Chapter 8 - Nerves of the Lower Limb

Describe the Nerve Plexuses of the Lower Limb

Peripheral nerves of the lower limb arise from:

–Lumbar plexus

• Formed by L1-L4 spinal nerves

• Primary peripheral nerves: femoral nerve & obturator nerve

–Sacral plexus

• Formed by L4-S4 spinal nerves

• Primary peripheral nerves: superior gluteal nerve, inferior gluteal nerve, & sciatic nerve (tibial division and common fibular division)

Note: L4 spinal nerve contributes to both lumbar & sacral plexus

*Every nerve in the lower trunk is a derivative of the lumbar-sacral plexus

Describe Innervation of Gluteal Muscles. Plexus, nerve, emerges, exits, muscles supplied

Superior gluteal nerve

–From sacral plexus

–Exits pelvis through greater sciatic foramen

• Emerges at superior margin of piriformis muscle

–Supplies gluteus medius, gluteus minimus, and tensor fasciae latae muscles

• Runs laterally, passing deep to m. gluteus medius (between gluteus medius and gluteus minimus)

Inferior gluteal nerve

–From sacral plexus

–Exits pelvis through greater sciatic foramen

• Emerges at inferior margin of piriformis muscle

–Supplies m. gluteus maximus only

Innervation of Anterior Thigh Muscles. Muscles supplied.

Femoral nerve

–Largest nerve from lumbar plexus

–In pelvic area, runs inferiorly within groove between mm. iliacus and psoas major

• Femoral nerve supplies m. iliacus, but not m. psoas major

–Femoral nerve then passes under inguinal ligament to enter femoral triangle region of proximal, anterior thigh

Muscles supplied by femoral nerve

• M. Iliacus

• M. Sartorius

• M. Quadriceps femoris (all four muscle heads)

• M. Pectineus (which is classified with muscles of the medial thigh compartment)

–Note that the femoral nerve supplies all muscles of the anterior thigh compartment, plus 2 additional muscles (mm. iliacus and pectineus).

Femoral triangle

–Region in proximal ⅓ of anterior thigh

–Borders:

• Inguinal ligament (superior)

• M. Adductor longus (medial)

• M. Sartorius (lateral)

–Contents: femoral nerve, femoral artery, and femoral vein

• M. Iliopsoas located deep to femoral nerve

• M. Pectineus located deep to femoral artery & vein

Muscles innervated by Femoral Nerve

Femoral Triangle

Innervation of Medial Thigh Muscles. Plexus, exit, muscles supplied.

Obturator nerve

–From lumbar plexus

–Exits pelvis via obturator foramen to enter medial thigh

• Penetrates through both obturator internus and obturator externus muscles as it exits pelvis

Note: only the obturator nerve, artery, and vein pass through the obturator foramen (no muscle exits pelvis through obturator foramen)

Muscles supplied by the obturator nerve

• M. Obturator externus (but not obturator internus)

• M. Gracilis

• M. Adductor longus

• M. Adductor brevis

• Adductor part of adductor magnus (but not hamstring part)

Note: obturator nerve supplies all muscles of the medial thigh, except m. pectineus and hamstring part of adductor magnus muscle

Obturator nerve and muscles supplied

Innervation of Posterior Thigh Muscles. Muscles supplied. Termination?

Sciatic nerve (largest nerve of the body)

–From sacral plexus

–Exits pelvis via greater sciatic foramen

• Emerges at inferior margin of m. piriformis

–Consists of 2 divisions:

• Tibial division of sciatic nerve

• Common fibular division of sciatic nerve

Sciatic nerve runs inferiorly within posterior thigh compartment

• In posterior thigh, tibial division and common fibular division joined together to form  sciatic nerve

Tibial division of sciatic nerve supplies:

• M. Semitendinosus

• M. Semimembranosus

• Long head of m. biceps femoris

• Hamstring part of adductor magnus muscle

Note: tibial division of sciatic nerve supplies all muscle components that have their origin from ischial tuberosity

Common fibular division of sciatic nerve supplies only:

• Short head of m. biceps femoris (origin from linea aspera of posterior femur)

Sciatic nerve terminates as it enters popliteal fossa

–Nerve physically divides into:

