In an attempt to compare the different survival rates of the various HTO techniques, Schallberger and colleagues21 conducted a retrospective study of OWHTOs and CWHTOs. At median follow-up of 16.5 years, comparative survival rates showed a trend of deterioration. Although data were limited, there were no significant differences in survival or functional outcome between the 2 techniques. In a recent randomized clinical trial, Duivenvoorden and colleagues5 compared these techniques’ midterm results (mean follow-up, 6 years). Clinical outcomes were not significantly different. There were more complications in the OWHTO group and more conversions to TKA in the CWHTO group. Considering these results, the authors suggested OWHTO without autologous bone graft is the best HTO treatment strategy for medial gonarthritis with varus malalignment of <12°.
The HTO results noted in these studies show a similar deteriorating trend; expected 10-year survivorship is 75%. Although modern implants and surgical techniques are being used, evidence supporting use of one surgical HTO method over another is lacking.
UKA for Medial Compartment OA
Indications
Since it was first introduced in the 1970s, use of UKA for single-compartment OA has been a subject of debate. The high failure rates reported at the time raised skepticism about the new treatment.22 Kozinn and Scott23 defined classic indications and contraindications. Indications included isolated medial or lateral compartment OA or osteonecrosis of the knee, age over 60 years, and weight under 82 kg. In addition, the angular deformity of the affected lower extremity had to be <15° and passively correctable to neutral at time of surgery. Last, the flexion contracture had to be <5°, and ideal ROM was 90°. Contraindications included high activity, age under 60 years, and inflammatory arthritis. Strict adherence led to improved implant survival and lower revision rates. Because of improved surgical techniques, modern implant designs, and accumulating experience with the procedure, the surgical indications for UKA have expanded. Exact thresholds for UKA inclusion, however, remain unclear.
The modern literature is overturning the traditional idea that UKA is not indicated for patients under age 60 years.23 Using KSS, Thompson and colleagues24 found that younger patients did better than older patients 2 years after UKA using various types of implants. Analyzing survivorship results, Heyse and colleagues25 concluded that UKA can be successful in patients under age 60 years and reported a 15-year survivorship rate of 85.6% and excellent outcome scores. Other authors have had similar findings.26-28
Evaluating the influence of weight, Thompson and colleagues24 found obese patients did not have a higher revision rate but did have slower progression of improvement 2 years after UKA. Cavaignac and colleagues29 concluded that, at minimum follow-up of 7 years (range, 7-22 years), weight did not influence UKA survivorship. Other authors30-33 have found no significant influence of BMI on survival.
Reports on preoperative radiographic parameters that can potentially influence UKA results are limited. In 113 medial UKAs studied by Niinimäki and colleagues,34 mild medial compartment degeneration, seen on preoperative radiographs, was associated with significantly higher failure rates. The authors concluded that other treatment options should be favored in the absence of severe isolated compartment OA.
Although the classic indications defined by Kozinn and Scott23 have yielded good to excellent UKA results, improvements in implants and surgical techniques35-38 have extended the criteria. The modern literature demonstrates that age and BMI should not be used as criteria for excluding UKA candidates. Radiographically, there should be significant isolated compartment degeneration in order to optimize patient-reported outcome and survivorship.
Outcomes
Improved implant designs and modern minimally invasive techniques have effected a change in outcome results and a renewed interest in implants. Over the past decade, multiple authors have described the various modern UKA implants and their survivorship. Reports published since UKA was introduced in the 1970s show a continual increase in implant survival. Koskinen and colleagues,39 using Finnish Arthroplasty Register data on 1819 UKAs performed between 1985 and 2003, found 10-year survival rates of 81% for Oxford implants (Zimmer Biomet), 79% for Miller-Galante II (Zimmer Biomet), 78% for Duracon (Howmedica), and 53% for PCA unicompartmental knee (Howmedica). Heyse and colleagues25 reported 10- and 15-year survivorship data (93.5% and 86.3%, respectively) for 223 patients under age 60 years at the time of their index surgery (Genesis Unicondylar implant, Smith & Nephew), performed between 1993 and 2005. KSS was good to excellent. Similar numbers in cohorts under age 60 years were reported by Schai and colleagues26 using the PFC system (Johnson & Johnson) and by Price and colleagues27 using the medial Oxford UKA. Both groups reported excellent survivorship rates: 93% at 2- to 6-year follow-up and 91% at 10-year follow-up. The outcome in older patients seems satisfactory as well. In another multicenter report, by Price and colleagues,40 medial Oxford UKAs had a 15-year survival rate of 93%. Berger and colleagues41 reported similar numbers for the Miller-Galante prosthesis. Survival rates were 98% (10 years) and 95.7% (13 years), and 92% of patients had good to excellent Hospital for Special Surgery knee scores.