Quantitative Gait Assessment before and after Limb Lengthening in a Patient with Achondroplasia: A Case Report.

Background: Achondroplasia, a common skeletal dysplasia, results from a gain-of-function mutation in the fibroblast growth factor receptor 3 gene. It is characterized by short-limbed dwarfism and is frequently associated with skeletal deformities, including genu varum and tibial bowing, which often impair gait and limit daily function. Although limb lengthening with an external fixator is a widely utilized intervention, quantitative evaluations of its effectiveness remain limited. Case: A 10-year-old boy with achondroplasia presented with progressive lower limb deformity and gait disturbance. Preoperative assessments revealed pronounced genu varum, tibial bowing, and mechanical axis deviation. Bilateral tibiofibular lengthening using the Taylor Spatial Frame was performed, achieving a 6-cm increase in limb length. The external fixator was removed 1 year postoperatively. Gait rehabilitation commenced 4 months postoperatively, with full independent ambulation achieved by 6 months. Quantitative assessments using the 6-minute walk test (6MWT) and three-dimensional gait analysis (3DGA) demonstrated improvements in walking distance, cadence, and a reduction in the Physiological Cost Index (0.29 to 0.1). Preoperative 3DGA revealed significant gait deviations, which improved postoperatively, including a 9.5° reduction in the Gait Profile Score. Discussion: Moment analysis indicated reductions in knee flexion and varus moments, suggesting improved gait efficiency. These findings suggest that limb lengthening enhances both limb alignment and functional gait performance. The integration of 3DGA and 6MWT with conventional radiographic evaluation offers a comprehensive assessment of treatment outcomes, reinforcing the effectiveness of surgical intervention and rehabilitation in patients with achondroplasia.