Effect of foot orthotics on running kinetics in adults with anterior cruciate ligament reconstruction: A controlled laboratory study

Individuals with anterior cruciate ligament reconstruction and pronated feet (ACLR-PF) often display abnormal running ground reaction forces (GRFs), which are associated with higher re-injury risk and post-traumatic osteoarthritis. While foot orthoses (FOs) are used to influence biomechanics, their effectiveness at various post-operative stages in this group remains unknown. This study aimed to evaluate the immediate impact of different FOs on GRFs during running in males with ACLR-PF at 6-, 12-, and 18-months post-operative, compared to a healthy control group. This controlled laboratory study with randomized repeated orthotic conditions included males with ACLR-PF at 6, 12, and 18-months post‑operative, as well as healthy controls. Forty-five right-footed males with ACLR-PF were divided into three groups based on post-operative duration: 6 ± 1 months (group A, n = 15), 12 ± 1 months (group B, n = 15), and 18 ± 1 months (group C, n = 15). A matched health control group (group D, n = 15) was also included. Participants ran at 3.2 m/s under four randomized footwear conditions: control shoe, placebo orthotic, double-density orthotic, and arch-support orthotic. Three-dimensional GRFs were collected using a force plate. ACLR-PF groups at 12- and 18-months showed significantly higher impact vertical peaks and vertical loading rates than the healthy group. The 6-months ACLR-PF group had a longer time-to-peak for the impact vertical peak. Peak positive free moment was higher in the 6- and 18-months ACLR-PF groups compared to controls. A significant main effect of FOs was detected, with the double-density orthotic significantly decreasing the peak positive free moment relative to the control shoe. Significant group-by-FOs interactions indicated that the impact of specific orthoses on peak posterior force, loading rate, and stance time depended on the post-operative stage. Abnormal loading patterns continue up to 18-months after ACLR in individuals with PF, highlighting a critical window for intervention. FOs, especially double-density designs, can immediately adjust specific maladaptive GRFs, such as lowering excessive rotational moments. An orthotic prescription should be customized to the individual's specific biomechanical deficits and the stage in the rehabilitation process. In this controlled laboratory study, double-density and arch-support FOs acutely modified selected GRFs in males with ACLR and PF across post-operative stages. These findings suggest that FOs may provide immediate biomechanical adjustments during running; however, the long‑term clinical relevance of these acute changes remains uncertain and requires longitudinal investigation.