Tibial Post Fracture in a Posterior-Stabilized Knee Prosthesis: A Case Report and Review of the Literature

Background:Tibial post fracture is an uncommon but likely underrecognized complication of posterior-stabilized (PS) total knee arthroplasty (TKA) that often remains undiagnosed because conventional radiographs may be unrevealing.We report a late tibial post fracture in a previously well-functioning PS TKA, highlighting the role of dynamic fluoroscopy in raising preoperative suspicion and the successful use of isolated polyethylene insert exchange in a carefully selected patient. Case Report:A 92-year-old man presented with acute mechanical pain, recurrent clicking, and subjective instability 16 years after primary PS TKA following a low-energy flexion-rotation movement.Plain radiographs showed no evidence of periprosthetic fracture, component loosening, or implant failure.Dynamic fluoroscopy during flexion, which reproduced the patient's symptoms, demonstrated abnormal anterior translation of the femoral component relative to the tibial insert during knee flexion, raising suspicion of cam-post mechanism failure.Revision surgery confirmed a fracture of the polyethylene tibial post with chronic wear at its base; the metallic components remained well fixed, without gross malposition.Isolated polyethylene insert exchange with a thicker insert restored intraoperative stability.At 4.5 months postoperatively, the patient demonstrated complete resolution of mechanical symptoms, with full extension, 100° to 110° of flexion, and preserved varus-valgus and anteroposterior stability. Conclusions:This case illustrates how dynamic fluoroscopy may raise preoperative suspicion of tibial post fracture in selected patients with symptomatic late PS TKA and inconclusive conventional radiographs.In our patient, isolated polyethylene insert exchange was effective after confirmation of preserved component fixation, alignment, and overall stability, supporting its use in appropriately selected cases.