Patient-reported outcomes at 1 and 2 years after total hip and knee arthroplasty: what is the minimum required follow-up?

Purpose: The purpose of this study was to test for differences between patient-reported outcome measures (PROMs) at 1 and 2 years following total hip (THA) or knee (TKA) arthroplasty.

Methods: Between 2015 and 2016, n = 469 and n = 414 patients underwent THA and TKA, respectively. Demographic and PROMs data were collected at 1 and 2 years post-operatively. PROMs included Veterans Rand 12-item (VR-12), Hip Injury and Osteoarthritis Outcomes Score (HOOS) Pain subscore, HOOS-Physical Function Short-form (HOOS-PS), Knee Injury and Osteoarthritis Outcomes Score (KOOS) Pain subscore, and KOOS-Physical Function Short-form (KOOS-PS). Paired t tests assessed differences between groups. N = 298 (65.8%) and n = 240 (64%) patients followed-up at 1 year, and 205 (72% of 1-year responders) and 174 (76%) at 2 years in the THA and TKA cohorts, respectively.

Results: No statistically significant differences were observed between 1 and 2 years for HOOS pain (p = 0.445), HOOS-PS (p = 0.265), VR-12 PCS (p = 0.239), VR-12 MCS scores (p = 0.342) in THA and TKA cohorts [KOOS pain (p = 0.242), KOOS-PS (p = 0.088), VR-12 PCS (p < 0.2757), VR-12 MCS scores (p < 0.075)]. There were statistically significant baseline differences between responders and non-responders (patients lost to follow-up), but differences were small and not clinically relevant. PROMs were not significantly different between 1- and 2-year time points for THA and TKA. Minimal demographic or baseline differences between responders and non-responders suggest a representative sample.

Conclusion: These data support a minimum follow-up of 1 year for studies with PROMs as the primary outcome variable following THA and TKA.