CERVICAL SPINE ANATOMY The cervical spine region involves the uppermost vertebrae of the spine and the connection to the skull. The region is considered one of the most challenging to treat using manual therapy interventions (Table 5.1). Table 5.1: General Information Regarding the Cervical Spine Region. Concept

Information

Bones Number of dedicated joints Anatomical regions

Seven primary bones of the cervical spine 37 joints, most mobile spinal region

Theoretical resting position Theoretical close-pack position Theoretical capsular pattern

2 distinct regions: upper (C0-1 to C1-2) and lower cervical spine (C2-3 to C7-T1) Slight extension Full extension Side bend and rotation equally limited, extension

UPPER CERVICAL SPINE ANATOMY The upper cervical segments are formed by the articulation of the occiput on C1 (OA joint) and the articulation of C1 on C2 (AA joint) (1). This region includes selective joints and ligaments but does not include an intervertebral disc (2). Of the two aspects of the cervical spine, the upper cervical spine is the most complex and predisposed to injury by trauma.

Figure 5.1: The Upper Cervical Spine Anatomy

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Within the OA joint, the cup-like configuration provides anatomical structure and stability along with an extensive connective tissue arrangement. The occipital condyles and the superior articular facets of the atlas slope downward and medially, providing an orientation that promotes upper cervical extension (3). The condylar arrangement leads to both an anterior and posterior atlantoodontoid articulation within the OA joint (3). The atlas (C1) is peculiar when compared to other vertebral bones because it has no vertebral body. The atlas is essentially a ring-like, hollow structure that is intimately attached to the axis. The atlas has no spinous process and consists of an anterior and a posterior arch and two lateral masses; the anterior arch forms about one-fifth of the ring. The atlas’s anterior surface is convex and presents at its center the anterior tubercle for the attachment of muscles.

Figure 5.2: The Atlas and Axis The axis (C2) is uniquely shaped as well and forms the pivot upon which the atlas rotates. The most distinctive characteristic of this structure is the strong odontoid process that rises perpendicularly from the upper surface of the body. The odontoid process of the axis is the attachment site of numerous ligaments and is considered an imperative structure of stability. The axis does have a bifid spinous process that is quite prominent and is the attachment site of numerous posteriorly oriented muscles. An extensive connective tissue arrangement exists in the upper cervical region where the range of motion between vertebrae is greater than any other spine segmental region (4). This

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complex arrangement is designed to control movement while providing stability through the interaction of various ligaments. The anterior longitudinal ligament, the anterior atlanto-dental ligament, the tectorial membrane, the dentate ligaments, and the cruciform ligaments are recognized as crucial contributors to stability, while some of the connective tissue elements such as the ligamentum nuchae and the anterior longitudinal ligament are considered controversial (5). The anterior longitudinal ligament, cruciform ligament, tectorial membrane, and nuchal ligament attach to the occiput, C1 and C2 (3) and the anterior occipitoatloid membrane, atlanto-odontoid ligament, apical ligament of the dens, Alar ligaments, posterior occipitoatloid membrane, and the atlantoaxial membrane are limited in attachment to two of the three bones (3). White and Panjabi (5) state that the cruciform ligament is the most important ligament of the C0-C1-C2 complex. This ligament consists of both transverse and vertical portions with the transverse portion providing the most important stabilizing function (3). Fundamentally, the primary role of the cruciform ligament is to prevent the atlas from translating anterior on the axis during flexion. Uncontrolled translation would result in compromising the spinal cord, medulla, and potentially the arteries of the neck. The dentate ligaments include the Alar and apical ligaments. The Alar ligaments are a pair of structures that attach to the dorsal-lateral surface of the dens and runs obliquely to the medial surfaces of the occipital condyles (4). During side bending of the head on the neck, the occipital portion of the Alar ligament on the side that is side flexed toward is relaxed, while the Alar ligament on the side opposite of the relaxed band is tightened. During rotation, the Alar tightens on the side opposite of the direction of rotation (6). Subsequently, the left Alar ligament tightens and restricts rotation of the head and C1 to the right (5). The tectorial membrane is an extension of the posterior longitudinal ligament (5). The tectorial membrane is located between the cruciform ligament and the atlas anteriorly and the anterior dura mater posteriorly and is thought to be a continuation of the anterior longitudinal ligament. It is proposed that this ligament may function to prevent traction-based movements (5). The key ligaments and connective tissue of the cervical spine are described in Table 5.2 and Table 5.3. Cook, Orthopedic Manual Therapy: An Evidence-Based Approach, 2/E © 2012 by Pearson Education, Inc., Upper Saddle River, NJ

