When Should a Unicompartmental Knee Arthroplasty Be Considered?

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Chapter 87 When Should a Unicompartmental Knee Arthroplasty Be Considered?

The first unicompartmental knee arthroplasty (UKA), the Polycentric, was released in 1968 by Gunston,¹ after which UKA became a viable treatment option for selected patients with unicompartmental osteoarthritis. Initial results for UKA in the 1970s were somewhat unimpressive, perhaps suggestive of the learning curve associated with the introduction of a novel technology.² After publication of improved UKA results in the 1980s and continued refinement of patient selection, technology, and surgical procedure, Kozinn and Scott³ published what have now become referred to as the “classic” indications for UKA.⁴ These inclusion and exclusion criteria were selected for an elderly, nonobese patient with noninflammatory medial compartment arthritis and intact ligaments. Although an important and widely quoted publication, the development of the classic indications for UKA was largely based on observational series often using survivorship as the sole outcome metric. Survivorship of UKA demonstrated equivalent survivorship in the first decade between UKA and total knee arthroplasty (TKA), but worse survivorship for UKA in the second decade. Thus, UKA was initially seen as a definitive procedure that would not need to be revised in an elderly patient.

Interest in UKA has been renewed since the 1990s associated with newer designs and minimally invasive surgery (MIS).⁵ This renewed interest may also be associated with the unmet burden of middle-aged patients with unicompartmental osteoarthritis of the knee.⁶ Without the underpinnings of strong evidenced-based indications, UKA is increasingly being recommended as a bridging procedure for younger patients with isolated osteoarthritis of the medial or lateral compartment,⁷ in addition to a definitive procedure in the older patient. Furthermore, some authors have expanded the indications to include patients with anterior cruciate ligament (ACL) deficiency and patients with significant patella-femoral arthritis. The variability and lack of consensus of indications for UKA have led to a reported range of potential candidates for UKA in a knee arthroplasty population of between 5% and 30%.⁸ Despite the fact that UKA preceded TKA and the renewed interest in UKA, the cumulative revision rates for UKA have not improved in Sweden since the 1970s. This is in distinction to TKA, which has seen a significant reduction in cumulative revision rate (CRR) over the same period.

OPTIONS

Surgical options for patients with unicompartmental osteoarthritis of the knee include proximal tibial osteotomy, TKA, chondral transplant with or without corrective osteotomy, and arthroscopic debridement.

Proximal tibial osteotomy has similar indications for a UKA, including lack of significant flexion contracture with intact range of motion. The results generally demonstrate 80% survivorship at 5 years and 60% survivorship at 10 years.¹⁰ The result, however, is often cosmetically unsatisfying and questions remain regarding the results of salvage procedures after UKA, such as TKA.¹¹ The traditional method, and that with the most evidence, is the closing wedge osteotomy, as described by Coventry.¹² Opening wedge osteotomy and opening wedge hemicallostosis osteotomy have become increasing popular.^13,¹⁴ Although long-term data are lacking, the techniques are appealing in that they tend to be more “physiologic” with respect to joint biomechanics because the osteotomy is usually performed below the tubercle, and they have been suggested to be more reproducible and reduce the incidence of adverse effects such as reversed tibial slope, intra-articular fracture, patellar baja, and medial proximal tibial overhang with metaphyseal-diaphyseal mismatch^11,¹⁵ (Level of Evidence IV). Proximal tibial osteotomy is generally reserved for younger patients with higher levels of demand (Level of Evidence V).

