Early Recovery Trajectories Identify Patients at Risk for Outcome Deterioration During Postoperative Years One to Five After Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: The purpose of our study was to determine whether early postoperative pain and functional assessments could identify clinically meaningful recovery trajectories that forecast deterioration in patient-reported outcomes during postoperative years one to five after medial unicompartmental knee arthroplasty (mUKA).

METHODS: We studied 207 patients who underwent primary mUKA between January 2016 and January 2021. Pain and function were assessed using the Numerical Rating Scale (NRS) and Oxford Knee Score (OKS) preoperatively and at postoperative one, three, and six months (early recovery window), as well as at postoperative one, two, and five years (postoperative years one to five recovery window). Growth mixture modeling was used to derive NRS and OKS trajectories separately. Early trajectories were subsequently linked to trajectories during postoperative years one to five using posterior probability-weighted modified Poisson regressions with robust standard errors, and effect estimates are presented as adjusted relative risks (aRR).

RESULTS: The two early NRS trajectories were identified: slow analgesia (17.9%) and rapid analgesia (82.1%). Early OKS trajectories were classified as rapid improvement (37.2%), rapid catch-up (37.2%), and slow improvement (25.6%). During postoperative years one to five, trajectories comprised pain progression (34.8%) versus low-pain maintenance (65.2%), and functional decline (24.6%) versus functional maintenance (75.4%). Transition probabilities were highly concentrated. Among patients who had early slow analgesia, the expected probability of pain progression during postoperative years one to five was 88.2%, whereas 70.4% of those who had early slow improvement transitioned to functional decline during postoperative years one to five. In the bridging models, early slow analgesia was associated with pain progression (aRR 2.41, P < 0.001). Compared with early slow improvement, rapid improvement (aRR 0.25, P < 0.001) and rapid catch-up (aRR 0.16, P < 0.001) were associated with a lower risk of functional decline.

CONCLUSION: After mUKA, unfavorable early pain and functional recovery trajectories identify patients at increased risk of deterioration in patient-reported outcomes during postoperative years one to five. Early postoperative monitoring may provide a practical warning signal to guide closer surveillance and targeted postoperative management.