What is lateral mass fixation in the cervical spine?

Lateral Mass Fixation in Cervical Spine

Lateral mass fixation is a posterior cervical spine stabilization technique that involves placing screws through the lateral masses of the cervical vertebrae (C3-C7) to provide rigid internal fixation after decompression procedures such as laminectomy. This technique has become the standard method of posterior cervical spine fixation for various surgical indications when posterior elements are absent or compromised 1.

Anatomical Considerations

Lateral mass fixation targets the lateral masses of the subaxial cervical spine (C3-C7), which are the bony structures lateral to the lamina and medial to the facet joints. Key anatomical parameters include:

• Average lateral mass depth: 12.83 ± 1.28 mm
• Average lateral mass width: 11.92 ± 0.96 mm
• Optimal screw length: 13-15 mm 2

Technique

The standard technique for lateral mass screw placement involves:

1. Entry point: The midpoint of the lateral mass (intersection of sagittal and axial planes of the posterior cortex)
2. Trajectory:
   • 30 degrees cranially (to avoid facet joint violation)
   • 20 degrees laterally (to avoid vertebral artery and nerve root injury)
3. Bicortical fixation: The screw exits on the ventral cortex of the lateral mass just lateral to the root of the transverse process 2

Several variations of this technique exist, including:

• Roy-Camille technique
• Magerl technique
• Anderson technique
• An technique

Each technique differs in entry points and trajectories, with the Magerl and Roy-Camille techniques showing more dispersive stress distribution and potentially lower risk of fixation fracture 3.

Clinical Applications

Lateral mass fixation is indicated in various cervical spine conditions:

• Cervical spondylotic myelopathy (CSM)
• Ossification of the posterior longitudinal ligament (OPLL)
• Trauma
• Instability after laminectomy
• Degenerative conditions requiring posterior stabilization

This technique is particularly valuable when posterior elements are compromised or when multilevel fixation is required 4.

Advantages Over Other Techniques

Laminectomy with lateral mass fusion has shown several advantages:

• Prevents post-laminectomy kyphosis
• Maintains spinal stability
• Provides excellent decompression of the spinal cord
• Results in significant neurological improvement in 71-97% of patients 4

In comparative studies, patients who underwent laminectomy and posterior fusion improved by an average of 2.0 Nurick grades, compared to 1.2 for anterior approaches and 0.9 for laminectomy alone 4.

Safety Profile

Lateral mass screw fixation has an excellent safety profile:

• Nerve root injury: Approximately 1.0% (95% CI, 0.3% to 1.6%) of patients
• Vertebral artery injury: Extremely rare, with no reported cases in large studies
• Hardware complications (screw/rod pullout, breakage, loosening): <1% of screws inserted
• Fusion success rate: 97-100% 1

A study of 1,662 lateral mass screws reported complications including:

• Lateral mass fracture during placement (27 screws)
• Nerve irritation with bicortical screws (3 cases)
• C5 root palsy after decompression (5 cases)
• Pseudarthrosis (6 cases)
• Screw pull-out (3 cases) 5

Potential Complications

While generally safe, surgeons should be aware of potential complications:

• Facet joint violation
• Nerve root injury
• Lateral mass fracture
• Hardware failure
• Pseudarthrosis
• Adjacent segment disease

Proper technique and understanding of cervical anatomy significantly reduce these risks 5.

Clinical Outcomes

Clinical outcomes following lateral mass fixation are generally favorable:

• Neurological improvement in 85-97% of patients
• JOA score improvement from 12.9 to 15.6
• Nurick score improvement from 2.6 to 1.8
• High fusion rates (97-100%) 4

A study of 115 patients with 673 lateral mass screws reported a 99.1% fusion rate with no neurologic or vascular injuries 6.

Comparison with Other Techniques

When compared to laminoplasty, laminectomy with lateral mass fixation:

• Shows similar neurological recovery
• May have higher complication rates in some studies
• Provides better stability in patients with pre-existing kyphosis 4

When compared to laminectomy alone, the addition of lateral mass fusion:

• Prevents progressive kyphosis (17% vs 12%)
• Reduces instability development
• May not significantly improve neurological outcomes in some studies 4

Lateral mass fixation has become the preferred posterior cervical fixation technique due to its reliability, safety profile, and excellent clinical outcomes when the posterior elements are compromised or absent.