Cervical spine instability is defined 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 not damaged or irritated and deformity or pain does not develop.
While most of definition is explanatory, the key term to remember is physiological l0ad.
Cervical spine instability may be caused by trauma, malignancy or infection and can be of two types
Acute Cervical Spine Instability
This is caused by acute injury to bone or ligament. This renders the spine unstable and places neural elements in danger of injury with subsequent loading or deformity.
Chronic Cervical Spine Instability
Often it is result of progressive deformity. It may cause increasing pain, a decrease in function or may cause neurological deterioration.
Cervical spine has anterior and posterior supporting structure. If the motion segment does not have functional anterior or posterior support, it should be considered unstable.
How To Check For Cervical Spine Instability
Radiologically, instability is checked by criteria given by White and Punjabi which is as follows
- Destruction or loss of function of anterior elements
- Destruction or loss of function of posterior elements
- Relative translation of vertebra in sagittal plane > 3.5 mm
- Angulation of one vertebra to another > 11 mm
- Positive stretch test for cervical spine.
- Damage to the cord
- Nerve root damage
- Abnormal narrowing of disc space
- Dangerous loading anticipated
Except for last three points, each point is given a score of 2. Last three points are given score of 1.
A positive score of more than 5 indicates instability.
Following xrays show an example of instability.
The xray above and below are of 38 years old lady who suffered from chronic neck pain. Her routine xray of cervical spine revealed a kyphotic deformity at C4-C5 level. Flexion and extension views were done. While the deformity got corrected in extension view, it got exaggerated in flexion suggesting dynamic cervical spine instability.
When stability is present, fusion of the unstable segments is indicated.
Stretch Test For Cervical Spine Instability
Stretch test is a useful test to determine cervical spine instability clinically. The test involves stretching of the cervical spine with the traction and determining the changes on xrays.
This test is contraindicated in an unstable injury.
What Is measured?
This test measures the displacement patterns of spine and identifies anterior and posterior disruption of ligaments.
The stretch test is always done under supervision of a physician.
How The Test Is Done?
A Crutchfield tong traction or head halter traction is applied.
A rolled towel is placed under patient’s head. The xray or C-arm image intensifier is readied and placed so as to take a lateral view. The film is placed as close to neck so that a wider view can be obtained.
An xray is taken before applying weights to the traction.
Add weights up to 10 pounds and increased in increments of 5 pounds. Allow a difference of 5 minutes between two increments.
The xray is taken after each addition.
The process can be repeated till one third of the body weight has been applied or the test is positive.
After each addition, neural status should be checked.
The test is considered positive
- If there is neurological deficit
- If there is some abnormal separation of anterior or posterior elements.
- If difference in interspace separation is more than 1.7 mm
- If angle between prestretch condition [without weights] and maximal weights is 7.5 degrees.
Cervical Spine Instability in Down Syndrome
Generalized ligamentous laxity caused by the collagen defects in Down syndrome can result in atlantoaxial and atlantooccipital instability. In these patients hypermobility of the spine is a feature but instability is that hypermobilty which jeopardizes neurological integrity.
Atlantoaxial instability occurs in approximately 10% to 20% of children with Down syndrome. Atlantooccipital instability incidence has been reported to be 60%.
Neurological symptoms are present in only 1% to 2.6% of patients with cervical instability, and the instability usually is discovered on routine screening examinations or on cervical radiographs obtained for other reasons.
Progressive instability leading to neurological symptoms is most common in boys older than 10.5 years of age.
Involvement of the pyramidal tract usually results in gait abnormalities, hyperreflexia, and motor weakness.
Neck pain, occipital headaches, and torticollis are other features.
Basic imaging includes anteroposterior, flexion and extension lateral, and odontoid views.
An atlantodens interval of more than 4 to 5 mm indicates instability. If the ADI is more than 6 to 7 mm, MRI or CT in flexion and extension is necessary to evaluate the space available for the spinal cord.
Restriction of high-risk activities usually is sufficient in children with Down syndrome and ADIs of 4 to 5 mm.
If the ADI is 6 to 7 mm, however, MRI or CT should be used to evaluate the risk of neurological compromise.
If the ADI is 10 mm or more, posterior fusion and wiring are recommended after reduction of te unstable C1-2 joint . If the reduction is not achievable, an in situ fusion should be done.
Postoperative immobilization in a halo-cast or -vest should be continued for 6 months.
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