Table 5.2: Joints of the Cervical Spine. Joint

Information

Intervertebral disc Zygapophyseal (facet) joints

First disc at C2-3; intervertebral discs at all subsequent inferior levels Synovial, planar, diarthrodial joints. All cervical joints are weight bearing in the upright postures. Facets are in a plane 45° between the frontal and horizontal planes. This allows significant movement in all 3 planes

Uncovertebral joints

Also described as the joints of von Luschka; formed by the uncovertebral process—a raised lip on the superior-lateral surface of the vertebral bodies. Develop by age 6–10. Convert the planar superior vertebral plateau to a concave beveled surface. The concave superior surface of the vertebra receives the vertebral body above and articulates with it to form the uncovertebral joint. Debated as to what type of joint it is (i.e., synovial, type, etc.). Limit side bending and guide flexion and extension

Table 5.3: Ligaments and Connective Tissue of the Cervical Spine. Name

Location

Function

Anterior longitudinal ligament

Attaches to the occiput, C1 and C2, the anterior occipitoatloid membrane, and the anterior aspects of the discs and vertebrae of the cervical spine Surround the condyles of the occipital bone and connect them with the articular processes of the atlas Extends from tip of the dens to anterior edge of foramen magnum Two ligaments that arise one on either side of the upper part of the odontoid process and, passing obliquely upward and lateral, are inserted into the rough depressions on the medial sides of the condyles of the occipital bone

Crucial contributor to stability. Helps retain form of intervertebral disc

Articular capsular ligaments

Apical

Alar

Transverse

Attaches to the occiput, C1 and C2 (10), and the anterior occipitoatloid membrane

Assist in stabilizing joint capsules

Controversial contributor to stability. Limits traction-based movements Crucial contributor to stability. During side bending of the head, the alar ligament on the side that is side flexed toward is relaxed, while the alar ligament on the side opposite is tightened. During rotation, the alar tightens on the side opposite of the direction of rotation. Subsequently, the left alar ligament tightens and restricts rotation of the head and C1 to the right Most important ligament of the C0C1-C2 complex. Prevents the atlas from translating anterior on the axis during flexion

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Ligamentum flavum Posterior longitudinal ligament

Overlies the space between the laminae of adjacent vertebrae and the neural arches Attaches to the occiput, C1 and C2, the anterior occipitoatloid membrane, and the posterior aspects of the discs and vertebrae of the cervical spine

Helps restrain hyperflexion Stabilizes flexion and reinforces posterior aspect of annulus

The muscles of the upper cervical spine are compartmentalized into three layers—the superficial, the middle, and the deep layer (7), each layer contributing different elements of mobility and stability to the upper cervical spine. Panjabi (8) described a form of dynamic stability response, which is provided by muscular control during movements in mid or early ranges. This concept is distinguished from passive stability, in which stabilization is obtained through passive structures such as ligaments, discs, bones, and joint capsules.

Summary • • •

The upper cervical spine demonstrates unique bony and ligamentous stabilization systems. The complex arrangement of ligamentous structure in the upper cervical spine is responsible for movement control and stability. It is theorized that different muscles of the upper cervical spine are responsible for stabilization and movement initiation.

