Evaluation and prediction of knee kinematics and kinetics in children with Blount disease

BACKGROUND: Blount disease primarily causes disturbance in the medial growth plate of the proximal tibia. This study aimed to 1) determine the kinematic and kinetic changes, 2) find the correlation between knee varus measured by gait analysis and radiographs, and 3) identify the predictors of increased internal knee valgus moment and impulse.

METHODS: This is a retrospective cohort study with the primary outcome being internal knee valgus moment impulse. Bivariate correlation analysis was performed to identify correlations, and linear mixed-effects regression models were established to determine predictors.

RESULTS: Included were 24 children aged 10.3 ± 3.7 years with Blount disease (12 bilateral, 17 male), comparing the unaffected limbs with the affected limbs, higher knee varus angle (KVA), internal tibial torsion, and internal knee valgus moment and impulse (P < 0.001) were found. Dynamic measurement of knee varus correlated with static radiographic measurements (P < 0.01). Despite different measurements, knee varus deformity and body mass index (BMI) predicted positively increased internal knee valgus moment impulse (N·m·s) (P < 0.001) (marginal R²=0.822, 0.798, and 0.839, respectively).

CONCLUSION: Children with Blount disease have significant knee varus, internal tibial torsion, and increased internal knee valgus moment impulse. Children with severe knee varus, higher body mass index, and internal tibial torsion are more likely to experience greater stress on the medial knee compartment or proximal tibial growth plate.