MD 2016 Back Muscles & Movements Applied Anatomy A/Prof Chris Briggs Anatomy & Neuroscience
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Learning Objectives Movements of back & effects on nerve roots. Organisation & functions of back muscles (superficial, intermediate & deep layers). Supply systems - blood & nerve supply Disc prolapse & pain associated with nerve root compression Disc degeneration & its consequences Suggested pre-reading Clinically Orientated Anatomy, Moore 7 th ed. Chapter 4, Back,.
Movements of Back Flexion Extension CIBA Clinical Symposia: Low Back Pain Flexion mainly occurs in lumbar spine enhanced by lumbar lordosis. Flexion causes nucleus to project posteriorly Hyperflexion stretches sciatic nerve & may cause nerve root pain In extension thoracic spine has minimal movement (retains kyphosis) but lumbar spine increases lordosis Hyperextension loads facet surfaces closes joints down
Lateral flexion Rotation Small degree LF in thoracic spine but limited by ribs. Most occurs in lumbar spine Similar pattern in rotation
Movements of Back (1) Enhanced by: Thickness of IV-discs - note wedgeshape at L5/S1 (2) Limited by: Orientation of articular facets control movement (in certain directions) Thoracic permit rotation in coronal plane Lumbar permit flexion/extension in sagittal plane Visible Human Project - National Library of Medicine Lumbosacral limit movement in sagittal plane Netter, F.H. Interactive Atlas of Human Anatomy. 3rd ed. Figs. 143A
Muscles of back regional & functional (1) Superficial (extrinsic) muscles - all attach to and act on the upper limb. They include: - trapezius - latissimus dorsi - rhomboids - levator scapulae Superficial muscles of the back (except trapezius) originate from cervical myotomes & are innervated by anterior rami. Nerves remain faithful to embryological origin Image from Anatomedia General Anatomy module Grant s Method of Anatomy 11 th ed (1989) Williams & Wilkins ISBN 0-683- 00374-7 Fig 29-5
Superficial muscles of back Anatomedia: Back Dissection module Note posterior rami penetrating (but not supplying) superficial muscles passing to skin
Intermediate muscles of the back Intermediate muscles (serratus posterior superior and inferior) act on the ribs and are innervated by anterior rami. Accessory muscles of respiration
Deep muscles of the back Deep muscles may be organized into: - Erector spinae (tend to run medial to lateral across 5-7 vertebral segments) - Spinalis, Longissimus & Iliocostalis - Regional subdivisions: capitis, cervicis, thoracic, lumborum -** Lateral border of erector spinae corresponds with angle of rib most common site of rib fracture -Transversospinalis (short muscles run from lateral to medial across fewer vertebral segments) -multifidus, rotatores. Grant s Method of Anatomy 11 th ed (1989) Williams & Wilkins ISBN 0-683-00374-7 Fig 29-9 & 10
Function of deep back muscles (1) Erector spinae are prime movers, responsible for (concentrically) returning the flexed trunk to the upright (extended) posture. They also work eccentrically in controlling flexion They are electrically quiet in full flexion dangers of lifting in flexed posture Muscles & Movements MA MacConaill & JV Basmajian, Williams & Wilkins 1969
(2) Transversospinalis - segmental stabilisers - act together with deep abdominal muscles (esp. transversus abdominis) forming corset around trunk via lumbar fascia - waste rapidly following back injury - back strengthened via contraction of deep abdominal muscles - core strengthening Netter, F.H. Interactive Atlas of Human Anatomy. 3rd ed. Figs. 143A
Dorsal type skin Superficial veins & lymphatics pass anteriorly - veins to azygos system - lymphatics to axillary (inguinal) nodes Arteries pass through muscles with dorsal rami to skin
Blood vessels & segmental supply Angiosomes of back Angiosome = vascular territory
Nerve supply of deep back muscles Posterior rami innervate: Thoracic DR - facet joints - deep back muscles Dermatomes - overlying skin Lumbar DR Peripheral nerve supply (posterior rami) & dermatomes of back
Back pain Compressive or neurogenic (nerve related) pain occurs when nerve roots are irritated or pinched. Common causes: - herniated discs - spinal stenosis
Disc prolapse Penetration of nucleus into (and through) annulus. 3 types: Postures likely to increase loads on lumbar I-V discs Posterior longitudinal ligament Netter, F.H. Interactive Atlas of Human Anatomy. 3rd ed. 146B Reflex muscle spasm
Contributors to disc prolapse -15 deg lumbar flexion forces nucleus posteriorly -15 deg rotation max torsion in annulus, only 50% fibres resist force - slight LF forces nucleus posterolaterally - be overweight - keep lower limbs fully extended - pick up heavy object near opposite foot - repeatedly do this while using laryngeal muscles to call for help
Nerve root compression Direction of lumbar disc prolapse note nerve root in upper part of foramen Anatomedia: Back module Nerve root affected by lumbar disc prolapse note narrow lumbosacral foramen, large lumbosacral disc & S1 nerve root
FRACTURES Pars inter-articularis Spondylolisis & listhesis of L4 on L5 and L5 on S1. Fracture at pars inter-articularis
Spondylosis & spinal stenosis With aging, bones tend to lose water, become less dense - (degenerative change) spondylosis - may cause an overgrowth of bone producing bony spurs (osteophytes) that can extend into the foramina, narrowing them (stenosis) & compressing exiting nerve roots. CIBA Clinical Symposia: Low Back Pain
Degenerative & systemic conditions www.arthritisvic.org.au/arth ritis/ankyspond.htm Images courtesy Prof Kim Bennell Compression fracture often associated with osteoporosis. Pain & limitation of function Other causes of back pain: Cardiovascular (eg. aortic aneurism) Neoplasia (particularly in older person) - Tumour metastasis (from lung, breast, thyroid, kidney, prostate) Infection Ankylosing spondylitis. Affects spine, joints of pelvis ultimately leading to fusion (ankylosis)