Latent Factor Structure of Pain, Walking Ability, Patient-Reported Outcomes, and Physical Activity at 1 Month After Hospital Discharge in Patients Undergoing Total Knee Arthroplasty

Background: Patients who underwent total knee arthroplasty (TKA) are assessed for pain, walking ability, patient-reported outcome (PRO), and daily physical activity, which may be interrelated. However, the structure underlying these multidimensional assessments remains unclear. Therefore, this study examined the latent factors underlying these indicators and generated hypotheses about their associations. Methods: In total, 28 patients with knee osteoarthritis (KOA) who underwent TKA on one knee were included in this study. Assessments performed 1 month postdischarge included resting and walking pain, the 10 m walk test, the Knee Injury and Osteoarthritis Outcome Score (KOOS) as a patient-reported outcome measure (PROM), and physical activity measures (1-week mean daily step count and day-to-day step-count variability). Factor analysis was performed, with the number of factors fixed at three. Results: The Kaiser–Meyer–Olkin measure of sampling adequacy was 0.75, indicating “middling” sampling adequacy, and Bartlett’s test of sphericity was significant (p < 0.001). Factor 1 showed high factor loadings for resting pain, walking pain, and all five KOOS subscales (Pain, Symptoms, Activities of daily living, Quality of Life, and Sport and Recreation). Factor 2 showed high factor loadings for resting pain, walking time during the 10 m walk test, and step count during the 10 m walk test. Finally, Factor 3 showed high factor loadings for mean daily step count and day-to-day step-count variability. Collectively, the three factors explained 77.517% of the total variance. Furthermore, a moderate positive correlation was observed between Factors 2 and 3 (r = 0.469). Conclusions: The postoperative status of patients with KOA at 1 month postdischarge after TKA may be categorized according to subjective knee status, walking ability, and physical activity patterns. Furthermore, a moderate positive correlation was observed between Factor 2 (walking ability) and Factor 3 (physical activity patterns). The results of this exploratory preliminary study should be regarded as hypothesis-generating. The structure and associations between factors should be validated in future longitudinal investigations with larger sample sizes and a more balanced sex distribution.