There is paucity of data for any direct prospective comparisons of UKA and TKA. Newman et al9 randomized 102 patients (mean age 69) suitable for either a UKA or TKA after arthrotomy. Patients in the UKA group showed less perioperative morbidity, regained knee movement more rapidly, and were discharged from the hospital sooner. At 5 years, two UKAs and one TKA had been revised; another TKA was radiologically loose. Pain relief was good in both groups, but the number of knees able to flex ? 120º was significantly higher in the UKA group (p < 0.001) and there were more excellent results in this group.
Ackroyd et al showed comparable survivorship in a non-randomized study between fixed-bearing UKA St Georg Sled and Kinemax knees at 10 years with better flexion in the UKA group.10 Amin at al11 also found higher postoperative range of motion in mobile-bearing UKA vs. matched cases of TKA. Walton et al12 also confirmed in a retrospective comparative study that patients with UKA had better activity and Oxford knee scores with increased return to sport than age, gender, and preop activity matched controls undergoing TKA. Willis-Owen et al13 have recently shown in a case control study that both medial and lateral UKA patients scores were indistinguishable from normal age- and gender-specific controls and clearly superior to TKA using the validated TKQ.14
Fixed vs. Mobile
A major consideration for the surgeon is whether to consider fixed- or mobile-bearing UKA.
In randomized studies of medial UKA, Li et al,15 Gleeson et al,16 and Confalonieri et al17 were unable to show any difference in functional outcomes of fixed-bearing vs. mobile-bearing UKA. Gleeson did find that the pain component of the Bristol Knee Score was significantly better for the fixed-bearing group (St Georg Sled) and that there was a higher early revision rate in the Oxford group. Conversely, the improved mobile-bearing kinematics may favour the latter in longer-term survivorship based on retrieval studies.18,19 Further, Li15 described improved kinematics of mobile-bearing (Oxford) UKA compared with patients treated with fixed-bearing (Miller-Galante) with a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05).
The functional results and outcomes for younger patients with fixed and mobile-bearing UKA would appear to be acceptable. Pennington et al20 reported on 41 consecutive patients 60 years of age or younger with Miller-Galante fixed-bearing UKR. At mean follow-up of 11 years, the Hospital for Special Surgery (HSS) score was excellent in 93% of cases. Although nine knees had progression of arthritis in the unresurfaced compartment, none of these knees were revised, and none of the patients had deterioration in the HSS Score, yielding 11-year survivorship of 92%.
Price et al21 reported the experience for the Oxford knee related to patient’s age and showed the 10-year all-cause survival for patients in the under 60 years of age group was 91% (95% CI 12), with mean HSS score at 10-year follow-up of 94 out of 100. Indeed, it is this author’s observation that some of the greatest benefits lie with active patients in their 50s who can benefit from the permissive activities of a well functioning UKA without sacrificing future conversion to TKA (Figures 1a,b).
Figure 1a. Postoperative AP radiograph of a 57-year-old male 7 years after mobile-bearing UKA for medial osteoarthritis of the knee
Figure 1b. Postoperative lateral radiograph of the same patient
What about Revision?
Of particular interest for the young active patient is the potential need for future revision. Several authors have confirmed that the majority of revisions of well performed UKA can be to primary components22-24 with comparable results to primary TKA. The evidence would also suggest that contrary to proximal tibia osteotomy survivorship, UKA shows greater longevity in a relatively undercorrected coronal alignment so as to minimize contralateral compartment wear (Figure 2). The benefits of smaller surgical exposures with UKA seem to cause less scarring in the joint and pretibial region with significantly less postoperative patella baja,25 easing exposure for later revisions. Robertsson et al26 surveyed Swedish patients operated on between 1981 and 1995 and found no difference in proportions of satisfied patients whether they had primarily been operated on with a TKA or a medial UKA, although patients revised from medial UKA were more satisfied than patients revised from primary TKA.
Figure 2. Standing AP radiographs 2 years post left medial mobile-bearing UKA in a 53-year-old man, showing preservation of the patient’s natural coronal tibiofemoral alignment.
Registry data show the usage of UKA to be at 7-8 % of all knee arthroplasty - significantly less than the 25% suggested by high-volume and designing surgical centres. For the surgeon treating medial or, less commonly, lateral unicompartment OA, there is clearly wide variation in the adoption and utilization of this technique. Nonetheless, the reported experience supports Scott,27 who claimed “Unicompartmental knee arthroplasty is the right operation for the right patient when performed by the right surgeon using the right surgical technique.”
Reprinted with permission from the Spring 2010 issue of COA Bulletin
- Berger RA, Nedeff DD Barden RM, et al. Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year follow-up. Clin Orthop 1999 Oct;(367):50-60.
- Murray DW, Goodfellow JW, O'Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br 1998 Nov;80(6):983-9.
- Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br 2001 Mar;83(2):191-4.
- Beard DJ, Murray DW, Rees JL, Price AJ, Dodd CA. Accelerated recovery for unicompartmental knee replacement-a feasibility study. Knee 2002 Sep;9(3):221-4.
- Reilly KA, Beard DJ, Barker KL, et al. Efficacy of an accelerated recovery protocol for Oxford unicompartmental knee arthroplasty--a randomised controlled trial. Knee 2005 Oct;12(5):351-7.
- Noble PC, Gordon MJ, Weiss JM, et al. Does total knee replacement restore normal knee function? Clin Orthop 2005 Feb;(431):157-65.
- Noble PC, Conditt MA, Cook KF, et al. The John Insall Award: Patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop 2006 Nov;452:35-43.
- Harrysson OL, Robertsson O, Nayfeh JF. Higher cumulative revision rate of knee arthroplasties in younger patients with osteoarthritis. Clin Orthop 2004 Apr;(421):162-8.
- Newman JH, Ackroyd CE, Shah NA. Unicompartmental or total knee replacement? Five-year results of a prospective, randomised trial of 102 osteoarthritic knees with unicompartmental arthritis. J Bone & Joint Surg - Br 1998 Sep;80(5):862-5.
- Ackroyd CE, Whitehouse S., Newman JH, Joslin CC. A comparative study of the medial St Georg sled and kinematic total knee arthroplasties. Ten-year survivorship. J Bone & Joint Surg- Br 2002 Jul;84(5):667-72.
- Amin AK, Patton JT, Cook RE, Gaston M, Brenkel IJ. Unicompartmental or total knee arthroplasty?: Results from a matched study. Clin Orthop 2006 Oct;451:101-6.
- Walton NP, Jahromi I, Lewis PL, Dobson PJ, Angel KR, Campbell DG. Patient-perceived outcomes and return to sport and work: TKA versus mini-incision unicompartmental knee arthroplasty. J Knee Surg 2006 Apr;19(2):112-6.
- Willis-Owen CA, Brust K, Alsop H, Miraldo M, Cobb JP. Unicondylar knee arthroplasty in the UK National Health Service: an analysis of candidacy, outcome and cost efficacy. Knee 2009 Dec;16(6):473-8.
- Weiss JM, Noble PC, Conditt MA, et al. What functional activities are important to patients with knee replacements? Clin Orthop 2002 Nov;(404):172-88.
- Li MG, Yao F, Joss B, et al. Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics. Knee 2006 Oct;13(5):365-70.
- Gleeson RE, Evans R, Ackroyd CE, Webb J, Newman JH. Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study. Knee 2004 Oct;11(5):379-84.
- Confalonieri N, Manzotti A, Pullen C, Confalonieri N, Manzotti A, Pullen C. Comparison of a mobile with a fixed tibial bearing unicompartimental knee prosthesis: a prospective randomized trial using a dedicated outcome score. Knee 2004 Oct;11(5):357-62.
- Psychoyios V, Crawford RW, O'Connor JJ, Murray DW. Wear of congruent meniscal bearings in unicompartmental knee arthroplasty: a retrieval study of 16 specimens. J Bone Joint Surg Br 1998 Nov;80(6):976-82.
- Collier MB, Engh CA Jr, McAuley JP, et al. Factors associated with the loss of thickness of polyethylene tibial bearings after knee arthroplasty. J Bone Joint Surg Am 2007 Jun;89(6):1306-14.
- Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg Am 2003 Oct;85-A(10):1968-73.
- Price AJ, Dodd CA, Svard UG, et al. Oxford medial unicompartmental knee arthroplasty in patients younger and older than 60 years of age. J of Bone & Joint Surg - Br 2005 Nov;87(11):1488-92.
- McAuley JP, Engh GA, Ammeen DJ. Revision of failed unicompartmental knee arthroplasty. Clin Orthop 2001 Nov;(392):279-82.
- Levine WN, Ozuna RM, Scott RD, Thornhill TS. Conversion of failed modern unicompartmental arthroplasty to total knee arthroplasty. J Arthroplasty 1996 Oct;11(7):797-801.
- Saldanha KA, Keys GW, Svard UC, et al. Revision of Oxford medial unicompartmental knee arthroplasty to total knee arthroplasty - results of a multicentre study. Knee 2007 Aug;14(4):275-9.
- Weale AE, Murray DW, Newman JH, Ackroyd CE. The length of the patellar tendon after unicompartmental and total knee replacement. J Bone Joint Surg - Br 1999 Sep;81(5):790-5.
- Robertsson O, Dunbar M, Pehrsson T, Knutson K, Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand 2000 Jun;71(3):262-7.
- Scott RD. Unicondylar arthroplasty: redefining itself. Orthopedics 2003 Sep;26(9):951-2.