Unicompartmental Knee Arthroplasty - An Option for Treating Unicompartmental Osteoarthritis
Unicompartmental knee arthroplasty (UKA) is one of several options in the treatment of unicompartmental knee osteoarthritis. Initial interest in UKA has been curtailed by the inferior long-term survivorship in comparison to total knee arthroplasty (TKA).1-4 Some interest in UKA persisted because of its purported functional superiority5 to TKA in terms of range of motion (ROM) and ease of rehabilitation and revision.6-8 A reduced risk of serious complications and infections when compared to TKA has also supported UKA as an attractive alternative.9 The improved cost effectiveness of UKA relative to TKA has further been claimed in recent literature.10,11
Minimally invasive surgery (MIS) has been linked to UKA, promoting an easier recovery, but the results of UKA with MIS surgery may be less favourable than through a standard approach12 and could risk compromise of implant position or fracture.13 Computer navigation may, however, improve accuracy when combined with MIS UKA. More recent literature has shown >90% survivorship beyond 10 years in carefully selected patients by experienced and appropriately trained surgeons.14 These results have been reproduced with both fixed and mobile-bearing designs.15-18
The ideal candidate for UKA is a thin patient with isolated medial compartment disease, mild varus deformity that is passively correctable, well preserved ROM, an intact ACL, and normal patellar and lateral compartments (Figures 1a-b). Certainly these indications have been expanded by some, including combined ACL reconstruction and UKA in young patients19,20 and osteonecrosis.21 Long-term outcomes in less-than-ideal patients are unknown and should be pursued with caution.22,23
Figure 1a. Preop AP (left) and lateral radiographs of left medial unicompartmental osteoarthritis of the knee
Figure 1b. Postoperative AP (left) and lateral medial UKA
Lateral UKA has shown less favourable outcomes in part due to implant positioning,24,25 as well as with the use of mobile-bearing implants that are more prone to instability in this compartment relative to medial UKA 26 (Figures 2a-b). Others have shown fixed-bearing lateral UKA to be a viable alternative to TKA in the appropriate patient.27
Figure 2a. AP (left) and lateral radiographs of a lateral UKA with dislocated bearing insert
Figure 2b. AP (left) and lateral radiographs of the failed UKA converted to a primary TKA
Inferior outcomes have been associated with low surgical volumes in the Swedish Knee Registry.28 The irony is that careful patient selection improves outcomes but reduces individual surgeon volumes. Only 10% of patients who are arthroplasty candidates meet the inclusion criteria for UKA. The solution to achieving excellent clinical outcomes – by maintaining high surgical volume and yet carefully selecting patients – has not been entirely resolved.
The notion that a UKA is half a TKA has been largely dispelled in the last decade.29 The techniques differ, and separate training in UKA and TKA has been more aggressively advocated.30
Better understanding of surgical technique – including maintaining a slight undercorrection of the deformity and achieving adequate polyethylene thickness and soft tissue balance – have contributed to improved outcomes.31-35 Introduction of newer implant designs and instrumentation such as computer navigation may improve future outcomes, but more evidence is needed.36-38
For the most part, excellent long-term outcomes of UKA have been reported in older, low-demand patients.9 More recently, with increasing demands for arthroplasty in younger patients, UKA has been advocated as a bone-conserving, time-buying procedure prior to TKA.39 One must be cautioned that the trade-off of bone conservation may be thinner polyethylene, which has been associated with earlier failure of UKA.40
The recent literature is conflicting as to whether the long-term outcomes of UKA are inferior in younger patients.1,41-43 The benefit of a more normal feeling knee that can later be revised with outcomes similar to a primary TKA is no doubt attractive. This notion is supported by data from the Swedish Registry44 but still remains controversial.45,46
Advocates of high tibial osteotomy (HTO) for unicompartmental disease would argue that UKA is not as durable as HTO and may be just as difficult to revise.47 Certainly most would agree that the mode of failure and the length of time that failure is undetected or left untreated determine the ease of converting either an HTO or UKA to a TKA.48 Polyethylene wear and tibial loosening and disease progression in other compartments of the knee remain a limiting factor for success in the long term49-51.
