| Lumbar plexus | |
|---|---|
 Plan of lumbar plexus. | |
 The lumbar plexus and its branches. | |
| Details | |
| From | T12,L1-L4 |
| Identifiers | |
| Latin | plexus lumbalis plexus lumbaris |
| TA98 | A14.2.07.002 |
| TA2 | 6517 |
| FMA | 5908 |
| Anatomical terms of neuroanatomy | |
Thelumbar plexus is a web of nerves (anerve plexus) in thelumbar region of the body which forms part of the largerlumbosacral plexus. It is formed by thedivisions of the first fourlumbar nerves (L1-L4) and from contributions of thesubcostal nerve (T12), which is the lastthoracic nerve. Additionally, the ventral rami of the fourth lumbar nerve pass communicating branches, thelumbosacral trunk, to thesacral plexus. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh.[1]
The plexus is formed lateral to theintervertebral foramina and passes throughpsoas major. Its smaller motor branches are distributed directly to psoas major, while the larger branches leave the muscle at various sites to run obliquely down through the pelvis to leave under theinguinal ligament with the exception of theobturator nerve which exits the pelvis through theobturator foramen.[1]
Theiliohypogastric nerve runs posterior to thepsoas major on its proximal lateral border to run laterally and obliquely on the anterior side ofquadratus lumborum. Lateral to this muscle, it pierces thetransversus abdominis to run above theiliac crest between that muscle andabdominal internal oblique. It gives off several motor branches to these muscles and a sensory branch to the skin of the lateral hip. Its terminal branch then runs parallel to theinguinal ligament to exit theaponeurosis of theabdominal external oblique above theexternal inguinal ring where it supplies the skin above the inguinal ligament (i.e. thehypogastric region) with theanterior cutaneous branch.[2]
Theilioinguinal nerve closely follows the iliohypogastric nerve on the quadratus lumborum, but then passes below it to run at the level of the iliac crest. It pierces the lateralabdominal wall and runs medially at the level of the inguinal ligament where it supplies motor branches to both transversus abdominis and sensory branches through the external inguinal ring to the skin over thepubic symphysis and the lateral aspect of thelabia majora orscrotum.[2]
Thegenitofemoral nerve pierces psoas major anteriorly below the former two nerves to immediately split into two branches that run downward on the anterior side of the muscle. The lateralfemoral branch is purely sensory. It pierces thevascular lacuna near thesaphenous hiatus and supplies the skin below the inguinal ligament (i.e. proximal, lateral aspect offemoral triangle). Thegenital branch differs in males and females. In males it runs in thespermatic cord and in females in theinguinal canal together with theteres uteri ligament. It then sends sensory branches to the scrotal skin in males and the labia majora in females. In males it supplies motor innervation to thecremaster.[2]
Thelateral cutaneous femoral nerve pierces psoas major on its lateral side and runs obliquely downward below theiliac fascia. Medial to theanterior superior iliac spine it leaves the pelvic area through the lateralmuscular lacuna it enters the thigh by passing behind the lateral end of the inguinal ligament . In the thigh it briefly passes under thefascia lata before it breaches the fascia and supplies the skin of the anterior thigh.[2]
Theobturator nerve leaves the lumbar plexus and descends behind psoas major on it medial side, then follows thelinea terminalis into thelesser pelvis, and finally leaves the pelvic area through theobturator canal. In the thigh, it sends motor branches toobturator externus before dividing into an anterior and a posterior branch, both of which continues distally. These branches are separated byadductor brevis and supply all thigh adductors with motor innervation:pectineus,adductor longus, adductor brevis,adductor magnus,adductor minimus, andgracilis. The anterior branch contributes a terminal, sensory branch which passes along the anterior border of gracilis and supplies the skin on the medial, distal part of the thigh.[3]
Thefemoral nerve is the largest and longest of the plexus' nerves. It gives motor innervation toiliopsoas,pectineus,sartorius, andquadriceps femoris; and sensory innervation to the anterior thigh, posterior lower leg, and hindfoot. In the pelvic area, it runs in a groove between psoas major and iliacus giving off branches to both muscles, and exits the pelvis through the medial aspect ofmuscular lacuna. In the thigh it divides into numerous sensory and muscular branches and thesaphenous nerve, its long sensory terminal branch which continues down to the foot.[3]
| Nerve | Segment | Innervated muscles | Cutaneous branches |
|---|---|---|---|
| Iliohypogastric | T12-L1 | ||
| Ilioinguinal | L1 | •Anterior scrotal nerves in males | |
| Genitofemoral | L1-L2 | •Cremaster in males | |
| Lateral femoral cutaneous | L2-L3 | • Lateral femoral cutaneous | |
| Obturator | L2-L4 | •Obturator externus | •Cutaneous ramus |
| Femoral | L2-L4 | ||
| Direct branches from plexus to muscle | |||
| Short, direct branches | L1-L3 | ||
| Short, direct branches | T12-L4 | ||
