Chapter 46: Back Anatomy

The soft tissues include thick, protective skin innervated primarily by the dorsal rami of spinal nerves (C2–C5, T2–L3, S2–S4, Co1), overlying the key fascial structures, most notably the thoracolumbar fascia, which encases the deep, intrinsic erector spinae muscles. This fascia is crucial for trunk load transfer and has been implicated as a source of pain due to its nociceptive nerve endings. The foundational support is the vertebral column, typically comprised of 33 vertebrae, exhibiting regional curvatures: cervical lordosis, thoracic kyphosis, and lumbar lordosis. Detailed vertebral features include the body, the neural arch elements (pedicles and laminae), and various lever-like processes (spinous, transverse, articular). The articulation occurs through the intervertebral discs—symphyses composed of an outer anulus fibrosus and an inner nucleus pulposus—and paired synovial facet (zygapophysial) joints, whose orientation determines regional mobility. Vascular supply is derived from dorsal branches of segmental arteries; the accompanying veins form intricate, valveless plexuses (internal and external) that allow for the potential, paradoxical spread of infection or malignancy (e.g., prostatic carcinoma) via the Batson's plexus system. Specialized articulations exist in the craniovertebral region (atlanto-occipital and atlanto-axial), where the transverse atlantal ligament provides essential stability for the dens of the axis (C2). The intrinsic muscles, supplied by the dorsal rami, are arranged in functional groups—splenius, erector spinae (iliocostalis, longissimus, spinalis), and spinotransverse (multifidus, rotatores)—which, beyond generating movement (extension, rotation), are vital dynamic stabilizers, crucial for maintaining core stability and providing proprioceptive feedback. Clinical relevance is highlighted by structural pathologies like spondylolisthesis or spinal stenosis, which narrow the vertebral or root canals, and by disc prolapse (most common at L4/L5 and L5/S1), which can compress spinal nerve roots. The chapter concludes with practical surface anatomy landmarks (like the vertebra prominens C7 and the supracristal plane L4/L5), which are essential for identifying underlying visceral levels and performing clinical procedures such as lumbar puncture.