Oxford Unicompartmental Knee Replacement: Literature Review

Abstract

Oxford unicompartmental knee replacement surgery (Biomet Orthopedics, Inc, Warsaw, Ind) provides excellent long-term results according to numerous published series,^1-16 with 10-year survivorship ranging from 91% to 100% and 15-year survivorship of 93%. Few knee prostheses can rival these results. Most of these cohorts included patients with anteromedial- or medial-specific disease, although some cohorts included patients with lateral-specific disease. Also, most cohorts were performed in patients with a mean age of >60 years, with a wide range of ages including patients in their 30s to 90s. Almost all of the arthroplasties were performed in patients with osteoarthritis, and some were performed in patients with avascular necrosis.

An extensive literature search was performed using all known medical reference databases and revealed a total of 54 articles on Oxford unicompartmental knee replacement surgery. Sixteen articles present survivorship data and are included in this review. The survivorship data are shown in the Table.

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Results

Goodfellow et al¹ presented the early 2- to 5-year follow-up on the first 103 Oxford unicompartmental knee replacement surgeries performed in 1988. The mean age of the patients was 70 years (range: 54-86 years). Survivorship was 91%. The patients underwent nine revisions, five due to component loosening, three due to meniscal-bearing dislocation, and one due to disease progression to the other compartments. Results were encouraging, considering that 27 (26%) of the 103 patients underwent lateral compartment Oxford unicompartmental knee replacement surgery. The investigators noted that the absence of the anterior cruciate ligament (ACL) was associated with a significantly greater incidence of failure. In fact, in 37 knees lacking a normal ACL, 6 (16.2%) failed compared with only 3 (4.8%) failures in 63 patients with ACLs. This was statistically significant (P<0.019). The investigators concluded that the procedure could be recommended for knees with severe unicompartmental osteoarthritis in which all the ligaments remain intact. Also, in patients who underwent lateral Oxford unicompartmental knee replacement surgery, 2 of the 27 arthroplasties failed because of bearing dislocation. It is expected that the results will be supported in future studies because of the mechanics and anatomy of the lateral compartment; bearing dislocation is commonly observed if Oxford unicompartmental knee replacement surgery is performed on the lateral side. Currently, Oxford unicompartmental knee replacement surgery is not recommended for lateral compartment disease.

In 1993, Carr et al² presented the results of 121 medial-specific Oxford unicompartmental knee replacement surgeries in patients with a mean age of 69 years (range: 57–81 years). Average follow-up was 3.8 years, and the investigators reported a 99% survivorship. The investigators recommended the following selection criteria for the Oxford unicompartmental knee replacement: (1) the presence of a functioning ACL; (2) fully correctable deformity; and (3) full thickness of articular cartilage remaining in the lateral compartment. Only one knee required revision for a loose tibial component. These results were comparable with those of tricompartmental knee arthroplasty and better than those of high tibial osteotomy for isolated medial unicompartmental disease.

In 1998, Murray et al³ published the Oxford medial unicompartmental arthroplasty 10-year survival study in the Journal of Bone and Joint Surgery British Edition. They reported on the outcome of 143 Oxford unicompartmental knee prostheses implanted for anteromedial osteoarthrosis in patients with normal ACLs. Only one patient was lost to follow-up. Mean follow-up was 7.6 years (range: 6-14 years), and the investigators reported a 10-year survivorship of 98%. There were no failures from polyethylene wear or aseptic loosening of the tibial component.

In 2000, Vorlat et al⁴ presented a 5-year follow-up study on the Oxford unicompartmental knee prosthesis in 41 patients and reported a 93% survivorship. Three revisions were performed (two for progression of lateral compartment disease and one for component malalignment). In two of the four patients who had a poor or moderate result, the indications were not strictly followed, and the investigators postulated that adhering to the Oxford group’s strict indications would reduce the number of poor results.

Svard and Price⁵ published a survival analysis of 124 Oxford unicompartmental knee replacements performed in Sweden. The mean age of the patients was 70 years (range: 51-86 years). The indication for surgery was anteromedial osteoarthritis. Three independent surgeons performed the procedures in a nonteaching hospital. All patients had normal ACLs, correctable varus deformity, and full thickness cartilage in the lateral compartment as described by Carr et al.² The average follow-up was 12.5 years (range: 10-15.6 years). The investigators reported a 4.8% revision rate with a 95% survivorship at 10 years. The investigators again concluded that in carefully selected patients, the implant is a reliable treatment for anteromedial osteoarthrosis of the knee.

