Compensatory strategy for ankle dorsiflexion muscle weakness during gait in patients with drop-foot.

BACKGROUND: Pathological movement patterns are characterized by abnormal kinematics, kinetics and muscle activations that alter the distribution of muscle forces during walking.

AIM: The objective of this study was to identify what compensatory strategy is evident in muscle force distribution in patients with drop-foot, in response to weakness in the dorsiflexor muscles.

METHODS: A sample of 10 patients with drop-foot were evaluated by a computerized gait analysis system and compared to a group of 10 healthy subjects. Muscle-actuated simulations of normal and drop-foot walking were performed using OpenSim software. A musculoskeletal model with 43 muscles acting on one lower extremity was used in order to perform the simulations. In order to evaluate the difference between muscle force curves in the healthy and the drop-foot populations, an integrals of each muscle curve were computed.

RESULTS: The group of patients with drop-foot exhibited an increased force integral for all muscle groups, except for the ankle evertors. The highest increases were observed for hip adductors (112%), hip extensors (88%), knee and hip flexors (83% and 50%, respectively) and for the plantarflexor (47%). These results were mainly influenced by the following muscles: flexor digitorum and hallucius, tibialis posterior and semitendinosus. The force integral for these muscles increased by more than 200% in the drop-foot group as compared to the control group. In addition, significant changes (>100%) were noted for the posterior thigh muscle group (semitendinosus, biceps femoris long and short head), which are responsible for bending the knee joint and straightening the hip joint.

CONCLUSIONS: It was proved that the loss in muscle force in individual muscle groups of the ankle joint are compensated for by the increased force and activity in other muscles acting on this joint and another muscles in neighbouring joints. The results may have important implications for physiotherapy treatments.