We can look forward to seeing continued use of UKA in appropriately selected younger patients linked with MIS surgery and computer navigation. The expanded indications will likely shift to more conservative indications. Regional arthroplasty centres will specialize in UKA to combine surgeon experience and volume to achieve optimum care.
- Koskinen, E., et al., Unicondylar knee replacement for primary osteoarthritis: a prospective follow-up study of 1,819 patients from the Finnish Arthroplasty Register. Acta Orthop, 2007. 78(1): p. 128-35.
- Furnes, O., et al., Failure mechanisms after unicompartmental and tricompartmental primary knee replacement with cement. J Bone Joint Surg Am, 2007. 89(3): p. 519-25.
- Amin, A.K., et al., Unicompartmental or total knee arthroplasty?: Results from a matched study. Clin Orthop Relat Res, 2006. 451: p. 101-6.
- Marmor, L., Unicompartmental knee arthroplasty. Ten- to 13-year follow-up study. Clin Orthop Relat Res, 1988(226): p. 14-20.
- Patil, S., et al., Can normal knee kinematics be restored with unicompartmental knee replacement? J Bone Joint Surg Am, 2005. 87(2): p. 332-8.
- Mullaji, A.B., A. Sharma, and S. Marawar, Unicompartmental knee arthroplasty: functional recovery and radiographic results with a minimally invasive technique. J Arthroplasty, 2007. 22(4 Suppl 1): p. 7-11.
- Johnson, S., P. Jones, and J.H. Newman, The survivorship and results of total knee replacements converted from unicompartmental knee replacements. Knee, 2007. 14(2): p. 154-7.
- Isaac, S.M., et al., Does arthroplasty type influence knee joint proprioception? A longitudinal prospective study comparing total and unicompartmental arthroplasty. Knee, 2007. 14(3): p. 212-7.
- Robertsson, O., Unicompartmental arthroplasty. Results in Sweden 1986-1995. Orthopade, 2000. 29 Suppl 1: p. S6-8.
- Slover, J., et al., Cost-effectiveness of unicompartmental and total knee arthroplasty in elderly low-demand patients. A Markov decision analysis. J Bone Joint Surg Am, 2006. 88(11): p. 2348-55.
- Soohoo, N.F., et al., Cost-effectiveness analysis of unicompartmental knee arthroplasty as an alternative to total knee arthroplasty for unicompartmental osteoarthritis. J Bone Joint Surg Am, 2006. 88(9): p. 1975-82.
- Luscombe, K.L., et al., Minimally invasive Oxford medial unicompartmental knee arthroplasty. A note of caution! Int Orthop, 2007. 31(3): p. 321-4.
- Yang, K.Y., S.J. Yeo, and N.N. Lo, Stress fracture of the medial tibial plateau after minimally invasive unicompartmental knee arthroplasty: a report of 2 cases. J Arthroplasty, 2003. 18(6): p. 801-3.
- Khanna, G. and B.A. Levy, Oxford unicompartmental knee replacement: literature review. Orthopedics, 2007. 30(5 Suppl): p. 11-4.
- Price, A.J., J.C. Waite, and U. Svard, Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop Relat Res, 2005(435): p. 171-80.
- Berger, R.A., et al., Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg Am, 2005. 87(5): p. 999-1006.
- Naudie, D., et al., Medial unicompartmental knee arthroplasty with the Miller-Galante prosthesis. J Bone Joint Surg Am, 2004. 86-A(9): p. 1931-5.
- Murray, D.W., J.W. Goodfellow, and J.J. O'Connor, The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br, 1998. 80(6): p. 983-9.
- Dervin, G.F., A.F. Conway, and P. Thurston, Combined anterior cruciate ligament reconstruction and unicompartmental knee arthroplasty: surgical technique. Orthopedics, 2007. 30(5 Suppl): p. 39-41.
- Pandit, H., et al., Combined anterior cruciate reconstruction and Oxford unicompartmental knee arthroplasty. J Bone Joint Surg Br, 2006. 88(7): p. 887-92.
- Myers, T.G., et al., Outcomes of total and unicompartmental knee arthroplasty for secondary and spontaneous osteonecrosis of the knee. J Bone Joint Surg Am, 2006. 88 Suppl 3: p. 76-82.