In 2002, Emerson et al⁶ reported on a comparison of mobile-bearing versus fixed-bearing unicompartmental knee replacements. There were 51 knees in the fixed-bearing group and 50 knees in the mobile bearing group (using the Oxford unicompartmental knee prosthesis). Average follow-up was 7 years for the mobile-bearing Oxford implant. Survivorship at 11 years was 99% for the Oxford implant and 93% for the fixed-bearing implant. The fixed-bearing knee implants failed significantly more often because of tibial component failure. In contrast, tibial component failures did not occur with the mobile-bearing implants. Mobile-bearing implants did not show a trend to fail because of progression of disease in the lateral compartment. Emerson’s series was the first series performed in the United States using Oxford unicompartmental knee replacement surgery.

Keys et al⁷ on reported 40 Oxford unicompartmental knee replacements in patients with a mean age of 68 years (range: 40-80 years) for medial osteoarthritis. Average follow-up was 7.5 years (range: 6-10 years), with no patients requiring revision. Survivorship was 100% at 10 years.

Rajasekhar et al⁸ reported on 135 Oxford unicompartmental knee replacements for medial compartment osteoarthritis in patients with a mean age of 71 years (range: 53-88 years). Patients were followed for 2 to 12 years, with a 10-year survivorship of 94%. The investigators reported that study results were comparable with those of the Oxford group and noted the importance of appropriate patient selection and good surgical technique.

The Oxford group continued to publish its results and, in 2005, Langdown et al⁹ reported on 29 Oxford unicompartmental knee prostheses implanted in patients with spontaneous osteonecrosis of the knee. The average age of patients was 71 years (range: 46-85 years). Patients were followed for an average of 5.2 years (range: 1-13 years) with a 10-year survivorship of 100%. Langdown et al⁹ compared their group of 29 Oxford unicompartmental knee replacements implanted for spontaneous osteonecrosis of the knee with a similar group of 28 Oxford unicompartmental knee replacements implanted for primary osteoarthrosis. They showed no difference in results and concluded that the use of the Oxford medial unicompartmental knee replacement for spontaneous focal osteonecrosis of the knee will give similar results to those obtained when used for patients with primary osteoarthrosis at short- to medium-term follow-up.

Price et al¹⁰ reported on a series of Oxford unicompartmental knee replacements implanted in patients <60 years and >60 years of age and compared the two groups. Fifty-two patients were <60 years of age, and 512 patients were >60 years of age. They noted a 10-year survivorship of 91% in patients <60 and a 96% survivorship in patients >60. Of the 512 Oxford knees implanted in patients >60 years of age, 20 revisions were performed, with the greatest number of revisions secondary to lateral compartment osteoarthrosis. The investigators concluded that for patients aged >50 years, should not be considered a contraindication to the procedure.

Verdonk et al¹¹ from Belgium, reported on a 2- to 14-year follow-up of the Oxford unicompartmental knee replacement. They treated 97 patients for medial compartment disease and 10 patients for lateral compartment disease. The mean age of the patients was 61 years. The investigators reported an overall survivorship of 86%. Of the 14 revisions performed, the most common cause of failure was component loosening.

Price et al¹² from Sweden presented long-term clinical results of 439 medial Oxford unicompartmental knee replacements and reported a 15-year survival rate of 93%. The investigators specifically addressed the size of the bearings in millimeters to assess whether survivorship would depend on bearing thickness. Ten-year survival rates for bearings <6 mm and >6 mm demonstrated no statistical difference (95% and 94%, respectively). The investigators concluded that an independent center can achieve excellent long-term clinical and survival results and that the survival of the implant was not reduced by the use of a thin polyethylene bearing.

Another independent 10-year survivorship analysis of the Oxford unicompartmental knee replacement was performed by Vorlat et al.¹³ The investigators presented data on 149 medial Oxford unicompartmental knee replacements. The mean age of patients was 66 years, and follow-up was 5.5 years. The investigators reported a cumulative survivorship rate of 82% at 10 years and concluded that Oxford unicompartmental knee prosthesis should be the first choice of implant for medial unicompartmental osteoarthrosis in patients <65 years of age. The investigators also reported that patients with previous high tibial osteotomy had less successful outcomes and recommended that the Oxford unicompartmental knee not be implanted in patients after previous osteotomy.

Treatment of younger patients with medial compartment disease remains controversial. Kort et al¹⁴ reported on 46 Oxford unicompartmental knee prostheses implanted in patients <60 years. Patients were followed from 2 to 6 years postoperatively, and survivorship was 96%. The investigators concluded that unicompartmental knee arthroplasty is an important option for medial compartment disease in patients <60 years of age. They also noted that obesity was related to higher risk of complications, early failure of the prostheses, and technical difficulties.

