6.18: Vertebral Column

Intro (142)

Great strength and size: supports skull, arms, legs, posture and propulsion.

-           big bony mass, and rugged ligaments, yet flexibility afforded by many jts.

Fetus lies flexed the C-curvature: primary curvature

-           the thoracic, sacral and coccygeal parts retain this

-           secondary curves (lordotic) develop in cervical and lumbar regions aided by muscles.

-           This change elongates the column into gentle bends, adds resilience

The shock absorbing parts are the discs.

The Vertebrae (143-5)

Ventral body, dorsal arch, enclose vertebral foramen (canal is all the foramina together)

-           3 processes arise from arch: spine and two transverse.

-           Lamina is that part b/n transverse process and spinous process

-           Pedicle is that b/n transverse process and body, is shorter than body to allow exit of spinal nerves through the intervertebral foramen

Inferior and superior articular processes are at where lamina and pedicle meet.

-           these are synovial / hyaline jts and their direction determines possible movements.

Site differences

Vertebrarterial foramen exist in each cervical transverse process

Costal facets are on the sides of each thoracic v.

Lumbar has neither of these: hence all 3 can be easily distinguished.

Ossification

In 3 parts: centrum and right and left halves of neural arch.

-           costal elements develop separately as ribs in thorax; their costal facets (on the body) are part of the arch, not the centrum.

-           costal elements initially develop in all vertebrae, vestigial other than in thorax; transverse process foramen of cervical vertebrae is a remnant

Cervical ribs are elongations of costal elements of C7; may pass a fibrous band down from C7 to 1st rib

-           subclavian a. and brachial plexus push up to pass over bands: may be compressed (173)

-           because bands are stringy they can do more damage than the smooth rib itself.

-           When a cervical rib is well developed, brachial plexus is more often prefixed (C4-8)

Transverse processes of lumbar vertebrae are really costal elements

-           true process is contracted into a small mass grooved by the posterior ramus; accessory process.

Sacral vertebrae are fused into a single bone as are their costal elements, which produce the lateral mass / crests and extending between anterior foramina on the front.

-           the articular surface for SI jt lies on the lateral mass.

Vertebral Joints (143-4)

Strong ligaments, small joints; articulations tight b/n bodes and flexible b/n neural arches

 
Links b/n bodies

Intervertebral discs, anterior and posterior longitudinal ligaments.

i) Discs:

Secondary cartilaginous jt (symphysis): a thin layer of hyaline cartilage on each body united by fibrous annulus fibrosus.

-           concentric laminae with alternate layers of fibres at right angles: strong in every direction

-           nucleus pulposus (remnant of notochord) lies near the back of the discs,  can herniate onto nerve roots near intervertebral foramen, or onto cord itself.  Usually posterolaterally

-           Nucleus is 15% of disc; is 90% H20 at birth, dehydrates to 70% in old age.  Water squeezes out during the day, but is reimbibed at night, changing height 1cm

-           Note on pl149 right that L5 herniation does not affect higher L5 root, but rather S1; similarly C7 impinged in C6 herniation, L5 in L4 herniation.

-           Luschka’s jts are connections b/n bodies on sides of C3-7 (?synovial; ?just degeneration)

ii) Ant longitudinal ligament:

From basiocciput of skull and anterior tubercle of atlas ® upper front of sacrum.

-           firmly united to periosteum of vertebrae, less so to discs; broadens downwards

iii) Post longitudinal ligament:

From back of axis ® anterior wall sacral canal.

-           serrated margins; narrows downwards, firmly united to discs, less so to bodies to allow veins.

-           continues upwards as the tectorial membrane. (15)

 
Links b/n arches (146)

Besides pedicles (gapped to allow intervertebral foramina) all parts of arch have synovial jts/ligaments.

i) Facets (zygapophyseal jts):

Between superior / inferior articular facets where pedicles & laminae meet

-           synovial, simple capsule (blends with flavum) (146 upper)

-           allow gliding movements depending on what direction they face.

-           Have their own segmental nerve supply from above & below (important in referring pain)

-           Do take a little weight, though most passes through bodies and discs.

ii) Ligamentum flava:

Very elastic (so yellowed), join contiguous laminae.

-           pass from front above to back of lamina below overlapping like roof tiles

-           extend from facet jts to midline where fused except where communicating veins penetrate.

