Back and Spine

Introduction

Lordosis – secondary curves (lumbar and cervical), bending backwards i.e. the concavity is posterior

Kyphosis – primary curves (sacral and thoracic), bending forwards, i.e. the concavity is anterior

Scoliosis – curve laterally i.e. S instead of I

Only the cervical vertebrae have transverse foramen (foramina transversium)

Only the thoracic vertebrae have articular facets for the ribs

The spinal nerves C1-C8 exit above their respective vertebrae, T1-S4 exit below their respective vertebrae

T7 is the most frequently fractured vertebra in the spine (because it is the deepest point in the spine’s lordosis)

As one ages one loses H₂O from the discs. Young discs are 88% H₂O. less water = less height

Skeletal Anatomy

There are 7 Cervical vertebrae, 12 Thoracic vertebrae, and 5 Lumbar vertebrae arranged on top of the Sacrum, 5 fused vertebrae that attach to the pelvis. The Coccyx, 4 fused vertebrae lie caudal to the sacrum.

Pedicle – (Latin for "little feet") the 2 posterior projections form the body that attach the 4 articular processes, the spinous process, the 2 transverse processes, and the lamina to the vertebral body.

Lamina – two broad plates of bone that for the roof of the vertebra foramen when they unite in the median plane.

Spinous Process – the process that projects out dorsally from the lamina.

Vertebra prominens – C7, because its spinous process can be palpated when the head is tilted forward.

Transverse process – the processes that project laterally from the vertebral arch

Atlas – the 1^st cervical vertebra

Axis – the 2^nd cervical vertebra, the Dens (Odontoid Process) arises from the axis and projects up to articulate the atlas

Foramen Transversarum – distinct for the cervical vertebrae, allows for passage of the vertebral arteries

Sacral promontory – an important OB landmark, the projecting anterior edge of the body of S1

Centrum – the ossification center for the central mass of the vertebral body

Annular epiphyses – 2 of the 5 secondary centers of ossification, one forms superiorly, the other inferiorly, to the centrum

Zygapophyseal facet – articular processes that arise from the junction of the pedicles and lamina. The superior articular facet projects superiorly, the inferior articular facet projects inferiorly.

Intervertebral foramen – formed by pedicles from a superior and an inferior vertebrae. Spinal nerves exit through these.

Costal facet – articulations for the ribs, on thoracic vertebrae

Vertebral canal – the collection of vertebral foramen in which the spinal cord (wrapped in meninges) travels

Joints

intervertebral discs – the fibrous annulus fibrosis surrounds the more cartilaginous nucleus pulposis

zygapophyseal – the synovial joint between the inferior articular facets of the superior vertebra and the superior articular facets of the inferior vertebra. These are surrounded by fibrous capsules that are looser in the cervical region.

craniovertebral – the atlanto-occipital and atlanto-axial joints, Synovial only, have no intervetebral discs and no facet joints

atlanto-occipital – the joint between the skull and the 1^st cervical vertebra (the altas). Allows nodding of the head.

atlanto-axial – between the 1^st and 2^nd vertebrae. Allows rotation of the head. Excess prevented by the alar ligaments.

Movements

flexion – touching your toes

extension – bending backwards

rotation – "doing the twist"

lateral flexion – bending to the side to touch your toes

Muscles

There are 3 groups of muscles on the back

Superficial (trapezius, latissimis dorsi) concerned with limb movemen

Intermediate (serratus anterior) concerned with respiration

Deep "intrinsic back muscles" concerned with movement of the vertebral column

All muscles posterior to the transverse process get innervation from the dorsal rami.

Intrinsic back muscles: have 3 layers

Superficial layer of deep back muscles

splenius (Greek, bandage)

Origin: inferior ½ of the ligamentum nuchae and the spinous process of T1-T6

Insertion: Sp. Capitus (head) lateral aspect of mastoid process and lateral 1/3^rd of the superior nuchal line of the occipital bone.

splenius cervicis (neck) posterior tubercles of C1-C4

Action: aloneÞ laterally flex and rotate head to the same side, togetherÞ extend head and neck

Innervation: dorsal rami of inferior cervical nerves

Intermediate layer of deep back muscles

erector spinae (3 vertical columns of muscle) – "I love sushi" from lateral to medial

(1) iliocostalis (lateral column)

(2) longissimus (intermediate column)

(3) spinalis (medial column)

Origin: a broad tendon attached to the posterior iliac crest, posterior sacrum, sacral and lumbar spinous processes.

Insertion:

Iliocostalis (3 parts)

1^st iliocostalis lumborum attached to inferior 6 ribs
2^nd iliocostalis thoracis attached to all ribs
3^rd iliocostalis cervicis attached to superior 6 ribs and posterior tubercles of C4-C6

Longissimus (3 parts)

1^st longissimus thoracis the tips of the transverse processes of all thoracic vertebrae and into the tubercels of the inferior 9 ribs.
2^nd longissimus cervicis extends from the superior thoracic transverse processes to the cervical transverse processes
3^rd longissimus capitus attaches to the mastoid process of the temporal bone

Spinalis (3 parts)

1^st spinalis thoracis

2^nd sp cervicus

3^rd sp. Capitus

Action: bilaterally, extends head and part of vertebral column. Unilaterally, laterally flexes head or vertebral column.

