CHAPTER 5 Structure and Function of the Spine


Superior articular facet


107


moves in counternutation when the sacral base moves posterior and superior and the apex moves anterior and inferior (Fig. 5.24B).


Superior articular process Body Spinous process Inferior articular process Inferior notch


Figure 5.20 The lumbar articular processes and facets are oriented in the sagittal plane, allowing increased flexion and extension. (From Roy S, Wolf SL, Scalzitti DA. The Rehabilitation Specialist’s Handbook, 4th ed. Philadelphia, PA: F. A. Davis Company, 2013: p. 48, with permission.)


Symmetrical pelvic motion on the sacrum in an ante- rior and posterior rotation is described as a pelvic tilt. An anterior pelvic tilt describes the rotation of the pelvis when the anterior superior iliac spine of the pelvis and the pubic symphysis move inferiorly. With excessive anterior tilt of the pelvis, there is an increase in lumbar extension. This motion decreases the space in the intervertebral foramen and moves the discal material in an anterior direction (Fig. 5.25A1 and A2). During a posterior pelvic tilt, these structures move in a superior direction, which decreases the lumbar lordosis and increases fl exion in the lumbar spine. This action increases the diameter of the intervertebral foramen and moves the nucleus pul- posus posteriorly (Fig. 5.25B1 and B2). Although the movement is small, the pelvis can also rotate around a vertical axis in a horizontal plane. It can move in abduc- tion and adduction in the frontal plane around a sagittal axis (Fig. 5.26).


SPINAL MUSCLES L5 30° Lumbosacral angle POSTERIOR SPINAL MUSCLES


Figure 5.21 A line parallel to the superior sacral border and a horizontal line form the lumbosacral angle.


minimal movement, as the superior, inferior, and poste- rior pubic ligaments support it, it widens in women to expand the pelvic area during childbirth. There is controversy concerning the kinematics of the SI joint, although it is recognized as having only an extremely small amount of motion (1 to 3 mm). Symmet- rical motion occurring at both SI joints can be described according to sacral movement. Nutation is movement of the sacrum when the base moves anterior and inferior while the apex moves posterior and superior (Fig. 5.24A). When the trunk moves into fl exion while in a stand- ing position, the sacrum moves in nutation. The sacrum


The posterior trunk muscles are categorized into super- fi cial, middle, and deep layers. The muscles of the superfi cial layer include the trapezius, latissimus dorsi, rhomboids, levator scapula, and serratus anterior. Func- tionally, these muscles infl uence the movement of the scapula during shoulder movement and are discussed in detail in Chapter 8. Bilateral activation of these muscles produces spinal extension in the region of the muscle, whereas unilateral contraction can cause lateral fl exion and rotation. For example, contraction of bilateral upper trapezius muscles produces cervical extension, but uni- lateral contraction causes ipsilateral lateral fl exion and contralateral rotation of the head and neck. By stabilizing the head and bringing their distal attachment toward the head, the upper trapezius muscles contract to elevate the scapulae. The levator scapula muscle is deep to the tra- pezius and attaches proximally to the transverse processes


Spinal muscles are paired and located on either side of the midline of the body. When they act together, they typi- cally produce fl exion or extension of the axial skeleton in the sagittal plane. If only one side contracts, the muscle tends to cause lateral fl exion in the frontal plane coupled with some amount of rotation in the horizontal plane. The location and function of the muscles are described next. Specifi c muscle attachments and nerve innervations as well as a summary of their functions are presented in Appendix A.


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