- Scott, R.D., Unicondylar arthroplasty: redefining itself. Orthopedics, 2003. 26(9): p. 951-2.
- Laskin, R.S., Unicompartmental knee replacement: some unanswered questions. Clin Orthop Relat Res, 2001(392): p. 267-71.
- Pennington, D.W., et al., Lateral unicompartmental knee arthroplasty: survivorship and technical considerations at an average follow-up of 12.4 years. J Arthroplasty, 2006. 21(1): p. 13-7.
- Scott, R.D., Lateral unicompartmental replacement: a road less traveled. Orthopedics, 2005. 28(9): p. 983-4.
- Emerson, R.H., Jr., Unicompartmental mobile-bearing knee arthroplasty. Instr Course Lect, 2005. 54: p. 221-4.
- Volpi, P., et al., Lateral unicompartimental knee arthroplasty: indications, technique and short-medium term results. Knee Surg Sports Traumatol Arthrosc, 2007. 15(8): p. 1028-34.
- Robertsson, O., et al., The routine of surgical management reduces failure after unicompartmental knee arthroplasty. J Bone Joint Surg Br, 2001. 83(1): p. 45-9.
- Grelsamer, R.P. and P. Cartier, A unicompartmental knee replacement is not "half a total knee": five major differences. Orthop Rev, 1992. 21(11): p. 1350-6.
- Lindstrand, A., et al., The introduction period of unicompartmental knee arthroplasty is critical: a clinical, clinical multicentered, and radiostereometric study of 251 Duracon unicompartmental knee arthroplasties. J Arthroplasty, 2000. 15(5): p. 608-16.
- Scott, R.D., Three decades of experience with unicompartmental knee arthroplasty: mistakes made and lessons learned. Orthopedics, 2006. 29(9): p. 829-31.
- Collier, M.B., et al., Patient, implant, and alignment factors associated with revision of medial compartment unicondylar arthroplasty. J Arthroplasty, 2006. 21(6 Suppl 2): p. 108-15.
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- Emerson, R.H., Jr., W.C. Head, and P.C. Peters, Jr., Soft-tissue balance and alignment in medial unicompartmental knee arthroplasty. J Bone Joint Surg Br, 1992. 74(6): p. 807-10.
- Jenny, J.Y., E. Ciobanu, and C. Boeri, The rationale for navigated minimally invasive unicompartmental knee replacement. Clin Orthop Relat Res, 2007. 463: p. 58-62.
- Hamilton, W.G., et al., Incidence and reasons for reoperation after minimally invasive unicompartmental knee arthroplasty. J Arthroplasty, 2006. 21(6 Suppl 2): p. 98-107.
- Cossey, A.J. and A.J. Spriggins, The use of computer-assisted surgical navigation to prevent malalignment in unicompartmental knee arthroplasty. J Arthroplasty, 2005. 20(1): p. 29-34.
- Repicci, J.A. and J.F. Hartman, Minimally invasive unicondylar knee arthroplasty for the treatment of unicompartmental osteoarthritis: an outpatient arthritic bypass procedure. Orthop Clin North Am, 2004. 35(2): p. 201-16.
- Cartier, P., J.L. Sanouiller, and R.P. Grelsamer, Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty, 1996. 11(7): p. 782-8.
- Gioe, T.J., et al., Knee arthroplasty in the young patient: survival in a community registry. Clin Orthop Relat Res, 2007. 464: p. 83-7.
- Price, A.J., et al., Oxford medial unicompartmental knee arthroplasty in patients younger and older than 60 years of age. J Bone Joint Surg Br, 2005. 87(11): p. 1488-92.
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- Robertsson, O., et al., Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand, 2000. 71(3): p. 262-7.
- Saldanha, K.A., et al., Revision of Oxford medial unicompartmental knee arthroplasty to total knee arthroplasty - results of a multicentre study. Knee, 2007. 14(4): p. 275-9.
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- Gill, T., et al., Revision total knee arthroplasty after failed unicompartmental knee arthroplasty or high tibial osteotomy. Clin Orthop Relat Res, 1995(321): p. 10-8.
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Reprinted with permission from the Summer 2008 issue of COA Bulletin