Differential corticomotor control of a muscle adjacent to a painful joint.

OBJECTIVE

To assess the effects of chronic knee pain on neural control of the nearby quadriceps muscle.

METHODS

Motor-evoked potentials (MEP) in response to transcranial magnetic stimulation (TMS) of the motor cortex, maximal M responses, patellar tendon responses, and EMG activity during maximal isometric contraction were recorded from the right vastus medialis oblique (VMO) and vastus lateralis (VL) muscles in 13 patients with chronic patellofemoral pain syndrome (PPS) and 13 healthy volunteers. MEP and maximal M responses were also recorded from the right extensor digitorum brevis (EDB) muscle.

RESULTS

MEP amplitudes from VMO and VL were larger in patients with PPS than in controls. On the other hand, maximal M responses, EMG activity with maximal voluntary contraction, and tendon responses were smaller in patients than in controls. Motor-evoked responses and maximal M responses of the EDB muscle did not show significant difference between the 2 groups.

CONCLUSIONS

These results indicate that chronic knee pain modulates central motor control of an adjacent muscle.