Temporal Relationship Among Pain, Fear, and Motor Function After Total Knee Arthroplasty: An Exploratory Study

BACKGROUND: Pain, fear, and motor function are interrelated. This study aimed to clarify their causal relationships by examining longitudinal changes from the preoperative to the acute postoperative period after total knee arthroplasty (TKA). METHODS: This exploratory prospective observational study included 27 inpatients (mean age, 74.1 years [SD = 9.9]; 40 knees). Pain, fear and motor function were assessed preoperatively and 1 and 2 weeks postoperatively. At each time point, rest pain, motion pain, fear of motion, and kinematic parameters of knee movement (velocity, angle, surplus null and spectral entropy) were measured. The cross-lagged panel model was used to estimate causal relationships. RESULTS: Longitudinal analysis revealed that reduced movement at 1 week predicted greater rest pain at 2 weeks, and higher rest pain at 1 week predicted more excessive movement irregularity at 2 weeks. Models including preoperative factors did not meet the goodness-of-fit criteria and were therefore excluded. CONCLUSIONS: Pain and motor function predicted each other through distinct factors and pathways during the acute postoperative recovery period after TKA. These interactions may contribute to persistent pain and functional limitations, highlighting the need for targeted early interventions. SIGNIFICANCE: Understanding the temporal relationships between acute postoperative pain and knee kinematics may provide insights into the mechanisms underlying prolonged recovery. SIGNIFICANCE STATEMENT: Excessive behavioural avoidance in the acute postoperative period may be involved in prolonged pain and motor dysfunction after total knee arthroplasty. In this study, longitudinal analysis of pain, fear, and motor impairment (behaviour) was conducted using a cross lagged panel model. Decreased range of motion in the acute phase predicted delayed pain recovery, whereas pain intensity predicted awkward movement. These results may indicate specific problems that should be addressed in the early postoperative period.