Anatomy Overhaul: The Lateral Pterygoid muscle

This is a section taken from my recent article in Canadian Chiropractor magazine.  For the full article click here

Anatomy
The lateral pterygoid muscle (LPM) is commonly described as consisting of two distinct heads (inferior and superior).  The inferior lateral pterygoid (ILPM), which is up to three times the size of its counterpart, arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone and extends upward, and outward through the infratemporal fossa to its insertion primarily on the anterior and medial aspect of the condylar neck.1   The superior lateral pterygoid (SLPM) originates at the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone and extends backward, downward, and outward to its insertion primarily on the medial aspects of the pterygoid fovea and the mandibular condyle as well as the anterior surface of the articular capsule, and the anterior margin of the articular disk.2  However the exact insertions of the SLPM, especially its relationship with the articular disk, has been the topic of much debate in the literature.  The ideas concerning the settling of the SLPM ranges from complete insertion into the disk, to partial insertion, to no insertion what so ever. However in a recent anatomic study by Akar et al (2009) which examined the muscle’s course in 25 adult human cadaver dissections under 2.5 x loupe magnification, they concluded that the main insertions of the SLPM head are not into the disk but into the condyle.1   As discussed below, this finding has obvious implications on the function of the lateral pterygoid muscle.

Function
This small muscle of mastication, as it is believed to be the primary muscle affected in TMJ disturbances.3  Despite its perceived importance, its function, like its anatomical landmarks, has been subject to debate.  The LPM is widely believed to play an important role in control of jaw movement due to the assumed anatomical insertion of the SLPM into the articular disk.  During opening, the LPM is believed to contract, and thus the SLPM is subsequently thought to draw the articular disc forward, thereby maintaining the relationship between it and the articular condyle.  However, it is now known that the 2 heads of the LPM are reciprocally innervated so that during opening of the mouth, the ILPM contracts while the SLPM relaxes.  The opposite occurs with closing.4   The disc-condyle relationship is actually maintained by the disc’s strong attachment to the condylar poles such that the disc also moves downward and forward in conjunction with the condyle during opening.1   In addition, Mahan et al (1983) suggests that the SLPM’s activity of pulling the disc forward is not anatomical as the SLPM’s major attachment is to the condyle and could pull the disk forward only if the insertion of this muscle is detached from the pterygoid fovea.5

1.  Askar GC, Govsa F, Ozgur Z.  Examination of the Heads of the Lateral Pterygoid Muscle on the Temporomandibular Joint.  J of Craniofacial Surg 2009; 20(1): 219-223.
2.  Turp JC, Minagi S.  Palpation of the lateral pterygoid region in TMD—where is the evidence?  J Dent 2001; 29(7): 475-483.
3.  Taskaya-Yilmaz N, Ceylan G, Incesu L, et al.  A possible etiology of the internal derangement of the temporomandibular joint based on the MRI observations of the lateral pterygoid muscle.  Surg Radiol Anat 2005; 27:19-24.
4.  Juniper RP.  Temporomandibular joint dysfunction: a theory based upon electromyographic studies of the lateral pterygoid muscle.  Br J Oral Maxillofac Surg 1984; 22(1):1-8.
5.  Mahan PE, Wilkinson TM, Gibbs CH, et al.  Superior and inferior bellies of the lateral pterygoid muscle EMG activity at basic jaw positions.  J Prosthet Dent 1983; 50:710-718.