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 unconstrained 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.
Fairbank6 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’Connor) 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 recognised 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 knee arthroplasties in the orthopaedic community. Joint registries have shown higher rates of revision compared with conventional TKAs, and many suggest that their use should be limited.12 This is despite the same registries showing better clinical results from partial knee arthroplasties than TKA.13
It has been well demonstrated from registry data that the thresholds for revision are different for partial knee arthroplasties and this goes partly to explain the increased revision rate.14 It has also been well documented that surgical experience is important and much has been and continues to be done to educate surgeons in appropriate indications and optimum surgical technique.15 There is good evidence that as surgeons undertake more partial arthroplasties as a percentage of their knee arthroplasty practice (up to 50%), their results improve.16
Data from joint registries not only show excellent clinical outcomes with more satisfied patients, they also show significantly lower complication rates with partial knee arthroplasty compared with TKA;1,17 which should appeal to patients, surgeons and those who contribute towards the cost of health care.
The unique design of the Oxford knee continues to generate much interest. In this supplement we can see the Oxford being successfully implanted all over the globe with excellent ten-year data from the United States18 and other European centres.19
As long-term survival of arthroplasty procedures have become more reliable, interest has been directed towards optimising knee function. The Oxford Knee has demonstrated excellent functional results,13 but current patient-reported outcome measures may not be sensitive enough to appreciate these differences fully. The paper by Professor Cobb’s group20 from Imperial College, London shows that gait patterns can be returned to near normal levels. The Oxford technique of implanting the prosthesis with reference to the ligaments allows almost normal knee kinematics and is likely to contribute to the high function and satisfaction levels that are often reported.
There is still much to learn and things to be improved, and as a result, the Oxford Partial Knee will continue to be developed to benefit the patients we see.
1 Goodfellow J , O’ConnorJ. The mechanics of the knee and prosthesis designJ Bone Joint Surg. [Br]1978;60-B:358–369. Google Scholar
2 Pandit H , JenkinsC, GillHS, et al.Unnecessary contraindications for mobile-bearing unicompartmental knee replacement. J Bone Joint Surg [Br]2011;93-B:622–628.CrossrefPubMed Google Scholar
3 Berend K , BerendM, DaluryD, et al.Consensus Statement of Indications and Contraindications for Medial Unicompartmental Knee Arthroplasty. J Surg Orthop Adv2015;24:252–256. Google Scholar
4 Tu Y , XueH, MaT, et al.Superior femoral component alignment can be achieved with Oxford microplasty instrumentation after minimally invasive unicompartmental knee arthroplasty. Knee Surgery, Sport Traumatol Arthrosc2016 May 25. (Epub ahead of print)CrossrefPubMed Google Scholar
5 Liddle AD , PanditH, O’BrienS, et al.Cementless fixation in Oxford Unicompartmental Knee Replacement: A multicentre study of 1000 knees. Bone Joint J2013;95-B:181–187.CrossrefPubMed Google Scholar
6 Fairbank T . Knee joint changes after meniscectomy. J Bone Joint Surg [Br]1948;30-B:664–670.PubMed Google Scholar
7 White S , LudkowskiP, GoodfellowJ. Anteromedial Osteoarthritis of the Knee. J Bone Joint Surg [Br]1991;73-B:582–586. Google Scholar
8 Bottomley NJ , KendrickBJL, RoutR, et al.The pattern of knee osteoarthritis presenting to a United Kingdom hospital [abstract]. British Orthopaedic Research Society . Annual Meeting; 2009. Google Scholar
9 Price AJ , ShortA, KellettC, et al.Ten-year in vivo wear measurement of a fully congruent mobile bearing unicompartmental knee arthroplastyJ Bone Joint Surg. [Br]2005;87-B:1493–1497. Google Scholar
10 Price AJ , SvärdU. A Second Decade Lifetable Survival Analysis of the Oxford Unicompartmental Knee Arthroplasty. Clin Orthop Relat Res2010;469:174–179.CrossrefPubMed Google Scholar
11 Price AJ , OppoldPT, MurrayDW, ZavatskyAB. Simultaneous in vitro measurement of patellofemoral kinematics and forces following Oxford medial unicompartmental knee replacement. J Bone Joint Surg [Br]2006;88-B:1591–1595.CrossrefPubMed Google Scholar
12 Baker PN , PetheramT, JamesonSS, et al.Comparison of patient-reported outcome measures following total and unicondylar knee replacements. J Bone Joint Surg [Br]2012;94-B:919–927. Google Scholar
13 Liddle A , PanditH, JudgeA, MurrayD. Patient-reported outcomes after total and unicompartmental knee arthroplasty: a study of 14,076 matched patients from the National Joint Registry for England and Wales. Bone Joint J2015;97-B:793–801.CrossrefPubMed Google Scholar
14 Rothwell A , TaylorJ, WirghtM, et al.13 Year Report. New Zeal Jt Regist2012:1–149. Google Scholar
15 Badawy M , EspehaugB, IndrekvamK, HavelinLI, FurnesO. Higher revision risk for unicompartmental knee arthroplasty in low-volume hospitals. Acta Orthop2014;85:342–347.CrossrefPubMed Google Scholar
16 Liddle AD , PanditH, JudgeA, MurrayDW. Optimal usage of unicompartmental knee arthroplasty: a study of 41,986 cases from the National Joint Registry for England and Wales. Bone Joint J2015;97-B:1506–1511.CrossrefPubMed Google Scholar
17 Liddle AD , JudgeA, PanditH, MurrayDW. Adverse outcomes after total and unicompartmental knee replacement in 101330 matched patients: A study of data from the National Joint Registry for England and Wales. Lancet2014;384:1437–1445. Google Scholar
18 Emerson RH , AlnachoukatiO, BarringtonJ, EnninK. The results of Oxford unicompartmental knee arthroplasty in the United States. Bone Joint J2016;98-B(10 Suppl B):34–40.CrossrefPubMed Google Scholar
19 Lisowski LA , MeijerLI, van den BekeromMPJ, PilotP, LisowskiAE. Ten to 15 year results of the Oxford Phase 3 mobile unicompartmental knee arthroplasty. Bone Joint J2016;98-B(10 Suppl B):41–47. Google Scholar
20 Jones GG , KottiM, CollinsR, et al.Gait comparison of unicompartmental and total knee arthroplasties with healthy controls. Bone Joint J2016;98-B(10 Suppl B):16–21.CrossrefPubMed Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attributions licence (CC-BY-NC), which permits unrestricted use, distribution, and reproduction in any medium, but not for commercial gain, provided the original author and source are credited.