LOWER CERVICAL SPINE ANATOMY The lower cervical segments include the segmental levels of C2-3 to C7-T1 and are noted more for their similarities than differences. All the segments exhibit intervertebral discs, uncinate processes, and spinous processes (5). Passive spine integrity is imposed by a combined stabilization effort of the zygapophyseal joints, uncinate processes, intervertebral discs, and other passive structures. Although all vertebrae demonstrate significant similarities, Lysell (9) considered the C2 vertebral body unique as a transitional vertebra that divides the functions of the cervical spine.

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Figure 5.3: The Lower Cervical Spine Anatomy There are five primary articulations between adjacent vertebrae (Table 5.4). The first is the intervertebral disc, which cushions and controls movement between two vertebral bodies. Two uncinate processes articulate laterally and provide control of side flexion–based movements, and two zygapophyseal joints guide movements such as rotation. The intervertebral discs allow movement in all three planes, plus torsion. The zygapophyseal joints are considered translational joints and allow sliding motions that depend on the orientation of the joint plane. The uncinate processes allow sliding movements as well but are thought to be limited to those associated with convex and concave movements such as side flexion and sagittal movements (5).

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Table 5.4: Key Connective Tissue of the Cervical Spine. Name

Location

Function

Tectorial membrane

Extension of the posterior longitudinal ligament. Attaches to the occiput, C1 and C2 and the anterior occipitoatloid membrane Physical continuation of the anterior longitudinal ligament and serves to connect foramen magnum with atlas Attaches to the occiput, C1 and C2, and the anterior occipitoatloid membrane Unites the posterior rim of the foramen magnum with the posterior aspect of the atlas The fibrous sheet that closes the interarcual space between the atlas and the axis

Crucial contributor to stability. May function to prevent traction-based movements

Anterior occipitoatloid membrane Ligamentum nuchae Posterior occipitoatloid membrane Atlantoaxial membrane

Restricts hyperextension motions

Controversial contributor to stability. May assist in reducing flexion Restricts hyperflexion motions Limits flexion and extension movements at AA joint

Cervical Intervertebral Disc Intervertebral discs make up the fibrocartilaginous joints between adjacent cervical vertebral bodies and are present at the levels of C2-3 to C7-T1. The intervertebral discs share passive control of movement with the uncinate processes and zygapophyseal joints and allow a specific range of motion throughout the cervical spine. Quality of range is dependent upon the thickness of the intervertebral discs relative to the horizontal dimensions of the vertebral bodies (10); subsequently, younger individuals that display greater disc heights also demonstrate greater range of motion on average. The cervical intervertebral disc has both similarities and dissimilarities to the lumbar disc. Similar to the lumbar spine, each intervertebral disc contains an annulus fibrosis and interiorly a gellike nucleus pulposus. However, unlike the lumbar disc, an annulus is lacking a posterior (11), and the separate physical disc-properties of a nucleus and annulus are reserved for younger populations. As one ages, the nucleus is replaced by fibrocartilage and other fiber components, typically occurring

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as early as the second decade of life (12). An additional dissimilarity is the fiber direction of the annulus, which is not crossed concentrically as in the lumbar spine but arranged horizontally, converging upward toward the anterior aspect of the superior adjacent vertebral body (11). Additionally, the annulus fibrosis does not encompass the entire perimeter of the disc (11), potentially predisposing the disc to degenerative processes such as horizontal fibrillation. As Bogduk and Mercer (13) note, “The cervical annulus is well developed and thick anteriorly; but it tapers laterally and posteriorly towards the anterior edge of the uncinate process on each side.” Beyond the uncovertebral joint, the primary integrity of the posterior disc is enclosed by the posterior longitudinal ligament (PLL). The PLL is located on the posterior surface of the vertebral bodies within the spinal canal and progresses from an attachment to the C2 vertebra to the dorsum of sacrum (14). Essentially, the PLL is constructed in two layers: a thick anterior layer that is firmly attached to the posterior annulus and vertebral bodies, and a thin posterior layer loosely attached to the thick anterior layer but completely unattached to the dura (21). The PLL does contribute significantly to segmental stability, specifically in patients with degenerative conditions (15), although its complete role during stabilization is controversial.

