Lower Limb Innervation, Nerve Injuries, Joints, and Arterial Supply — Comprehensive Study Notes

Segmental Innervation of the Muscles of the Lower Limb

Muscles crossing the anterior side of the hip: innervated by $L2-L3$ .
Muscles crossing the anterior side of the knee: innervated by $L3-L4$ .
Muscles crossing the anterior side of the ankle: innervated by $L4-L5$ .
Muscles crossing the posterior side of the hip: innervated by $L4-L5$ .
Muscles crossing the posterior side of the knee: innervated by $L5-S1$ .
Muscles crossing the posterior and lateral side of the ankle: innervated by $S1-S2$ .
Gluteal region: medial and intermediate portions are innervated by $S1-S2$ .

Nerve Injuries And Abnormalities Of Gait

Nerve injuries affect how the body moves during walking (gait). Review source: Nerve Supply LE (nabil ebraheim). (Reference link provided in slides.)

Superior Gluteal Nerve

Innervates gluteus medius and gluteus minimus.
Deficit leads to weakness in abduction of the hip.
Impairment of gait: patient cannot keep the pelvis level when standing on one leg.
Sign: Trendelenburg gait (pelvis drops on the side opposite the lesion when standing on one leg).
Associated effects: weakness in medial rotation of the thigh.

Inferior Gluteal Nerve

Innervates gluteus maximus.
Deficit causes weakened hip extension.
Difficulty rising from a sitting position or climbing stairs.

Femoral Nerve

Innervates hip flexors and knee extensors (primary motor supply to quadriceps; and iliacus via its tibial contribution through the femoral nerve context).
Deficits: weakened hip flexion and weakened extension of the knee.
Sensory loss: anterior thigh; medial leg and medial foot.

Lateral Femoral Cutaneous Nerve

Purely sensory; loss of sensation over the skin of the lateral thigh.
Origin: posterior divisions of $L2-L3$ spinal nerves.
No motor fibers.
Anterior branch supplies the anterolateral thigh to the knee.
Posterior branch runs down the posterolateral thigh along the iliotibial tract, contributing terminal filaments across lateral and posterior thigh surfaces.
(Branch noted as Group A in slides.)

Obturator Nerve

Motor: loss of adduction of the thigh.
Sensory: loss over the medial thigh.
Common injury mechanism: anterior hip dislocation can damage the nerve.

Sciatic Nerve

Posterior divisions labeled as $L4-L5-S1$ with involvement in sciatica.
Muscle effects depend on distal branching (tibial and common fibular components):
- Hamstring group affected (posterior thigh).
- Adductor magnus (partly) can be involved (designated as (L4-S3)).
Common sites of deformity or nerve compression include compression from tight piriformis and hip dislocation, and femoral fracture considerations.
Symptoms/signs typically include radiating pain in the posterior thigh and leg down to the foot, possible atrophy in posterior thigh, leg, and foot regions.
Posterior hip dislocation can commonly damage the sciatic nerve.

Tibial Nerve

Weakness in knee flexion (due to distal innervation patterns).
Supplies all the sole of the foot via three branches: $ext{Medial calcaneal branches}, ext{Medial plantar nerve}, ext{Lateral plantar nerve}$ .
Functional deficits:
- Weakness in plantarflexion and inverted foot.
- Sensory loss on the leg (except the medial side) and plantar aspect of the foot.

Common Fibular (Peroneal) Nerve

Lesions produce deficits from both the deep and superficial fibular nerves.
Most frequently damaged nerve of the lower limb due to its superficial position at the neck of the fibula.
Clinically: loss of dorsiflexion at the ankle (Foot drop), loss of eversion, sensory loss on the lateral leg and dorsum of the foot.

Superficial Fibular Nerve

Motor: loss of eversion of the foot.
Sensory: sensory loss on the dorsum of the foot except for the first web space.
Branches referenced: Saphenous (from femoral), Lateral sural (from common fibular), Sural (from common fibular and tibial).
Deep fibular nerve mentioned as another component for dorsum sensory territory (first web space).

