13.3 Required Basic Anatomical and Biomechanical Knowledge

13.3.1 Sections of the Cervical Spine

Due to its morphology, biomechanics, and the presence or absence of intervertebral disks, the cervical spine is divided anatomically and functionally into (▶ Fig. 13.4):

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Fig. 13.4 Sections of the cervical spine.

  • Upper cervical spine:

    • anatomically: atlas and axis;

    • functionally: C0/C1 and C1/C2 segments; also called the segments without intervertebral disks.

  • Lower cervical spine:

    • anatomically: C3–C7;

    • functionally: C2/C3 to T3/T4 segments; also called the segments with intervertebral disks.

13.3.2 Anatomy of the Lower Cervical Spine

The physiological curvature of the cervical spine is lordotic, with the C3/C4 segment usually positioned horizontally (White and Panjabi, 1990).

The vertebral body’s end plate is very narrow, favoring rotation. The vertebral foramen is very large due to the long laminae of the vertebral arches. The spinal cord only occupies approximately 50% of the vertebral foramen’s very wide diameter. The large vertebral foraminae provide the dural sac with a generous amount of space to move in during large cervical movements (White and Panjabi, 1990).

The wide laminae are well developed (being approximately as wide as an index finger) and can be palpated underneath the muscles. They are located at the level of the spinous processes. The articular processes protrude from the end of the laminae.

The zygapophysial joints (ZAJs) form the “articular column” (see ▶ Fig. 13.4) that is almost as wide as the row of transverse processes. The vertebrae, as a whole, have very wide bases due to the extremely lateral position of the joints, which results in the lower cervical spine not being particularly ideal for movement into lateral flexion. A narrow base (less distance between the left and right ZAJs), as is seen in the lumbar spine, is more conducive to lateral flexion.

The spinous processes are bifurcated down to C6. The bifurcation at C2 is very large and extremely asymmetrical. The spinous processes decrease in size down to C6. A large spinous process is seen again at C7 and is not bifurcated at this level. The asymmetrical bifurcations in the spinous processes interlock during extension and optimize the range of motion for the lordosis.

The transverse process is composed of two tubercles that connect laterally and form a hole at one point. This foramen transversarium has a diameter of approximately 4.5 to 5 mm, which almost corresponds to the diameter of the vertebral artery.

The anterior tubercle is a rudiment of a rib, while the posterior tubercle represents the actual transverse process. These two tubercles turn the transverse process into more of a groove than a process. The groove runs diagonally and is oriented anterolaterally (▶ Fig. 13.5).

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Fig. 13.5 Typical vertebra in the lower cervical spine.

The groove is at its narrowest in its medial section and is bordered by bones on all sides. The uncinate process forms the anterior border; the superior articular process of the ZAJ the posterior border.

The artery and the ventral ramus of the spinal nerve cross paths at this bony constriction (▶ Fig. 13.6). Both of these conductive pathways can be compressed and irritated by protruding osteophytes associated with severe degenerative changes in the segment. Of all the sections of the vertebral column, stenosis of the intervertebral foramen most often irritates nerves in the cervical spine.

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Fig. 13.6 Neurovascular cross.

The uncinate process (also called the uncus of body) deserves a special mention. This process forms the side rim of the vertebral body’s end plate and its size increases in the more superior vertebrae. The uncinate processes are the largest on the C3 end plate. They develop between the ages of 2 and 24 and later form the uncovertebral joint with the more superiorly positioned vertebral body. During this development, the intervertebral disks tear on the outer sides from approximately the age of 10 onward (▶ Fig. 13.7). This can lead to bisection of the disk (Rauber and Kopsch, 2003). When this occurs, the contents of the nucleus pulposus neither leak out nor does the segment become thinner. This bisectioning is complete between the ages of 45 and 50. This is a natural adaption of the intervertebral disks in response to the large translation of the vertebra during cervical spine flexion and extension. The uncinate processes act as rails and guide this translation movement. The bisectioning of the disk is the reason why whiplash can cause height to increase by up to 2.5 cm (abnormal ability to separate) within seconds and is especially seen in the C2/C3 segment.

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Fig. 13.7 Formation of horizontal tears in the cervical intervertebral disk.

How Does this Affect Palpation?

In the cervical spine, a relatively large number of bony structures, joints, and muscles can be reached and differentiated from one another using palpation. Important reference points include the accessible spinous processes (C2, C5–C7) and the laminae of every cervical vertebra inferior to C2. The fact that the spinous process and laminae of a vertebra are located at the same level is very convenient for palpatory orientation.

