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.
The instability may be caused by trauma, malignancy or infection,
Instability can be of two types
Acute 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 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 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 instability.
Treatment
When stability is present, fusion of the unstable segments is indicated.
Actually the largest and most significant break in the posterior line is at C5/C6 when the disc height is significantly increased. Indicating tears at this level. The example is a bit pathetic, I am sure you can do better. We had Jefferson burst fractures that were unseen with standard views and almost full dislocations
Dr Arun Pal Singh Reply:
June 9th, 2011 at 3:18 pm
@Rick Lambert,
Thanks for pointing that. I think arrow got misplaced. I would surely publish a better xray when I have one.
If you have the image you just mentioned, would you care to share.