PROPRIOCEPTIVE MECHANISMS IN THE CRUCIATE LIGAMENTS - AN ELECTROMYOGRAPHIC STUDY ON REFLEX ACTIVITY IN THE THIGH MUSCLES

The hypothesis of a proprioceptive mechanism arising from mechanorecep tors in the cruciate ligaments and with efferences to the thigh muscle s is investigated in an animal model. Electromyographic (EMG) studies of the quadriceps and hamstrings muscles ct cre performed in six sheep anesthetized by intravenous injection of chloralose on applying stati c and dynamic shear farces to isolated fascicle bundles in the anterio r (ACL) and posterior (PCL) cruciate ligaments at 200 to 500 N and 50 to 200 N/sec, respectively, With the help of an external fixator, the knee joint position mas varied at 25 to 150 degrees. The relative prel oad of the anteromedial and posterolateral fascicles in the ACL and th e anterior and posterior fascicles in the PCL induced by variation of the joint angle was measured with the help of strain gages. By static and dynamic loading of the anteromedial group of the ACL, EMG activity in the hamstrings increases significantly to 159 +/- 22 and 257 +/- 4 6 mu Vseconds, respectively (p < 0.001), with a simultaneous suppressi on of the quadriceps activity, Static and dynamic loading of the poste rolateral ACL group results in a significant excitation of the quadric eps with mean potentials of 142 +/- 29 and 173 +/- 23 mu Vseconds, res pectively (p < 0.001). Mechanical shear applied both to the anterior a nd posterior fascicles of the PCL induces a significant activation of the ipsilateral quadriceps muscles with a simultaneous inhibition of t he hamstrings (p < 0.001). The quality of mechanical loading, i.e., st atic or dynamic shear, determines the degree of muscular recruitment s ignificantly (p < 0.01). The joint angle contributes to a modulation i n the quantitative EMG excitation, Linear regression analysis of the i ntegrated EMG potential values and the amount of passive preload induc ed by the respective joint position results in a close correlation (r = +0.78 to +0.86). The results lead to the conclusion that a proprioce ptive mechanism exists that arises from the cruciate ligaments and inf luences the tone in the thigh muscles. The degree of muscle excitation on mechanical ligament loading is modulated by the amount of preload in the ACL and PCL and the quality of load applied.