1.2 Lumbar spine & back

Question 1

Structure of vertebral column

Answer 1

Primary curvatures - thoracic, sacrococcygeal
Secondary curvatures - cervical, lumbar

Arranged into:

• vertebral column (IV joints & discs, vertebral canal & IV foramen)
• 2 x muscle compartments (superficial/extrinsic and deep/intrinsic muscles)

Question 2

Sacrum & coccyx

Answer 2

• Orientation of S1 facet surfaces are in coronal plane
• Presence of anterior and posterior sacral foraminae for nerve roots & vessels
• Sacral canal and hiatus (esp. sacral veins)
• Variable number of coccygeal vertebrae

Question 3

Blood supply & venous drainage

Answer 3

Lumbar arteries run lateralward and backward on bodies of lumbar vertebrae to the intervals between adjacent transverse processes and continue into the abdominal wall (posterior intercostals).

• lateral sacral
• arterial supply only to outer 1/3

Vertebral blood drains via basivertebral vein into internal vertebral venous plexus, which then drains into external vertebral venous plexus (external to dura mater).

Question 4

Centres of ossification

Answer 4

• 3 primary centres in body, & each neural arch.
• 5 secondary centres (at puberty) at tips of spinous & transverse processes, and the upper and lower margins of body (annular epiphysis).
• Secondary centres normally close during late adolescence, when vertebral growth is complete.
• *Epiphyseal growth plate can be mistaken for a fracture.

Question 5

IV discs

Answer 5

• Annulus fibrosus (fibrocartilage) attaches to adjacent vertebral bodies, keeping them together.
• in layers, perpendicular fibres, hence when lifting whilst twisting, only 50% of fibres are positioned to resist load.
• Nucleus pulposus (remnant of notochord) is deformable, but doesn’t change mass (except with age, there is a loss of water). Function is to keep vertebrae apart.

The weight bearing function of IV discs is also supported by end plate cartilage.

Question 6

Nerve supply to disc

Answer 6

Recurrent meningeal nerve contains sensory and sympathetic fibres.

Supply is to outer 1/3 - potential source of pain.

Question 7

Joints of vertebral arches

Answer 7

• Synovial joints
• Fibrous capsule - lax to permit movement
• Capsule supplied by branches of posterior rami, which also supply intrinsic muscles and overlying skin

Question 8

What defects occur in the lumbosacral joint?

Answer 8

Spondylolysis = defect in pars inarticularis of vertebra
Listhesis/spondylolisthesis = forward displacement of a vertebra, especially the fifth lumbar vertebra, most commonly occurring after a break or fracture.

*L4 on L5 and L5 on S1

Question 9

Superficial muscles of the back

Answer 9

• All attach to and act on the upper limb
• Trapezius
• Latissimus dorsi
• Rhomboids
• Levator scapulae
• LD, R, LS innervated by anterior rami
• T innervated by XI cranial nerve (spinal accessory n’)

Question 10

Deep muscles of the back

Answer 10

Erector spinae - prime mover that is responsible for returning flexed body to upright posture via concentric contraction

• tend to run medial to lateral across 5-7 vertebral segments
• Spinalis, Longissimus, Iliocostalis

Transversospinalis - short segmental muscles that act as stabilisers

• run from lateral to medial across vertebrae
• waste rapidly following injury
• multifidis, rotatores, semispinalis