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mandible anatomy ENT fracture sites
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Here is a comprehensive ENT viva guide on the Mandible, organized by key topics:
MANDIBLE — ENT Viva Guide
1. ANATOMY OF THE MANDIBLE
Parts
The mandible consists of:
- Body (horizontal part) — divided into the base (lower) and alveolar part (upper, tooth-bearing)
- Ramus (vertical part, bilateral) — meets the body at the angle of the mandible
Key Landmarks on the Body
- Mental protuberance — midline swelling on the anterior surface
- Mental tubercles — lateral to the protuberance
- Mental foramen — midway between upper and lower borders of the body; transmits the mental nerve and vessels (branch of inferior alveolar nerve)
- Oblique line — ridge from the anterior border of the ramus onto the body; site of attachment for muscles that depress the lower lip
Key Landmarks on the Ramus
| Feature | Detail |
|---|---|
| Coronoid process | Triangular; attachment for temporalis muscle |
| Condylar process | Head (forms TMJ) + Neck (has pterygoid fovea for lateral pterygoid) |
| Mandibular notch (sigmoid notch) | Between coronoid and condylar processes |
| Mandibular foramen | On medial surface of ramus; entry of inferior alveolar nerve + vessels |
| Lingula | Just anterosuperior to mandibular foramen; attachment of sphenomandibular ligament |
| Mylohyoid groove | Below mandibular foramen; carries the nerve to mylohyoid |
| Medial surface, posteroinferior | Roughened for medial pterygoid muscle attachment |
| Lateral surface | Smooth; mostly for masseter muscle attachment |
— Gray's Anatomy for Students, p. 1114
2. MUSCLES OF MASTICATION (Mandibular Attachments)
| Muscle | Attachment on Mandible | Action | Nerve |
|---|---|---|---|
| Masseter | Lateral surface of ramus | Elevation | Masseteric n. (V3) |
| Temporalis | Coronoid process + anterior margin of ramus | Elevation + Retraction | Deep temporal nn. (V3) |
| Medial pterygoid | Medial surface near the angle | Elevation + side-to-side | Nerve to medial pterygoid (V3) |
| Lateral pterygoid | Pterygoid fovea on neck of condyle | Protrusion + depression + side-to-side | Nerve to lateral pterygoid (V3) |
Depression of the mandible: digastric, geniohyoid, mylohyoid (all V3/ansa cervicalis) + lateral pterygoid + gravity
— Gray's Anatomy for Students, p. 1116
3. TEMPOROMANDIBULAR JOINT (TMJ)
- Type: Synovial joint
- Articular surfaces: Head of mandible ↔ Articular fossa + articular tubercle of the temporal bone
- Articular surface covering: Fibrocartilage (not hyaline — unique feature, commonly asked!)
- Articular disc: Divides the joint into upper (gliding) and lower (hinge) compartments
- Ligaments:
- Lateral (temporomandibular) ligament — main ligament
- Sphenomandibular ligament — sphenoid spine → lingula
- Stylomandibular ligament — styloid process → angle of mandible
Movements:
- Elevation — temporalis, masseter, medial pterygoid (powerful)
- Depression — digastric, geniohyoid, mylohyoid, lateral pterygoid
- Protraction — lateral pterygoid (mainly), medial pterygoid
- Retraction — posterior temporalis, geniohyoid, digastric
4. MANDIBLE FRACTURES
Incidence
Mandible fractures are the 2nd most common facial fracture after nasal fractures. They account for ~37.5% of all maxillofacial fractures.
Common Causes
Assaults, motor vehicle crashes, falls.
