19th February 2024

Lumbosacral plexus

Lumbar plexus

The lumbar plexus originates from the anterior rami of the L1-L4 spinal nerves, and they will combine to contribute towards six major nerves. The six nerves that arise from the lumbar plexus include:

• Iliohypogastric nerve
  • Contains the T12 and L1 spinal roots. It provides sensory innervation to the lateral gluteal region. 
  • Motor innervation is provided to the internal oblique and transverse abdominis muscle.
• Ilioinguinal nerve
  • Contains nerve roots from the L1 spinal nerve. 
  • It provides motor innervation to the transverse abdominis and internal obliques. 
  • Sensory innervation is provided to the skin of the anteromedial thigh. Sensation is also supplied to the root of the penis and anterior scrotum in males, while it supplies the mons pubis and labia majora in females. 
• Genitofemoral nerve
  • Contains the L1 and L2 nerve roots. 
  • Provides motor function to the cremasteric muscle. 
  • The genital branch provides sensory innervation to the anterior scrotum in males and the mons pubis and labia majora in females. Its femoral branch provides sensory innervation to the anterior thigh. 
• Lateral cutaneous nerve of the thigh
  • Contains the L2 and L3 spinal roots.
  • Provides sensation to the anterior and lateral thigh down to the knee.
• Obturator nerve
  • Contains the L2, L3 and L4 spinal roots. 
  • Motor innervation to the medial thigh (obturator externus, adductor longus, adductor brevis, adductor magnus, gracilis)
  • Sensory innervation to the medial thigh
• Femoral nerve
  • Contains the L2, L3 and L4 spinal roots
  • Motor innervation to the anterior thigh (iliacus, pectineus, sartorius and quadriceps femoris)
  • Sensory innervation to the anterior thigh and medial leg. 

Sacral plexus

The sacral plexus is the network of nerves that supplies the lower limbs, predominantly arising from the S1-S4 spinal nerves. It also receives contributions from the L4 and L5 spinal nerves. Five major nerves arise from the sacral plexus and leave the pelvic wall via the greater sciatic foramen. The following major nerves are derived from the sacral plexus:

• Superior gluteal nerve
  • Contains the L4, L5 and S1 spinal roots. 
  • Motor innervation to the gluteus minimus, gluteus medius and the tensor fascia lata
• Inferior gluteal nerve
  • Contains the L5, S1 and S2 spinal roots
  • Motor innervation to the gluteus maximus. 
• Posterior femoral cutaneous nerve of the thigh
  • Contains the S1, S2 and S3 spinal roots
  • Provides sensory innervation to the posterior surface of the thigh, leg and the perineum.
• Pudendal nerve
  • Contains the S2, S3 and S4 spinal roots
  • Motor innervation to the perineal muscles, urethral sphincter, anal sphincter and levator ani.
  • Sensory innervation is provided to the penis, clitoris and most of the perineal skin. 
• Sciatic nerve
  • Contains the L4, L5, S1, S2 and S3 spinal roots
  • Motor innervation to the posterior compartment of this thigh (biceps femoris, semimembranosus, semitendinosus and the ischial portion of the adductor magnus)
  • It divides further into two major branches after passing the popliteal fossa
    • Tibial nerve
      • Motor innervation to the posterior compartment of the leg and some intrinsic muscles of the foot
      • Sensory innervation to the posterolateral leg, lateral foot and sole of the foot. 
    • Common peroneal/fibular nerve
      • Motor innervation to the anterior and lateral compartments of the leg and intrinsic muscles of the foot
      • Sensory innervation to the lateral aspect of the leg and the dorsum of the foot. 

Image Source: Wikimedia Commons (2010). Lumbar plexus, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/7/73/Lumbar_plexus.svg (Accessed: 9 January 2024).