Valgus Tibial Component Placement: A Novel Risk Factor for Tibial Fracture in Cementless Oxford® Partial Knee Arthroplasty.

The Oxford® Partial Knee (OPK; Zimmer Biomet, Warsaw, IN, USA) is a widely used unicompartmental knee arthroplasty (UKA) system. We report a case in which valgus malpositioning of the tibial component relative to the resection surface may have contributed to an early postoperative fracture. A 70-year-old woman underwent bilateral cementless OPK arthroplasty. On the left side, the tibial component was inserted in valgus alignment relative to a slight varus resection. Postoperative CT revealed a non-displaced tibial fracture. Internal fixation was performed, and bone healing proceeded uneventfully. The fracture was likely caused by valgus alignment of the component relative to the tibial cut, producing an eccentric loading, thereby generating a wedge effect and rotational force. Contributing factors for this malpositioned component placement may have included inadequate osteophyte removal, oversized component impingement on the medial collateral ligament (MCL), meniscal cuff interposition, and malaligned keel slot preparation. Bone union was achieved with stable fixation and biological bone ingrowth. Valgus malpositioning of the tibial component relative to the resection surface represents a previously unreported risk factor for periprosthetic tibial fracture in cementless OPK. Careful intraoperative technique can reduce this risk, and bone healing remains achievable following fracture.