Growth Modulation by Tension Band Plate in Achondroplasia With Varus Knee Deformity: Comparison of Gait Analysis Measurements

Abstract

Background: Limited evidence exists concerning growth modulation by tension band plate (TBP) to correct varus deformity in patients with achondroplasia with limited growth due to FGFR3 gene mutation. We evaluated the efficacy of TBP in children with achondroplasia with genu varum and reported the static radiographic and dynamic motion data to determine parameters that impact the rate of deformity correction.

Methods: Patients with achondroplasia with genu varum who underwent TBP surgery for growth modulation were studied. Those with at least 1 year of follow-up with TBP were included. Radiographic parameters were measured. Growth velocity of femoral/tibial length was calculated separately. Patients were deemed successful or unsuccessful. Spearman correlation analysis and Student t test were used to describe statistical results.

Results: Twenty-two patients (41 limbs; 12 girls) fulfilled our criteria. Mean age at TBP surgery was 7.6±2.4 years. Thirty-six femoral TBP and 41 tibial TBP were in place for 24.5±9.7 months. Mean mechanical axis deviation, mechanical lateral distal femoral angle, and medial proximal tibial angle preoperatively were 30.1±7.6 mm, 97.2±6.4, and 80.3±4.3 degrees, and 11±15.6 mm, 87.4±5.9, and 84.7±5.3 degrees at last follow-up ( P <0.001). Fifteen limbs were successfully straightened; 4 limbs were in more varus than the initial deformity. Twenty-four limbs with TBP were still undergoing correction. In successful limbs, mean age at surgery was 6.5±1.7 years and duration of TBP was 29.9±7.8 months. In 4 unsuccessful limbs, mean age at surgery was 11.7±1.2 years. Analysis in the gait laboratory included physical examination with the measurement of knee varus and kinematic varus based on a posterior view static standing photograph. Photographic measurement of varus was higher than the radiographic measurement.

Conclusions: Growth modulation by TBP surgery is a reliable and simple technique to correct genu varum in achondroplasia. An early age at TBP implementation (mean: 6.5 y) is crucial to successfully correct the varus knee deformity. Furthermore, we recommend early and regular surveillance of achondroplasia for progressive varus knee deformity.

Level of evidence: Level IV-cohort study.