This is of assistance when the exact level of structures, for example, the ZAJ and the transverse process, is being determined. The laminae can be used to fix a vertebra during certain manual therapy techniques.

When all accessible ZAJs (articular column) are palpated from superior to inferior, the protruding processes and the more concave sections between the processes have an undulating shape (▶ Fig. 13.8).

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Fig. 13.8 Palpating a zygapophysial joint (ZAJ).

The cervical transverse processes are aligned diagonally in an anterolateral direction so that the ventral rami and the brachial plexus can be palpated between the sternocleidomastoid and the descending part of the trapezius (see “Supraclavicular Triangle of the Neck” below).

13.3.3 Lower Cervical Spine Biomechanics

The range of motion in the cervical spine is dependent on age and gender (Penning, 2000). Young women are the most mobile. The largest range of motion is seen with rotation, followed by flexion and extension. Lateral flexion has the smallest range of motion. Lateral flexion is quite complicated in the cervical spine and is mainly used in association with rotation (coupled movement).

The alignment of the ZAJ surfaces is crucial for determining how rotation and lateral flexion are conducted. The joint surfaces are large and flat and are aligned at an average angle of 45° anteriorly and superiorly toward the end plate (▶ Fig. 13.9; Dvořák et al., 1998). Penning (2000) reported a large variation in angles. In connection with cervical lordosis, therapists can note that the joint surfaces are generally aligned anteriorly and superiorly toward the eye socket.

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Fig. 13.9 Alignment of the zygapophysial joints (ZAJs) in the sagittal plane.

Almost all lower cervical joint spaces are aligned horizontally in the frontal plane. Only the C2/C3 segment is angled in a superior direction (▶ Fig. 13.10).

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Fig. 13.10 Alignment of the zygapophysial joints (ZAJs) in the frontal plane.

Due to the alignment of the joint surfaces, rotation is inevitably coupled with lateral flexion and the axis of rotation is tilted (▶ Fig. 13.11). Corresponding to this, rotation to the right is accompanied by lateral flexion to the right, regardless of whether the cervical spine is positioned in flexion or extension. Lateral flexion to the right is also accompanied by rotation to the right. The range of the coupled motion is surprisingly large in the cervical spine. Lysell (1969) stated that approximately 8° of lateral flexion at the C2/C3 segment is connected with approximately 6° of coupled rotation.

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Fig. 13.11 Position of the axes of rotation.

During lateral flexion to the right and the associated ipsilateral rotation, the joint surfaces on the right glide together (convergence), just as they do during extension. The joint surfaces on the left glide away from one another (divergence), similar to the movement during flexion (▶ Fig. 13.12).

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Fig. 13.12 Movement of the joint surfaces during lateral flexion and rotation to the right.

How Does this Affect Palpation?

Therapists use the two previously described relationships to their advantage when palpating the lower cervical facet joints (inferior to C2/C3) during movement: the degree of coupling and the movement of the joint surfaces as they converge.

Therapists aim to feel the posteroinferiorly directed swaying of the joint processes as the ZAJ moves (see “Facet Joints” below). They therefore facilitate lateral flexion with rotation to the right when they are palpating the right side, so that the joint process moves toward the palpating finger. Movement is facilitated via lateral flexion and causes the segment to rotate extensively. If rotation was facilitated first, it would take quite a while for C1/C2 to reach end-range rotation and for rotation to be transferred onto the inferior segments.

Penning (2000) has explained the kinematics during flexion and extension very well. His study results describe the momentary rotation axes for flexion and extension and were radiologically determined for every 5° of movement. The investigators discovered a relationship between the superior joint processes and the end plate, which determines the position of the axis for rotation. In the upper intervertebral disk segments the axis is located in the inferior vertebra and results in the superior vertebra undergoing a large translation movement in addition to tilting during flexion and extension (▶ Fig. 13.13). In the lower intervertebral disk segments, the axis is found near the intervertebral disk. The tilting movement is therefore very large and the translation minimal (▶ Fig. 13.14).

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Fig. 13.13 Position of the rotation axis for flexion and extension at C2/C3.

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Fig. 13.14 Position of the rotation axis for flexion and extension at C6/C7.

The large translation, for example, in the C2/C3 segment, produces strong shear forces that act on the intervertebral disk. These forces must be seen as having a direct relationship with the bisectioning of the intervertebral disk and the development of the uncinate process.

