Variation in KOOS JR improvement across total knee implant designs: a cohort study from Michigan Arthroplasty Registry Collaborative Quality Initiative.

Background and purpose:  Arthroplasty registries report revision risk, but patient-reported outcomes may also measure implant performance. We aimed to evaluate (i) change in patient-reported outcome measures (PROMs) across multiple total knee arthroplasty (TKA) designs in a regional registry, (ii) the association of patellar resurfacing on the change in PROMs, and (iii) the variation in PROMs change within implants with or without patellar resurfacing.

Methods:  This is a cohort of primary TKAs from Michigan Arthroplasty Registry Collaborative Quality Initiative (MARCQI) performed between January 1, 2017 and September 30, 2021. The dependent measure was change in KOOS JR. Independent variables were implant name and patellar resurfacing. Multivariate modeling adjusted for patient-level factors. A previous report suggests a change of 23 points in KOOS JR as clinically relevant in achieving acceptable pain/function levels. A clinically relevance ratio (CRR) of those achieving the threshold of 23 points to the overall group was calculated for each implant.

Results:  18 implant designs met the inclusion criteria. There were 51,606 cases with complete preoperative and postoperative KOOS JR matched pairs. There was variation in improvement from preoperative to postoperative unadjusted KOOS JR scores across implant designs (P < 0.001), ranging from 18.7 (95% confidence interval [CI] 16.8-20.6) to 27.0 (CI 24.9-29.2). Patellar resurfacing resulted in greater KOOS JR improvement 1.0 (CI 0.5-1.5, P < 0.001). Of the cases with resurfaced patellae, the CRR was 50.2% (CI 49.7-50.7). For cases without resurfaced patellae, the CRR was 47.2% (CI 45.9-48.5). The association of implant design persisted whether the patella was resurfaced or not, evident in the adjusted mean change in KOOS JR (P < 0.001), ranging from 20.1 (CI 17.6-22.6) to 25.5 (CI 24.3-26.7) for resurfaced and from 17.0 (CI 13.9-20.1) to 23.3 (CI 20.3-26.2) for not resurfaced, and the CRR difference (P < 0.001), ranging from 45.8% (CI 42.5-48.6) to 55.8% (CI 50.4-60.8) for resurfaced and from 37.9% (CI 27.4-44.7) to 51.4% (CI 43.9-56.6) for not resurfaced.

Conclusion:  Implant design and patellar resurfacing both show an association with KOOS JR improvement. Variations in implant design persist whether the patella is resurfaced or not. Implant selection and patellar resurfacing may be associated with patient outcomes.