Fracture of the polyethylene tibial post in a posterior cruciate-substituting total knee arthroplasty mimicking patellar clunk syndrome

Fracture of the tibial post in posterior cruciate-substituting total knee arthroplasty has been described in several reports. Additionally, wear of the cam and post mechanism, including polyethylene debris generation and osteolysis of the peri-implant bone stock as been described. Users of a cam and post type posterior stabilized total knee arthroplasty are also familiar with the rare occurrence of the “patellar clunk syndrome,” in which suprapatellar fibrous nodular scar tissue becomes entrapped in the intercondylar box of the femoral component as the knee extends from the flexed position and produces a palpable and sometimes audible “clunk.” This condition is easily managed with arthroscopic excision of the scar tissue. A small series of 5 patients who presented with symptoms of a patellar clunk syndrome but who in fact had a fracture of the tibial post causing subluxation of the femur on the tibia is presented. The diagnostic characteristics that will help differentiate between the 2 problems is highlighted.