Sunday, January 8, 2017

Temporomandibular joint: Notes for MBBS exam

In today's blog, we will be showing you how to write answers of joint in your theory exams.

Example question: TMJ
I would like you guys to know that since there is a lot of time limitation in theory exams, you should:
1. Draw diagrams ("Anatomy paper without diagram is as good as flower without fragrance!")
2. Name everything  you know
3. Elaborate

Before the exam, choose the diagrams you would draw for sure and optional diagrams ("If I get time...")


Part 1: Diagrams!



I  really like  this diagram because it shows the actions of the muscles with the attachment and origins. If you understand this diagram, you don't need to mug anything up!


Part 2. Name everything!

Type of joint: Synovial condylar joint .

Articular surface: Consists of the temporal bone and mandibular bone.
An articular disc prevents friction between the two articular surfaces.

Capsule: Not well defined.

Ligaments of the TMJ are:
Temporomandibular ligament
Sphenomandibular ligament
stylomandibular ligament.

Blood supply: Superficial temporal and maxillary arteries.Veins follow the arteries.

Nerve supply: Auriculotemporal nerve and masseteric nerve.

Movements:
Depression: Lateral pterygoid (Most part!) and digastric.
Mnemonic: Lateral lowers the jaw.
Elevation: Medial pterygoid, Masseter, Temporalis.
Protrusion: Lateral and Medial pterygoid, Masseter.
Retraction: Temporalis, Masseter.

Part 3: Elaborate!

Articular surface:
The articular surface is divided into two parts:
The stationary or proximal part is temporal bone which contains glenoid fossa between posterior glenoid spine and the articular eminence of temporal bone.
The moving or distal part contains mandibular bone.
Mandible is divided into a body and 2 rami. Each ramus has coronoid process and mandibular condyles.
Mandibular condyles are located  at posterosuperior part with each having lateral and medial pole. Mandibular condyl fits into glenoid fossa and coronoid process serves as an attacment to muscles.

Articular disc:
The articular disc of TMJ is biconcave.
The disc allows the convex surface of articular eminence and convex surface of mandibular to remain congruent through out the motion.
The anterior and posterior segment is vascular and innervated by nerves, only middle segment is avascular due to this it is used as force - accepting segment.
The disc appears to be firmly attached to lateral and medial pole of the condyles of Mandible but not to the capsule of TMJ.
The disc is firmly attached to the condyle below and freer to the articular eminence above.
It distributes the weight across TMJ by increasing area of contact.
It also prevents friction between two articular surface.

Ligaments and capsule:
Capsule is not well defined. It includes short fibers running from temporal bone to disc and from disc to condyle (Remember condyle only provides attachment!)

The primary ligaments of the TMJ include the temporomandibular ligament, sphenomandibular ligament and stylomandibular ligament.
The temporomandibular ligament is divided into two parts:The outer part is attached to the condyle [ Use as attachment :) ] and to articular eminence. It serves as suspensory ligament.
The inner portion is attached to lateral portion of the condyle, articular eminence, posterior portion of disc. The inner portion resists posterior motion of condyle.

Sphenomandibular ligament: It is attached from spine of sphenoid bone and to the middle part of the articular surface of the ramus of mandible. It is the remnant of the Meckel's cartilage. (Everything is in name of ligament!)

Stylomandibular ligament: It is a band of deep cervical fascia. It is attached from styloid process of temporal bone to the posterior border of ramus of mandible.

Movements:

1. Depression: (Lady dog gets mad)
- Lateral pterygoid. (Most part!)
- Digastric.
- Geniohyoid.
- Mylohyoid.
  
2. Elevation: (Anti-gravity muscles) (Emilie met masters (in) Temple)
- Medial pterygoid.
- Masseter.
- Temporalis.

3. Protrusion: (Propose Linda and Minda (in front of ) Mass)
- Lateral & Medial pterygoid.
- Masseter.

4. Retraction (R-T-M like A-T-M) 
- Temporalis.
- Masseter.

Applied anatomy:
1. In operations on the TMJ the 7th nerve and the auriculotemporal nerve branch of 5th nerve should be preserved.
 2. Dislocation therapy: Reduction is done by depressing the jaw with the thumbs placed on the last molar teeth and at the same time elevation of teeth.

Relations: This is the most confusing and challenging part but if you are good in imagination ,you can do it very well! It's NOT important to write the relations in the exam if you do not have the time.

Lateral: (Look into your cheek and tell what you can find)
1. Skin and fascia.
2. Parotid gland .
3. Branches of facial nerve.

Medial: (2 bones, 2 nerves, 1 artery)
1. Tympanic plate.
2. Spine of sphenoid.
3. Auriculotemporal and chorda tympani nerves.
4. Middle meningeal artery.

Anterior: (LAMe)
1. Lateral pterygoid .(L)
2. Masseteric nerve and artery. (Me)
(A in LAMe is for anterior,yeah I know it's a Lame kind of mnemonic! :D).

Posterior: (POST PASs)
1. Parotid gland.(P)
2. Auriculotemporal nerve.(A)
3. Superficial temporal vessels.(Ss)

Superior:
1. Middle cranial fossa.
2. Middle meningeal vessels.

Inferior:
Maxillary artery and vein.

That's all!

- IkaN and Ojas

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