Deep Fibular Nerve

Motor: weakened inversion; loss of extension of the digits; loss of dorsiflexion (foot drop).
Sensory: loss on the anterolateral leg and the first web space between the toes.

Common Peroneal Nerve (Summary of Injury Mechanisms)

Mechanisms of injury (MOI) include obstetric or anesthesia stirrups, lying on the side during anesthesia without padding, tight plaster casts of the leg, and trauma such as fracture of the fibular neck.
Clinical presentation: impaired ankle dorsiflexion and toe dorsiflexion, foot drop; compensatory gait with hip and knee flexion (steppage gait).
Sensory deficits: over the anterior and lateral leg, dorsum of the foot including the first web space.

Arterial Supply and Major Anastomoses

Major arteries involved in the lower limb:
- Obturator artery: supplies medial compartment of the thigh.
- External iliac artery.
- Femoral artery.
- Profunda femoris artery.
- Medial circumflex femoral artery: supplies the head of the femur; risk of avascular necrosis if blood supply is compromised (especially with femoral neck fracture).
- Lateral circumflex femoral artery.
- Popliteal artery: supplies the knee joint.
Important note: Most of the blood supply to the head of the femur arises from the medial femoral circumflex artery, which runs alongside the neck; fracture of the femoral neck can compromise this supply, leading to avascular necrosis of the femoral head.
Arterial supplies in the leg compartments:
- Anterior tibial artery runs with the deep fibular nerve in the anterior compartment.
- Dorsalis pedis artery: pulse felt on the dorsum of the foot, lateral to the tendon of extensor hallucis longus.
- Posterior tibial artery runs with the tibial nerve in the posterior compartment.
- Fibular (peroneal) artery supplies the lateral compartment.
- Lateral plantar artery, plantar arterial arch, medial plantar artery.

The Hip Joint: Anatomy and Ligaments

The hip joint is a synovial ball-and-socket joint; multiaxial diarthrotic.
Bony components: head of femur and acetabulum.
Acetabulum: horseshoe-shaped; inferior deficiency at the acetabular notch; acetabular labrum deepens the socket.
Transverse acetabular ligament spans the acetabular notch.
Capsule and ligaments reinforce the joint:
- Ligament of the head of the femur (ligamentum teres).
- Transverse acetabular ligament.
- Acetabular labrum and cartilage.
Additional structures in proximity: tendon of the rectus femoris; acetabular fossa.
Major ligaments reinforcing the capsule include:
- Iliofemoral ligament (aka ligament of Bigelow): strongest capsular ligament; Y-shaped; apex at the anterosuperior iliac spine region; base along trochanteric line; two main bands (lateral and medial) and possibly three bands; resists overextension.
- Pubofemoral ligament: reinforces anterior and inferior capsule.
- Ischiofemoral ligament: reinforces posterior capsule.
- Zona orbicularis (ring-like deep capsule fibers) and the cotyjoint membranes.
Other protective structures: zona orbicularis; acetabular labrum deepens socket; ligaments reinforce capsule against dislocations.
Blood supply to the femoral head is primarily via retinacular arteries arising from the medial and lateral circumflex femoral arteries; the acetabular branch supplies the head via the ligamentum teres.
Key vascular note: Medial femoral circumflex artery provides most of the arterial supply to the femoral head along the neck; fractures of the femoral neck can cause avascular necrosis of the femoral head.

Movements of the Hip and Associated Muscles

Flexion: iliopsoas, rectus femoris, sartorius.
Extension: gluteus maximus, hamstrings.
Abduction: gluteus medius and minimus, sartorius, tensor fascia lata, piriformis, upper fibers of gluteus maximus.
Adduction: adductor muscles, pectineus, gracilis.
Lateral rotation: piriformis, obturator internus and externus, superior and inferior gemelli, quadratus femoris, gluteus maximus.
Medial rotation: anterior fibers of gluteus medius and minimus, tensor fascia lata.
Circumduction: combination of the movements listed above.

