AN45.1-3 | Posterior abdominal wall — Glossary

Complex multilayered fascial envelope enclosing the back extensors; three layers in the lumbar region fusing laterally at the lateral raphe to give origin to transversus abdominis and internal oblique

Main extensor muscle column of the back; three columns (medial to lateral: spinalis, longissimus, iliocostalis); supplied by segmental dorsal primary rami

Deep back muscle spanning 2-4 segments; thickest in the lumbar region; critical for lumbar core stability; atrophy linked to chronic low back pain

Nerve plexus formed from the ventral rami of L1-L4 within the substance of the psoas major muscle; gives rise to the femoral, obturator, and other nerves

Largest branch of the lumbar plexus (L2-L4 posterior divisions); supplies quadriceps for knee extension and saphenous nerve for medial leg sensation

Branch of the lumbar plexus (L2-L4 anterior divisions); passes through the obturator foramen to supply the hip adductors and medial thigh sensation

Purely sensory nerve (L2-L3); exits under the inguinal ligament near the ASIS; compression causes meralgia paraesthetica

Compression neuropathy of the LFCN under the inguinal ligament causing burning pain and numbness on the lateral thigh; common in pregnancy and obesity

Major flexor of the hip arising from the lumbar vertebral bodies and transverse processes; the lumbar plexus forms within it; psoas abscess from spinal TB tracks along it

Muscle of the posterior abdominal wall from the 12th rib to the iliac crest; lateral flexion and fixation of the 12th rib during respiration

Branch of the lumbar plexus (L1-L2); genital branch supplies the cremaster muscle (cremasteric reflex); femoral branch supplies femoral triangle skin

Branch of L1; runs through the inguinal canal supplying sensation to the inguinal region and anterior scrotum/labia; at risk during hernia surgery

Branch of L1; supplies the lower abdominal wall musculature and skin above the inguinal region

Longest purely sensory branch of the femoral nerve; supplies the medial leg and foot down to the medial malleolus

Superficial reflex: stroking the medial thigh (L1-L2 dermatome) causes ipsilateral cremasteric contraction elevating the testis; absent in testicular torsion

Cold abscess from TB of lumbar vertebrae (Pott's disease) tracking along the psoas sheath to present as a fluctuant swelling in the femoral triangle

Posterior branch of a spinal nerve supplying the deep back muscles (erector spinae, transversospinalis) and overlying skin of the back

Herniation of the nucleus pulposus compressing a nerve root; L4-L5 disc compresses L5 root; L5-S1 disc compresses S1 root

Deep back muscles running from transverse to spinous processes: semispinalis (longest), multifidus (intermediate), rotatores (shortest)

Dynamic muscular control of the lumbar spine provided primarily by multifidus posteriorly and transversus abdominis anterolaterally via the thoracolumbar fascia

Site where the posterior and middle layers of the thoracolumbar fascia fuse laterally, giving origin to the internal oblique and transversus abdominis muscles