-           Stretched by spinal flexion; elastic quality lends antigravity assistance when leaning forwards.

iii) Supraspinous ligament:

Run along tips of adjacent spinous processes; strong fibrous bands; lax in extension.

-           drawn taut in flexion, then support spine

-           replaced by ligamentum nuchae in the neck (14) single sheet from C7 up ® occiput.

iv) Interspinous ligaments:

Relatively weak sheets between spinous processes.  Fuse with supraspinous ligs.

v) intertransverse ligaments:

Weak sheets, join transverse processes along adjacent borders.

Vertebral Column

Bodies become larger downwards to support weight to pelvis / ischial tuberosities

Curvatures partly because bodies are wedge shaped, mostly because discs are more wedge-shaped

Canal: progressively smaller downwards

-           intervertebral foramen lodge spinal nerves and posterior root ganglia & arteries/veins

Movements
Lumbar region

Facets lie in AP plane, lock limiting rotation; allow good flexion / extension & lateral flexion.

Thoracic region

T12-L1 is lumbar type.  Flexion / extension, lat flexion possible throughout.

Elsewhere facets face back & laterally and curved: rotation possible, though rib splinting limiting.

Hence it is the most versatile region.

Cervical region

Upper facets face back and upwards, lower down and forwards (reciprocal)

Flexion / extension free, but pure rotation impossible.

Lateral rotation complicated: facets slide in such a way that a some rotation occurs.

 

Special vertebrae movements (15)

Atlas (12):

Lacks a centrum. Thick lateral mass on each side, joined by an anterior arch.

Upper facets kidney-shaped and concaved to meet occipital condyle

Lower facets round and flat for atlantoaxial jt

-           spinal nerves run behind these facets, rather than behind them like most C-vertebrae.

Axis (12):

Dens articulates with anterior arch of atlas, bears no weight (this goes through lateral masses).

Low axis articulations are ordinary for cervical vertebrae (disc and two uncovertebral joints)

Bifid spinous process is large, due to suboccipital triangle muscles attaching from above.

Atlanto-occipital joint

Hyaline coverings; synovial cavity with lax but strong capsule attached to margines of both bones

C1 innervation.

Allows flexion and extension separate to C-spine and considerable lateral flexion; no rotation.

-           eg in ‘sniffing the morning air’, neck is flexed, but atlanto-occipital jt extended.

Centre of gravity in anterior jt, so extensor muscles maintain tone.

-           flexion is by gravity, actively by SCMs together and longus capitis; lat flexion by unilateral action of SCM, trapezius, splenius capitus.

Ant & Post Atlanto-Occipital Membranes

From foramen to respective arches of atlas.  Posterior has gap for vertebral artery and C1.

C1 innervation.

Median Atlantoaxial jt

Ie dens articulation.  Hyaline cartilage, capsule at edges, small synovial jt.

-           dens held in place by transverse ligament with large bursa between.

Lateral Atlantoaxial jt

B/n inferior facet of atlas and axis, circular, flat hyaline jts, lax capsule

C2 innervation

Accessory ligaments connect axis to occiput, bypassing atlas:

i)                       tectorial membrane: continuation of post long lig; ® anterior foramen magnum in front of dura, to which it is strongly attached

ii)                     transverse ligament: back of dens, with weaker longitudinal band = cruciform lig (this contacts tectorial membrane); important as backwards displacement of dends would cause fatal compression of the medulla – prevents this.

iii)                   Apical ligament: joins apex of dens to anterior foramen magnum (notochord remnant)

iv)                   Alar ligaments: Paired. From sides of dens ® margins of foramen magnum.  Strong; limit head rotation.

Movements of atlantoaxial jt: rotation in a vertical axis passing through dens.

-           atlas rotates by anterior arch, and transverse limb of cruciform ligament glides around dens

-           and lateral facets glide also; hence dead rotates over curved surfaces.

Muscles causing this = SCM, splenius capitus, inferior oblique.

Blood Supply of vertebrae (157-8)

Segmental from vertebral ascending and deep cervical (all off subclavian), intercostal, lumbar and lateral sacral arteries.

Veins described in Vertebral Canal section.

Extensor Muscles

Run along whole length of column skull ® sacrum.  Posterior rami. Bulge to either side of midline.

