Muscular compensation and lesion of the anterior cruciate ligament: Contribution of the soleus muscle during recovery from a forward fall

Background. Knee stability following an anterior cruciate ligament lesion has been widely studied. Only recent studies focused on the contribution of the soleus muscle. Our purpose was to characterize the dynamic and muscular activity of balance recovery in healthy subjects and patients with an anterior cruciate ligament rupture. The role of the soleus was investigated in the ipsilateral compensation developed to stabilize the knee and in the contralateral compensation to recover balance. Methods. Twelve anterior cruciate ligament deficient patients, ten anterior cruciate ligament repaired patients and 14 control subjects were recorded during a forward fall involving stepping to recover balance. Findings. The dynamic of the centre of gravity remained normal when compared to the control group regardless of the treatment, suggesting an adapted compensation to knee instability in this situation. A bilateral increase in soleus activity was related to an increased duration in the balance recovery process in all patients. Patients used one of two strategies to recover balance regardless of the treatment: reducing the step length, involving an early recruitment of the soleus before heel contact, or anticipating braking with a similar step length requiring a predominant activity of the hamstrings. Interpretations. These results suggest that bilateral activity of the soleus is involved to compensate for instability and highlight the contribution of the soleus to rehabilitation after an anterior cruciate ligament lesion, not only as a compensatory muscle acting at the knee level but also at a higher level in the bilateral control of stance.