Alteraciones bioquímicas

morphologically different from the C2–C3 level, still share common characteristics. The cervical intervertebral joints are a saddle shape in which the inferior surface of the superior vertebra is concave in the sagittal plane and the superior sur- face of the inferior vertebra is concave on the trans- verse plane. Additionally, the orientation of the superior surface of the inferior vertebrae is oblique, sloping caudally and anteriorly, while the anterior inferior border of each vertebra forms a lip that hangs towards the anterior superior edge of the ver- tebrae below. Consequently, the plane of the inter- vertebral disc is set obliquely to the long axis of the vertebral bodies (Bogduk & Mercer, 2000) and to the plane of the apophyseal joints (Penning, 1988). This geometry dictates that the primary motion at this level is flexion and extension around a transverse axis of rotation. Studies on the flexion– extension centres of motion revealed that their loca- tion changes from a dorso-caudal location on the body of the C3 vertebrae, moving progressively to the centre of the C7 cranial end plate, maintaining an equal distance from the mid-perpendicular apophyseal joint spaces. Consequently, the pattern

of motion for flexion and extension of the cervical spine consists of gliding in the upper segments of the typical cervical spine while in the lower levels the pattern is one of tilting which is the most stable (Penning, 1988).

A literature review (White & Panjabi, 1978) con- cluded that the representative angle for flexion– extension for C3–C4 is 13, 12 for C4–C5, 17 for C5–C6, 16 for C6–C7 and 9 for C7–T1. However, Panjabi et al (2001) reported the smaller average ranges of motion for flexion–extension of 7.7for C3–C4, 10.1for C4–C5, 9.9for C5–C6, 7.1for C6–C7.

A more recent study (Wu et al, 2007) reported mean flexion and extension of the cervical motion seg- ments. More specifically, they reported a mean of 7.56of flexion coupled with a mean of 0.98 mm of anterior translation and 9.05 of extension coupled with 1.13 mm of posterior translation at C3/C4 levels. The corresponding results were 9.86 flexion with 1.15 mm of anterior translation and 11.24of exten- sion with 1.26 mm of posterior translation of the C4/C5 level, 9.24of flexion with 1.15 mm of ante- rior translation and 9.88of extension with 1.19 mm of posterior translation at the C5/C6 level. For the C6/C7level, flexion was measured at 9.73 with 0.93 mm of anterior translation and 7.91of extension coupled with 0.29 mm of posterior translation.

The fact that the cervical intervertebral joints are saddle joints means that the vertebra is also free to move side to side in the plane of the facets around an oblique axis perpendicular to the plane of the facets, in an angle of 45 to the transverse plane (Bogduk & Mercer, 2000). However, this axis does not pass through the apophyseal joints or the discs but through the cranial vertebral body (Penning, 1988). The geometry of the articular surfaces and the movement around the oblique axis dictate that horizontal rotation and side-flexion are always coupled to the same side (Bogduk & Mercer 2000; Penning, 1988). Not surprisingly all studies report- ing on the coupling motion of rotation and side- flexion of the motion segments from C3 to T1 agree that the coupling is always on the same side regard- less of which of the two side-bends or rotation is the initiating movement (Cook et al, 2006). The only exception is the contralateral coupling with lateral flexion initiation reported in the study of Ishii et al (2006) at the C7/T1 level.

Further studies have determined the centre of rotational motion to be localized in the ventral

contour of the vertebral body for both lateral flexion and rotation (Lysell, 1969; Penning, 1988). The position of the centre of rotation anteriorly means that during coupled rotation and side-flexion, more movement occurred at the posterior part of intervertebral joint and less at the anterior.

This characteristic movement pattern is reflected by the morphology of the intervertebral disc. The cervical intervertebral disc is distinctively different from the lumbar one in that it lacks concentric annulus fibrosus, and its core is fibrocartilaginous and has the consistency of soap (Mercer & Bogduk, 1999). The annulus fibrosus is thicker anteriorly and consists of layers of fibres that arise out of the superior surface of the inferior vertebra and insert on the inferior surface of the inferior vertebra. The outer layer of the annulus is orientated vertically at its central part and obliquely at its lateral parts from inferio-lateraly at its origin from the uncinate processes to anteriorly at the inferior margin of the superior vertebra (Mercer & Bogduk, 1999). The thickness of the annulus is about 2 to 3 mm. The deeper fibres of the annulus are orientated obliquely from inferio-laterally to superio-medially and interwoven with the corresponding fibres of the opposite side, towards the midline. The deeper fibres follow the same pattern but they insert more towards the midline of the superior vertebra (Mercer & Bogduk, 1999). This arrangement is con- sistent with the vertebrae pivoting about its anterior end as the majority of the fibres are arranged as an inverted ‘V’ pointing its apex at the centre of rotation (Bogduk & Mercer, 2000).

The annulus fibrosus is largely lacking posteriorly with only a few fibres in a lamina of about 1 mm thickness, vertically orientated. However, for the larger part of the posterior disc to the uncinate pro- cesses there is no annulus (Bogduk & Mercer, 2000; Mercer & Bogduk, 1999). Another characteristic of the cervical disc is the development of transverse fissures at the posterior part of the cervical discs. The fissures first appear at the age of 9 years as clefts in the unconvertebral region and progressively extend medially to form transverse clefts in the third decade of life (Bogduk & Mercer, 2000). With age, the clefts have a tendency to break through transversely, resulting in the posterior disc being comprised of two parts (Mercer & Jull, 1996). It is not clear if the development of transverse fis- sures is a result of the development of the uncinate processes, an early pathological change, or the result

of the shearing forces of rotation (Mercer & Jull, 1996). Whatever the explanation, their presence allows or facilitates axial rotation (Bogduk & Mercer, 2000).

