Lateral Tibial Plateau Fracture Following Medial Unicompartmental Knee Arthroplasty: A Case Report

Medial unicompartmental knee arthroplasty (mUKA) is a well-established surgical option for isolated medial compartment osteoarthritis. While tibial medial plateau fractures are recognized postoperative complications, lateral plateau fractures are exceptionally rare. To our knowledge, this report presents, for the first time, a case of a complete lateral tibial plateau fracture immediately following mUKA. A 76-year-old man with a 30-year history of left knee pain and a diagnosis of osteoarthritis underwent cementless mUKA (Oxford system). Postoperative radiographs taken on the day after surgery revealed a Schatzker Type I lateral tibial plateau fracture. The articular surface was undisturbed, and the bone fragment remained stable, likely due to fibular support. Conservative treatment was implemented without weight-bearing restrictions. No braces were used, and no rest restrictions were imposed. Bone union was achieved, with no progression of displacement. At one-year follow-up, the patient was pain-free and able to ambulate independently. This case highlights a rare but significant complication: a complete lateral tibial plateau fracture following mUKA. Unlike previously reported cases of lateral insufficiency fractures, this fracture was complete and occurred immediately postoperatively. The etiology remains unclear, but fibular stabilization notably facilitated successful conservative management without weight-bearing restrictions. The Japan Orthopaedic Association Score before surgery was 60, but improved to 75 one year after surgery. The Knee Society Score before surgery was 60, but improved to 95 one year after surgery. The Oxford Knee score before surgery was 19, but improved to 50 after surgery. This case underscores the importance of recognizing such rare complications and demonstrates that conservative treatment can achieve excellent clinical outcomes in cases of stable fractures.