SEGMENTAL SENSORY INNERVATION OF THE ANTERIOR CRUCIATE LIGAMENT AND THE PATELLAR TENDON OF THE CATS KNEE

We performed a study in cats to describe and quantify the segmental se nsory innervation of the anterior cruciate ligament of the knee. We al so studied the patellar tendon to show that transport occurs from an e xtraarticular, dense connective tissue structure and to obtain compara ble quantitative information. We injected a tracer (horseradish peroxi dase HRP, coupled to wheat germ agglutinin WGA) in the anterior crucia te ligament and observed the reaction product in the articular nerves of the injected knee and in the cell bodies of ipsilateral dorsal root ganglia. In these experiments, we found an average of 26 (13-52) labe led neurons, mostly large, after injecting the anterior cruciate. More than half of the labeled neurons were found in the dorsal root gangli on of L7 (last lumbar segment in the cat). We counted an average of 20 4 (17-426) labeled neurons, mostly small, after injecting the patellar tendon. More than half of these labeled neurons were found in the L5 spinal ganglion. No product was observed in contralateral spinal gangl ia. Surgical ablation of the medial and lateral articular nerves (MAN and LAN) before injecting HRP-WGA in the anterior cruciate ligament, s howed that the remaining afferents in the posterior articular nerve (P AN) projected mainly to L7. After excision of PAN, the projection was maintained through MAN and LAN, mostly to L5. Our quantitative data sh ow that the anterior cruciate ligament is poorly innervated, a compare d to the patellar tendon. The anterior cruciate segmental sensory inne rvation is directed to L7 (corresponding to the main ventral root form ing the sciatic nerve in the cat), but also to L5 and L6 (main femoral nerve ventral roots). These segmental data indicate that anterior cru ciate innervation influences muscle tone regulation, not only of the h amstrings (neuromuscular system of the sciatic nerve), but also of the quadriceps muscle (neuromuscular system of the femoral nerve).