TKA has similar or better survivorship to UKA in the first decade and better survivorship in the second decade.^16,¹⁷ As such, TKA is more reliable and is appropriate for older patients who may outlive their UKA. TKA has similar satisfaction rates to medial UKA (82%).¹⁸ TKA has the major advantage over UKA of being able to accommodate major ligament releases and resections, including the ACL and PCL, as well as significant bone resection to address deformity. The survivorship of TKA is adversely affected by younger age and obesity.¹⁹^–²²

Fresh osteochondral allografting has been recommended for the treatment of large focal defects. Matched osteochondral surfaces are transplanted from the donor to the recipient host, often with an unloading osteotomy. Reasonable success rates have been reported, but this technique has limitations in that it requires immunosuppressive drugs, carries the risk for disease transfer, and requires a large catchment area to find suitable donors.^23,²⁴ This technique has had limited success at a few centers around the world. Chondral transplant has been advocated for focal defects in one of the femoral condyles.²⁵^–²⁷ Although it has been possible to grow chondrocytes in vitro, results of transplanted chondrocytes have been mixed because of the large biomechanical forces to which the immature chondral cells are exposed.

Arthroscopic debridement of the knee for unicompartmental arthroplasty has been shown in general to be ineffective ²⁸ (Level of Evidence I). However, evidence suggests that arthroscopic debridement can relieve symptoms temporarily for patients with mechanical symptoms, such as catching or locking, associated with arthritis²⁸ (Level of Evidence I).

EVIDENCE

Unfortunately, UKA studies in the literature with high levels of evidence are limited (Table 87-1). In a randomized trial, Newman and colleagues²⁹ compared 52 TKAs with 50 fixed-bearing UKAs. All patients were selected for surgery as candidates for UKA using the classic indications of intact cruciate ligaments: “normal” other compartments, flexion deformity less than 15 degrees, and varus/valgus less than 15 degrees. The mean age at surgery was 69 years. Patients in the UKA group had less morbidity, shorter length of stays, and better range of motion both in the short and the long term (109.3 vs. 102.6 degrees). Two failures occurred in the UKA group and one in the TKA group, with an additional pending failure. The number of knees able to flex greater than 120 degrees was proportionally greater in the UKA group. Pain relief was similar in both groups using the Bristol Knee Score. The authors conclude that UKA gives better results than TKA at 5 years in patients who meet the conservative criteria for UKA (Level of Evidence I).

TABLE 87-1 Summary of Studies with Levels of Evidence Greater Than II for Unicompartmental Knee Arthroplasty

Amin and coworkers ¹⁶ report on a matched study of 54 consecutive UKAs compared with 54 consecutive TKAs. The two groups of patients were matched for age, sex, body mass index, preoperative range of movement, and preoperative Knee Society scores. The mean follow-up period was 59 months in both groups. Classic selection criteria were used for the UKA group. The UKA was mobile bearing. The survivorship for the UKA group at 5 years was 88% compared with 100% for the TKA group. Subjective outcomes were similar for both groups. The range of motion was greater for the UKA group. This study differed from Newman and colleagues’²⁹ work in that the patients with TKA were not candidates for UKA, and the UKA was mobile bearing (Level of Evidence III).

Stukenborg-Colsman and investigators ³⁰ completed a prospective, randomized trial comparing UKA with proximal tibial osteotomy. The selection criteria for the patients were medial unicompartmental osteoarthritis, varus malalignment less than 10, flexion contraction less than 15 degrees, minimal ligament instability, and age older than 60 years. The osteotomies were performed according to Coventry’s¹² technique and the UKAs were fixed bearing. Thirty-two patients received osteotomies and 28 received UKAs with mean follow-up period of 7.5 years. The UKA group had fewer intraoperative and postoperative complications, had a greater percentage of patients with good or excellent results on the Knee Society Score, and had a better 7- to 10-year survivorship rate of 77% compared with 60%. The authors conclude that UKA offered better long-term results compared with Coventry-type proximal tibial osteotomy in patients older than 60 years (Level of Evidence I).

UKA has experienced a resurgence in interest since the last 1990s partly because of its adaptability to MIS. Despite the popularity of MIS, most data to support its use are anecdotal or of a low quality of evidence. Furthermore, reported MIS results are most often associated with a specific implant of interest, hence the results may not be generalizable to all implant/instrument types. Carlsson and coauthors ³¹

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