Cervical Instability

Original Editor - Mary-Kate McCoy and Heather Lampe as part of the Temple University EBP Project

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Definition/Description

Cervical instability describes a wide range of conditions from neck pain and deformation without any clear proof over little malformations too complete failure of intervertebral connection. White et al (1975) described cervical stability as the loss of ability of cervical spine under physiological loads to maintain relationships between vertebrae in such a way, that spinal cord or nerve roots are damaged or irritated and deformity or pain develops.

Clinically Relevant Anatomy

The cervical spine consist of 7 separate vertebrae. The first two vertebrae (referred as upper cervical spine) are highly specialized and differ from the other 5 cervical vertebrae (lower cervical) regarding anatomical structure and function.

The upper cervical spine is made of the atlas (C1) and the axis (C2). It comprises of two joint structures: one in between os occipital and atlas (atlanto-occipital joint), the other one between atlas and axis, which forms the atlanto-axial joint. The atlantoaxial joint is responsible for 50% of all cervical rotation; the atlanto-occipital joint is responsible for 50% of flexion and extension.

The craniocervical junction (atlanto-occipital joint), the lower atlanto-axial joint and other cervical segments are reinforced by internal as well as external ligaments. They secure the spinal stability of the cervical spine as a whole, together with surrounding postural muscles and allow cervical motion. They also provide proprioceptive information throughout the spinal nerve system to the brain.

The cervical spine has sacrificed stability for mobility and is therefore vulnerable to injury.
The total ROM of a spinal segment may be divided into two zones:
- Neutral zone: motion occurring in this zone is produced against a minimal passive resistance.
- Elastic zone: motion occurring in occurring near the end-range of spinal motion is produced against increased passive resistance.

There are many authors that identified common components of spinal stability. Panjabi on conceptualized the components into 3 functionally integrated subsystems of the spinal stabilizing system: ^{[10]Level of Evidence 4,[11]Level of Evidence 2C}

• The passive subsystem:

- Consists of vertebral bodies, facet joints and capsules, spinal ligaments (lig. longitudinale anterius and posterius, ligamentum interspinosum, lig. Interspinosus and lig. Flavum).^{[17]Level of Evidence 2A}
- Passive tension from spinal muscles and tendons.
- Provides significant stabilization of the elastic zone and limits the size of the neutral zone.
- Acts as a transducer and provides the neural control subsystem with information about vertebral position and motion

• The active subsystem:

- Consists of spinal muscles and tendons, such as: M. multifidus cervicis, M. Longus capitis and the M. Longus Colli.[18]Level of Evidence 5
- Generates forces required to stabilize the spine in response to changing loads.
- Controls the motion occurring within the neutral zone and contributes to maintain the size the size of the neutral zone.
- Acts also as a transducer by providing the neural control subsystem with information about the forces generated by each muscle.

• The neural control subsystem:

- Consists of peripheral nerves and the central nervous system.
- Receives information from the transducers of the passive and active subsystems about vertebral position, vertebral motion, and forces generated by spinal muscles. The subsystem determines the requirements for spinal stability and acts on the spinal muscles to produce the required forces.

Clinical instability of the spine occurs when the neutral zone increases relative to the total ROM, the stabilizing subsystems are unable to compensate for this increase, which causes a poor and uncontrolled quality of motion in the neutral zone. ^{[10] Level of Evidence 4, [3] Level of Evidence 2C,[17] Level of Evidence 2A.}

Risk Factors

The following risk factors are associated with the potential for bony or ligamentous compromise of the upper cervical spine:

• History of trauma (e.g. whiplash, rugby neck injury)
• Throat infection
• Congenital collagenous compromise (e.g. syndromes: Down’s, Ehlers-Danlos, Grisel, Morquio)
• Inflammatory arthritides (e.g. rheumatoid arthritis, ankylosing spondylitis)
• Recent neck/head/dental surgery.

Characteristics/Clinical Presentation

Until this day there is no golden standard or acceptable measurement to diagnose cervical instability. Cervical instability is diagnosed as a combination of clinical findings and X-ray both dynamic and static. It is generally accepted that cervical instability is caused by trauma (one major trauma or repetitive microtrauma), rheumatoid arthritis or a tumor. Cervical instability leads to degenerative changes which effects the motion segment but may not be confused with severe incapacity or other signs of spinal cord compression.
A list of clinical findings composed by Magee et al:

• Neckpain
• Complaints of locking/catching in the neck
• Weakness of the neck
• Altered ROM
• Neck pain and/or headaches provoked by sustained weightbearing postures and a relieve of those complaints in non-weighbearing positions
• Hypermobility and soft end-feeling in passive therapie
• Poor cervical muscle strength (multifidus, longus capitis, longus colli)

The findings in X-ray from Cervical Spine by Clark CL that combined with clinical findings can lead to a diagnosis of cervical instability.

Differential Diagnosis

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Diagnostic Procedures

MRI images could be useful to screen the integrity of the vertebral ligaments. Taking images during an anterior shear test or a distraction test shows a greater intervertebral distance and an increase in direct length of the ligaments.

Outcome Measures

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Examination

Little is known about the diagnostic accuracy of upper cervical spine instability tests.

• Sharp-Purser Test 
• Transverse Ligament Stress Test
  

Medical Management

In the past few decades nonoperative maneuvers like traction, cast immobilization and long periods of bed rest had been replaced by the use of instrumentation to stabilize the spine after a trauma. This method can reduce the risk of negative sequelae of long term bed rest. The cervical stability can be received by using posterior fixation such as lateral mass plating, processus spinosus or facet wiring and cervical pedicle screws. The choice of which fixation is best, can be made by the surgeon after seeing a CT-scan or MRI. In a retrospective study of Fehlings, the cervical spine stabilization was successful in 93% off the cases.  Obviously this fixation procedure also holds some risks. It is possible that the spinal cord, vertebral artery, spinal nerve and facet joints get injured. Levine et al. reported radicular symptoms in 6 of their 72 patients.

Key Research

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Resources

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Clinical Bottom Line

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Recent Related Research (from Pubmed)

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References

10. K.A. Olson, D. Joder, Diagnosis and treatment of Cervical Spine Clinical Instability, Journal of Orthopaedic & Sports Physical Therapy, April 2001. ^{[10]Level of Evidence 4}