Describe Odontoid (Dens) Fracture in detail.
Definition
The odontoid process (dens) is the peg of the axis (C2) around which the atlas rotates, held by the transverse ligament. A dens fracture results from flexion or extension forces (RTA in the young, a fall in the elderly). It is important because the type-II fracture is prone to non-union and to instability that threatens the cord.
| Anderson–D’Alonzo | Location | Note |
|---|---|---|
| Type I | Tip of the dens (avulsion) | Rare; usually stable |
| Type II | Base of the dens (junction with body) | Commonest; high non-union rate |
| Type III | Extends into the C2 body | Broad cancellous surface; unites well |
Clinical Features & Investigations
Neck pain and stiffness, often with the patient supporting the head with the hands; neurological deficit is variable. Diagnosis is by the open-mouth (odontoid peg) radiograph and, definitively, CT; MRI assesses the transverse ligament and cord.
Management
Type I and III fractures generally unite with external immobilisation (collar or halo vest). Type II is problematic: undisplaced fractures may be treated in a halo, but displacement, age > 50 and high non-union risk favour surgical fixation — anterior odontoid screw or posterior C1–C2 fusion.
DANGER / REMEMBER
The elderly tolerate halo immobilisation poorly and type-II fractures have a high non-union rate in this group — surgical fixation or a well-fitted hard collar is often preferred over prolonged halo treatment, which the frail elderly tolerate badly and which carries its own respiratory and skin risks.
Non-union & its Determinants
The type-II fracture is notorious for non-union because the fracture line lies at the narrow junction of dens and body, a watershed with a poor blood supply and a small cross-sectional area of cancellous contact. Risk factors for non-union include displacement > 5 mm, angulation, advanced age, delayed treatment and posterior displacement. A united type-III fracture, by contrast, has a broad cancellous surface and heals reliably. Non-union may produce chronic instability (os odontoideum-like) threatening the cord.
Type II has the highest non-union rate and often needs fixation.
KEY POINT
Key points TO remember
- Dens fracture around which C1 rotates; flexion/extension mechanism.
- Anderson–D’Alonzo I (tip), II (base — commonest, non-union), III (body — unites well).
- Open-mouth view + CT; MRI for ligament/cord.
- I & III → immobilise; II → halo or surgery (odontoid screw / C1–C2 fusion).
EXAM TIP
Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.
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