus osteoarthritic knees scheduled for total knee arthroplasty (TKA). A navigation system was used to measure hip-knee-ankle angle (HKA) in all knees at maximum extension and 30˚ and 60˚ flexion, before and after osteophyte removal and with and without external 10 N-m valgus torque loads. Subsequently, resected osteophyte widths were measured. Mean correction angle per 1 mm of osteophyte removal was calculated, and the threshold angle was calculated with the receiver operating characteristic curve. HKA differences were compared against deformities larger and smaller than the threshold angle. Mean osteophyte width was 7.1±2.20 mm. Osteophyte removal produced a mean 3.1° correction, which equaled a 0.4° correction per 1 mm of osteophyte width removal. The varus deformity threshold angle was 9.5°. However, when comparing groups with angles larger and smaller than the threshold angle, there was no significant difference in HKA difference between each step and flexion angle. The threshold angle for expected correction with medial osteophyte removal was 9.5˚. However, because there were no differences in correction between those with angles larger or smaller than this, medial structure contracture seemed to be unrelated to the severity of deformity.