Page 360 - Kinesiology of the musculoskeletal system foundations for physical rehabilitation

336 Section III Axial Skeleton

Tectorial membrane Posterior view Alar ligament
(cut) Occipital bone
Atlanto-occipital
FIGURE 9-44. A posterior view of the atlanto-axial joint complex. Occipital condyle Dens joint
The posterior arch of the atlas, tectorial membrane, and transverse
ligament of the atlas are cut to expose the posterior side of the Atlanto-axial Atlas Transverse
dens and the alar ligaments. The dashed lines indicate the (apophyseal) process
removed segment of the transverse ligament of the atlas. joint capsule Transverse
ligament (cut)
Ligamentum Axis Tectorial
flavum (cut) membrane (cut)

Spinous process

TABLE 9-7. Approximate Range of Motion for the Three Planes of Movement for the Joints of the Craniocervical Region

Joint or Region Flexion and Extension Axial Rotation Lateral Flexion
(Sagittal Plane, Degrees) (Horizontal Plane, Degrees) (Frontal Plane, Degrees)

Atlanto-occipital joint Flexion: 5 Negligible About 5
Atlanto-axial joint complex Extension: 10 35-40 Negligible
Intracervical region (C2-C7) Total: 15 30-35 30-35
Total across craniocervical region Flexion: 5 65-75 35-40
Extension: 10
Total: 15
Flexion: 35-40
Extension: 55-60
Total: 90-100
Flexion: 45-50
Extension: 75-80
Total: 120-130

The horizontal and frontal plane motions are to one side only. Data are compiled from multiple sources (see text) and subject to large intersubject variations.

The alar ligaments are tough fibrous cords each about 1 cm smell, and equilibrium. The individual joints within the cra-
in length with a thickness of a common pencil.33,57 As shown niocervical region normally interact in a highly coordinated
in Figure 9-44, each ligament passes laterally and slightly manner. Table 9-7 lists typical ranges of motion contributed
upward from the apex of the dens to the medial sides of the by each area of the craniocervical region.* Because of the
occipital condyles. Clinically referred to as “check ligaments,” large range and variability in the data presented in the litera-
the alar ligaments are respected for their ability to resist, or ture, the actual values listed in this table are more useful for
check, axial rotation of the head-and-atlas relative to the appreciating the relative kinematics among joints, and less as
dens.149 The pair of ligaments is loose in the neutral position a strict objective guide for evaluating movement in patients.
but becomes increasingly taut during axial rotation; the liga-
ment located contralateral to the side of the rotation exhibits Osteokinematics of Flexion and Extension
slightly greater resistance to the movement.45,57,172 In addition About 120 to 130 degrees of combined flexion and extension
to limiting axial rotation, the alar ligaments also restrict the occur across the entire craniocervical region. From the neutral
extremes of all other potential motions at the atlanto-occipital position of about 30 to 35 degrees of extension (resting lor-
joint. dosis), the craniocervical region extends some additional 75 to
80 degrees and flexes 45 to 50 degrees (Figures 9-45 and 9-46).
Intracervical Apophyseal Joints (C2 to C7) Extension exceeds flexion throughout the craniocervical
The facet surfaces within apophyseal joints of C2 to C7 are region, on average by a margin of just over 1.5 to 1.
orientated like shingles on a 45-degree sloped roof, approxi-
mately halfway between the frontal and horizontal planes (see In addition to muscles, connective tissues limit the
Figure 9-18, C2-C3 articulation). This orientation enhances extremes of craniocervical motion. For example, the ligamen-
the freedom of movement in all three planes, a hallmark of tum nuchae and interspinous ligaments provide significant
cervical arthrology. restraint to the extremes of flexion, whereas the approxima-
tion of the apophyseal joints limits the extremes of exten-
SAGITTAL PLANE KINEMATICS sion.163 Flexion is also limited by compression forces from the
The craniocervical region is the most mobile region within anterior margin of the annulus fibrosus, whereas extension is
the entire vertebral column. Highly specialized joints facili- limited by the compression forces from the posterior margin
tate precise positioning of the head, involving vision, hearing, of the annulus fibrosus. Additional tissues that limit or restrict

*References 20, 24, 58, 65, 147, 156, 197.