Kinesiophobia and knee biomechanical characteristics in patients with postoperative tibial plateau fractures across body mass index categories: a cross-sectional mediation analysis

OBJECTIVE: To investigate knee biomechanical characteristics and kinesiophobia levels across different body mass index (BMI) categories in patients following tibial plateau fracture surgery, and to examine the mediating role of kinesiophobia in the relationship between BMI and knee biomechanical outcomes. METHODS: ), with 20 patients per group, alongside 20 healthy controls (Group D). Kinesiophobia and knee function were assessed using the Tampa Scale for Kinesiophobia-17 (TSK-17) and the Lysholm Knee Scoring Scale, respectively. A three-dimensional motion capture system synchronized with a force platform was used to collect spatiotemporal gait parameters and knee kinematic and kinetic data. Between- and within-group bilateral limb differences were analyzed, and correlation analysis, multiple linear regression, and bootstrap mediation analysis were performed to examine the mediating effect of kinesiophobia. RESULTS: Between-group comparisons revealed that Lysholm scores progressively decreased (Group A: 73.80 ± 4.74; Group B: 77.95 ± 2.86; Group C: 81.65 ± 3.63), whereas TSK-17 scores progressively increased (Group A: 57.00 ± 3.88; Group B: 51.40 ± 3.44; Group C: 46.70 ± 4.66) with increasing BMI (P < 0.01). On the affected side, cadence (Group A: 60.90 ± 12.56; Group D: 105.90 ± 4.61 steps/min), gait velocity (Group A: 0.58 ± 0.19; Group D: 1.08 ± 0.06 m/s), and sagittal plane range of motion (Group A: 47.46° ± 9.46°; Group D: 67.23° ± 2.82°) progressively decreased, whereas sagittal plane moments progressively increased (Group A: 680.35 ± 130.98; Group D: 225.13 ± 85.78 N·m) across BMI groups (P < 0.01). Within-group comparisons demonstrated that sagittal plane range of motion on the affected side was significantly smaller than that on the unaffected side, and that joint moments were significantly greater on the affected side across all three patient groups (P < 0.05); however, no significant bilateral differences were observed in the control group. Mediation analysis indicated that kinesiophobia partially mediated the relationship between BMI and gait velocity on the unaffected side (indirect effect = - 0.01; 95% CI [- 0.03, - 0.00]) as well as between BMI and sagittal plane moments on the affected side (indirect effect = 7.45; 95% CI [0.43, 18.56]), with mediation proportions of 48.4% and 27.5%, respectively. CONCLUSION: Patients with postoperative tibial plateau fractures and higher BMI exhibited significantly worse knee function, greater kinesiophobia, and compromised biomechanical characteristics, including slower gait, reduced sagittal plane range of motion, and elevated knee joint moments. Kinesiophobia partially mediated the adverse effects of elevated BMI on gait velocity and sagittal plane moments. Clinical rehabilitation programs should incorporate BMI-stratified individualized interventions integrating weight management with targeted psychological support to reduce kinesiophobia. TRIAL REGISTRATION: Chinese Clinical Trial Registry ChiCTR2500101020. Registered on 18/04/2025.