Age-Related Functional Decline Following Total Knee Arthroplasty: Risk Adjustment is Mandatory

Background: Patient-reported outcome measures (PROMs) are being used increasingly to determine the success of total knee arthroplasty (TKA). Our goal is to investigate whether advanced age is associated with lower PROM scores. Methods: We used our hospital's TKA registry to examine the relationship between age and PROMs in all patients 50-90 years of age who underwent unilateral or simultaneous bilateral primary TKA between 2007 and 2011 with a primary diagnosis of osteoarthritis. All 5 domains of the Knee Injury and Arthritis Outcomes Score (KOOS) and the Lower Extremity Activity Scale (LEAS) at baseline, 2 years, and 5 years were collected. The association between age and PROM score was assessed by piecewise linear regression using generalized estimating equations, adjusting for demographics, comorbidity, and baseline score. Results: Significant nonlinear relationships among age, KOOS subdomains, and LEAS were found. The placement of the age spline knot was at 70 years for KOOS Symptom and 68 years for KOOS Pain, KOOS Activities of Daily Living (ADL), and LEAS. The KOOS Symptom domain showed a significant worsening between 2-year and 5-year follow-up (P <.05) as patients got older. Conclusion: We found an age-related decline in KOOS Pain, KOOS Symptom, KOOS ADL, and LEAS scores. The best fitting spline knots were at 68 (KOOS Pain, KOOS ADL, and LEAS) and 70 years (KOOS Symptoms), respectively. This demonstrates that there is a critical age at which functional decline begins regardless of the quality of the TKA surgery. Our findings will help surgeons accurately guide patient expectations after TKA based on age. Level of Evidence: Level II, prognostic study.