Hansen: Netter's Clinical Anatomy, 2nd Edition - with Online Access 2 BACK 1. INTRODUCTION 4. MUSCLES OF THE BACK REVIEW QUESTIONS 2. SURFACE ANATOMY 5. SPINAL CORD 3. VERTEBRAL COLUMN 6. EMBRYOLOGY FINAL 1. INTRODUCTION ELSEVIERl VertebraeNOT prominens: the spinous process of the C7- vertebra, usually the most prominent The back forms the axis (central line) of the human process in the midline at the posterior base of body and consists of the vertebral column, spinal cord, the neck supporting muscles, and associated tissues (skin, OFcon- l Scapula: part of the pectoral girdle that sup- nective tissues, vasculature, and nerves). A hallmark of ports the upper limb; note its spine, inferior human anatomy is the concept of “segmentation,” and angle, and medial border the back is a prime example. Segmentation and bilat l Iliac crests: felt best when you place your eral symmetry of the back will be obvious as you hands “on your hips”; an imaginary horizontal study the vertebral column, the distribution of the line connecting the crests passes through the spinal nerves, the muscles of th back, and its vascular spinous process of the L4 vertebra and the supply. intervertebral disc of L4-L5, a useful landmark Functionally, the back is involved in three primary for a lumbar puncture or epidural block tasks: l Posterior superior iliac spines: an imaginary CONTENThorizontal line connecting these two points l Support: the vertebral column forms the axis of passes through the spinous process of S2 (second the body and is critical for our upright posture sacral segment) (standing or si ting), as a support for our head, as an PROPERTYattachment point and brace for move- 3. VERTEBRAL COLUMN ments of our upper limb, and as a support for transferring the weight of our trunk to the The vertebral column (spine) forms the central axis of lower limbs the human body, highlighting the segmental nature of l Protection: the vertebral column protects the all vertebrates, and is composed of 33 vertebrae dis- spinal cord and proximal portions of our spinal tributed as follows (Fig. 2-2): nervesSAMPLE before they distribute throughout the body l Cervical: seven total; first two called the atlas l Movements: muscles of the back function in (C1) and axis (C2) movements of the head and upper limb and l Thoracic: twelve total; each articulates with a in support and movements of the vertebral pair of ribs column l Lumbar: five total; large vertebrae for support of the body’s weight l Sacrum: five fused vertebrae for stability in the 2. SURFACE ANATOMY transfer of weight from the trunk to the lower limbs Key Landmarks l Coccyx: four total; Co1 often is not fused, but Key surface landmarks are shown in Figure 2-1 and Co2-Co4 are fused (a remnant of our embry- include the following bony landmarks: onic tail) 41 http://www.us.elsevierhealth.com/product.jsp?isbn=9781437702729 Hansen: Netter's Clinical Anatomy, 2nd Edition - with Online Access External occipital protuberance Ligamentum nuchae Spinous process of C7 vertebra Trapezius m. Spine of scapula Deltoid m. Infraspinatus m. Medial border of scapula Teres Inferior angle of s apula major m. Spinous process of T12 vertebra Latissimus dorsi m. Iliac crest Thoracolumbar f scia FINAL Posterior superior iliac spine Sacrum ELSEVIERNOT FIGURE 2-1 Key Bony and Muscular Landmarks of the- Back Left lateral view Posterior view OF Atlas (C1) C1 Axis (C2) Cervical C2 curvature Cervical Level Corresponding structure vertebrae C7 C2-3 Mandible T1 T1 C3 Hyoid bone C4-5 Thyroid cartilage CONTENTC6 Cricoid cartilage Thoracic Thoracic C7 Vertebra prominens vertebrae curvature T3 Spine of scapula PROPERTY T8 Point of inferior vena cava pierces diaphragm T10 Xiphisternal junction T12 T10 Point of esophagus entering stomach L1 T12 Point of aorta entering abdomen L1 End of spinal cord Lumbar SAMPLE vertebrae Lumbar L3 Subcostal plane curvature L5 L3-4 Umbilicus L5 L4 Bifurcation of aorta L4 Iliac crests Sacrum (S1-5) S2 End of dural sac Sacral curvature Coccyx FIGURE 2-2 Vertebral Column 42 http://www.us.elsevierhealth.com/product.jsp?isbn=9781437702729 Hansen: Netter's Clinical Anatomy, 2nd Edition - with Online Access CHAPTER 2 BACK 43 CLINICAL FOCUS Scoliosis Scoliosis is abnormal lateral curvature of the spine, which also includes an abnormal rotation of one vertebra upon the other. In addition to scoliosis, other accentuated curvatures of the spine include kyphosis (hunchback) and lordosis (swayback). Pathologic anatomy of scoliosis Spinous process deviated to concave side Lamina thinner, vertebral canal narrower on Rib pushed concave side posteriorly; thoracic cage narrowed Verteb al body distorted toward c nvex side Rib pushed laterally and FINAL anteriorly Convex side Concave side Gauging trunk alignment Section