• Tibial nerve

• Common fibular nerve

Tibial and common fibular nerves then cross the knee to enter the leg

Innervation of Posterior Thigh Muscles

Summary: Thigh Muscle Innervations

The thigh is divided into 3 compartments, but is supplied by 4 nerves

• Each compartment has exceptions to its nerve supply

Femoral nerve

–Supplies all anterior thigh muscles + 2 other muscles

• Mm. Sartorius and quadriceps femoris

• Also supplies mm. iliacus and pectineus

Obturator nerve

–Supplies all medial thigh muscles (with 2 exceptions)

• Supplies mm. obturator externus, gracilis, adductor longus, adductor brevis, & adductor part of adductor magnus

• Does not supply m. pectineus or hamstring part of adductor magnus muscle

Tibial division of sciatic nerve

–Supplies all posterior thigh muscles and muscle components that take origin from ischial tuberosity

• Semitendinosus, semimembranosus, long head of biceps femoris, and hamstring part of adductor magnus

• Note: adductor part of adductor magnus muscle has origin from ischiopubic ramus (not ischial tuberosity)

Common fibular division of sciatic nerve

–Supplies short head of m. biceps femoris only

• Origin from linea aspera of posterior femur

• Only posterior thigh muscle component that does not originate from ischial tuberosity

Describe the Popliteal Fossa. Borders. Nerves

The popliteal fossa is the diamond-shaped depression located behind the knee joint

Borders:

–Superior-medial: m. semitendinosus

–Superior-lateral: m. biceps femoris

–Inferior-medial: medial head of m. gastrocnemius

–Inferior-lateral: lateral head of m. gastrocnemius

Contents of the popliteal fossa

–Tibial nerve - derived from tibial division of sciatic nerve

• Runs inferiorly, down mid-line of popliteal fossa

• Passes deep to gastrocnemius muscle to enter posterior leg

–Common fibular nerve - derived from common fibular division of sciatic nerve

• Runs inferiorly and laterally, next to m. biceps femoris, to enter lateral leg

–Popliteal artery and popliteal vein

• Located deep to tibial nerve

• Continue into posterior leg

Tibial Nerve

Tibial nerve - a terminal branch of the sciatic nerve

• Runs inferiorly down mid-line of popliteal fossa

• Enters superficial posterior leg by passing between medial & lateral heads of m. gastrocnemius

• Passes deep to m. soleus to enter deep posterior leg compartment

• Passes posterior to medial malleolus to enter plantar foot*

Tibial nerve - supplies all muscles of posterior leg

• Superficial posterior leg muscles: mm. gastrocnemius, soleus, & plantaris

• Deep posterior leg muscles:   mm. popliteus, tibialis posterior, flexor hallucis longus, & flexor digitorum longus

Tibial nerve enters plantar foot

• Supplies all muscles of plantar foot: mm. abductor hallucis, abductor digit minimi, flexor digitorum brevis, & quadratus plantae

Common Fibular Nerve

Common fibular nerve - second terminal branch of sciatic nerve

–Runs inferiorly along superior-lateral border of popliteal fossa

• Follows m. biceps femoris

• Crosses posterior side of lateral knee

–Passes superficial to neck of fibula (just inferior to fibula head) - enters lateral leg compartment

–Terminates by dividing into:

• Superficial fibular nerve

• Deep fibular nerve

Superficial Fibular Nerve

Superficial fibular nerve

–Runs inferiorly within lateral compartment of leg

• Located superficially (just under crural fascia of leg)

–Supplies both muscles of the lateral leg:

• Mm. fibularis longus and fibularis brevis

Deep Fibular Nerve

Deep fibular nerve

–Dives deep and continues into anterior compartment of leg

• Runs inferiorly within anterior leg compartment

• Located deep, next to interosseous membrane

–Supplies all anterior leg muscles:

• Mm. tibialis anterior, extensor hallucis longus, extensor digitorum longus, & fibularis tertius

–Crosses ankle and passes to dorsal foot - supplies dorsal foot muscles

• Mm. extensor hallucis brevis & extensor digitorum brevis

Fibular Nerve Injuries

Most common lower limb nerve injury is to branches of common fibular nerve as they cross superficial to neck of fibula

–Injury to superficial fibular nerve

• Foot is inverted (loss of strong evertor muscles - fibularis longus & brevis)

–Injury to deep fibular nerve

• Unable to dorsi(*flex*) foot (loss of all anterior leg muscles)

• Produces “foot drop” - toes drag as foot is swung forward during walking

Describe the Sciatic Nerve Path