Strike Angle Variability During Walking In ACL Reconstructed Patients Measured By Smart Shoes

BACKGROUND: Anterior cruciate ligament (ACL) injuries are one of the most serious sports injuries. The main treatment methods are ACL reconstruction (ACLR) and following rehabilitation for regaining daily movement, such as walking. It is reported that the gait of ACLR patients is improved markedly in the early postoperative period (2-3 months), but the movement variability during gait remains increased even after more than one year. We have focused on the variability of the strike angle (the angle between foot and floor in the sagittal plane at the initial heel contact) acquired by shoes with built-in sensors (smart shoes). PURPOSE: To determine the sequential changes of the strike angle variability during gait in ACLR patients from 2 to 6 months. METHODS: Eight ACLR patients wore smart shoes and walked on a treadmill with a speed of 4 km/h at 2, 4, and 6 months postoperatively. The strike angle for each step was calculated from the foot's acceleration and angular velocity data during walking using the gait analysis software ORPHE ANALYTICS. The coefficient of variation (CV = standard deviation/mean) of the strike angle was calculated for each leg. The effects of limbs (involved and uninvolved limbs) and postoperative time (2, 4 and 6 months) on the strike angle CV were tested by two-way ANOVA and multiple comparisons (α = 0.05). RESULTS: Significant main effects were identified for the limbs (p = 0.021) and the postoperative time (p = 0.031) on strike angle CV. On the involved limb, strike angle CV decreased as the time passed by (2 months: 0.130 ± 0.060, 4 months: 0.092 ± 0.021, 6 months: 0.086 ± 0.042), indicating a simple main effect of the postoperative time (p = 0.038). In contrast, no simple main effect of the postoperative time was found for the uninvolved side (p = 0.728). Simple main effects of limbs were found at 2 (p = 0.032) and 4 months (p = 0.016), but no longer at 6 months (p = 0.166). CONCLUSION: The strike angle variability in ACLR patients was quantified using smart shoes and its postoperative change from 2 to 6 months was evaluated. The strike angle CV was greater on the involved limb than on the uninvolved limb and decreased over time. The strike angle CV is thought to reflect the postoperative gait recovery in ACLR patients. In addition, smart shoes can be a novel and simple clinical measurement modality that quantifies the gait function. Supported by: This work was supported by JSPS KAKENHI Grant Number 24 K23833.