40 years of the Oxford Knee

The Oxford Partial Knee (Zimmer Biomet, Bridgend, United Kingdom) has been used for the last four decades. Very few products make it to this milestone, not least in the world of medicine with the constant drive for innovation and improvement. The original design concept of John Goodfellow and John O'Connor, a fully congruent mobile meniscal bearing articulating with spherical femoral and flat tibial components , has remained unchanged. 1 That does not mean the 'Oxford' has not evolved. Over the course of 40 years, much work has been done in better understanding indications for its use, 2,3 improving instrumentation to allow accurate and more reproducible implantation through smaller incisions, 4 and design changes to improve fixation and durability of the components. 5 In 1976, knee arthroplasty was still in its infancy. Engineers and surgeons were concerned with polyethylene wear with uncon-strained designs, but as they increased congruity of the articulating surfaces, necessarily increased force was transmitted to the implant bone interface and high rates of loosening were observed. Fairbank 6 had previously recognised the importance of the meniscus and noted its load-bearing properties. By conforming to the joint surfaces and moving with the knee, it could significantly increase the surface area over which load was transmitted, thereby reducing the pressure on the articular surfaces. Loss of this structure clearly led to abnormal forces in the knee and the development of medial compartment osteoarthritis. Surgeon (Goodfellow) and engineer (O'Con-nor) met and set out to design a knee prosthesis that would minimise wear and reduce stresses through the implant bone interfaces. The Oxford Knee was introduced initially as a bi-compartmental procedure. Fairly soon thereafter , anteromedial osteoarthritis was recog-nised as a path anatomical pattern, 7 and this has been increasingly recognised as the predominant pattern of osteoarthritis we treat. 8 Partial knee arthroplasty surgery was introduced. The design philosophy of the Oxford has stood the test of time. Multiple studies have shown very low levels of polyethylene wear (0.01 mm/year) if no impingement is observed. 9 The implant has well-documented long-term survival rates, even into the second decade, showing the durability of the bone implant interfaces. 10 The technique allows the implant to be positioned balancing the ligaments and restoring their natural tensions. This restores the knee kinematics to pre-disease levels, 11 and leads to high function and better satisfaction than with conventional TKA designs. There are, however, still concerns about partial …