--- module: 076-01 language: en chapter: 76 title: "Back, Spinal Column, Upper Limb, and Lower Limb Anatomy" module_title: "Back, vertebral column, spinal canal, and axial support" source_sha256: 0d59a62f2a7024d902206eae23110c23cca9470d538ed989186489042a0980f2 --- # Back, vertebral column, and spinal canal ## Axial role of the back ### Mobile protective column linking skull, thorax, pelvis, limbs ### Balances stability, flexibility, load, neural protection #### Small changes affect pain, movement, nerves, mechanics ## Vertebral column by region ### Typical vertebra: anterior body, posterior arch #### Stacked vertebral foramina form the canal #### Pedicle notches form intervertebral foramina ### Cervical: small bodies, transverse foramina #### Vertebral artery usually enters at the sixth level #### Atlas lacks a body, supports occipital condyles #### Axis dens is the pivot for atlas rotation ### Thoracic: rib facets, coronal-oriented facets #### Favour rotation, limit flexion and extension ### Lumbar: large bodies, sagittal-oriented facets #### Permit flexion and extension, resist rotation ### Sacrum: five fused vertebrae #### Passes axial load to pelvic ring via sacroiliac joints ### Coccyx anchors pelvic-floor structures ## Curves and load transmission ### Primary kyphoses reflect fetal flexion ### Secondary lordoses develop with head lifting and standing ### Curves distribute load and add resilience #### Deviations judged against age and symptoms ### Bodies enlarge inferiorly as cumulative load rises ### Lumbosacral angle creates anterior shear #### Resisted by facets, discs, ligaments, muscle ### Sitting loads ischial tuberosities, standing acetabula ### Scoliosis: lateral curve with vertebral rotation #### Rib prominence from thoracic rotation #### Structural persists, functional may correct ## Discs and joints ### Annulus lamellae resist torsion and tension ### Nucleus distributes compression by hydrostatic pressure ### Largely avascular disc fed through endplates ### Imaging degeneration is common without pain ### Posterolateral herniation where PLL is weaker #### Can affect a traversing nerve root ### Facet orientation guides and limits movement ### Uncovertebral osteophytes can narrow foramina ### Atlanto-axial joints permit rotation #### Transverse ligament holds dens to atlas #### Disruption threatens the upper cord ## Spinal ligaments ### Anterior longitudinal ligament limits extension ### Posterior longitudinal ligament limits flexion ### Ligamenta flava recoil from flexion, prevent buckling ### Supraspinous ligament expands into ligamentum nuchae ### Passive stability and mechanosensory input #### Can calcify, thicken, tear, or become lax ## Spinal canal and coverings ### Cord ends near L1 or L2 as conus medullaris #### Cauda equina descends within the dural sac #### Filum terminale anchors cord and dura ### Spinal nerves split into dorsal and ventral rami #### Dorsal rami supply intrinsic back structures #### Ventral rami supply anterolateral trunk and limbs ### Meninges: pia, arachnoid, dura #### Epidural fat and internal vertebral venous plexus #### Denticulate ligaments stabilise the cord ### One anterior, two posterior spinal arteries #### Anterior territory covers much of anterior two-thirds #### Vulnerable in aortic disease or surgery #### Great medullary artery varies in side and level ### Lumbar puncture below usual cord termination #### Needle crosses ligaments, epidural space, dura ## Back muscles ### Extrinsic superficial: trapezius, latissimus dorsi ### Intermediate serratus posterior: ribs, respiration ### Intrinsic deep muscles supplied by dorsal rami #### Erector spinae: iliocostalis, longissimus, spinalis #### Transversospinalis: semispinalis, multifidus, rotatores #### Suboccipital muscles fine-tune head movement ### Stability is dynamic coordination #### Multifidus and abdominal wall add segmental stiffness #### Diaphragm and pelvic floor regulate pressure ## Anatomical syndromes ### Radiculopathy follows nerve-root irritation #### Dermatome and myotome overlap make patterns approximate ### Cervical or thoracic stenosis causes myelopathy #### Upper motor-neuron signs below the lesion ### Lumbar stenosis: claudication relieved by flexion ### Cauda equina: saddle loss, bladder, bowel #### Urgent localisation and decompression assessment ### Visible degeneration does not prove the pain generator