Figure 5.4: The Cervical Intervertebral Disc: Concept Adapted from Mercer and Bogduk, 1999 (11)

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The Cervical Facet (Zygapophyseal) The cervical facet, or zygapophyseal, joints are progressively oblique from the cephalic segments to the caudal segments (16) and connect the lamina of each vertebral body. There are two facet joints between each pair of vertebrae, one left and one right, which are primarily designed to allow the vertebral bodies to rotate with respect to one another. The lower cervical segments are convex or concave and are nearly 45 degrees in inclination. There is some degree of angular change from cephalic to caudal in normal individuals, although this change is not constant or normative across subjects (17). In healthy individuals, the uneven surfaces within the zygapophyseal joints are filled by an invagination of the posterior capsule called a meniscoid (18). Meniscoids are fatty and highly innervated and frequently are involved in entrapment impairments on the cervical spine. Meniscoids function similarly to the meniscus of the knee in improving joint congruency. The posterior capsule is less thick than the anterior capsule, often integrates with a meniscoid and the multifidi musculature, and is vulnerable to injury (10). During degenerative conditions, the posterior capsule becomes lax and allows possible displacement during neutral postures. Additionally, degenerative progression often causes the meniscoids to atrophy and virtually disappear, thus decreasing the integrity and stability of the zygopophyseal joints even further (19). In normal subjects or those that experience early degenerative changes, articular facet impingements are common in large synovial folds, while subluxation of the facet is more common when the meniscoids have degenerated or represent less space within the facet (20). The anterior joints do not articulate with meniscoids and have capsules that are normally lax and permit large ranges of movement during neutral postures (10).

Figure 5.5: The Cervical Zygopophyseal Joints Cook, Orthopedic Manual Therapy: An Evidence-Based Approach, 2/E © 2012 by Pearson Education, Inc., Upper Saddle River, NJ

Uncinate Processes (The Joint of Luschka) The uncinate processes, or the joints of Luschka (21), are unique to the cervical spine and are found at levels C3 to C7. Essentially, these saddle-like formations increase the joint surface of the vertebral body of the above segment with the lower segment. Uncinate processes are developed during childhood and fully mature by the second decade (21). Lateral fissures in the disc create a transformation that enlarges the lateral aspect of the annulus and encourages the articulation of the uncovertebral joints. By the second and third decade of life, the uncinate processes become fully articular with the development of a pseudosynovial joint (21). The contact points are covered with articular cartilage and are considered true articulations but do exhibit a unique characteristic of both fibrocartilage and vascular contact points. The anterior part of the joint capsule of the uncovertebral joint blends with the annulus fibrosis of the disc (19). The uncinate processes contribute significantly to control of sagittal and coronal range of motion (22). Degeneration of the uncinate processes is one of the chief reasons behind cervical spondylogenic changes and cervical radiculopathy (19). These degenerative processes appear to coincide with intervertebral disc alterations of proteoglycan content (21).

Selected Muscular Anatomy Bergmark (23) suggests that muscles within the trunk are best divided into local and global groups. The local muscles are deep and the global muscles are generally superficial. The deep portions of some of the local muscles have their insertion and origin at the vertebrae in order to control the curvature of the spine and provide stiffness to maintain mechanical stability. Bergmark (23) also suggested that local muscles often attach directly to the joint capsules. Global muscles tend to be larger and are primarily responsible for transferring and balancing external loads during prime movements. While global muscles undergo significant length change and function very little to control joint stability, local muscles undergo little length change. Most local muscles maintain an isometric contraction during their responsibility of stabilization, with specific focus of controlling shear forces at the insertion site. Subsequently, the role of the deep and local muscles is quite different from one Cook, Orthopedic Manual Therapy: An Evidence-Based Approach, 2/E © 2012 by Pearson Education, Inc., Upper Saddle River, NJ

another, a phenomenon that is very prevalent in patients with chronic neck pain (24). Falla et al. (24) report that the deep cervical flexor muscles, the longus capitis and longus colli are related intimately with the cervical osseous and articular elements, and serve an important role in control of spinal elements, which cannot be replicated by the more superficial anterior muscles. Anatomically, sternocleidomastoid has no attachments to the cervical vertebrae and does not play a role in cervical stabilization. In some cases, cocontraction of the deep and superficial muscles is required for the muscles to stiffen or stabilize the segments, especially in functional mid-ranges (24).

