Modern Indications, Results, and Global Trends in the Use of Unicompartmental Knee Arthroplasty and High Tibial Osteotomy in the Treatment of Isolated Medial Compartment Osteoarthritis
Authors’ Disclosure Statement: The authors report no actual or potential conflict of interest in relation to this article.
In this review, we evaluate the modern indications, subjective outcome scores, and survivorship results of unicompartmental knee arthroplasty (UKA) and high tibial osteotomy (HTO) in the treatment of isolated medial compartment degeneration of the knee. In addition, in a thorough review of the literature, we evaluate global trends in the use of both methods. In our evaluation of articles, we note that inclusion criteria are relatively broader for UKA than for HTO, where age and body mass index should be considered before HTO surgery in order to optimize clinical outcome and survivorship results. Exact thresholds for UKA inclusion have been studied, but there is no clear definition. Both methods have good to excellent subjective outcome scores. Expected 10-year survivorship results are in favor of UKA (90%) over HTO (75%). However, controlled data directly comparing both methods are lacking. The broad range of UKA inclusion criteria and good to excellent subjective and survivorship results have led to an increase in UKA use among Western practices, whereas use of HTO in patients with isolated single-compartment osteoarthritis has been decreasing.
An increasingly number of patients with symptomatic isolated medial unicompartmental knee osteoarthritis (OA) are too young and too functionally active to be ideal candidates for total knee arthroplasty (TKA). Isolated medial compartment OA occurs in 10% to 29.5% of all cases, whereas the isolated lateral variant is less common, with a reported incidence of 1% to 7%.1,2 In 1961, Jackson and Waugh3 introduced the high tibial osteotomy (HTO) as a surgical treatment for single-compartment OA. This procedure is designed to increase the life span of articular cartilage by unloading and redistributing the mechanical forces over the nonaffected compartment. Unicompartmental knee arthroplasty (UKA) was introduced in the 1970s as an alternative to TKA or HTO for single-compartment OA.
UKA is a joint resurfacing procedure in which the affected degenerative compartment is treated with an implanted prosthesis and the nonaffected compartments are preserved (Figure 1).
Since the introduction of these methods, there has been debate about which patients are appropriate candidates for each procedure. Improved surgical techniques and implant designs have led surgeons to reexamine the selection criteria and contraindications for these procedures. Furthermore, given the increasing popularity and use of UKA, the question arises as to whether HTO still has a role in clinical practice in the surgical treatment of medial OA of the knee.
To clarify current ambiguities, we review the modern indications, subjective outcome scores, and survivorship results of UKA and HTO in the treatment of isolated medial compartment degeneration of the knee. In addition, in a thorough review of the literature, we evaluate global trends in the use of both methods.
High Tibial Osteotomy for Medial Compartment OA
Indications
Before the introduction of TKA and UKA for single-compartment OA, surgical management consisted of HTO. When the mechanical axis is slightly overcorrected, the medial compartment is decompressed, ensuring tissue viability and delaying progressive compartment degeneration.
Decompression is established with multiple techniques, including opening-wedge HTO (OWHTO) (Figure 2), closing-wedge HTO (CWHTO) (Figure 3), and chevron and dome osteotomies.
The current controlled data are limited and do not favor one technique over another.4,5
Traditionally, HTO is indicated for young (age <60 years), normal-weight, active patients with radiographic single-compartment OA.6 The knee should be stable and have good range of motion (ROM; flexion >120°), and pain should be localized to the tibiofemoral joint line.
Over the past few decades, numerous authors have reported similar inclusion criteria, clarifying their definition. This definition should be further refined in order to optimize survivorship and clinical outcomes.
Confirming age as an inclusion criterion for HTO, Trieb and colleagues7 found that the risk of failure was significantly (P = .046) higher for HTO patients older than 65 years than for those younger than 65 years (relative risk, 1.5). This finding agrees with findings of other studies, which suggests that, in particular, young patients benefit from HTO.8-11
Moreover, there is a clear relation between HTO survival and obesity. In a study of 159 CWHTOs, Akizuki and colleagues12 reported that preoperative body mass index (BMI) higher than 27.5 kg/m2 was a significant risk factor for early failure. Using BMI higher than 30 kg/m2 as a threshold, Howells and colleagues9 found significantly inferior Knee Society Score (KSS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) results for the obese group 5 years after HTO.
Radiographic evidence of severe preoperative compartment degeneration has been associated with early conversion to TKA. Flecher and colleagues11 and van Raaij and colleagues13 both concluded the best long-term survival grades are achieved in HTO patients with mild compartment OA (Ahlbäck14 grade I). The question then becomes whether these patients should be treated nonoperatively instead.15,16The literature supports strict adherence to inclusion criteria in the selection of a potential HTO candidate. Age, BMI, and the preoperative state of OA should be taken into account in order to optimize clinical outcome and survivorship results in patients about to undergo HTO.
Outcomes
Multiple authors have described or compared the midterm or long-term results of the various surgical HTO techniques. Howells and colleagues9 noted overall survival rates of 87% (5 years after CWHTO) and 79% (10 years after CWHTO). Over the 10-year postoperative period, there was significant deterioration in clinical outcome scores and survivorship. Others authors have had similar findings.17-19 van Raaij and colleagues13 found that the 10-year probability of survival after CWHTO was 75%. In 455 patients who underwent lateral CWHTO, Hui and colleagues8 found that 5-year probability of survival was 95%, 10-year probability was 79%, and 15-year probability was 56%. Niinimäki and colleagues10 used the Finnish Arthroplasty Register to report HTO survivorship at a national level. Using conversion to TKA as a cutoff, they noted 5-year survivorship of 89% and 10-year survivorship of 73%. To our knowledge, 2 groups, both in Japan, have reported substantially higher 15-year survival rates: 90%12 and 93%.20 The authors acknowledged that their results were significantly better than in other countries and that Japanese lifestyle, culture, and body habitus therefore require further investigation. At this time, it is not possible to compare their results with Western results.
