Polyethylene Tibial Post Fracture in a Posterior Stabilized (Genesis II) Total Knee Arthroplasty

Abstract

).Posterior stabilizing knee prostheses have been increasing in popularity recently due to some studies showing excellent long-term survivorship, more consistent kinematics, technical ease, and higher range of motion.1,2 The posterior stabilized knee relies on a cam and post mechanism to replicate native femoral rollback. One of the major potential complications of this system is post fracture. This occurs in less than 1% of most total knees. 3 These patients usually present with a history of a "pop," effusion, and instability. Diagnosis is usually made clinically or by arthroscopic evaluation. Treatment is typically with a polyethylene liner exchange. 4 Case ReportA 45-year-old white male patient presented with left knee osteoarthritis. He presented with a 10-degree varus deformity of his left knee and range of motion was from full extension to 110 degrees of flexion. He also had an incompetent anterior cruciate ligament and posterior cruciate ligament by physical examination. He failed treatment with anti-inflammatories, physical therapy, and injections. Due to the pain and resulting physical disability, the patient underwent a left total knee arthroplasty using a Genesis II total knee system (Smith and Nephew; Memphis, TN). A size 7 Oxinium (Smith and Nephew)femoral component, size 6 tibial component, 38 mm patella button, and 13 mm high flexion posterior stabilized polyethylene insert were used. Intraoperatively, the patient was found to have good stability to varus/valgus as well as anterior/ posterior testing. The patella tracked well and there were no signs of midflexion instability. Range of motion intraoperatively was full extension to 120 degrees of flexion. The surgery went without complication, and the patient did well in the postoperative period. Approximately 4 years later, the patient felt pain in the left knee while completing personal resistance squats at the gym. He continued to experience multiple episodes of his knee locking up with continuing pain. Physical examination showed increased posterior sag and laxity with evidence of midflexion instability. X-rays did not show any signs of loosening of any components or signs of instability (►Fig. 1A, B). Based on the clinical findings and the patient's symptoms, he was taken back to the operating room for open exploration and possible revision. The patient's previous midline incision and medial parapatellar arthrotomy were utilized. Immediately upon exposing the joint, the fractured post was found sitting anterior to the polyethylene insert and tibial component (►Fig. 2). The femoral, tibial, and patellar components were inspected and found to be stable and well fixed. The insert was then Keywords ► Genesis II ► posterior stabilized knee ► tibial post fracture AbstractThis study reports the case of a fractured polyethylene tibial post in a 49-year-old white male patient at 4 years status post a left posterior stabilized total knee arthroplasty. The patient was doing extremely well postoperatively until he felt pain in the left knee while completin...

Catastrophic Failures of the Tibial Post in a Bicruciate Substituting Total Knee Prosthesis

“…On the post's intraoperative evaluation, there were no signs of significant wear due to post impingement. Similar to other post failure reports in deep flexion, the fracture likely occurred due to increased force on the post during squat exercises [ 23 ]. To our knowledge, there has only been one other reported case of tibial post fracture with the JI-BCS implant.…”

“…Few cases of tibial post breakage in PS TKA have previously been reported. To our knowledge, 5 previous cases have been reported in the NexGen prosthesis (Zimmer, Warsaw, IN) [ 4 , [19] , [20] , [21] , [22] , [23] , [24] ]. Chiu et al.…”