Altered phase-transitions in tibialis anterior and medial gastrocnemius during walking after limbsaving surgery

ObjectiveIn normal gait onset activity in tibialis anterior at end stance is closely linked to reduction in activity in medial gastrocnemius. Is a similar transition also present in patients undergoing limb-saving surgery?MethodsNineteen subjects after limb-saving surgery of the lower extremity and ten age-matched controls were compared. Patients walked on a treadmill at their preferred speed. Bipolar surface EMG activity was recorded from the tibialis anterior and the medial gastrocnemius.ResultsPatients showed asymmetry in gait. In controls a close tibialis anterior and medial gastrocnemius connection was seen. The close link between ipsilateral tibialis anterior and medial gastrocnemius was absent in patients.Instead, a link was found between tibialis anterior onset in the affected and medial gastrocnemius onset in the non-affected leg.ConclusionsThis finding suggests that two control mechanisms can be seen: a contralateral connection between tibialis and gastrocnemius and a less important ipsilateral connection. This means that automated phase switching in patients does not rely primarily on ipsilateral mechanisms but that instead the onset of the ipsilateral swing is linked to the moment of load acceptance by the contralateral leg These results are strikingly similar to those obtained in simulated limping by normal subjects.SignificancePatients after limbsaving surgery have a clinically significant problem that creates aberrant gait patterns. This study provides new information about linking of ankle dorsiflexors and plantarflexors, as well as reporting the uncoupling of this mechanism in these patients after major surgery.