The Knee Joint

The knee forms three articulations: femoropatellar, medial tibiofemoral, and lateral tibiofemoral.
Primary movements: flexion and extension; functionally a hinge joint.
Weight-bearing and stability depend on surrounding muscles (quadriceps femoris, hamstrings) and multiple ligaments.
Structural features include the patellofemoral joint, menisci, ligaments, bursae, and joint capsule.

Ligaments and Menisci of the Knee

Medial (tibial) collateral ligament (MCL):
- Extends from the medial epicondyle of the femur to the medial tibia.
- Firmly attached to the joint capsule and to the medial meniscus.
- Prevents lateral displacement (abduction) of the tibia relative to the femur.
Lateral (fibular) collateral ligament (LCL):
- Extends from the lateral femoral condyle to the head of the fibula; not attached to the lateral meniscus.
- Prevents medial displacement (adduction) of the tibia relative to the femur.
Anterior cruciate ligament (ACL): intracapsular; attaches to the anterior aspect of the tibia and courses to the lateral condyle of the femur (superior, posterior, and lateral path).
- Function: prevents anterior displacement of the tibia under the femur; tension is greater when the knee is extended; weaker than the PCL.
Posterior cruciate ligament (PCL): intracapsular; attaches to the posterior aspect of the tibia and to the medial condyle of the femur (superior, anterior, and medial path).
- Function: prevents posterior displacement of the tibia under the femur; tension greatest when the knee is flexed.
Menisci:
- Medial meniscus: C-shaped, firmly attached to MCL; less mobile; more commonly injured.
- Lateral meniscus: circular and more mobile; not attached to the fibular collateral ligament.
- Function: deepen the articulating surfaces, improve congruence, and act as shock absorbers.
Common knee injuries:
- The three most common injured structures: tibial collateral ligament (MCL), medial meniscus, and ACL — Often described as the Terrible or Unhappy Triad; typically from a blow to the lateral aspect of the knee with the foot planted.

The Knee Joint – Clinical Tests and Common Injuries

Anterior Drawer sign: tests integrity of the ACL; involves tibial translation anteriorly when the femur is stabilized.
Posterior Drawer sign: tests integrity of the PCL; posterior translation of the tibia.
Injury to ACL may present with a positive anterior drawer test; PCL injury with posterior drawer sign.

The Ankle Joint

The ankle is the articulation between the distal tibia and fibula with the talus (ankle) and involves the distal tibiofibular and talocrural joints.
The distal ends of the tibia and fibula form a socket that is wider anteriorly than posteriorly to allow talar movement.
The ankle is a synovial hinge-type joint reinforced by a strong capsule and ligaments.
Ligaments of the ankle:
- Medial collateral (deltoid) ligament, which is strong and consists of:
  1) Anterior tibiotalar
  2) Posterior tibiotalar
  3) Tibionavicular
  4) Tibiocalcaneal
- Tibio-calcaneal (often referred to as part of the deltoid complex).
- Lateral collateral ligaments (weak):
  1) Anterior talofibular (ATF)
  2) Posterior talofibular (PTF)
  3) Calcaneofibular (CF)
Neurovascular supply to the ankle region is essential for function and sensation (details summarized in the neurovascular section below).
Common movements and their primary muscles:
- Dorsiflexion: tibialis anterior, extensor hallucis longus (EHL), extensor digitorum longus (EDL); fibularis tertius contributes.
- Plantarflexion: gastrocnemius, soleus (triceps surae); plantaris; fibularis longus and brevis; tibialis posterior; flexor digitorum longus; flexor hallucis longus.
Important clinical signs:
- Anterior drawer sign at the ankle indicates ATF laxity.

Arterial Supply To The Foot and Ankle Regions

Arterial pathways in the leg and foot include:
- Femoral artery becomes the popliteal artery behind the knee, giving rise to genicular arteries around the knee.
- Posterior tibial artery and anterior tibial artery supply respective compartments; dorsalis pedis arises from the anterior tibial artery in the foot.
- Perforating connections exist between the tibial and fibular/peroneal systems via the arcuate and other anastomoses, forming a robust collateral network.
Note on the sole and plantar arch: medial and lateral plantar arteries contribute to the plantar arterial arch; deep plantar and dorsal arterial networks link dorsal and plantar aspects.

