Insertions of the lateral pterygoid muscle: an anatomic study of the human temporomandibular joint.

The objective of this investigation was to evaluate the anatomic relationships of the lateral pterygoid muscle with the disc-condyle complex using an acrylic embedding technique to obtain anatomic serial cuts of a solid block containing the temporomandibular joint (TMJ) and the neighboring structures. The fibers of the upper and lower heads were found to be fused in front of the TMJ and to constitute medially a strong muscular wall. The lateral third of the anterior band of the disc was free of any muscle insertions and related anteriorly with loose connective tissue; the middle third showed fibers that run under the anterior band of the disc and attached in the upper part of the condylar fovea. Only the medial portion demonstrated both fibers running into the disc and fibers inserting into the bone. The fibers inserted into the bone run under those attached into the disc and terminated below the medial pole of the condyle binding the disc tightly over the medial pole. This study demonstrates that the main insertions of the superior head are not into the disc but into the condyle. Considering the anatomic organization of the upper head, the explanation of anterior displacement of the disc due to a spastic activity of this muscle alone is not probable. Hypotonicity, not hyperactivity, of the upper head may contribute to an anterior and medial disc displacement.