Knee Instability From Late Posterior Cruciate Ligament Rupture in Total Knee Arthroplasty: A Case Report

BACKGROUND: In cruciate-retaining (CR) total knee arthroplasty (TKA), late posterior cruciate ligament (PCL) attenuation or rupture, though uncommon, can result in anteroposterior instability and progressive component wear. This can be difficult to diagnose since traditional imaging often appears normal. CASE PRESENTATION: A 61-year-old woman with rheumatoid arthritis and prior CR TKA was referred to physical therapy with a diagnosis of iliotibial band (ITB) syndrome. She reported progressive, painless grinding, shifting, and perceived knee instability. Examination findings were inconsistent with the referring diagnosis of ITB syndrome and raised concern for anteroposterior instability. OUTCOME AND FOLLOW-UP: Despite normal radiographs and computed tomography (CT) scans, mechanical symptoms persisted. Advocacy by the physical therapist prompted further evaluation, which identified suspected PCL rupture and posterior femoral subluxation. Revision surgery later confirmed component wear. DISCUSSION: This case highlights challenges identifying late PCL rupture in a CR TKA leading to instability with resultant component wear. The importance of clinician vigilance, avoidance of common biases, and collaborative interdisciplinary care are emphasized. JOSPT Cases 2026;6(1):1-4. Epub 8 January 2026. doi:10.2519/josptcases.2026.0218