The uncovertebral joints control lateral flexion and ensure that the coupling of segmental rotation and lateral flexion is transferred quickly onto the next inferiorly located segment (▶ Fig. 13.15). As joints that develop with age, the uncovertebral joints can also cause local lateral cervical symptoms during lateral flexion when disorders are present.

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Fig. 13.15 Uncovertebral joints during lateral flexion.

13.3.4 Anatomy of the Occiput and the Upper Cervical Spine

The upper cervical spine is responsible for supporting the sense and balance organs (Herdman, 2000), for example, by coupling eye and head movements (cervico-ocular reflex) with the aim of stabilizing the field of vision.

The upper cervical spine “contains the most complex, unique, and highly specialized structures” in the vertebral column (White and Panjabi, 1990). Anatomy varies greatly at the junction between the head and the cervical spine. These deviations from the norm affect the expected results of the local palpation of bony structures to a limited extent only. The effect of some anatomical variations is so extreme, and even pathological, that they are described as deformities. The following deformities directly influence palpation:

  • Minimal development of the occipital condyles causes the dens to protrude into the inner skull. The malformations are labeled “primary basilar impressions” (von Lanz and Wachsmuth, 1979) and may result in neurological deficits. When condyles have a flattened form, it is difficult to palpate the transverse process of the atlas as the process is found directly underneath the occiput.

  • When the atlas and occiput are fused together, the C0/C1 segment is immobile (occipitalization; present in less than 1% of the population).

Occipital Bone

The occiput is composed of two large areas:

  • Posterior section: squamous part of the occipital bone.

  • Inferior section: lateral and basilar parts.

The squamous part of the occipital bone (▶ Fig. 13.16) is the rounded posterior region of the roof of the skull. It is connected to the parietal bones via the lambdoid suture and the temporal bones via small lateral sutures. It is divided into two flat areas called the occipital plane and the nuchal plane. Each area has a different function. The nuchal plane is covered by the neck muscles and is separated from the occipital plane by the superior nuchal line. The transverse lines and ridges, protrusions, and areas found on the nuchal plane can be palpated particularly well.

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Fig. 13.16 Posterior aspect of the occipital bone.

The external occipital protuberance is the most prominent point. It represents the end of a medium-sized crest that travels in a posterosuperior direction from the foramen magnum and also marks the site of insertion for the ligamentum nuchae. Von Lanz and Wachsmuth (1979) describe this reference point very precisely. The shape of the protuberance varies greatly and it often tapers downward. It is only well developed in approximately 11% of all individuals. The point protruding the most is called the “inion.” This elevation is more developed in pets (e.g., dogs and cats) than in humans. This is due to larger loads being applied to the ligamentum nuchae of these animals, which in turn places more tension on the site of insertion.

The position of the three transverse ridges can be described in relation to the protuberance:

  • Highest nuchal line. This convex line starts directly on the protuberance and extends laterally and somewhat superiorly. It is the line of insertion for the extensive mimic muscles that are able to move the scalp and the ears to some extent. It is rarely well developed and may also be completely absent.

  • Superior nuchal line. This widely arched, convex line also travels laterally, extending from a position slightly inferior to the protuberance. Von Lanz and Wachsmuth (1979) estimate that approximately 37% of all superior nuchal lines are well developed. The large intrinsic muscles are noticeable directly below this line: semispinalis cervicis, splenius capitis, and the descending part of the trapezius.

  • Inferior nuchal line. This line is found 1 finger width inferior to the protuberance. It first travels transversely and later bends anteriorly, almost at a right angle. The transverse section meets with the superior nuchal line laterally. Together, both of these lines can form a palpable elevation: the retromastoid process (von Lanz and Wachsmuth, 1979). The inferior nuchal line marks the site of insertion for the deep neck muscles (rectus and obliquus muscles).

The inferior aspect of the occipital bone is divided into two sections (▶ Fig. 13.17). The lateral part is characterized by the area surrounding the foramen magnum. With its diameter of 3 to 3.5 cm and its bulging rim, the foramen magnum forms a passage for the spinal cord and other structures. Two biconvex condyles are found laterally and are divided into two separate parts in 5% of the population (Rauber and Kopsch, 2003). The division of the joint cartilage is an indication of the different types of loading applied to the cartilage surfaces during flexion and extension at the C0/C1 segment. As already mentioned, anatomy also varies considerably here. The condyles are aligned so that they converge anteriorly. The basilar part is similar to a wedge-shaped piece of bone and is connected to the sphenoid bone anteriorly.

Dec 4, 2021 | Posted by in GENERAL SURGERY | Comments Off on 13.3 Required Basic Anatomical and Biomechanical Knowledge

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