Brachial Plexus

Formation

Components

Fig. 7.53 — Brachial Plexus schematic and axillary artery relationships (Gray's Anatomy for Students)

Fig. 7.52 — Major components in the neck and axilla (Gray's Anatomy for Students)

1. Roots

• Anterior rami of C5, C6, C7, C8, T1
• Pass between the anterior and middle scalene muscles
• Receive gray rami communicantes from the sympathetic trunk
• Lie superior and posterior to the subclavian artery

2. Trunks (3)

3. Divisions (6)

• Each trunk splits into an anterior and a posterior division
• Anterior divisions → nerves supplying anterior (flexor) compartments
• Posterior divisions → nerves supplying posterior (extensor) compartments
• No peripheral nerves arise directly from divisions

4. Cords (3)

Branches

From the Roots

From the Trunks

From the Cords

The median nerve is formed by contributions from both lateral (C5–C7) and medial (C8–T1) cords.

Anatomical Variations

• Prefixed plexus (3–5% of individuals): contribution shifted up; strong C4, minimal/no T1
• Postfixed plexus (3–5%): shifted down; minimal C5, contribution from T2
• These variations must be considered when the clinical deficit doesn't fit the expected pattern of a plexopathy

Lesions of the Brachial Plexus

Upper Trunk (C5–C6) — Erb–Duchenne Palsy

• Caused by: birth trauma (shoulder dystocia), forceful separation of neck and shoulder
• Paralysis of: deltoid, biceps, brachialis, brachioradialis
• Posture: arm hangs adducted, internally rotated, forearm pronated ("waiter's tip")
• Sensory loss: lateral arm/forearm

Lower Trunk (C8–T1) — Klumpke Palsy

• Caused by: Pancoast tumor, forced abduction of arm, birth trauma (breech delivery)
• Paralysis of: intrinsic hand muscles (interossei, hypothenar, thenar)
• "Claw hand" deformity
• Sensory loss: medial arm/forearm and medial two fingers
• May include Horner syndrome (ptosis, miosis, anhidrosis) if T1 sympathetic fibers involved

Traumatic Plexopathy

• Most common cause: traction injuries in motor vehicle accidents (especially motorcyclists propelled from the vehicle)
• Other causes: gunshot wounds, fracture-dislocations of shoulder/humerus, radiation (delayed), Pancoast tumors, neuralgic amyotrophy (Parsonage–Turner syndrome)

Clinical Pearls

• Serratus anterior weakness (long thoracic nerve, C5–C7) → winged scapula — tested by asking patient to push against a wall
• Suprascapular nerve is the only branch from a trunk; it exits at Erb's point (junction of C5 + C6)
• The posterior cord contains fibers from all five roots (C5–T1) — posterior cord lesions affect the entire posterior compartment of the upper limb
• The intercostobrachial nerve (lateral cutaneous branch of T2) is not part of the brachial plexus but often co-injured in axillary dissection

Temporomandibular Joint (TMJ)

Anatomy

Fig. 56.23 — The TMJ in closed, partially open, and wide-open positions (Rosen's Emergency Medicine)

The Articular Disc (Meniscus)

• A biconcave fibrocartilaginous disc that sits between the condyle and the temporal bone
• Divides the joint into two compartments:
  • Superior (upper) joint space — between disc and temporal bone; allows gliding/translation
  • Inferior (lower) joint space — between disc and condyle; allows rotation/hinging
• Anteriorly attached to the lateral pterygoid muscle (upper head)
• Posteriorly attached to the bilaminar zone (retrodiscal tissue) — richly vascularized and innervated

A formal thick capsule is absent at the anteromedial portion of the joint; this looser synovial tissue permits translation to occur.

Capsule & Ligaments

Muscles of Mastication Acting on the TMJ

Trismus (inability to open) results from spasm of the masseter, temporalis, and medial pterygoid.

Innervation & Blood Supply

• Innervation: Auriculotemporal nerve and masseteric nerve — both branches of V3 (mandibular division of trigeminal nerve)
• Blood supply: Superficial temporal artery and maxillary artery — branches of the external carotid artery

TMJ Disorders (TMD)

Etiology

• Jaw clenching and grinding (bruxism) associated with stress — most common
• Parafunctional habits (microtrauma)
• Macrotrauma (single injury)
• Tooth malocclusion is rare as a standalone cause

Clinical Features

Disc Displacement (Internal Derangement)

• Produces an audible click on opening (and sometimes a reciprocal click on closing)
• Normal range of motion
• Often asymptomatic and requires no treatment

• Acts as a physical barrier to condylar translation
• Maximum opening limited to 25–30 mm
• No click
• May be painful

Fig. 89.1 — Anterior disc displacement with reduction (Cummings Otolaryngology)

TMJ Dislocation

Mechanism

• Condyle translates anterior to the articular eminence and becomes locked in the anterosuperior aspect of the eminence
• Masseter, temporalis, and medial pterygoid go into spasm — trismus prevents spontaneous reduction
• Caused by: extreme yawning, prolonged dental procedures, trauma, dystonic drug reactions

Clinical Features

• Mouth stuck open, unable to close
• Drooling, garbled speech
• Visible/palpable depression in the preauricular area
• Unilateral: jaw deviates to the opposite side
• Bilateral: symmetric jaw protrusion

Reduction Technique

Fig. 56.24 — Normal, open, dislocated positions and reduction maneuver (Rosen's Emergency Medicine)

1. Procedural sedation and analgesia (masseter relaxation is essential)
2. Patient seated upright, clinician in front
3. Thumbs placed on the buccal sulcus lateral to the lower molars (wrap thumbs in gauze)
4. Apply downward pressure on the molar ridge while rotating the chin upward and backward
5. Condyle clears the eminence → masticatory muscles contract the jaw shut

Post-reduction imaging not required for atraumatic dislocation. If trauma is suspected, obtain Panorex or CT first to exclude fracture before manipulation.

Management of TMD

Differential Diagnosis of TMJ Pain

• Pulpitis / odontogenic infection
• Otitis media
• Sinusitis
• Parotitis
• Trigeminal neuralgia
• Headache disorders
• Cervical spine disease