Innervation: dorsal rami of spinal nerves

Deep layer of the deep back muscles – Next 3 are known as the Transversospinal muscle because their fibers run for the transverse to the spinous processes

Semispinalis – (3 parts, thoracis, cervicis, and capitus)

Origin: transverse processes from ~T10 and up

Insertion: spinous processes of superior vertebrae

Action: bilaterally, extend thoracic and cervical regions, Unilaterally, rotate these regions towards the opposite side

Innervation: the dorsal rami of the cervical nerves

Multifidus – divided into many bundles, covers the laminae of S4 to C2, fibers pass superiomedially from the vertebral arches to the spinous processes spanning 1 to 3 vertebrae

Actions unilaterally, flexes the trunk laterally and rotates towards the opposite side, bilaterally, extend the trunk and stabilize the vertebral column.

Innervation: dorsal rami of the cervical spinal nerves

Rotatores – short muscles that run the length or the vertebral column

Origin – transverse process of one vertebrae

Insertion – the spinous process of the vertebrae immediately superior

Actions – rotate the superior vertebra to the opposite side and stabilization

Innervation – the dorsal rami of the spinal nerves

Interspinales – small muscles that unite the spinous processes of consecutive vertebrae

Action lateral flexion of superior vertebra, bilaterally extend the vertebral column

Innervation dorsal rami of the cervical spinal nerves

Intertransversarii – small muscles that unite the transverse processes of consecutive vertebrae. Similar action to interspinales

Innervation from the ventral rami of cervical spinal nerves

levator costarum – 12 muscles in the thoracic region

Origin the transverse process of thoracic vertebra

Insertion the rib immediately below

Action aid in respiration (by raising ribs during inspiration)

Innervation lateral division of the dorsal rami of the spinal nerves.

Additional Structures

Spinal cord – travels down through the spinal canal, usually ends at L1-L2 giving rise to the Cauda equina (L4 in kids)

Meninges – protective membranes that cover the spinal cord (out to in Dura mater, Arachinoid mater, Pia mater)

cervical enlargement – extends form C4-T1, where the ventral rami of the brachial plexus leave the spinal cord.

lumbar enlargement – T11-L1, the swelling of the spinal cord where lumbar and sacral plexi nerves leave.

dorsal root – entering the cord contain afferent or sensory fibers from sensory nerve endings

ventral root – leaving the cord contain efferent or motor fibers which are distributed to muscles and glands

dura mater – (Latin; hard mother) tough outermost membranous covering of the spinal cord

arachnoid mater – (greek; spider) delicate filamentous avascular intermediate covering of the spinal cord

subarachnoid space – between the arachnoid mater and pia mater, contains CSF

spinal ganglion – dorsal root ganglia, where the cell bodies of the axons making up the dorsal root are.

extradural space – space between the ligamentous walls of the spinal canal and the dura mater, contains fat and loose CT.

filum terminale – a slender fibrous strand that descends with the cauda equina, leaves the inferior end of the dural sac and passes through the sacral hiatus to insert into the dorsum of the coccyx. A remnant of spinal cord from the tail.

cauda equina – the bundle of nerve rootlets in the subarachnoid space caudal to the termination of the spinal cord

conus medularis – the inferior end of the spinal cord tapers abruptly into the conus medularis

anterior longitudinal ligament – strong fibrous band that covers and connects the anterior aspects of the bodies of the vertebrae and intervertebral discs. Extends from the sacrum to C1 (atlas)

posterior longitudinal ligament – narrower/weaker than the anterior long ligament. Runs on the posterior aspect of the vertebral bodies within the vertebral canal. Runs from C2 to the sacrum and prevents protrusion of the intervertebral discs.

ligamentum flavum – (yellow ligaments), attach the lamina of adjacent vertebrae, attach to the anterior surface of the inferior borders of the superior vertebra’s laminae and attach to the posterior surface of the inferior vertebra’s laminae.

basivertebral vein – drains the vertebra, exits through a foramen on the posterior surface of the vertebral body

cruciate ligament – a cross at the base of the skull, made from the transverse ligament of the atlas (from one tubercle of the atlas’s lateral mass to the other) and the superior and inferior bands that connect the occipital bone to the axis

Clinical Significance

spondylolysis – if the L5 vertebra has two parts (either congenital or acquired) and the posterior stays in the normal relation with the sacral arch while the anterior is still in it’s place in the vertebral column. 5% incidence.

spondylolisthesis – a spondylolysis where the anterior part moves anteriorly (anterior displacement of the vertebra from the vertebral column), this can put pressure on the spinal nerves and cause back pain.

spina bifida – failure of fusion of the laminae of the vertebral arch, may be herniation of the meninges or spinal cord.

disc herniation – a protrusion of the nucleus pulposa (usually posteriolaterally), that may compress an adjacent spinal nerve root and cause symptoms (typically low back and leg pain)

rheumatoid arthritis – can destroy the transverse ligament of the atlas, making a person prone to injury via the dens being set free and driven into the cervical region of the spinal cord causing quadriplegia or death.

lumbago – acute mid and low back pain that radiates down the posterolateral aspect of the thigh often caused by a disc protrusion at L5/S1.

Sciatica – pain resulting from irritation of the sciatic nerve