Muscle force imbalances predict clubfoot recurrence risk: A musculoskeletal modelling approach

Idiopathic clubfoot, primarily treated with the Ponseti method, recurs in 20-40 % of cases, often within the first two years post-treatment. This recurrence is commonly linked to imbalances in the inverting and everting muscle and ligament forces surrounding the foot, disrupting ankle-foot joint alignment during gait. This study aimed to evaluate the biomechanical factors contributing to clubfoot recurrence using advanced musculoskeletal modeling.

Experimental data, including 3D segment positions, lower limb muscle activity, and ground reaction forces, were collected from a typically developing child walking at a comfortable speed. Optimal muscle fiber lengths and tendon slack lengths of ankle-foot muscles were subsequently optimized on a lower extremity musculoskeletal model. To address the research question, maximum isometric evertor muscle strength and invertor muscle stiffness were then systematically manipulated on the musculoskeletal model. Additionally, ankle-foot joint geometry was altered to mimic progressive clubfoot recurrence. The impact of these changes on the ankle-foot joint moment balances was assessed by inverse dynamic analysis.

The musculoskeletal modelling approach was sensitive to subtle changes in muscle strength, joint stiffness, and joint geometry (10 %, 5 % and 3 degrees). In the absence of deforming inversion forces, only 30 % of normal evertor muscle strength was required to maintain typical ankle-foot kinematics. Increasing invertor muscle stiffness significantly increased evertor strength demands. An increase in inversion joint stiffness by >30 % leads to an inability of the model to maintain typical ankle-foot kinematics. Changes in ankle, subtalar, and midfoot joint alignment mimicking clubfoot recurrence further influenced muscle moment arm balances, though increasing deformity did not reduce evertor muscle moment arms compared to invertor muscle moment arms.

This study demonstrates the potential of advanced musculoskeletal modeling to uncover mechanical factors underlying clubfoot recurrence. The findings provide a foundation for incorporating patient-specific data in future research to validate clinical predictions. This approach could facilitate more personalized treatment strategies, improving long-term outcomes for children with recurrent clubfoot.