Medial Unicompartmental Arthroplasty of the Knee

Jason M. Jennings, MD, DPT; Lindsay T. Kleeman-Forsthuber, MD; Michael P. Bolognesi, MD


J Am Acad Orthop Surg. 2019;27(5):166-176. 

In This Article

Survival Data and Outcomes

Considerable discrepancy exists between cohort and registry studies on UKA survival and clinical outcomes, with registries consistently showing worse outcomes.[29] One explanation is that registries include multiple different implants performed by surgeons with varying levels of clinical experience. In addition, many of the clinical outcome studies have been performed by design surgeons. A systematic review of cohort and registry studies found that the average 10-year survival for UKA was 90.5% in cohort studies but only 84.1% in registries.[29] The 15-year survival was 87% and 69.6%, respectively. While registries provide critical information on trends over time, cohort studies may allow better understanding of how specific implants perform at single-center institutions by higher volume surgeons.

Cohort Survival Data of Unicompartmental Knee Arthroplasty

Overall, cohort studies have shown promising long-term results for UKA implants (Table 2). In a cohort study, Pandit et al[30] showed 10-year survival of 94% and 15-year survival of 91% in their series of 1,000 medial UKAs with an MB implant. Similarly, Lisowski et al[27] showed 15-year survival of 90.6% with revision occurring at mean of 5.7 years. Another study by Foran et al[48] demonstrated 20-year survival of 90% in their series of 62 FB implants. Several other studies have shown high 10-year survival ranging from 90.6% to 96% with wide variability in the indications for revision (Table 2).

Cohort Survival Data of Unicompartmental Knee Arthroplasty Versus Total Knee Arthroplasty

There is great interest in outcomes of UKA compared with those of TKA because TKA is often the alternative surgical procedure considered for patients. Lyons et al[3] compared 5,606 TKAs with 279 UKAs and found higher clinical outcome scores in UKA patients at 2-year follow-up. Survival was slightly higher in the TKA group with 5-year survival of 98% and 95% for TKA and UKA, respectively, and 10-year survival of 95% and 90%.[3] Another study by Lim et al[1] demonstrated comparable results in their series of UKA and TKA patients with better functional scores in the UKA group, but higher overall revision rate of 6.3% for UKA compared with 3% for TKA. The UKA group experienced lower medical complications and had lower incidence of infection and wound complications than the TKA group.[1] Lombardi et al[2] also reviewed their series of UKA and TKA patients and found better early knee range of motion, shorter hospital stay (1.4 days versus 2.2 days), and higher Knee Society functional scores in the UKA group. No difference between groups was found in regard to return to work or recreational activities at final follow-up.[2] Although these studies demonstrate short- and midterm benefits with UKA, few studies compare long-term clinical outcomes between UKA and TKA.

Registry Survival Data

National registries vary widely in how UKA outcomes are reported with some providing more specific information than others (Table 3). The Australian database with 46,094 UKAs contains the largest population of UKAs with some of the longest follow-up.[31] They report 14.6% UKA revision rate at 10 years and 21% revision at 15 years, with the most common indications for revision being aseptic loosening (43.5%), progression of osteoarthritis (29.4%), and unexplained pain (9.5%).[31] Risk factors for earlier revision include female gender and younger age. The lowest revision rate was seen in patients aged 65 to 74 years with the 10-year survival of 87%.[31] The National Joint Registry (NJR) for England, Wales and Northern Ireland database reports data on FB (31.3% of UKAs) and MB (67.5%) implants separately.[32] The 10-year survival for FB implant is slightly higher at 89.2% compared with 87.6% for MB implant.[32] The overall risk for revision of UKAs is 2.9 times higher than what is observed for TKA. The New Zealand registry reports UKA survival of 89% at 10 years and 83.3% at 15 years.[33] They recognized better performance for certain implants with the lowest revision rate seen in the uncemented Oxford (Zimmer Biomet) with 10-year survival of 96%. The Norwegian database reports very low UKA survival of 79% at 10 years and 72% at 20 years.[34]

In a review of the Finnish registry, Niinimäki et al[35] compared 4,713 UKAs with 83,511 cemented TKAs. They found lower survival in the UKA group at all time points with the 5-year survival of 89.4% and the 15-year survival of 69.6% compared with those in TKA at 96.3% and 88.7%, respectively. The higher risk for revision in the UKA group remained elevated even after controlling for age and gender.[35] The US Medicare database has demonstrated similar results.[36] Revision rate for the UKA group was 4.7% at 5 years compared with 2.0% for TKA, with no improvement in risk after controlling for covariates.[36] As registry reporting continues to improve, there will hopefully be better insight into the reason for these high failure rates and how UKA compares with TKA outcomes long-term.