A pilot study of gait compensation for limb-length discrepancy in children and adolescents: threshold values and compensatory strategies in the sagittal plane

The critical threshold of limb-length discrepancy (LLD) at which compensation strategies are initiated in pediatric patients is unclear. We used spatiotemporal parameters to determine the LLD threshold at which compensatory gait is induced in skeletally immature patients and analyzed these compensatory patterns in terms of kinematics and kinetics. The findings for 20 children who experienced LLD-associated gait discomfort and underwent three-dimensional gait analysis between 2016 and 2019 were reviewed. Using spatiotemporal parameters, the LLD threshold that causes gait asymmetry was determined by receiver operating characteristic (ROC) analysis. Patients were grouped into those with an LLD greater than the cutoff value and those without. The kinematics and kinetics of the two groups were compared. The ROC curve showed that step length was a critical indicator of gait compensation. The area under the curve was 0.882 for both absolute LLD and LLD ratio, with threshold values of 14.06 mm and 1.85%, respectively. The group with LLDs above the threshold showed significant interlimb differences in the hip flexion angle, ankle dorsiflexion angle, and hip joint moment in the sagittal plane ( P = 0.005, P = 0.015, and P = 0.047, respectively). Compensatory strategies for LLD began when the absolute LLD was 14.06 mm or the LLD ratio was 1.85%. These strategies included hip joint flexion, increased hip joint moment of the longer limb, and ankle joint plantar flexion of the shorter limb. Thus, even with LLD less than 2 cm, asymmetries may exist in joint kinematics and kinetics.