The morphological and geometrical characteris- tics discussed above support a pattern of movement of the typical cervical intervertebral movement of coupled side-flexion and rotation of the same side, in which the superior vertebra pivots about its ante- rior part and slides with its posterior. Few studies have reported on the ranges of motion of the inter- vertebral segments. At the C3/C4 level, White and Panjabi (1978) reported representative angles of 11 of side-bending and 11 of rotation. Mimura et al (1989) reported a 5.8 rotation from right to left at this level coupled with a side-flexion of 6.2 and a 2.9 of extension at this level. Penning and Wilmink (1987) reported a mean of 3 of rotation from right to left. Ishii et al (2004a) reported 4.5 of axial rotation coupled with lateral-bending at the same side, extension, inferior translation, oppo- site lateral translation and posterior translation. Ishii et al (2006) found 3.5 of lateral-bending coupled with axial rotation of the same side, flexion, supe- rior translation lateral translation to the opposite side and anterior translation of the vertebra. Simi- larly, Panjabi et al (2001) reported 5.1 of axial rotation from right to left and 9.1 of lateral- bending from right to left.

For the C4/C5 level, White and Panjabi (1978) reported a mean 11 of right to left side-flexion and a mean 12 of rotation from left to right and Penning and Wilmink (1987) reported a mean 6.8 of rotation from right to left while Mimura et al (1989) reported a mean of 4.2 rotation from right to left with a mean of 6.2 of lateral-bending to the same side and a mean of 2.1of extension. For the same level, Panjabi et al (2001) reported a mean of 6.8right to left rotation and 9.3mean right to left side-flexion. Ishii et al (2004a) found that the C4/C5 level rotates to a mean of 4.6and it is cou- pled with ipsilateral side-flexion, extension and con- tralateral lateral translation while Ishii et al (2006) reported a mean of 3.3 of lateral-bending coupled with ipsilateral rotation, flexion, superior trans- lation, contralateral coupled lateral and posterior translation.

At the C5/C6 level, White and Panjabi (1978) reported a representative angle of 8 of lateral- bending and an angle of 10 of rotation, while Penning and Wilmink (1987) reported a mean of

6.9 of rotation at this level from right to left. Mimura et al (1989) state an average of 5.4of total rotation coupled with a mean of 4 of ipsilateral lateral-bending and 2.1 of flexion, while Panjabi et al (1988) reported a mean of 5.1 of rotation and a 6.5 of lateral-flexion respectively. Ishii et al (2004b) reported a mean of 4 of rotation coupled with ipsilateral lateral-bending, flexion, superior, opposite lateral and anterior translation while side- flexion, according to Ishii et al (2006) was measured to an average 4.3 coupled with ipsilateral rota- tion, flexion superior, opposite lateral translations. Similarly, for the C6/C7 level the average range of side-flexion reported by White and Panjabi (1978) was 7 and 9 of rotation. An average range of 5.4 of rotation has been reported by Penning and Wilmink (1987) and a slightly higher average range of 6.4 coupled with ipsilateral lateral-bending of 2.7 and 2.5 of flexion has been reported by Mimura et al (1989). An even lower rotation range of motion has been reported by Panjabi et al (2001) at 2.9 and an average range of lateral- bending of 5.4. Similarly, Ishii et al (2006) reported an average of 5.7 of lateral-bending coupled with ipsilateral rotation, flexion, superior and contralateral lateral translation; there was also an average range of rotation of 1.6 coupled with ipsilateral lateral-bending, flexion, superior opposite lateral and anterior translation of the vertebra.

At the C7–T1 level the average ranges, according to White and Panjabi (1978), are 4 for lateral- bending and 8 for rotation, while Penning and Wilmink (1987) reported 2.1 of rotation. Ishii et al (2004a) reported an average of 1.5of rotation coupled with ipsilateral lateral-bending, flexion, superior, opposite lateral and anterior translation. However, Ishii and colleagues’ results (Ishii et al, 2006) disagree with the results of more studies at this level as they report a mean of 4.1 of lateral- bending coupled with contralateral rotation to a mean of 0.4 also coupled with flexion, superior ipsilateral lateral translation. The results of the studies of Ishii et al (2006) and Ishii et al (2004a) reveal that regardless of which movement initiates the coupling, the range of the lateral flexion compo- nent of the movement is greater in range than the rotation component. Furthermore, there is no pro- gressive reduction of the available range, as is expected from the top to the bottom of the typical cervical spine column.

Clinical point

Whilst rotation and lateral flexion are coupled

ipsilaterally the motion segment also undergoes a small degree of contralateral translation in the mid to upper cervical spine. It is possible that motion segments that are likely to benefit from manipulative techniques, inducing cavitation-mediated improvement in passive movement, will be those that have developed a reduction in this contralateral side glide. The perception and use of contralateral side glide is at the centre of the assessment for and the treatment with manipulative thrust techniques.

Assessment of the mid and