Although various modern implants have had good to excellent results, the historical question of what type of UKA to use (mobile or fixed-bearing) remains unanswered. To try to address it, Peersman and colleagues42 performed a systematic review of 44 papers (9463 knees). The 2 implant types had comparable revision rates. Another recent retrospective study tried to determine what is crucial for implant survival: implant design or surgeon experience.43 The authors concluded that prosthetic component positioning is key. Other authors have reported high-volume centers are crucial for satisfactory UKA results and lower revision rates.44-46
Results of these studies indicate that, where UKAs are being performed in volume, 10-year survivorship rates higher than 90% and good to excellent outcomes can be expected.
UKA vs HTO
Cohort studies that have directly compared the 2 treatment modalities are scarce, and most have been retrospective. In a prospective study, Stukenborg-Colsman and colleagues47 randomized patients with medial compartment OA to undergo either CWHTO (32 patients) with a technique reported by Coventry48 or UKA (28 patients) with the unicondylar knee sliding prosthesis, Tübingen pattern (Aesculap), between 1988 and 1991. Patients were assessed 2.5, 4.5, and 7.5 years after surgery. More postoperative complications were noted in the HTO group. At 7- to 10-year follow-up, 71% of the HTO group and 65% of the UKA group had excellent KSS. Mean ROM was 103° after UKA (range, 35°-140°) and 117° after HTO (range, 85°-135°) during the same assessment. Although differences were not significant, Kaplan-Meier survival analysis was 60% for HTO and 77% for UKA at 10 years. Results were not promising for the implants used, compared with other implants, but the authors concluded that, because of improvements in implant designs and image-guided techniques, better long-term success can be expected with UKA than with HTO.
In another prospective study, Börjesson and colleagues49 evaluated pain during walking, ROM, British Orthopaedic Association (BOA) scores, and gait variables at 1- and 5-year follow-up. Patients with moderate medial OA (Ahlbäck14 grade I-III) were randomly selected to undergo CWHTO or UKA (Brigham, DePuy). There were no significant differences in BOA scores, ROM, or pain during walking between the 2 groups at 3 months, 1 year, and 5 years after surgery. Gait analysis showed a significant difference in favor of UKA only at 3 months after surgery. At 1- and 5-year follow-up, no significant differences were noted.
To clarify current ambiguities, Fu and colleagues50 performed a systematic review of all (11) comparative studies. These studies had a total of 5840 (5081 UKA, 759 HTO) patients. Although ROM was significantly better for the HTO group than the UKA group, the UKA group had significantly better functional results. Walking after surgery was significantly faster for the UKA group. The authors suggested the difference might be attributed to the different postoperative regimens—HTO patients wore a whole-leg plaster cast for 6 weeks, and UKA patients were allowed immediate postoperative weight-bearing. Regarding rates of survival and complications, pooled data showed no significant differences. Despite these results, the authors acknowledged the limitation of available randomized clinical trials and the multiple techniques and implants used. We share their assertion that larger prospective controlled trials are needed. These are crucial to getting a definitive answer regarding which of the 2 treatment strategies should be used for isolated compartment OA.
Current Trends in Use of UKA and HTO
Evaluation of national registries and recent reports showed a global shift in use of both HTO and UKA. Despite the lack of national HTO registries, a few reports have described use of TKA, UKA, and HTO in Western populations over the past 2 decades. Using 1998-2007 data from the Swedish Knee Arthroplasty Register, W-Dahl and colleagues51 found a 3-fold increase in UKA use, whereas HTO use was halved over the same period. Niinimäki and colleagues52 reported similar findings with the Finnish National Hospital Discharge Register. They noted a steady 6.8% annual decrease in osteotomies, whereas UKA use increased sharply after the Oxford UKA was introduced (Phase 3; Biomet). These findings are consistent with several reports from North America. In their epidemiologic analysis covering the period 1985-1990, Wright and colleagues53 found an 11% to 14% annual decrease in osteotomies among the elderly, compared with an annual decrease of only 3% to 4% among patients younger than 65 years. Nwachukwu and colleagues54 recently compared UKA and HTO practice patterns between 2007 and 2011, using data from a large US private payer insurance database. They noted an annual growth rate of 4.7% in UKA use, compared with an annual 3.9% decrease in HTO use. Furthermore, based on their subgroup analysis, they speculated there was a demographic shift toward UKA, as opposed to TKA, particularly in older women. Bolognesi and colleagues55 investigated further. Evaluating all Medicare beneficiaries who underwent knee arthroplasty in the United States between 2000 and 2009, they noted a 1.7-fold increase in TKA use and a 6.2-fold increase in UKA use. As there were no substantial changes in patient characteristics over that period, the authors hypothesized that a possible broadening of inclusion criteria may have led to the increased use of UKA.