Fracture Sites (Frequency)
| Site | Frequency |
|---|---|
| Condyle | 41.2% (most common) |
| Symphysis/parasymphysis | 31.5% |
| Body | 12.6% |
| Angle | 7.3% |
| Coracoid/coronoid | 4.8% |
| Ramus | 2.6% (least common) |
Key point: A fracture of the mandibular body is accompanied by a contralateral fracture (often condylar neck) in approximately 50% of cases — because the mandible is a ring-like structure. — Grainger & Allison's Diagnostic Radiology
Classification of Fracture Sites
| Region | Definition |
|---|---|
| Symphyseal | Between the two mental foramina (midline = symphysis; off-midline = parasymphysis) |
| Body | Between mental foramen and angle |
| Angle | Region of third molar, behind dentition |
| Ramus | Behind angle; posterior edge of fracture behind angle |
| Subcondylar | Traverses sigmoid notch, exits behind angle |
| Vertical ramus | Sigmoid notch fracture exiting anterior to angle |
| Coronoid | Extends anteriorly from sigmoid notch |
| Alveolar | Separates tooth-bearing segment from rest of mandible |
— K.J. Lee's Essential Otolaryngology, p. 1108
Favorable vs. Unfavorable Fractures
- Favorable: Muscles pull fragments together (compress the fracture line)
- Unfavorable: Muscles distract fragments apart — harder to stabilize
Clinical Features of Mandible Fracture
- Malocclusion (key sign)
- Jaw deviation (toward the fracture side)
- Trismus / pain on jaw movement
- Lower lip/chin numbness (inferior alveolar nerve injury)
- Mucosal ecchymosis / floor of mouth hematoma
- Step deformity on palpation
Imaging
- OPG (orthopantomogram) — first-line for mandible fractures
- CT face — gold standard for complex fractures; 3D reconstruction aids surgical planning
- X-ray PA face + lateral oblique views
Management
- Occlusal restoration first — arch bars are the primary means of establishing correct occlusion (intermaxillary fixation, IMF)
- Fixation principles:
- Mini-plate (1.5–2.0 mm, monocortical) along the "ideal line of osteosynthesis" — below tooth roots, overcomes distraction at alveolar border
- Mandibular reconstruction plate (≥2.0 mm, bicortical) along inferior border for severe fractures
- Lag screws for overlapping/symphyseal fractures
- Subcondylar fractures:
- Closed treatment with elastic MMF (preferred in children) — "forced adaptation"
- Open reduction via submandibular (Risdon) incision, retromandibular (transparotid), or preauricular approach
— K.J. Lee's Essential Otolaryngology, p. 1114; Schwartz's Principles of Surgery
5. MANDIBLE DISLOCATION
- Head of mandible dislocates anteriorly (most common) over the articular tubercle
- Causes: wide mouth opening, yawning, trauma
- Clinical features: Open mouth that cannot close, jaw deviated contralaterally, pain
- Management: Manual reduction — thumbs on lower molars, press down and back (Hippocratic method); local anesthesia/sedation if needed
6. NERVE SUPPLY — QUICK VIVA POINTS
| Nerve | Relevance to Mandible |
|---|---|
| Inferior alveolar nerve (V3) | Enters mandibular foramen, runs in mandibular canal → exits at mental foramen as mental nerve |
| Mental nerve | Sensation to lower lip and chin |
| Nerve to mylohyoid | In mylohyoid groove on medial ramus |
| Lingual nerve | Passes medial to mandible near third molar area (at risk during wisdom tooth extraction) |
| Marginal mandibular branch (VII) | Crosses the body of mandible anterior to masseter — at risk in submandibular incisions |
7. EDENTULOUS MANDIBLE
- After tooth loss, the alveolar part is resorbed from top down → bone becomes thin and atrophic
- More vulnerable to fracture with less trauma
- More difficult to repair due to limited bone stock for screw fixation
- Increased risk at the mental foramen level
8. HIGH-YIELD VIVA FACTS
| Fact | Answer |
|---|---|
| Most common mandibular fracture site | Condyle (41%) |
| Most common facial fracture | Nasal bone; mandible is 2nd |
| Joint surface covered by | Fibrocartilage (not hyaline) |
| Lingula is attachment for | Sphenomandibular ligament |
| Muscle that depresses mandible | Digastric, mylohyoid, geniohyoid |
| Most powerful mandibular elevators | Temporalis + masseter + medial pterygoid |
| Nerve at risk in wisdom tooth surgery | Lingual nerve and inferior alveolar nerve |
| Nerve at risk in submandibular incision | Marginal mandibular branch of VII |
| Ring fracture rule | Body fracture → ~50% chance of contralateral condylar fracture |
| Edentulous mandible fracture is difficult because | Atrophic bone, limited fixation points |
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