Anatomical studies of the lateral pterygoid muscle by the superior approach and a review of the literature.

There have been a number of physiological and anatomical reports on the lateral pterygoid muscle. They include some unclear points, and no agreement has been reached from the results so far. Most of the pevious studies have been performed by the lateral approach. Few reports have been made by the superior approach which is useful for investigation of the muscle.We dissected 26 temporomandibular joints from 14 adult cadavers by the superior approach and studied the muscle, as well as its functions, reviewing the literature.The lateral pterygoid muscle varied with the cadaver in the number of the head as follows; 7.7% of all specimens had single head, 3.8% had the lateral and medial heads, 57.6% had the superior and inferior heads, and 30.7% had three heads, i.e. superior, inferior and medial. This result indicates that the lateral pterygoid muscle was substantially different from cadaver to cadaver. The muscle fibers were so crowded with each other and with those of the temporal muscle that only 8 cases had the superior and inferior head's muscle which could be completely separated from each other. The superior head laid at an angle of 7.0 degrees medially with respect to the line perpendicular to the horizontal long axis of the mandibular head, the inferior head was at an angle of 19.1°, and the medial head was at an angle of about 37.7° to this reference line, on average. The superior head of the muscle was attached to the pterygoid fovea of the mandibular head except that the superficial layer of the superior head was attached to the inferior surface of the disk. The medial head of the muscle appeared to be inserted into the medial border of the disk and the medial capsule. In addition to the lateral pterygoid muscle, the temporal muscle of some specimens were attached to the anterosuperior stratum of the disk through the fibrous tissues and, sometimes, directly to the anterolateral part of the disk.We support, in principle, the previous reports that the lateral pterygoid muscle has generally two heads. We observed that, however, many variations of the muscle existed in terms of the individual their age, and their sex, and that the muscle fibers considerably crossed each other. Therefore, although we cannot deny the possibility that the superior head and inferior head of the lateral pterygoid muscle would function differently, we do not support that the superior and inferior heads of the muscle move antagonistically on electromyogram.