To assess the effect of each step of medial soft-tissue releases on the joint gap angle during posterior-stabilised total knee arthroplasty (TKA). 82 women and 9 men (mean age, 72 years) with medial osteoarthritic knees underwent 100 posterior-stabilised TKAs, in which release of superficial fibres of the medial collateral ligament (MCL) were required using the gap control technique. The order of releases was the superficial MCL, the pes anserinus, and then the semi-membranosus. The superficial MCL was released selectively. The effect of each step of medial soft-tissue releases in full extension and in 90o flexion was compared. After all medial soft-tissue releases, the mean joint gap angles decreased from 8.7o to 3.8o varus in flexion and from 4.4o to 1.4o varus in extension. The total effect of medial soft-tissue releases was significantly larger in flexion than in extension (4.9o±3.2o vs. 3.0o±2.0o, p<0.0001), except for the release of posterior fibres of the superficial MCL. The effect of release of the semi-membranosus in flexion was largest. The release effect was significantly greater in flexion than in extension during posterior-stabilised TKA; the joint gap technique may be more reliable in medial osteoarthritic knees with moderate and severe varus instability.
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