Age-Related Differences in Pain, Function, and Quality of Life Following Primary Total Knee Arthroplasty: Results From a FORCE-TJR (Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement) Cohort.

Background: The impact of age on patient outcomes after total knee arthroplasty (TKA) remains controversial. Age has shown no effect on outcome in some studies, while others have reported better or worse outcome in younger patients. The aims of this study were to determine the differences in pain, function, and quality of life (QoL) reported 1 year after TKA across different age groups.

Methods: A prospective, multicenter cohort of 11,602 unilateral primary TKA patients was evaluated. Demographic data, comorbid conditions, and patient-reported outcome measures including the knee injury and osteoarthritis outcome score (KOOS), KOOS-12, KOOS Joint Replacement, and Short-Form health survey (12-item) were collected preoperatively and at 1-year postoperatively. Descriptive statistics were generated, stratified by age [<55 years (younger adult), 55 to 64 years (older adult), 65 to 74 years (early elder), and ≥ 75 years (late elder)], and differences in pain, function, and QoL among the 4 age groups were evaluated using Chi-square and Kruskal-Wallis tests. Multivariate regression models with 95% confidence interval were performed to determine if age was predictive for KOOS pain and function scores.

Results: Prior to surgery, younger patients (<55 years) reported worse KOOS pain (39), function (50), and QoL (18) scores with poor mental health score (47) than other older patient groups. The mean preoperative score differences across the age groups in the KOOS total score (9.37), KOOS pain (11.61), KOOS-12 pain (10.14), and KOOS/KOOS-12 QoL (12.60) reached the calculated minimal clinically important difference. At 1 year after TKA, younger patients (<55 years) reported lower KOOS pain, function, and QoL scores when compared to older patients (≥ 75 years). The differences in 1-year postop scores among the 4 age groups (ranging from 4.0 to 12.2) reached the minimal clinically important difference for pain (10.4) and QoL (12.2). Younger patients (<55 years) achieved higher baseline to 1-year pain (36.8 points), function (30.3 points), and QoL (40.7 points) score changes when compared to older patients aged ≥ 75 years. Although statistically significant, the differences in score changes among the age groups were clinically irrelevant. The multivariate regression analyses showed that age was a significant predictor for pain, but not for function at 1 year where KOOS pain score was predicted to be higher (less pain) (β = 6.17; 95% confidence interval 4.12- 8.22) (P < .001) in older patients (≥ 75 years) when compared to younger patients (<55 years).

Conclusion: A TKA provides a dramatic improvement in pain, function, and QoL in all age groups. However, there are age-related clinically significant differences in preoperative pain, QoL, and mental health and in final postoperative pain and QoL scores with younger patients (<55 years) reporting more pain, less QoL, and worse preoperative mental health. The patient-reported outcome measure data presented here can be used clinically to improve shared decision-making and patient expectations prior to TKA.