Early mechanical failure after contemporary primary total knee arthroplasty (TKA) is driven by a well-documented sequence of events: periprosthetic infection, component loosening, arthrofibrosis, and instability. Clinically, flexion instability (FI) and arthrofibrosis are traditionally viewed as polar opposites on the failure spectrum. Flexion instability presents as an unstable knee characterized by deep mid-flexion laxity, sudden giving-way, and chronic joint effusion. Arthrofibrosis presents as a stiff, locked knee resulting from the uninhibited proliferation of dense intra-articular scar tissue.
However, a highly challenging subset of patients presents with a deeply confusing, paradoxical clinical profile: symptomatic flexion instability masked by severe, concomitant arthrofibrosis (FI+A). In these patients, the joint’s intrinsic mechanical laxity is physically hidden by secondary soft-tissue scarring, presenting a significant diagnostic dilemma in the clinic. Surgeons frequently wonder if revising a knee with both severe stiffness and severe laxity will yield the same functional success as revising isolated instability. We evaluated a large multi-surgeon database out to midterm follow-up to provide definitive clarity on this complex matchup.