Practical and Clinical Correlations

Low back pain related to nerve root compression can involve L4, L5, S1; common radiculopathies present with pain, numbness, motor weakness, and reflex changes (e.g., diminished knee and ankle jerks).
Osgood-Schlatter disease: a growing adolescents condition from repetitive traction apophysitis at the tibial tubercle; common in sports with running and jumping; usually self-limited after growth stops.
Nerve injury patterns help localize lesions:
- Trendelenburg sign indicates superior gluteal nerve (L4-S1) palsy.
- Foot drop suggests common peroneal/fibular nerve involvement (L4-S2).
- Sensory findings help differentiate superficial vs deep peroneal involvement (e.g., first web space with deep peroneal involvement).
Common knee injury triad (Terrible/Unhappy Triad): ACL + MCL + medial meniscus due to a lateral blow with the foot planted; injury patterns may vary with mechanism.

Key Anatomical Relationships and Notes

Proximal femur head blood supply: mainly via the medial femoral circumflex artery; fractures of the femoral neck risk avascular necrosis of the femoral head due to disrupted retinacular arteries.
Hip joint ligaments provide stability against dislocation and excessive movements; iliofemoral (Y-shaped) is the strongest capsular ligament; pubofemoral and ischiofemoral ligaments provide additional stabilization.
Ligamentum teres, transverse acetabular ligament, and acetabular labrum contribute to acetabular stability and joint nutrition; the labrum deepens the socket for the femoral head.
The knee relies on a combination of ligaments, menisci, and muscular support for stability; injury patterns often involve multiple structures due to the knee’s role in weight-bearing and locomotion.

Quick Reference: Nerve Levels to Key Structures (selected)

$L2-L3$ : hip adductors and some thigh flexors; hip flexion and abduction reinforcement via femoral and obturator contributions.
$L3-L4$ : knee extensors and patellar reflex contributions; anterior compartment innervation patterns.
$L4-L5$ : ankle dorsiflexion and inversion components; tibial/fibular contributions at the ankle.
$L5-S1$ : hamstrings and sciatic distribution; posterior thigh to leg and foot functions.
$S1-S2$ : gluteal region distribution (as per slide), and lateral/posterior compartments at the thigh/leg depending on branching.

Illustrative Scenarios (hypothetical exam-type prompts)

If a patient presents with a positive Trendelenburg sign and cannot maintain a level pelvis on one leg, suspect injury to the $N^ ext{ Superior Gluteal}$ nerve or its proximal innervation to gluteus medius/minimus.
A patient with foot drop and sensory loss over the dorsum of the foot likely has injury to the $N^ ext{ Common Peroneal}$ (fibular) nerve, often at the fibular neck.
After a hip fracture, evaluate for possible compromised blood supply to the femoral head due to injury of the $medial femoral circumflex$ artery to assess AVN risk.
Ankle sprain with laterastic lateral symptoms may implicate the ATF ligament injury and lateral collateral ligament complex involvement.

Summary of Key Terms to Remember

Nerves: Superior Gluteal, Inferior Gluteal, Femoral, Obturator, Lateral Femoral Cutaneous, Sciatic, Tibial, Common Fibular (Peroneal), Deep Fibular, Superficial Fibular, Saphenous, Sural, Lateral Sural.
Joints: Hip, Knee, Ankle; their ligaments and key supporting structures.
Ligaments: Iliofemoral (Y-shaped), Pubofemoral, Ischiofemoral, Ligamentum Teres, Transverse Acetabular Ligament, Acetabular Labrum; Deltoid (Medial Collateral), Lateral Collateral (ATF, PTF, CF) of the ankle.
Clinical signs: Trendelenburg gait, anterior/posterior drawer signs, Terrible/Unhappy Triad, Osgood-Schlatter disease.

References to Visual/Source Material

Review: Nerve Supply of the Lower Extremity (Nabil Ebraheim) – YouTube resource cited in slides.
Additional diagrams include the hip joint capsule, ligaments, arterial supply pathways, and knee/ankle joint anatomy (refer to slide deck for labeled diagrams and color-coded relationships).