New Insights on the Pterygoideus Lateralis
Dear Bodywork Colleagues
The Musculus Pterygoiddus Lateralis (one of the smallest and most hidden jaw muscles) has been a focus of particular interest for many of us. Based on the anatomy of this muscle and on some clinical experience it had been assumed by several of us that
1) this muscle has a direct influence on what happens inside of the jaw joint
2) that a skillful hand is able to palpate and manipulate this muscle directly with intraoral work.
Both of these assumptions appear as more questionable now, according to new research data.
1) Musculus Pterygoidalis Lateralis has less effect on intraarticular TMJ dynamics than had been assumed.
The superior head of this musculus pterygoideus lateralis (MPL sup) has been speculated to have a significant influence on the positioning of the disc as well as other intra-articular dynamics of the TMJ. Yet more recent research details do not support this hypothesis. Several reasons are given for this:
- The MPL sup. inserts only in 50% of the people at the capsule; and even when it does so, it is only with a small part of its fibers (Müller et al 1992)
- The orientation of the anterior collagen fibers of the discus is not in line with the direction of the MPL sup. (Müller et al 1992).
- The MPL sup is not activated in excursive disc movements (Mahan et al 1983, Gibbs et al 1984)..
Gibbs ChH, Mahan PE, Wilkinson TM, Mauderli 1984 EMG Activity of the superior belly of the lateral pterygoid muscle in relation to other jaw muscles. J Prosthet Dent 51:691-Langendoen, J, Müller J, Jull GA 1997
The retrodiscal tissue of the temporo-mandibular joint.
Clinical anatomy and its role in arthropathies 2(4):191-8
Mahan PE, Wilkinson TM, Gibbs A, Mauderli A, Brannon LS 1983 Superior and inferior
bellies of the lateral pterygoid muscle EMG activity at basic jaw positions. J Prosthet
Müller J, Schmid Ch, Vogl Th, Bruckner G, Randzio J 1992 Morphologisch nachweisbare
Formen von intraartikulären Dysfunktionen der Kiefergelenke. Dtsch Zahnärztl Z 47:416-423
2) It seems very questionable that the MPL can be palpated intraorally.
The following is from the abstracts of a related study, published in the Journal of Prosthetic Dentistry 2000 May;83(5):548-54.
Clinical anatomy and palpability of the inferior lateral pterygoid muscle
Stratmann U, Mokrys K, Meyer U, Kleinheinz J, Joos U, Dirksen D, Bollmann F.
STATEMENT OF PROBLEM: The intraoral palpation technique of the inferior belly of the inferior lateral pterygoid (ILP) muscle is a standard diagnostic examination method for temporomandibular joint dysfunction syndrome, although different studies have revealed inconsistent results.
PURPOSE: This study assessed the feasibility of the ILP muscle palpation by a simulated clinical setting.
MATERIAL AND METHODS: Three dentists performed a bilateral palpation of the ILP muscle in 53 fresh and unfixed human cadavers and decided whether the muscle was palpable or unpalpable. In a second step, it was observed through the dissected infratemporal fossa, whether the examiner's finger did or did not touch the ILP muscle by simulating the performed palpation. Palpatory findings were supplemented by 1-dimensional measurements for determination of topographic relations of the ILP muscle within the infratemporal fossa. For statistical analysis, sensitivity, specificity, and negative and positive predictive values of the palpation technique were calculated. Interexaminer agreement was estimated with the kappa value.
RESULTS: In 86 of 106 dissected specimens, a superficial fascicle of the medial pterygoid muscle was found in direct proximity to the ILP muscle. In these cases, a residual distance of 7.8 +/- 3.2 mm remained between the ILP muscle and buccinator fascia indented by the tip of the examiner's finger. In 10 of 20 specimens with an absent superficial fascicle, the finger was able to reach the ILP muscle.
CONCLUSION: It is recommended that the ILP muscle palpation technique should no longer be considered as a standard clinical procedure because it is nearly impossible to palpate the ILP muscle anatomically and because the risk of false-positive findings (by palpation of the medial pterygoid muscle) is high.
(Highlighting by bold face and color added by the author).