Neuromuscular reflexes contribute to knee stiffness during valgus loading

Area of Science:

• Biomechanics
• Neuroscience
• Orthopedics

Background:

• Knee joint reflexes are known to be elicited by angular perturbations.
• The contribution of these reflexes to joint stiffness remains unquantified.
• A stabilizing role for knee reflexes is widely proposed but lacks empirical evidence.

Purpose of the Study:

• To quantify the mechanical contribution of reflex muscle contractions to knee joint stiffness.
• To investigate the effect of reflex responses on medial-lateral knee stability.
• To test the hypothesis that reflex activation increases knee joint stiffness in the adduction/abduction direction.

Main Methods:

• Applied abducting positional deflections to the knee using a servomotor.
• Recorded joint torque response with a six degree-of-freedom load-cell.
• Measured electromyography (EMG) activity in quadriceps and hamstrings muscles.
• Utilized a linear, second-order, delayed model for knee joint dynamics analysis.

Main Results:

• Reflexes elicited by periarticular tissue afferents significantly increased knee joint adduction-abduction stiffness.
• The observed reflex stiffness demonstrated dependence on background muscle activation.
• Knee joint stability in the medial-lateral direction was enhanced by reflex activation.

Conclusions:

• Reflex activation of knee muscles is sufficient to enhance joint stabilization.
• This reflex-mediated stiffness plays a crucial role in managing medial-lateral knee loading during functional activities.
• Findings support the proposed stabilizing role of knee joint reflexes.