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Lateral Mass Fracture – Causes, Symptoms & Treatment

A lateral mass fracture is a break in the bony lateral blocks of the first cervical vertebra (atlas, C1). It is often caused by axial compression and requires prompt imaging and assessment.

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Things worth knowing about "Lateral mass fracture"

A lateral mass fracture is a break in the bony lateral blocks of the first cervical vertebra (atlas, C1). It is often caused by axial compression and requires prompt imaging and assessment.

What is a Lateral Mass Fracture?

A lateral mass fracture is a fracture involving the lateral masses of the first cervical vertebra, known as the atlas (C1). The lateral masses are the thick, rectangular bony blocks on either side of the atlas that connect its anterior and posterior arches. They form the articular surfaces between the skull (occipital condyles) and the second cervical vertebra (axis, C2). Fractures in this region belong to the category of upper cervical spine injuries and can carry neurological significance depending on their severity and displacement.

Causes

Lateral mass fractures typically result from high-energy trauma to the cervical spine. Common mechanisms include:

Axial compression: impact on the top of the head, such as diving into shallow water or motor vehicle accidents
High-velocity trauma: road traffic accidents with forceful axial loading
Falls from height: direct force transmitted through the skull to the atlas
Combined flexion-compression injuries: simultaneous bending and axial loading of the cervical spine

Lateral mass fractures frequently occur alongside other atlas fractures, including the classic Jefferson fracture (burst fracture of the atlas), or in combination with injuries to the axis (C2).

Symptoms

Symptoms vary depending on the extent of the injury. Common clinical features include:

Neck pain and tenderness in the upper cervical region
Restricted range of motion of the cervical spine, particularly rotation and lateral bending
Muscle spasm of the neck and shoulder musculature
Occipital headache, often radiating from the base of the skull
In severe cases: neurological deficits such as numbness or weakness in the arms or legs; in cases of significant spinal cord compression, tetraparesis may occur

Given the proximity of C1 to the brainstem, significant displacement poses a potential risk of life-threatening spinal cord compression.

Diagnosis

Diagnosis requires imaging studies. Standard investigations include:

Plain X-ray of the cervical spine: useful as a first step but may miss small or non-displaced fractures
Computed tomography (CT): the gold standard; provides detailed assessment of fracture morphology, displacement, and involvement of adjacent structures
Magnetic resonance imaging (MRI): used as a complementary tool to evaluate ligamentous injuries, spinal cord compression, and soft tissue damage

An important diagnostic criterion is the degree of lateral overhang of the atlas over the axis: a combined bilateral overhang exceeding 6.9 mm (the Spence rule) suggests rupture of the transverse atlantal ligament and indicates an unstable injury.

Classification

Lateral mass fractures are classified within the broader framework of atlas fracture systems, including the Landells and Van Peteghem classification and the AO Spine classification. Clinically relevant types include:

Isolated lateral mass fracture: involves only the lateral bony block without arch involvement
Combined fracture with anterior or posterior arch: corresponds to Jefferson fracture variants
Displaced vs. non-displaced fracture: determines the treatment approach (conservative vs. surgical)

Treatment

Conservative Management

Stable, minimally displaced lateral mass fractures without neurological deficits are typically managed conservatively:

Immobilization with a rigid cervical collar (e.g., Philadelphia collar) or a halo vest device for several weeks (typically 8–12 weeks)
Pain management with analgesics and anti-inflammatory medications
Regular follow-up imaging (CT or X-ray) to monitor fracture healing

Surgical Management

Unstable fractures, significant displacement, ligamentous rupture, or neurological deficits may require surgical intervention:

Atlantoaxial or occipitocervical fusion: surgical stabilization of the affected spinal segment
Reduction and internal fixation: restores normal anatomical alignment

The prognosis for isolated, stable lateral mass fractures is generally favorable; most patients achieve full recovery without permanent neurological sequelae.

References

Vaccaro AR et al. – Spine Trauma. Thieme Medical Publishers, 2nd edition (2019).
Aebi M, Arlet V, Webb JK – AO Spine Manual: Principles and Techniques. Thieme (2007).
Ryken TC et al. – Management of isolated fractures of the atlas in adults. Neurosurgery. 2002;50(3 Suppl):S120–S125. Available via PubMed.

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