The Unstable Knee

Abstract

Excessive soft-tissue laxity is frequently encountered in severely deformed arthritic knees undergoing TKA. It is usually uni- or biplanar where the lateral side (in varus deformity) or medial side (in valgus deformity) shows excessive laxity with or without an associated posterior laxity (in hyperextension deformity). However, rarely, an arthritic knee undergoing TKA may also show multiplanar or global laxity where there is significant medial, lateral and posterior ligamentous insufficiency along with significant bone loss. Although extremely rare in osteoarthritis or rheumatoid arthritis, severe or global knee instability may be secondary to a neuromuscular disorder (such as post-poliomyelitis, spinal neuropathy) or due to post-traumatic global ligamentous insufficiency.