Innervation to the Lower Limbs

The innervation of the lower limbs can be summarized as:

1. Femoral nerve

   • This is formed from the lumbar plexus of nerves from L2-L4 spinal nerves

   • It is formed in the abdomen within the psoas major muscle and runs downwards and laterally between the psoas and iliacus muscles

   • It enters the thigh through the femoral triangle, running outside the femoral sheath, lateral to the femoral artery, vein, and lymphs

   • Branches of the femoral nerve are:

     • Branches to the anterior thigh muscles

     • Articular branches to the hip and knee joints

     • Cutaneous branches to the anteromedial thigh, this includes the saphenous nerve which is its terminal cutaneous branch. This nerve in turn travels through the adductor canal with femoral vessels and descends long with the saphenous vein to provide somatosensory innervation to the skin around the medial ankle and foot

   • This nerve provides motor innervation to the anterior thigh muscles and sensory innervation to regions of the hip, knee, anteromedial thigh, medial ankle, and foot

2. Obturator nerve

   • This is formed from the lumbar plexus of nerves from L2-L4 spinal nerves

   • It travels down the lateral pelvic walls, crosses the pelvic brim anterior to the sacroiliac joint and posterior to the common iliac vessels before entering the obturator canal to travel to the medial thigh

   • Branches of the obturator nerve are:

     • Anterior branches travel between and innervate the adductor longus and adductor brevis as well as gracilis muscles. It also innervates the pectineus muscle. It then pierces the fascia lata to continue as the cutaneous branch of the obturator nerve

     • Posterior branches pierce the obturator externus muscle and travel between the adductor brevis and adductor magnus muscles to innervate the obturator externus and adductor magnus muscles.

   • This nerves provides motor innervation to the muscles of the medial thigh except the hamstrings portion of the adductor magnus and pectineus muscles and sensory innervation to the medial thigh

3. Sciatic nerve

   • This is formed from the lumbosacral plexus of nerves from L4-S3 spinal nerves

     1. It travels through the sciatic foramen inferior to the piriformis muscle and continues deeps to the gluteus maximus and is the most lateral structure to exit the sciatic foramen before continuing in the posterior region of the thigh deep to the biceps femoris muscle

     2. Branches of the sciatic nerve are:

        • Branches to the posterior thigh muscles and articular branches to all the joints in the lower limbs.

        • Its terminal branches are the tibial and common fibular nerve at the apex of the popliteal fossa

     3. This nerves provides motor innervation to posterior thigh muscles, all the muscles in the leg and foot, and sensory innervation to the skin in the leg and foot

4. Tibial nerve

   • This nerve is the continuation of the sciatic nerve which branches at the apex of the popliteal fossa

   • It runs through the popliteal fossa, lateral and superior to the femoral vein before continuing superior to the popliteus muscle. In the posterior leg, it travels down eventually reaching the tarsal tunnel which it goes through between the flexor digitorum longus and flexor hallucis longus muscles

   • Branches of the tibial nerve are:

     • Branches to posterior leg muscles

     • Articular branches to the knee joint

     • Sural nerve which provides cutaneous innervation

     • Its terminal branches are the medial and lateral plantar nerves at the flexor retinaculum

   • It provides motor innervation to the muscles of the posterior leg, and muscles of the foot, and sensory innervation to the knee, posterior and lateral regions of the leg, and latera region of the foot

5. Fibular nerves

   • These nerves are the continuation of the sciatic nerve which branches at the apex of the popliteal fossa

   • Common fibular nerve

     • This follows the medial border of the biceps femoris muscle and divides into the deep and superior fibular nerves at the fibular head

     • This gives off articular branches to the knee joint. Its terminal branches include the superficial and deep fibular nerves

     • This provides motor innervation to the short head of the biceps femoris muscle, muscles of the lateral and anterior leg, and intrinsic muscles of the foot. It provides sensory innervation to the skin over the regions of the lower posterolateral leg, upper lateral leg, anterolateral leg, dorsum of the foot, and between the first two toes.

   • Superficial fibular nerve

     • This follows the lateral leg

     • This provides sensory innervation to the posterior and lateral leg and lateral region of the foot

   • Deep fibular nerve

     • This follows the anterior leg

     • This provides motor innervation to the anterior leg, muscles responsible for dorsiflexion of the foot at the ankle joint, and intrinsic muscles of the foot. It also provides sensory innervation to the webbed space of skin between the first and second toes

Clinical Notes:

1. The sciatic nerve is the largest nerve in the body and it could be injured from improperly administered gluteal injections or by being compressed by the piriformis muscle. Injury of the sciatic nerve may result in paralysis of the hamstring group of muscles, paralysis of leg muscles resulting in foot drop, or sensory loss below the knee with the exception of the region receiving innervation by the saphenous nerve.