Authors’ Disclosure Statement: The authors report no actual or potential conflict of interest in relation to this article.
In large studies, the failure modes of lateral unicompartmental knee arthroplasty (UKA) are usually presented in combination with medial UKA, which is mainly due to low surgical frequency of lateral UKA. Because lateral UKA differs from medial UKA in anatomic and kinematic characteristics, failure modes of lateral UKA should not be presented in combination with medial UKA. Therefore, we performed a systematic review to assess failure modes in lateral UKA and compared failure modes in cohort studies with those found in registry-based studies. A search performed in PubMed, Embase, and Cochrane identified 25 studies (23 cohort studies and 2 registry-based studies) that were eligible in presenting failure modes in lateral UKA. Most common failure modes in lateral UKA were progression of osteoarthritis (OA; 29%), aseptic loosening (23%), and bearing dislocation (10%). In cohort studies, progression of OA was more common (36%) than bearing dislocation (17%) and aseptic loosening (16%), while in the registry-based studies, aseptic loosening (28%) was more common than progression of OA (24%) and bearing dislocation (5%). In conclusion, progression of OA is the most common failure mode in lateral UKA. In the future, both cohort studies and registry-based studies should report the failure modes of medial and lateral UKA separately.
In 1975, Skolnick and colleagues1 introduced unicompartmental knee arthroplasty (UKA) for patients with isolated unicompartmental osteoarthritis (OA). They reported a study of 14 UKA procedures, of which 12 were at the medial and 2 at the lateral side. Forty years since this procedure was introduced, UKA is used in 8% to 12% of all knee arthroplasties.2-6 A minority of these procedures are performed at the lateral side (5%-10%).6-8
The considerable anatomical and kinematical differences between compartments9-14 make it impossible to directly compare outcomes of medial and lateral UKA. For example, a greater degree of femoral roll and more posterior translation at the lateral side in flexion9,10,13 can contribute to different pattern and volume differences of cartilage wear.15 Because of these differences, and because of implant design factors and lower surgical volume, lateral UKA is considered a technically more challenging surgery compared to medial UKA.12,16,17
Since isolated lateral compartment OA is relatively scarce, current literature on lateral UKA is limited, and most studies combine medial and lateral outcomes to report UKA outcomes and failure modes.3,4,18-20 However, as the UKA has grown in popularity over the last decade,2,21-25 the number of reports about the lateral UKA also has increased. Recent studies reported excellent short-term survivorship results of the lateral UKA (96%-99%)26,27 and smaller lateral UKA studies reported the 10-year survivorship with varying outcomes from good (84%)14,28-30 to excellent (94%-100%).8,31,32 Indeed, a recent systematic review showed survivorship of lateral UKA at 5, 10, and 15 years of 93%, 91%, and 89%, respectively.33Because of the differences between the medial and lateral compartment, it is important to know the failure modes of lateral UKA in order to improve clinical outcomes and revision rates. We performed a systematic review of cohort studies and registry-based studies that reported lateral UKA failure to assess the causes of lateral UKA failure. In addition, we compared the failure modes in cohort studies with those found in registry-based studies.
Patients and Methods
Search Strategy and Criteria
Databases of PubMed, Embase, and Cochrane (Cochrane Central Register of Clinical Trials) were searched with the terms “knee, arthroplasty, replacement,” “unicompartmental,” “unicondylar,” “partial,” “UKA,” “UKR,” “UCA,” “UCR,” “PKA,” “PKR,” “PCA,” “prosthesis failure,” “reoperation,” “survivorship,” and “treatment failure.” After removal of duplicates, 2 authors (JPvdL and HAZ) scanned the articles for their title and abstract to assess eligibility for the study.
The full text of these eligible articles was further viewed and useful studies were selected using the inclusion and exclusion criteria. The references of these articles were scanned for additional studies and national registries (Figure).
Inclusion criteria were: (I) English language articles describing studies in humans published in the last 25 years, (II) retrospective and prospective studies, (III) featured lateral UKA, (IV) OA was indication for surgery, and (V) included failure modes data. The exclusion criteria were studies that featured: (I) only a specific group of failure (eg,bearing dislocations only), (II) previous surgery in ipsilateral knee (high tibial osteotomy, medial UKA), (III) acute concurrent knee diagnoses (acute anterior cruciate ligament rupture, acute meniscal tear), (IV) combined reporting of medial and lateral UKA, or (V) multiple studies with the same patient database.
Data Collection
All studies that reported modes of failure were used in this study and these failure modes were noted in a datasheet in Microsoft Excel 2011 (Microsoft).
The data of failures of lateral UKA are presented in Table 1 and are divided in cohort studies and registry-based studies. The final failure mode rates were presented in percentages (Table 2).
Statistical Analysis
For this systematic review, statistical analysis was performed with IBM SPSS Statistics 22 (SPSS Inc.). We performed chi square tests and Fisher’s exact tests to assess a difference between cohort studies and registry-based studies with the null hypothesis of no difference between both groups. A difference was considered significant when P < .05.
Results
Through the search of the databases, 1294 studies were identified and 26 handpicked studies were added. Initially, based on the title and abstract, 184 of these studies were found eligible.
After reviewing the full text of these articles, 25 studies (23 cohort studies and 2 registry-based studies) met the inclusion criteria and were included for the analysis of lateral UKA failure (Figure).
A total of 366 lateral UKA failures were included. The most common failure modes were progression of OA (29%), aseptic loosening (23%), and bearing dislocation (10%). Infection (6%), instability (6%), unexplained pain (6%), and fractures (4%) were less common causes of failure of lateral UKA (Table 2).
One hundred fifty-five of these failures were reported in the cohort studies. The most common modes of failure were OA progression (36%), bearing dislocation (17%) and aseptic loosening (16%). Less common were infection (10%), fractures (5%), pain (5%), and other causes (6%). In registry-based studies, with 211 lateral UKA failures, the most common modes of failure were aseptic loosening (28%), OA progression (24%), other causes (12%), instability (10%), pain (7%), bearing dislocation (5%), and polyethylene wear (4%) (Table 2).
When pooling cohort and registry-based studies, progression of OA was significantly more common than aseptic loosening (29% vs 23%, respectively; P < .01). It was also significantly more common in the cohort studies (36% vs 16%, respectively; P < .01) but no significant difference was found between progression of OA and aseptic loosening in registry-based studies (24% and 28%, respectively; P = .16) (Table 2).
When comparing cohort with registry-based studies, progression of OA was higher in cohort studies (36% vs. 24%; P < .01). Other failures modes that were more common in cohort studies compared with registry-based studies were bearing dislocation (17% vs 5%, respectively; P < .01) and infections (10% vs 3%, P < .01). Failure modes that were more common in registry-based studies than cohort studies were aseptic loosening (28% vs 16%, respectively; P < .01), other causes (12% vs 6%, respectively, P = .02), and instability (10% vs 1%, respectively, P < .01) (Table 2).
