Anatomic examination of the upper head of the lateral pterygoid muscle using magnetic resonance imaging and clinical data.

The aim of this work was to ascertain the different kinds of insertion of the upper head of the lateral pterygoid muscle (LPM) on the temporomandibular joint and to clarify its physiology to understand its possible role in the dysfunction at the temporomandibular joint. Magnetic resonance imaging examinations were used in this work to achieve a direct view of the LPM on a large number of selected patients with dysfunction at the temporomandibular joint.The study population was composed of 92 patients, of whom 74 were women and 18 were men. Their age range was from 19 to 53 years (mean age, 31 years). The images were analyzed using the following parameters: symmetry of morphologic insertions of the upper head of the LPM, types of muscular insertion divided into 3 groups (A, single bundle on the capsule and condyle; B, one bundle on the disk and a second bundle on the condyle; and C, one bundle only on the disk), and relationship between disk position regarding the condyle in patients with disk dislocations with or without reduction and upper head of the LPM. The chi-square test was used to measure the magnitude of the results.It is possible to impute to the C-type insertion morphology a negative prognostic value for a long-term improvement of disk pathology and to consider the possibility that this muscle may contribute to dislocating the disk when its insertion was directed only on the disk itself. When the upper head of the LPM was inserted on the disk, the percentage of disk dislocation without reduction was greater.