The Vertebral Foramen and Nerve Roots Each nerve root exits above the correspondingly numbered vertebral body from C2 to C7 in regions identified as intervertebral foramen. Nerve roots in the cervical spine are identified by the caudal segment of the intervertebral foramen. For example, the C3 nerve root exists above C3 vertebral body, as does the C5 nerve root above the C5 body. This occurs because C1 exits between the occiput and atlas (1). The intervertebral canals are a special concern because these structures house the vertebral artery as it courses to the posterior aspect of the skull. The relatively large amount of rotation available at C1-2 allows a kinking to occur to the vertebral artery on the contralateral side, in which the head is rotated (5), an action which is often the cause behind selected vertebrobasilar insufficiency responses in patients. White and Panjabi (5) suggested that 45 degrees of rotation is enough to kink the vertebral artery, thus potentially compromising blood flow.

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Figure 5.6: The Kinking of the Vertebral Artery during Rotation The spinal column is covered by a variety of structures. The lateral aspect is covered posteriorly by the lateral aspects of a superior and inferior lamina. The ligamentum flavum provides the ventral cover and is attached to two-thirds of the undersurface of the superior lamina. Inferiorly, the ligamentum flavum is attached to the superior edge of the lower lamina (25). Posteriorly, from cephaled to caudal, the neural foramen’s parameter is bound by 1 to 2 mm of the superior (descending) and inferior (ascending) facets. The superior and inferior boundaries of the neural foramen are formed by the superior and inferior vertebral pedicles (25). Of all the vertebral spinal foramina, the largest diameter is at C2-C3, which progressively decreases in size to the C6-C7 level. In a nondamaged segment, the nerve root occupies between 25 and 33% of the foramina space (8).

Summary • • • •

The lower cervical anatomy is dissimilar to the upper cervical anatomy. The cervical intervertebral discs exhibit dissimilar characteristics to those of the lumbar spine. The uncovertebral joints develop in the second decade of life and become more prominent with degenerative changes in the intervertebral disc. The intervertebral foramen and spinal column are predisposed to anatomical changes and may be the origins of cervical radiculopathy and myelopathy.

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CERVICAL SPINE BIOMECHANICS THE DETAILS Fundamentally, there are two disparate regions to the cervical spine—the upper cervical spine and the lower cervical spine. Within this textbook, there are two points of consideration associated with biomechanics of the cervical spine—range of motion and coupling behavior. (Table 5.5). Range of motion is presented in two forms—gross cervical movement and individualized segmental movements. Using the 3-Space Isotrak measurement system, Trott et al. (26) outlined normative, average gross range-of-motion values for the age groups 20–59. They found the average flexion values were 45.1 to 57.5 degrees, average extension 60 to 76.1 degrees, average left rotation 63.4 to 71.7 degrees, average right rotation 70.4 to 78 degrees, average left lateral flexion, 32.4 to 45.5 degrees, and average right lateral flexion 35.4 to 47.6 degrees. The lower values represent the age group of 50–59, identifying a notable decline of range of motion with age. Table 5.5: General Biomechanics and Movements of the Cervical Spine. Topic

General Biomechanics and Movement

Limitation of movement

The facet orientation of the cervical spine tends to limit extension and guides side bending and rotation. Flexion and extension are pure movements because they do not include secondary motions such as side bending or rotation. Rotation occurs as a unit between O-C1-C2. The head and the atlas move together on the axis. Alar ligaments resist movement of the head, not movement of the atlas, as they connect C2 to the head and not to C1.

