Fracture of Two Moderately Cross-Linked Polyethylene Tibial Inserts in a TKR Patient

Highly cross-linked polyethylene has become the gold standard in total hip replacement for its wear resistance. Moderately crosslinked polyethylene is now available for total knee replacement (TKR), although concerns about reduced mechanical strength have prevented widespread adoption. The purpose of this report is to describe an unusual case where a patient underwent cruciate retaining TKR using a moderately crosslinked polyethylene tibial insert that went on to fracture twice in the same location across the primary and first revision surgery. The first tibial insert was 10？mm thick and was implanted for 16 months. The second tibial insert was 15？mm thick and was implanted for 11 months. Both fractured along the posterior aspect of the medial articular surface. The lack of a specific event leading to these fractures and the fact that they occurred twice in the same location in the same patient suggest that caution is still necessary regarding the introduction of crosslinked polyethylene for TKR surgery. 1. Introduction Highly cross-linked polyethylene was introduced for THR in the last decade and has since demonstrated excellent long-term wear resistance, leading to its acceptance as the new clinical standard for THR implants [1]. Adoption of cross linking for TKR has been more controversial, as the cross linking process can decrease the mechanical properties of the polyethylene in addition to increasing its wear resistance [2]. In in vitro testing, TKR implants made with moderate cross linking of the polyethylene have shown decreased wear and similar mechanical strength compared to implants using conventional polyethylene, and on this basis moderately cross-linked polyethylene inserts have been introduced for clinical use [3–5]. Most early clinical reports of cross-linked polyethylene in TKR report favorable results, with good wear resistance [6]. However, there have been reports of fractures of highly cross-linked polyethylene in TKR, with all-polyethylene patellar components, at the tibial post of posterior stabilized tibial inserts, and across the condylar surface of CR inserts [7–11]. The purpose of this report is to describe an unusual case in which a patient had a fracture of the moderately cross-linked polyethylene tibial insert of their total knee replacement, at the same posteromedial articular surface location, across two different surgeries in the same joint, within a short period of implantation. 2. Case Presentation The patient was a woman who underwent primary TKA surgery in October 2010 on her left knee, for osteoarthritis involving the