LITMIR.BIZ

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      There is controversy about the precise action of the pterygoid muscle. However, it is clear that this is an important muscle in protrusion of the mandible, which occurs when both right and left muscles act synchronously. When the pterygoid muscle on one side contracts, the effect is to pull the mandible laterally towards that side.

Parafunction

In parafunction, there appears to be increased activity in both superior and inferior pterygoids which appears to cause pain referred to the preauricular region when the muscle is examined against resistance. In addition, it is thought possible that sustained tonic contraction of the superior pterygoid muscle can be a factor in anteromedial displacement of the intra‐articular disc.

Examination

      This muscle is not accessible to digital palpation and should be examined against resistance. The patient should be asked to open the mouth to a certain point; the operator's hand is then placed under the chin and resistance is applied by the examiner. If there is lateral pterygoid tenderness discomfort will be felt in the preauricular region. In addition, this muscle can be examined by resisting lateral movements. The patient should slide the jaw across to one side and the operator applies resistance to this lateral movement. If there is lateral pterygoid tenderness, pain in the contralateral side to the pressure will be elicited (Chapter 3).

Medial pterygoid muscle

This muscle arises from the medial surface of the lateral pterygoid plate and the lateral aspect of the medial pterygoid plate and inserts into the angle of the mandible on the medial surface opposite the insertion of the masseter (Figure 2.13).

Figure 2.13 Medial pterygoid showing ramus of mandible sectioned: medial pterygoid muscle.

      (Figure courtesy of Dr Paul Rea and Caroline Morris, University of Glasgow.)

Function

The action of this muscle is elevation of the mandible, but it also assists in protrusion and lateral excursions of the mandible.

Parafunction

      This is not a muscle that can be reliably examined clinically so the effect of parafunction on the muscle is just conjecture.

Examination

      The medial pterygoid muscle is not accessible for manual or digital palpation.

Cervical muscles

These are many muscles including the digastric, mylohyoid, geniohyoid, and stylohyoid muscles (Figure 2.14).

Figure 2.14 Cervical muscles.

      (Figure courtesy of Dr Paul Rea and Caroline Morris, University of Glasgow.)

The two muscles in this group that mainly merit consideration are the digastric and mylohyoid muscles. The digastric muscle has two separate parts: an anterior and posterior belly; the two bellies have quite different actions. They are connected by an intermediate tendon that runs through a fibrous sling on the hyoid bone.

The mylohyoid muscle is a thin sheet of muscle arising on the inner aspect of the mandible from the whole length of the mylohyoid line. The two halves of this muscle meet in a median raphe, which inserts into the body of the hyoid bone. This muscle forms the floor of the mouth, separates the submandibular and sublingual regions, and is unattached posteriorly (Figure 2.15).

Figure 2.15 The mylohyoid muscle.

      (Figure courtesy of Dr Paul Rea and Caroline Morris, University of Glasgow.)

Function

      The suprahyoid muscles raise the hyoid bone and the larynx. They can also depress the mandible together with the tongue and the floor of the mouth, but only when the infrahyoid muscles stabilise the hyoid bone. The posterior belly of the digastric is, in addition one of the retruding muscles of the mandible.

This group of muscles also acts to depress the hyoid bone and larynx during swallowing. The infrahyoid and suprahyoid muscles always contract bilaterally (Figure 2.16).

Figure 2.16 The infrahyoid and suprahyoid muscles.

      (Courtesy of Dr Paul Rea and Caroline Morris, University of Glasgow.)

Parafunction

There is little evidence to directly link the suprahyoid muscles to parafunctional symptoms apart from the digastric muscle. This muscle is found to be tender either behind the ascending ramus of the mandible or in the submandibular region in patients who have a parafunctional bruxist habit, which they perform on their anterior teeth.

Examination

      Tenderness in the posterior and/or anterior belly of the digastric can be recorded by digital palpation. In this instance, discomfort can be elicited by palpating behind the ascending ramus of the mandible or in the submandibular area below the body of the mandible. Tenderness in this muscle arises in patients who demonstrate bruxism on their anterior teeth with the mandible in protrusion.

      The other suprahyoid, infrahyoid, and cervical muscles are difficult to examine apart from sternocleidomastoid, which can be examined by asking the patient to place the chin towards the shoulder and palpating the origin and insertion of the muscle on the opposite side.

Sternocleidomastoid muscle

The sternocleidomastoid muscle has two heads, one originating in the sternum and one in the clavicle; insertion of this muscle is into the mastoid process. When the sternocleidomastoid muscles act together they flex the neck. When one acts on its own it flexes the neck laterally and rotates the head.

These are important muscles to consider if your patient has, for instance, had a whiplash cervical extension/flexion injury and complains of generalised facial and cervical spine pain (Figure 2.17).

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