The Study: The shift of segmental contribution ratio in patients with herniated disc during cervical lateral bending
- There has been an underestimation of "the importance of objective spinal motion imaging assessment in the frontal plane".
- In lateral bending each segment contributes to the total magnitude of lateral flexion.
- Some segmental levels may contribute more or less to the total than is appropriate for that level.
- The authors looked at 92 subjects, half of which were healthy and half had suffered from a herniated disc at either C4/5 or C5/6.
- The subjects performed lateral bending while being viewed on videofluroscopy.
- They started in the neutral position and then smoothly laterally flexed their cervical spines all the way to the right and without stopping then flexed all the way to the left and returned to the neutral starting position. The total process lasted approximately 5 seconds.
- Compared to the normal patients those with herniated discs showed "a significant increase in segmental contribution ratio of C3/4...".
- In other words, the C3/4 motor unit of the disc herniated patients contributed a greater percentage to the total movement than occurred in the healthy subjects.
- Likewise, there was also a decrease in the contribution of the C5/6 level in the disc herniation patients. (Remember those with herniations had them at either C4/5 or C5/6.)
- In disc patients "segmental contribution shifted toward the middle cervical spine".
- To put this more into perspective, for healthy patients the "intervertebral angulation during cervical lateral bending" was 8.37 plus or minus 2.11 degrees for C3/4 and 7.19 plus or minus 2.29 degrees in the C5/6 area. In the disc patients it was 7.83 plus or minus 1.79 degrees for C3/4 and 5.13 plus or minus 2.05 degrees for C5/6. So, even though the disc injured patients showed a slight decrease in bending motion at the C3/4 level, the C5/6 areas exhibited an even greater decrease resulting in a greater percentage of the total lateral bending movement being contributed by the C3/4 segment.
Disc herniation resulted in reduced motion in both the lower and mid cervical spine however, the percentage of the total lateral bending motion contributed by the mid cervical area was increased in comparison to healthy patients.
It makes sense to me that if one area is injured it will contribute less to the total moment and an uninjured area will therefore show a greater contribution to the total movement. I did like the idea of using imaging to measure intersegmentally rather than just an overall range of motion. However, I think that pretty much the same study could have been made with just neutral and a left and right lateral flexion views. What really stands out to me is that if you mess up the structure then you mess up the function. That altered structure causes altered function is intuitive, but how much structural alteration does it take to create a certain amount of altered function, that is the question. Studies like this are a step in that direction.
Reviewer: Roger Coleman DC
Editor: Mark R. Payne DC
Reference: Lan HC, Chen HY, Kuo LC, You JY, Li WC, Wu SK. The shift of segmental contribution ratio in patients with herniated disc during cervical lateral bending. BMC Musculoskelet Disord 2014;15:273
Link to Abstract: http://www.ncbi.nlm.nih.gov/pubmed/25112463
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