Joints - TMJ

Question 1

Articulating surfaces of the TMJ

Answer 1

Three surfaces:

1) Mandibular fossa
2) Articular tubercle of the squamous temporal bone
3) Head of the mandible

However the bones never come into contact with each other. They are separated by an articular disc.

The surfaces of the bones are lined with fibrocartilage

Question 2

Ligaments of the TMJ

How many?

Purpose

Answer 2

There are three extracapsular ligaments:

1) Lateral ligament - articular tubercle to mandibular neck - prevents posterior dislocation of the joint.
2) Sphenomandibular ligament - sphenoid spine to mandible.
3) Stylomandibular ligament - thickening of fascia of parotid gland to mandible - along with facial muscles, it supports the weight of the jaw.

Question 3

Movements of the TMJ

Muscles involved?

Movements?

Answer 3

Produced by muscles of mastication and hyoid muscles.

There are two divisons of the TMJ with different functions.

1) Protrusion and retraction

Upper part of the joint.

Anterior and posterior movements of the jaw.

Muscles involved -

Lateral pterygoid muscle - protrusion

Temporalis (posterior fibres) - retraction

Lateral movement of the jaw is produced by alternately protruding and retracting the mandible of each side.

2) Elevation and depression

Lower part of the joint.

Gravity (or digastric, geniohyoid and mylohyoid in resistance) - depression.

Masseter, temporalis, medial pterygoid muscles - elevation.

Question 4

Neurovascular supply of the TMJ

Answer 4

Branches of the external carotid.

1) Superficial temporal branch
2) Deep auricular
3) Ascending pharyngeal
4) Maxillary

Innervation:

1) Auriculotemporal nerve (apart of the mandibular branch)
2) Masseteric nerve (apart of the mandibular branch)

Question 5

Clinical relevance - temporomandibular joint dislocation

Aetiology?

Associated nerves?

Types?

Answer 5

Can occur via a blow to the side of the face, yawning, or taking a large bite.

The head of the mandible ‘slips’ out of the mandibular fossa, and is pulled anteriorly.

Patient becomes unables to close their mouth. The facial and auriculotemporal nerves run close to the joint and can be damaged if injury is high energy.

Posterior dislocations are possible but rare. Requires a large amount of force to overcome the postglenoid tubercle and strong intrinsic lateral ligament.