Nerves of the Lower Limb Flashcards
Lumbar Plexus
The anterior rami of the L1-L4 spinal roots divide into several cords. These cords then combine together to form the six major peripheral nerves of the lumbar plexus.
A useful memory aid for the branches of the lumbar plexus is: I, I Get Leftovers On Fridays.
This stands for the Iliohypogastric, Ilioinguinal, Genitofemoral, Lateral cuteanous nerve of the thigh, Obturator and Femoral.
Iliohypogastric Nerve
The iliohypogastric nerve is the first major branch of the lumbar plexus. It runs to the iliac crest, across the quadratus lumborum muscle of the posterior abdominal wall. It then perforates the transversus abdominis, and divides into its terminal branches.
Roots: L1 (with contributions from T12).
Motor Functions: Innervates the internal oblique and transversus abdominis.
Sensory Functions: Innervates the posterolateral gluteal skin in the pubic region. (Tip: an easy way to remember that the IlioHypogastric comes before the IlioInguinal is that H comes before I in the alphabet!)
Ilioinguinal Nerve
The ilioinguinal nerve follows the same anatomical course as the larger iliohypogastric nerve. After innervating the muscles of the anterior abdominal wall, it passes through the superficial inguinal ring to innervate the skin of the genitalia and middle thigh.
Roots: L1.
Motor Functions: Innervates the internal oblique and transversus abdominis.
Sensory Functions: Innervates the skin on the superior antero-medial thigh. In males, it also supplies the skin over the root of the penis and anterior scrotum. In females, it supplies the skin over mons pubis and labia majora.
Genitofemoral Nerve
After leaving the psoas major muscle, the genitofemoral nerve quickly divides into a genital branch, and a femoral branch.
Roots: L1, L2.
Motor Functions: The genital branch innervates the cremasteric muscle.
Sensory Functions: The genital branch innervates the skin of the anterior scrotum (in males) or the skin over mons pubis and labia majora (in females). The femoral branch innervates the skin on the upper anterior thigh.
Lateral Cutaneous Nerve of the Thigh
This nerve has a purely sensory function. It enters the thigh at the lateral aspect of the inguinal ligament, where it provides cutaneous innervation to the skin there.
Roots: L2, L3
Motor Functions: None.
Sensory Functions: Innervates the anterior and lateral thigh down to the level of the knee.
Obturator Nerve
See more detailed information here
Roots: L2, L3, L4.
Motor Functions: Innervates the muscles: obturator externus, pectineus, adductor longus, adductor brevis, adductor magnus, gracilis.
Sensory Functions: Innervates the skin over the medial thigh.
Femoral Nerve
See more detailed information here.
Roots: L2, L3, L4.
Motor Functions: Innervates the muscles: Illiacus, pectineus, sartorius, all the muscles of quadriceps femoris.
Sensory Functions: Innervates the skin on the anterior thigh and the medial leg.
Sacral Plexus
The anterior rami of the S1-S4 spinal roots (and the lumbosacral trunk) divide into several cords. These cords then combine together to form the five major peripheral nerves of the sacral plexus.
Leave the pelvis via the greater sciatic foramen – these nerves enter the gluteal region of the lower limb, innervating the structures there.
Remain in the pelvis – these nerves innervate the pelvic muscles, organs and perineum.
A useful memory aid for the major branches of the sacral plexus is ‘Some Irish Sailor Pesters Polly’. This stands for Superior Gluteal, Inferior Gluteal, Sciatic, Posterior cutaneous nerve of thigh, Pudendal.
Superior Gluteal Nerve
The superior gluteal nerve leaves the pelvis via the greater sciatic foramen, entering the gluteal region superiorly to the piriformis muscle. It is accompanied by the superior gluteal artery and vein for much of its course.
Roots: L4, L5, S1.
Motor Functions: Innervates the gluteus minimus, gluteus medius and tensor fascia lata.
Sensory Functions: None.
A useful memory aid for the major branches of the sacral plexus is ‘Some Irish Sailor Pesters Polly’. This stands for Superior Gluteal, Inferior Gluteal, Sciatic, Posterior cutaneous nerve of thigh, Pudendal.
Inferior Gluteal Nerve
The inferior gluteal nerve leaves the pelvis via the greater sciatic foramen, entering the gluteal region inferiorly to the piriformis muscle.
It is accompanied by the inferior gluteal artery and vein for much of its course.
Roots: L5, S1, S2.
Motor Functions: Innervates gluteus maximus.
Sensory Functions: None.
