Topic Overview

Additional Features of Muscles of the Back

Functional Groups

• Extrinsic (superficial & intermediate):

  • Connect upper limb & thoracic wall with vertebral column.

  • Involved mainly in upper limb & respiratory movements.

• Intrinsic (deep):

  • Lie deep to thoracolumbar fascia.

  • Concerned with posture and spinal movements.

Layerwise Arrangement

Superficial Layer (extrinsic)

• Trapezius, latissimus dorsi, levator scapulae, rhomboids.

• Act on upper limb by moving scapula & humerus.

Intermediate Layer (extrinsic)

• Serratus posterior superior, serratus posterior inferior.

• Accessory muscles of respiration.

Deep Layer (intrinsic, true back muscles)

• Splenius group (splenius capitis, splenius cervicis).

• Erector spinae group (iliocostalis, longissimus, spinalis).

• Transversospinalis group (semispinalis, multifidus, rotatores).

• Short segmental muscles (interspinales, intertransversarii, levatores costarum).

• Function → maintain posture, extend, rotate, and laterally flex vertebral column.

Nerve Supply

• Extrinsic muscles → supplied by ventral rami (except trapezius by accessory nerve).

• Intrinsic muscles → supplied by dorsal rami of spinal nerves.

Blood Supply

• Segmental branches of posterior intercostal, lumbar, and sacral arteries.

Clinical Importance

• Accessory nerve injury → trapezius paralysis → shoulder droop.

• Dorsal scapular nerve injury → rhomboid weakness → scapula displaced laterally.

• Thoracodorsal nerve injury → paralysis of latissimus dorsi → difficulty in climbing.

• Back pain → commonly from strain of intrinsic muscles or spasm.

• Pott’s spine (TB of vertebrae) → secondary spasm of back muscles.

• Lumbago → pain due to strain of erector spinae.

• Herniation of disc → reflex spasm of paravertebral muscles.

Functional Testing

• Trapezius → ask patient to shrug shoulders against resistance.

• Latissimus dorsi → test during resisted climbing/pulling.

• Rhomboids → palpate medial scapular border during retraction.

• Erector spinae → ask patient to extend trunk against resistance.