Thursday, December 17, 2009

Coupling mechanisms in cervical spine



Radiographic study: coupling of cervical motions in lateral head translations.
The clinically common posture of lateral head translation results in an S-shaped cervical spine and may occur in side impact trauma. This posture has not been studied for cervical coupling patterns or range of motion (ROM) (2).

In a radiographic experimental study (2) on 20 subjects lateral (a mean of 51 mm) translation was produced by translating the head over a fixed thorax. The major coupled motion was lateral bending (z-axis rotation). The following was found:

1. S-shape in cervical spine was created & there is change in direction at C4–C5 disc space.
2. Upper cervical (C3–C4) lateral bending was contralateral to the main motion of head translation direction. Lower cervical and upper thoracic lateral bending was ipsilateral.
3. During the translation other segmental motions averaged less than 1 mm and 1°.

This study shows in cervical spine side bending usually there in nil-minimal involvement of rotational movements. On cervical spine observations if the spine is bend to the rt side it also rotated to the rt side.

Clinical implications: manual repositioning of cervical disc is described by Cyriax method via employing lateral translations in cervical spine (4).

Review of cervical spine coupling behavior (1):
1. 100% agreement in coupling direction (side flexion and rotation to the same side) in lower cervical vertebral segments (C2-3 and lower) but
2. Variation in coupling patterns in the upper cervical segments of occiput-C1 (during side flexion initiation) and C1-2.

Upper cervical spine coupling mechanics:

3-D MRI study (3) reveals:

1. The normal atlanto-occipital axial rotation varies approximately between (2-3) degrees. Similarly, atlanto-axial axial rotation is approximately (32-40) degrees.
2. With contribution of atlanto-occipital axial rotation the contribution of atlanto-axial axial rotation reduces.
3. Coupling mechanism is as follows:
a. Lateral bending is coupled with opposite side axial rotation at both atlanto-occipital & atlanto-axial levels. The degrees of coupling at for atlanto-occipital & atlanto-axial are different. For the atlanto-occipital joint side bending opposite side rotation is between 3-6 degrees, and for atlanto-axial joint side bending opposite side rotation is between 1-7 degrees.
b. In extension atlanto-occipital joint can axially rotate 10-18 degrees and atlanto-axial joint 4-10 degrees.

References:

1. Cook C et al; Coupling behavior of the cervical spine: a systematic review of the literature. J Manipulative Physiol Ther. 2006 Sep;29(7):570-5.


2. Deed E Harrisona et al ; Cervical coupling during lateral head translations creates an S-configuratio. Arthroscopy. Volume 15, Issue 6, Pages 436-440 (July 2000)


3. Ishii T et al; Kinematics of the upper cervical spine in rotation: in vivo three-dimensional analysis. Spine (Phila Pa 1976). 2004 Apr 1;29(7):E139-44.


4. Criax J; Text book of orthopaedic medicine vol.II, 11th edition, AITBS publication





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