through scoliotic vertebrae; d creased vertebral Characteristic distortion of vertebra height and disc thickness on and rib in thoracic scoliosis (inferior view) concave side ELSEVIERNOT Several Common Abnormal Curvatures of the Spine - Disorder Definition Etiology Scoliosis (illustrated) Accentuated lateralOF and rotation l curve of Genetic, trauma, idiopathic; occurs in tho acic or lumbar spine adolescent girls more than boys Kyphosis Hunchback, accentuated flexion of thoracic Poor posture, osteoporosis spin Lordosis Swayback, accentuated Weakened trunk muscles, extens on of lumbar spine late pregnancy, obesity CONTENT PROPERTY Viewed from the lateral aspect (see Fig. 2-2), one Typical Vertebra can identify the following: A “typical” vertebra has several consistent features SAMPLE (Fig. 2-3): l Cervical curvature (cervical lordosis): this cur- vature is acquired secondarily when the infant can support the weight of its own head l Body: the weight-bearing portion of a vertebra l Thoracic curvature (thoracic kyphosis): a that tends to increase in size as one descends primary curvature present in the fetus (imagine the spine the spine in the “fetal position”) l Arch: a projection formed by paired pedicles l Lumbar curvature (lumbar lordosis): this cur- and laminae vature is acquired secondarily when the infant l Transverse processes: the lateral extensions assumes an upright posture and supports its from the union of the pedicle and lamina weight l Articular processes (facets): two superior and l Sacral curvature: a primary curvature present two inferior facets for articulation with adjacent in the fetus vertebrae http://www.us.elsevierhealth.com/product.jsp?isbn=9781437702729 Hansen: Netter's Clinical Anatomy, 2nd Edition - with Online Access 44 CHAPTER 2 BACK TABLE 2-1 Key Features of the Cervical Vertebrae Atlas (C1) Ringlike bone; superior facet articulates with occipital bone Two lateral masses with facets No body or spinous process C1 rotates on articular facets of C2 Vertebral artery runs in groove on posterior arch Vertebral body Axis (C2) Dens projects superiorly Pedicle Strongest cervical vertebra Other Cervical Vertebrae (C3 to C7) Transverse Vertebral process foramen Large triangular vertebral foramen Transverse foramen, through which vertebral artery passes Superior C3 to C5: short bifid spinous process articular process Accessory process C6 to C7: long spinous process Lamina C7 called vertebra prominens Spinous process Narrow intervertebral foramina FINAL Nerve roots at risk of compression Superior articular process Pedicle Transverse process ELSEVIERNOT Intervertebral - disc 1 OF Inferior articular l Spinous process: a projection that extends p ocess posteriorly from the union of two laminae 2 l Vertebral notches: superior and inferior semi- circular features that in articulated vertebrae Inferior form an intervertebral foramen (two semicircu- vertebral notch lar notches form a circle) l Intervertebral foramina: the opening formed 3 Intervertebral foramen by the vertebral notches that is traversed by spinal nerve roots and associated vessels CONTENTl Vertebral foramen (canal): a foramen formed Superior from the vertebral arch and body that contains 4 vertebral the spinal cord and its meningeal coverings notch l Transverse foramina: apertures that exist in PROPERTY transverse processes of cervical vertebrae only and transmit the vertebral vessels 5 Articular facet for sacrum Regional Vertebrae SAMPLE The Cervical Vertebrae The cervical spine is composed of seven cervical ver- FIGURE 2-3 Features of a Typical Vertebra as tebrae. The first two cervical vertebrae are unique and Represented by the L2 Vertebra (Superior View) and are termed the atlas (C1) and axis (C2) (Fig. 2-4). The by the Articulated Lumbar Vertebrae atlas (C1) holds the head on the neck and gets its name from Atlas, the god of mythology who held the world on his shoulders. The axis (C2) is the point of articulation where the head turns on the neck, provid- ing an “axis of rotation.” Key features of the cervical vertebrae are summarized in Table 2-1. The cervical region is a fairly mobile portion of the spine, allowing for flexion and extension as well as rotation and lateral bending. http://www.us.elsevierhealth.com/product.jsp?isbn=9781437702729 Hansen: Netter's Clinical Anatomy, 2nd Edition - with Online Access CHAPTER 2 BACK 45 Anterior tubercle Anterior arch Articular facet for dens Transverse process Lateral mass Vertebral foramen Superior articular facet for atlas Transverse foramen Dens Superior articular surface of Posterior arch lateral mass for occipital condyle Posterior tubercle Posterior articular facet (for transverse ligament of atlas) Atlas (C1): superior view Transverse process Inferior articular process Spinous process