Minimally invasive techniques have gained widespread popularity. Luscombe et al¹⁵ reported on a prospective series of 78 Oxford medial unicompartmental knee replacement surgeries using the minimally invasive surgical incision, the phase 3 Oxford unicompartmental knee replacement, in 78 patients followed for 2 years postoperatively. They noted no statistically significant difference at 2-year follow-up compared with the nonminimally invasive technique using the same device. Overall survivorship was 95%.

Pandit et al¹⁶ also reported on phase 3 minimally invasive surgery Oxford medial unicompartmental knee replacement surgery. Their series included 132 unicompartmental knee replacements, with an average follow-up of 7 years (range: 1-8 years). Survival rate at 7 years was 97.3%. The investigators concluded that the minimally invasive phase 3 Oxford unicompartmental knee replacement is a reliable and effective procedure.

Conclusion

In carefully selected patients, the Oxford unicompartmental knee replacement has demonstrated excellent long-term survivorship and predictable reliability, not only as reported by the designers from Oxford, but also as reported by many independent centers across Europe and the United States.

The importance of adhering to strict indications for the use of this particular prosthesis cannot be overemphasized. The indications include an intact ACL, bone-on-bone osteoarthrosis of the medial compartment, and patients who have correctable deformity.

References

1. Goodfellow JW, Kershaw CJ, D’A Benson MK, O’Connor JJ. The Oxford knee for unicompartmental osteoarthritis. The first 103 cases. J Bone Joint Surg. 1988; 70:692-701.
2. Carr A, Keyes G, Miller R, O’Connor J, Goodfellow J. Medial unicompartmental arthroplasty: A survival study of the Oxford meniscal knee. Clin Orthop Relat Res. 1993; 295:205-213.
3. Murray DW, Goodfellow JW, O’Connor JJ. The Oxford medial unicompartmental arthroplasty. A ten-year survival study. J Bone Joint Surg. 1998; 80:983-989.
4. Vorlat P, Verdonk R, Schauvlieghe H. The Oxford unicompartmental knee prosthesis: a 5-year follow-up. Knee Surg Sports Traumatol Arthrosc. 2000; 8:154-158.
5. Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br. 2001; 83:191-194.
6. Emerson RH, Hansborough T, Reitman RD, Rosenfeldt W, Higgins LL. Comparison of a mobile with a fixed-bearing unicompartmental knee implant. Clin Orthop Relat Res. 2002; 404:62-70.
7. Keys GW, Ul-Abiddin Z, Toh EM. Analysis of first forty Oxford medial unicompartmental knee replacements from a small district hospital in UK. Knee. 2004; 11:375-377.
8. Rajasekhar C, Das S, Smith A. Unicompartmental knee arthroplasty. 2- to 12-year results in a community hospital. J Bone Joint Surg Br. 2004; 86:983-985.
9. Langdown AJ, Pandit H, Price AJ, et al. Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee. Acta Orthop. 2005; 76:688-692.
10. Price AJ, Dodd CA, Svard UG, Murray DW. Oxford medial unicompartmental knee arthroplasty in patients younger and older than 60 years of age. J Bone Joint Surg Br. 2005; 87:1488-1492.
11. Verdonk R, Cottenie D, Almqvist KF, Vorlat P. The Oxford unicompartmental knee prosthesis: a 2-14 year follow-up. Knee Surg Sports Traumatol Arthros. 2005; 13:163-166.
12. Price AJ, Waite JC, Svard U. Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop Relat Res. 2005; 435:171-180.
13. Vorlat P, Putzeys G, Cottenie D, et al. The Oxford unicompartmental knee prosthesis: an independent 10-year survival analysis. Knee Surg Sports Traumatol Arthrosc. 2006; 14:40-45.
14. Kort NP, van Raay JJ, van Horn JJ. The Oxford phase III unicompartmental knee replacement in patients less than 60 years of age. Knee Surg Sports Traumatol Arthrosc. October 2006; Epub.
15. Luscombe KL, Lim J, Jones PW, White SH. Minimally invasive Oxford medial unicompartmental knee arthroplasty. A note of caution! Int Orthop. August 2006; Epub.
16. Pandit H, Jenkins C, Barker K, Dodd CA, Murray DW. The Oxford medial unicompartmental knee replacement using a minimally-invasive approach. J Bone Joint Surg. 2006; 88:54-60.

Authors

Drs Khanna and Levy are from the Department of Orthopedics, the University of Minnesota, St Paul, Minn.

Dr Khanna has no financial interests in the materials mentioned herein. Dr Levy is a consultant for the sponsor and has received financial contributions from them in the past 12 months.