The Lumbar Spine and Pelvis: Muscles Anatomy

Vocabulary flashcards covering the anatomical origins, runs, insertions, actions, and nerve supplies for muscles of the posterior trunk, anterior-lateral trunk, lumbar spine, and pelvis.

Erector spinae group

The group of deep posterior trunk muscles consisting of three subgroups: Iliocostalis (lumborum, thoracis, cervicis), Longissimus (thoracis, cervicis, capitis), and Spinalis (thoracis, cervicis, capitis).

Transversospinal group

The group of deep posterior trunk muscles positioned deep to the erector spinae group, consisting of Semispinalis (thoracis, cervicis, capitis), Multifidi, and Rotatores (brevis and longus).

Short segmental group

The deepest group of posterior trunk muscles consisting of short segmental muscles: Interspinalis and Intertransversarii.

Iliocostalis lumborum

Origin: Iliac crest and tuberosity, Sacrum, Spinous process of T11 – L5 and supraspinous ligaments; Run: Up and out via slips; Insertion: Inferior border of lower 6 ribs; Action: Unilateral: Ipsilateral side flexion/rotation, Bilateral: Trunk extension; Nerve Supply: Adjacent posterior primary rami.

Longissimus thoracis

Origin: Transverse processes of lumbar vertebrae and adjacent fascia; Run: Up and out; Insertion: Transverse processes of all 12 thoracic vertebrae and lower ten ribs; Action: Unilateral: ipsilateral side flexion/rotation, Bilateral: trunk extension; Nerve Supply: Adjacent posterior primary rami.

Spinalis thoracis

Origin: Spinous processes of T11 – L2; Run: Upwards; Insertion: Spinous processes of T1 – T6; Action: Unilateral: ipsilateral side flexion/rotation, Bilateral: trunk extension; Nerve Supply: Adjacent posterior primary rami.

Semispinalis thoracis

Origin: Transverse processes of lower thoracic vertebrae (T6 – T10); Run: Up and in; Insertion: Spinous processes C6 – T2; Action: Unilateral: contralateral rotation, Bilateral: trunk extension; Nerve Supply: Adjacent posterior primary rami.

Multifidus

Origin: Sacrum, Fascia overlying erector spinae, Transverse processes; Run: Up and in; Insertion: All spinous processes C2 – L5 (fibres span 1 to 4 vertebrae); Action: Unilateral: contralateral rotation, Bilateral: trunk extension, Stabilisation; Nerve Supply: Adjacent posterior primary rami.

Rotatores

Origin: Transverse processes; Run: Up and in; Insertion: Laminae 1-2 levels above; Action: Unilateral: contralateral rotation, Bilateral: trunk extension, Stabilisation; Nerve Supply: Adjacent posterior primary rami.

Interspinalis

Origin/Run/Insertion: Fibres run vertically between adjacent spinous processes; Action: Trunk extension, Stabilisation; Nerve Supply: Adjacent posterior primary rami.

Intertransversarii

Origin: Pairs of slips, lateral between transverse process and medial from accessory process of lumbar vertebrae; Run: Vertically; Insertion: Adjacent transverse/accessory process; Action: Ipsilateral trunk lateral flexion, Stabilisation; Nerve Supply: Adjacent anterior or posterior primary rami dependent on position.

Rectus abdominis

Origin: Symphysis pubis, Pubic crest; Run: Up, wider superiorly; Insertion: Xiphoid process, Costal cartilage of ribs 5-7; Action: Trunk flexion; Nerve Supply: Anterior primary rami of lower six or seven thoracic nerves (T6/7 – T12).

External oblique

Origin: Outer borders of lower 8 ribs & costal cartilages; Run: Down and medial; Insertion: Outer lip anterior two thirds of iliac crest, Large aponeurosis inserting into linea alba and pubic tubercle (forms inguinal ligament and part of rectus sheath); Action: Unilateral: contralateral rotation, ipsilateral side flexion, Bilateral: trunk flexion, increases intra-abdominal pressure; Nerve Supply: Anterior primary rami lower six thoracic nerves T7 – T12.

Internal oblique

Origin: Thoracolumbar fascia, Lateral 2/3 inguinal ligament, Iliac crest; Run: Upwards and medially; Insertion: Lower four ribs, Linea alba, Pubic tubercle (via aponeurosis); Action: Unilateral: ipsilateral rotation, side flexion, Bilateral: trunk flexion, increases intra-abdominal pressure; Nerve Supply: Anterior primary rami of lower six thoracic and first lumbar nerve (T7 – L1).

Transversus abdominis

Origin: Thoracolumbar fascia, Inner anterior iliac crest, Lateral 1/3 inguinal ligament, Costal cartilage of lower six ribs; Run: Horizontally; Insertion: Linea alba via aponeurosis, Pubic crest; Action: Increases intra-abdominal pressure, Non direction-specific activation with variety of tasks; Nerve Supply: Anterior primary rami of lower six thoracic and first lumbar nerve (T7 – L1).

Quadratus lumborum

Origin: Posterior iliac crest, Iliolumbar ligament; Run: Upwards and medially; Insertion: Medial half lower border of 12th rib, Transverse processes L1 – L5; Action: Unilateral: ipsilateral lateral flexion, keeping pelvis level in single leg stance (non-weight bearing side), Bilateral: lumbar extension; Nerve Supply: Anterior primary rami T12 – L3/4.

Psoas major

Origin: Vertebral bodies, transverse processes and discs T12 – L5; Run: Down and forwards, under the inguinal ligament then passes backward and laterally; Insertion: Lesser trochanter of femur with iliacus; Action: Hip flexion, Lumbar flexion and ipsilateral side flexion; Nerve Supply: Anterior rami L1 – 3/4.