Sciatic Nerve
Roots: L4, L5, S1, S2, S3
Motor Functions:
Tibial portion – Innervates the muscles in the posterior compartment of the thigh (apart from the short head of the biceps femoris), and the hamstring component of adductor magnus. Innervates all the muscles in the posterior compartment of the leg and sole of the foot.
Common fibular portion – Short head of biceps femoris, all muscles in the anterior and lateral compartments of the leg and extensor digitorum brevis.
Sensory Functions:
Tibial portion: supplies the skin of the posterolateral leg, lateral foot and the sole of the foot.
Common fibular portion: supplies the skin of the lateral leg and the dorsum of the foot.
Posterior Femoral Cutaneous
The posterior cutaneous nerve of thigh leaves the pelvis via the greater sciatic foramen, entering the gluteal region inferiorly to the piriformis muscle. It descends deep to the gluteus maximus and runs down the back of the thigh to the knee.
Roots: S1, S2, S3
Motor Functions: None
Sensory Functions: Innervates the skin on the posterior surface of the thigh and leg. Also innervates the skin of the perineum.
Pudendal Nerve
This nerve leaves the pelvis via the greater sciatic foramen, then re-enters via the lesser sciatic foramen. It moves anterosuperiorly along the lateral wall of the ischiorectal fossa, and terminates by dividing into several branches.
Roots: S2, S3, S4
Motor Functions: Innervates the skeletal muscles in the perineum, the external urethral sphincter, the external anal sphincter, levator ani.
Sensory Functions: Innervates the penis and the clitoris and most of the skin of the perineum.
(Tip – an easy way to remember the functions of the pudendal nerve is S2, S3, S4 keeps poo off the floor!)
Tibial Nerve
Nerve roots: L4-S3
Sensory: Innervates the skin of the posterolateral leg, lateral foot and the sole of the foot.
In the popliteal fossa, the tibial nerve gives off cutaneous branches. These combine with branches from the common fibular nerve to form the sural nerve. This sensory nerve innervates the skin of the posterolateral side of the leg and the lateral side of the foot.
The tibial nerve also supplies all the sole of the foot via three branches:
Medial calcaneal branches: These arise within the tarsal tunnel, and innervate the skin over the heel.
Medial plantar nerve: Innervates the plantar surface of the medial three and a half digits, and the associated sole area.
Lateral plantar nerve: Innervates the plantar surface of the lateral one and a half digits, and the associated sole area.
Motor: Innervates the posterior compartment of the leg and the majority of the intrinsic foot muscles.
The tibial nerve innervates all the muscles in the posterior compartment of the leg. They are divided into a deep and superficial compartment:
Deep
Popliteus – Laterally rotates the femur on the tibia to unlock the knee.
Flexor hallucis longus – Flexes the big toe and plantar flexes the ankle.
Flexor digitorum Longus – Flexes the other digits and plantar flexes the ankle.
Tibialis posterior – Inverts the foot and plantar flexes the ankle.
Superficial
Plantaris – Plantar flexes the ankle.
Soleus – Plantar flexes the ankle.
Gastrocnemius – Plantar flexes the ankle and flexes the knee.
Tarsal Tunnel Syndrome
This is a condition where the tibial nerve is compressed within the tarsal tunnel (posterior to the medial malleolus). There are varying causes, of which the main three are:
- Osteoarthritis
- Rheumatoid arthritis
- Post-trauma ankle deformities
Patients complain of paraesthesia in the ankle and sole of the foot, which can radiate up the leg slightly. It is aggravated by activity and relieved by rest.
Tarsal tunnel symptoms can be treated conservatively by anti-inflammatory drugs and changes in footwear. If these interventions are not successful, the flexor retinaculum can be cut surgically, which releases the pressure.
Damage to the Common Fibular Nerve
The common fibular nerve is most commonly damaged by a fracture of the fibula, or the use of a tight plaster cast. The anatomical course of the common fibular nerve causes it to wrap round the neck of the fibular, and so any fractures of the fibular neck can cause nerve palsy.
Patients with common fibular nerve damage will lose the ability to dorsiflex the foot at the ankle joint. Hence the foot will appear permanently plantarflexed – known as footdrop. They may also present with a characteristic gait, as a result of the footdrop (for more information, see Walking and Gaits).
There will also be a loss of sensation over the dorsum of the foot, and lateral side of the leg. Innervation is preserved on the medial side of the leg (supplied by the saphenous nerve, a branch of the femoral), and the heel and sole (supplied by the tibial nerve, a branch of the sciatic).
Straight Leg Raise and Periopheral Nerve test
Sciatic Nerve and Tibial Nerve
Tibial Nerve
Sural Nerve
Common Peroneal Nerve
Nerve Root (Disc Prolapse)
