Odontoid Fracture

An odontoid (dens) fracture is a break of the odontoid process of the second cervical vertebra (axis), which holds the atlas against the transverse ligament and is the pivot for head rotation. It accounts for 10 to 20% of cervical spine fractures and about 60% of axis fractures.

It has a bimodal pattern: young adults after high energy trauma (motor vehicle collision, diving) and older adults over 65 years after low energy falls, where it is the commonest cervical fracture.

The Anderson and D'Alonzo classification describes three types.

• Type I: avulsion of the tip, rare, stable.
• Type II: fracture through the base of the dens at its junction with the body, about 60%.
• Type III: fracture extending into the body of the axis, about 30%.

Type II fractures have a high rate of nonunion because the blood supply at the waist is poor.

Neurological deficit occurs in under 10 to 15% at presentation, but death at the scene occurs in some high energy injuries.

Risk factors for nonunion of type II fractures are age over 50 years, displacement over 5 mm, angulation over 10 degrees, posterior displacement, comminution, and delayed treatment.

Complications are nonunion (30 to 80% with collar treatment in older patients), malunion, dysphagia and aspiration, respiratory complications with halo vests, cord compression, vertebral artery injury and death (mortality in older adults at 1 year is up to 20 to 30%).

Pathophysiology.

Combined hyperflexion, hyperextension and rotation load the dens through the transverse ligament and alar ligaments. The watershed zone at the base of the dens is poorly vascularised and the thin cortical bone is fragile in osteoporosis. Anterior displacement is more common in flexion, and posterior displacement in extension.

Neck pain, usually upper and occipital, with the patient supporting the head with the hands, limited neck rotation, and tenderness over the upper cervical spine. Dysphagia and a prevertebral swelling occur with displaced fractures. Neurological symptoms (paraesthesia, weakness, myelopathic signs) are uncommon, and respiratory arrest occurs in severe injury. In older adults, the injury may present only as neck pain after a fall.

Examine under spinal precautions: airway, swallowing, neck, cranial nerves, motor and sensory function, reflexes, and signs of associated head and other cervical injuries.

• CT of the cervical spine with sagittal and coronal reformats (the key test): fracture type, displacement, angulation, comminution, atlantoaxial alignment, associated C1 or C2 fractures (a C1 ring fracture accompanies about 5%).
• Open mouth and lateral radiographs are insufficient alone; flexion and extension films only when CT is unclear and the patient is alert.
• MRI to assess ligaments (transverse ligament rupture), cord injury and prevertebral haematoma; CT angiography of the neck if the fracture extends into the transverse foramen or neurological signs suggest vertebral artery injury.
• Bone density assessment and osteoporosis workup in older patients; frailty and anaesthetic risk assessment.

Differential diagnosis.

• Os odontoideum and congenital ossicle.
• Hangman fracture and Jefferson (C1 burst) fracture.
• Atlantoaxial rotatory subluxation, transverse ligament rupture and rheumatoid pannus.
• Calcium pyrophosphate deposition (crowned dens syndrome) and infection.

Treatment depends on the type, displacement, age, frailty and nonunion risk. The goals are union, alignment and avoidance of cord injury, with minimal complications in older patients.

Type I. Rigid collar for 6 to 12 weeks; stable unless there is occipitocervical instability (check with MRI and dynamic imaging).

Type II.

• Young patients with displacement over 2 mm or angulation: surgery is preferred.
• Anterior odontoid screw fixation (one or two screws) preserves C1 to C2 rotation (about 50% of cervical rotation) and has union rates of 80 to 95%.
• Avoid anterior screw fixation with osteoporosis, an oblique fracture line running anterior inferior to posterior superior, short neck or barrel chest that prevents screw trajectory, transverse ligament rupture, or delayed fracture older than 6 to 8 months.
• Posterior C1 to C2 fusion (screw rod or transarticular screws, with bone graft) is used when anterior fixation is unsuitable, in comminuted or irreducible fractures, or in older adults. Union is 90 to 100%, with loss of about half of cervical rotation.
• Halo vest immobilisation for 12 weeks in selected young patients gives union rates of 60 to 70%.
• In patients over 65 years halo vest carries a high rate of complications (pneumonia, pin site problems, mortality) and is generally avoided.
• Older frail patients with minimally displaced fractures: collar treatment for 12 weeks is an option, and many tolerate a fibrous nonunion.
• The decision between surgery and collar depends on fitness, displacement and patient goals. Mortality is similar in both groups in many series, but union rates are higher with surgery.

Type III. Rigid collar or halo vest for 8 to 12 weeks, with union in over 90%; surgery for displacement over 5 mm, instability, or failure.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose.

With severe penicillin allergy, give vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

Perioperative adjuncts. Awake fibre optic intubation with minimal neck movement when the fracture is unstable; dexamethasone 8 mg intravenously once at induction for airway swelling in anterior surgery (monitor glucose in diabetes).

Analgesia.

• Paracetamol 1 g orally every 6 hours (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Oral morphine 2.5 to 5 mg every 4 hours as needed in older adults for up to 1 to 2 weeks. Start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2; titrate to 5 to 10 mg.
• Monitor sedation, delirium and respiration on morphine; prescribe a laxative.
• Avoid NSAIDs while fusion is awaited and in older patients with renal or gastrointestinal risk.
• Dysphagia after anterior surgery or in a collar: speech and swallow assessment, thickened fluids, and nutrition support.

Thromboprophylaxis. Enoxaparin 40 mg subcutaneously once daily while mobility is reduced (20 mg once daily at creatinine clearance under 30 mL/min; check the platelet count on days 5 to 14), with mechanical prophylaxis until then.

Osteoporosis treatment (older patients). Calcium 1000 to 1200 mg daily in total, vitamin D 800 to 2000 units daily, and alendronate 70 mg orally once weekly (avoid with oesophageal disorders and creatinine clearance under 35 mL/min).

Zoledronic acid 5 mg intravenously once yearly is an alternative (after correcting vitamin D deficiency and checking calcium and renal function). Bisphosphonate does not delay union in clinical practice.

Monitoring. Neurological examination and airway check in the first 24 to 48 hours. CT or radiographs at 2 weeks, 6 weeks, 3 months and 6 months to monitor reduction, union and implant position. Flexion and extension films at 3 to 6 months for stability.

Also monitor swallowing, pressure points under the collar (skin checks twice daily), and halo pin sites (daily cleaning with saline).

Referral and escalation. Every suspected odontoid fracture needs spinal precautions and transfer to a spinal service. Emergency referral for neurological deficit, airway compromise, displaced fractures, or vertebral artery signs.

Special groups.

• Older adults: balance the risk of nonunion against the risk of surgery and halo vest complications; discuss goals and frailty; early mobilisation and nutrition.
• Children: epiphyseal separation of the dens through the neurocentral synchondrosis; collar or halo for 8 to 12 weeks, with good healing.
• Rheumatoid arthritis and osteoporosis: higher failure rates of anterior screws; posterior fusion.
• Anticoagulated patients: assess bleeding risk and plan surgery with the prescribing team.