Several methods of measurement for cervical range of motion are presented within the literature (27,28), the more sophisticated and expensive the method, the more reliable and valid the reported range-of-motion scores. Traditionally, most manual therapy clinicians measure three cardinal planes of motion (sagittal, coronal, and frontal) with a standard goniometer—a method that has exhibited fair reliability when specific guidelines are followed (Table 5.6). Nilsson et al. (29) suggest that goniometric measurements exhibit good reliability when combined movements are measured (for instance, total range of motion of flexion and extension) versus selecting an arbitrary neutral or zero

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point as a starting reference. Others whom have used the zero point method (29,30) have reported interclass coefficient values of 0.6 to 0.8, values that are moderately acceptable. For research purposes, a device that provides more accuracy in range of motion is beneficial, but for clinical purposes, the goniometric measure appears to be efficient and reliable. Table 5.6: Range-of-Motion Values for the Cervical Spine (in degrees). Joint OA AA C2-7 Total

Flexion 5 5 35 45–50

Extension 10 10 70 85

Rotation 0 40–45 45 90

Side bending 5 0 35 40

Upper Cervical Spine Range of Motion The primary planar motion at C0-1 is flexion/extension, characterized by total segmental range of motion values of 25 degrees (5). Unilateral lateral flexion is limited to 5 degrees, as is unilateral rotation (5) (Table 5.7). Table 5.7: Joint Specific Biomechanics and Movement of the Occipital-Atlanto Joint. Region

Biomechanics and Movement

OA flexion and extension

This joint generally follows the convex-concave rule, with the convex portion describing the OA joint motion with the glide opposite the direction of movement of the bone. For example, during flexion, the occipital condyles roll anterior (forward) and glide posterior (backward). The condyles roll backward during extension and slide in the direction opposite of the roll

OA rotation

There is no significant rotation at the OA joint

OA joint lateral flexion

A small amount of side-to-side rolling of the occipital condyles occurs over the superior articular facets of the atlas. At the extremes of lateral flexion there is a slight unilateral joint approximation on the side of the lateral flexion and a slight joint separation on the side opposite the lateral flexion. Thus, the head slides upon the atlas away from the direction of side flexion. Lateral glide occurs with the atlas shifting to the side of tilt (i.e., the TP of C1 translates into the concavity)

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The axial-atlanto (AA) joint allows for 50% of all cervical rotation motion (5). The occipital atlantal joint (OA) is responsible for 50% of flexion and extension of the complete cervical spine (1). Unilateral side flexion accounts for 5 total degrees whereas flexion/extension measures 20 degrees during combined values (5). It has been stated that the essential movement of the upper cervical spine occurs between the occiput and C2 and is regulated by the atlas (2). In all motion initiations, whether proximal or distal to the upper cervical spine, C1 is mobile and the movement of the occiput and C2 predicates on the initiation of the movement (2). Table 5.8: Joint Specific Biomechanics and Movement of the Atlanto-Axial Joint. Region

Biomechanics and Movement

AA Flexion and extension

Has ~15 degrees of flexion and extension, with the atlas pivoting forward during flexion and backward during extension

AA Rotation

The inferior facet of the atlas glides across the superior facet of the axis. These surfaces are slightly convex when the articular cartilage is considered. This rotation is coupled with a significant amount of extension (and sometimes flexion) depending on the alignment of forces through the axis

AA Joint lateral flexion

There is essentially no lateral flexion at the AA joint. If lateral flexion is seen on a radiograph, it may be indicative of a fracture

Lower Cervical Spine Range of Motion White and Panjabi (5) reported the mid-lower cervical range-of-motion values with a wide degree of variability (Table 5.9). C2-3, C3-4 C6-7 and C7-T1 display the lowest segmental combined flexion/extension ranges, while C4-5 and C5-6 exhibit the highest values. Unilateral side flexion progressively declines from cephaled to caudal, dropping from a peak of 10–11 degrees at C2-3, C34, and C4-5 to a low of 4 degrees at C7-T1. Unilateral rotation is greatest at C3-4 to C6-7, with nearly comparative values throughout. One exception is the lowest recorded value for unilateral rotation at C7-T1, with a reported range of 0 to 7 degrees.