-           posterior-most is splenius in neck, elsewhere posterior covering is thoracolumbar fascia.

Deepest are interspinales and intertransversales (small and unimportant)

Remainder form intermediate and superficial masses collectively called: transversospinalis and erector spinae, each of which is composed of 3 groups.

-           transversospinalis = rotatores, multifidus and semispinalis

-           erector spinae = iliocostalis, longissimus and spinalis.

 

Deep layer (162)

Interspinalis join adjacent spinous processes (alongside interspinous ligaments).

Intertransversales join adjacent transverse processes.

 
Intermediate layer (161-2)

Transversospinalis: transverse processes ® spines (hence name).

-           rotatores: confined to thorax which rotates; base to transverse process ® root of spinous above

-           multifidus: back of sacrum, lumbars, transverse processes ® spinous process 2-3 above

-           semispinalis: on multifidus, from transverse ® spinous (thorax to skull only); divided into s. thoracis, s. cervicis, and s. capitis (most powerful; lies beneath splenius and trapezius and is chief extensor of the head)

 

Superficial layer (Erector spinae) (161)

Arises: back of sacrum and sides of iliac crest ® divides into two bundles:

-           iliocostalis lateral ® angles of lower six ribs ® then slips pass up to angle of 6th rib ® then slips run up to transverse processes of C5-8.

-           Longissimus thoracis: (medial) ® gutter b/n transverse processes and ribs ® slips up to lower cervical vertebrae (longissimus cervicis) ® slips to mastoid process deep to splenius capitus (longissimus capitis).

In neck, the extensors are bound down by splenius (sheet from upper thoracic spinous processes and supraspinous ligament, and ligamentum nuchae)

-           whole superficial layer is like a bandage holding down the deeper extensors at back of neck.

Most medial part is generally called spinalis.

Back of Neck (160)

Muscles connect skull to spine and pectoral girdle.

Ligamentum nuchae in midline separates sides; fibroelastic septum (see Pl 14)

-           from external occipital crest ® bifid spinous processes of C-vertebrae & deep cervical fascia.

Beneath trapezius and SCM lies splenius

® beneath splenius lies semispinalis capitis and longissimus capitis

® beneath these are deeper structures: below massive C2 process is semispinalis cervicis, above is right and left suboccipital triangles.

Suboccipital triangle (164)

Bounded by rectus capitis posterior major, and superior and inferior obliquus muscles. (See 164)

-           floor = posterior arch of atlas and atlanto-occipital membrane; suboccipital (C1), greater occipital (C2) nerves and occipital artery run across it.

Rectus capitis posterior major

Outer process of C2 ® lateral inferior nuchal line.  Extends, rotates head back to own side

Inferior obliquus capitus

Outer process of C2 (below rectus) ® back of atlas.  Rotates atlas back to own side.

Superior obliques capitus

From transverse C1 ® lateral mid-nuchal line.  Weak head extension.

Innervation: all by C1.

Vertebral artery

Ascends through foramina of transverse processes of C6-1 (anterior to spinal nerves)

® spinal branch to each intervertebral foramen

® at C1-2 jt, passes laterally with posterior curvature (Pl 164) allowing rotation at this point.

® emerges at transverse process of C1 on floor of suboccipital triangle

® grooves posterior atlas arch then enters foramen magnum.

Occipital artery passes along occipitomastoid suture deep to digastric and longissimus capitis

® runs across roof of suboccipital triangle ® scalp.

-           companion veins form rich plexus in and around semispinalis.

Vertebral veins

Plexus descends alongside vertebral artery in and out of foramina

-           collects blood from semispinalis capitis and suboccipital triangle muscles

-           ® two true vertebral veins emerge at C6/7 ® brachiocephalic.

Nerves

C1 (suboccipital) posterior ramus runs in artery groove on back of posterior arch of atlas.

® the two recti, obliquus, and upper semispinalis capitis.

-           anterior ramus winds around lateral mass b/n it and artery ® b/n rectus capital lateralis and anterior to join cervical plexus

-           neither branch reaches skin.

C2 (greater occipital nerve) is posterior ramus. Emerges below posterior arch of ramus.

-           curls around lower inferior oblique ® roof of suboccipital triangle, prices semispinalis

-           ® skin of scalp to vertex.