Femoral Coronal Malalignment is Associated With Failure in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: Femur-first (FF) technique for mobile-bearing medial unicompartmental knee arthroplasty (UKA) has been described as an alternative to tibia-first (TF) technique. The aim of this study was to compare the radiographic results in UKAs using FF or TF techniques and their influence on failure rates. METHODS: We retrospectively reviewed 288 UKAs with a minimum 2-year follow-up. There were 147 knees in the TF and 141 knees in the FF cohorts. Alignment parameters and overhang were assessed as outliers and far outliers. The mean follow-up was 6 years (range, 2 to 16), the mean age was 63 years (range, 27 to 92), and 45% of patients were women. Univariate and multivariate statistical analyses were carried out with Cox regression models. RESULTS: There were 13 and 6 revisions in the TF and FF cohorts, respectively. The FF had lower rates of femoral coronal alignment (FCA) or femoral sagittal alignment outliers compared to the TF (5.7% versus 19%, P = .011). Tibial coronal alignment and tibial sagittal alignment did not significantly differ between the techniques (22.7% in FF versus 29.9% in TF, P = .119). Overhang outliers did not differ significantly between the groups. Younger age was associated with a higher revision rate (P = .006), while FF versus TF, sex, body mass index, and postoperative mechanical axis did not show statistically significant associations. In multivariate analysis, FCA outliers and younger age were significantly associated with revision. CONCLUSIONS: The FF technique in mobile-bearing UKA resulted in fewer FCA outliers compared to TF. Despite improved knee alignment with the FF technique, FCA outliers and younger age were associated with a higher revision rate, independent of technique.

A proposed modification to the Kellgren and Lawrence classification for knee osteoarthritis using a compartment-specific approach.

Purpose: Since Kellgren and Lawrence (KL) originally classified knee osteoarthritis, several authors have reported varying levels of reliability and a lack of uniformity in the use of this classification system. We propose several modifications to the KL classification including the use of a compartment-specific approach that we hypothesize will lead to a better understanding of knee OA while maintaining an adequate interobserver and intraobserver reliability. Methods: We propose the addition of the lateral and skyline-view radiographs to the standard anteroposterior (AP) and lateral projections in the evaluation. Also suggest a more precise definition of the evaluated parameters; the addition of the subchondral cancellous bone as parameter of evaluation; and the assessment of medial tibiofemoral compartment (MTFC), lateral tibiofemoral compartment (LTFC) and patellofemoral compartment (PFC) separately resulting in a compartment-specific KL staging score rather than a single overall KL score. Six evaluators (two knee surgeons, two radiologists and two knee fellows) used the modified KL classification to classify 230 randomly selected knees on two separate occasions. Reliabilities were assessed by calculating Krippendorff's ⍺ coefficients. Results: Two hundred and ten knees were included for final evaluation and analyses (53% left knees; 65% females; mean age 56 years old). Average interobserver reliability was moderate for all compartments (0.51 for the MTFC; 0.51 for the LTFC; and 0.56 for the PFC). Average intraobserver reliability was substantial for all compartments (0.63 for the MTFC; 0.65 for the LTFC; and 0.7 for the PFC). Experienced evaluators showed a higher intraobserver reliability than less-experienced evaluators. Conclusions: A modified compartment-specific KL classification enables a practical and detailed description of knee OA involvement and demonstrates acceptable interobserver and intraobserver reliability. Level of Evidence: Level III.