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Table 5.9: Joint Specific Biomechanics and Movements of the C2-C7 Region of the Cervical Spine. Region

Biomechanics and Movement

C2-C7 Flexion and extension

Up to 20–25% of total cervical flexion takes place at the OA and AA joints, leaving the remaining 75–80% at C2-C7. Extension is limited by the inferior articular facet of the superior vertebra as this vertebra slides inferior and posterior relative to the superior facet of the inferior vertebra. Flexion is the reverse of the above process and is limited by ligamentous and capsular tension. On average there is approximately 20° of sagittal plane motion between each of the segments from C2-3 and C6-7. The largest displacement tends to occur at C5-6.

C2-C7 Rotation

Rotation is guided primarily by the spatial orientation of the facet joints. The inferior facets slide posteriorly and somewhat inferiorly on the same side as rotation and anteriorly and somewhat superiorly on the side opposite the rotation. Rotation is greatest in the more cranial segments.

C2-C7 Lateral flexion

Lateral flexion occurs primarily in the C2-7 segments. There is ~5° lateral flexion at the OA joint and none at the AA joint.

Coupling Biomechanics Cook et al. (31) reported on the coupling patterns of the cervical spine in a detailed summary of three-dimensional (3-D) investigations. Five studies qualified as 3-D analyses of coupling motion with side-bend initiation, and Table 1 outlines those findings. Every study identified the simultaneous occurrence of the coupled movements of flexion and rotation at all levels tested. Generally, there was remarkable agreement among all studies at the majority of segmental levels. All studies that tested CO-1, C2-3, C3-4, C4-5, C5-6, C6-7, and C7-1 found consistent side-bend and axial rotation to the same side. Two studies reported that side-bend and axial rotation occurred in opposition at C1-2, and two others found coupling movement to the same side. Five studies measured rotation,; two of which measured all levels. Similar to side-bend initiation, axial rotation initiation demonstrated strong agreement among researchers. All studies that

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tested C0-1, C1-2, C3-4, C4-5, C5-6, C6-7 and C7-1, demonstrated absolute agreement. Levels C0-1 and C1-2 exhibited side bend to the opposite direction as the initiated movement of axial rotation. The spinal levels C2-3, C3-4, C4-5, C5-6, C6-7 and C7-1 exhibit side bend to the same direction as the initiated movement of axial rotation. Only two studies reported the movement values of C2-3 and C3-4 and found rotation and side flexion occurred to the same side. It is worth noting that Fryette’s laws of physiological motion (32) are not included in this chapter’s discussion of coupling. In 1954, Fryette’s findings were published and were largely based upon the findings of Lovett (33). Fryette’s perception of coupling of the cervical region was that, “side bending is accompanied by rotation of the bodies of the vertebrae to the concavity of the lateral curve, as in the lumbar (spine)” (32). The findings of Fryette are not included because they did not contain a systematic, investigatory method of evaluation and were 2-D at best. Lastly, the ability to perform a specific movement by use of apposition during coupling has recently been questioned (34). The concept of “locking” the cervical spine to allow movement to one area was recently tested and movement occurred in other aspects of the spine. Although this mechanism (locking) may be useful for a more focused, target-specific technique, apposition (which is based on the concept of coupling) does not appear to wholly stabilize segments outside the targeted segment.

Summary • • • • •

With reference to biomechanical movement, the upper cervical spine is mostly responsible for physiological rotation, and flexion and extension movements. Coupling patterns of the upper cervical spine at C1-2 are somewhat unpredictable during side flexion initiation but are predictable during rotation initiation. C1 is mobile during all forms of movement whether caudally or cephalically initiated. The lower cervical spine demonstrates equivocal percentages of biomechanical movements in all ranges of physiological motion. The lower cervical spine demonstrates a consistent and predictable coupling pattern regardless of the initiation of motion; side flexion and rotation occur to the same side.

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