Lower Limb Anatomy

The lower limb comprises of three main joints – the hip, knee and ankle.

Muscles:
These are categorized by their actions on the hip joint:

Flexion – Psoas major + Iliacus (attaches to lesser trochanter) + Sartorius (from ASIS to medial tibial condyle)
Extension – Gluteus maximus and hamstrings

Adduction – done medial compartment of thigh, supplied by obturator nerve
Abduction – gluteus medius and minimus insert onto greater trochanter, supplied by superior gluteal nerve

Medial rotation – Anterior fibres of gluteus medius and minimus
Lateral rotation – gluteus maximus + lateral rotators (piriformis, obturators) which attach to greater trochanter

Blood supply:
Femoral head gets blood from retinacular fibres of capsule from superficial femoral artery
– Ligamentum teres in children has a branch of obturator artery, but this is negligible in adults.

Muscles:
These are divided into anterior, medial and posterior compartments:

i) Anterior:
Quadriceps femoris (Rectus femoris, vastus lateralis/medialis/intermedius)
– Arise from femur and hip bone and have a common tendon via patella onto tibial tuberosity
– They all extend the knee and rectus femoris also flexes hip
– The anterior compartment is supplied by the femoral nerve

ii) Medial:
3 adductors (adductor magnus, brevis, longus) arise from ischiopubic ramus
– They insert down the femoral shaft onto the linea aspera
– Gracilis and Pectineus run down medial thigh and also adduct thigh
– Obturator externus is a lateral rotator of the hip
– These are all supplied by the obturator nerve

iii) Posterior:
This compartment extends the hip and flexes the knee
– Semimembranosus and semitendinosus arise from ischial tuberosity –> insert onto medial tibial condyle
– Biceps femoris has two heads from ischial tuberosity + femur –> inserts onto lateral head of fibula
– They are all supplied by the tibial nerve, except short head of biceps (common fibular nerve)

Soft tissue:
– Fascia lata is thick fascia which divides muscles into compartments.
– It forms the iliotibial tract laterally which receives tensor fascia latae + gluteus maximus
– As this fascia is so tight a fracture of the femur can lead to compartment syndrome

Knee

Femoral condyles articulate with tibial condyles and patella articulates with the anterior surface of femur.
– Patella sits in trochlea groove, and is at risk of dislocating laterally, especially in teenage girls
– Capsule is deficient anteriorly and is instead completed by quadriceps tendon.
– The medial tibial condyle has an attachment area for 3 important muscles (sartorius, gracilis and semitendinosus). This is known as the pes anserinus (“Goose’s foot”)

Ligaments:
Bony contours do not give stability and so you need support from the ligaments.

Collateral:
Medial and lateral collaterals extend from femur to tibia medially and head of fibular laterally
– Medial collateral injured by valgus strain, whereas lateral is hurt by varus strain

Cruciate:
ACL connects anterior part of intercondylar eminence to lateral femoral condyle
–> Prevents forward displacement of tibia on femur

PCL connects posterior part of intercondylar eminence to medial femoral condyle
–> Prevents backward displacement of tibia on femur, important when going downhill

A completely extended knee is “locked” – this means you can stay upright without muscular effort.
– Hence flexion must first be initiated by popliteus to rotate femur on tibia, “unlocking” the knee.

Behind the knee joint is a diamond-shaped space called the popliteal fossa, bounded by diverging hamstrings and distally heads of gastrocnemius. It contains:
– Popliteal artery + vein
– Lymph nodes
– Tibial nerve and common fibular nerve
– Sural nerve

Leg

Bones:
The leg is formed by the tibia medially and the fibula laterally. The medial margins of these bones forms interosseous membrane, which makes inferior tibiofibular joint fibrous.

– Tibia – Tibial plateau articulates with femur, extends distally to articulate with talus and has medial malleolus

– Fibula- Head articulates with tibia and extends laterally to articulate with tales and has lateral malleolus.

Muscles: These can be divided into anterior, lateral and posterior compartments of the leg.

i) Anterior:
Tibialis anterior + Extensor hallucis longus, extensor digitorum longus + Fibularis tertius
– These muscles are dorsiflexors of the ankle (+toes/hallux) and cause inversion.
– These are supplied by the deep branch of the common fibular nerve

ii) Lateral:
Fibularis longus (inserts into first metatarsal) + fibularis brevis (fifth metatarsal)
– These cause eversion of the foot at subtalar joint + plantarflexion
– Supplied by the superficial branch of the common fibular nerve

iii) Posterior:
– Superficial muscles: Gastrocnemius, Plantaris and soleus
–> These insert into common calcaneal (Achilles) tendon to plantarflex ankle + flex knee

– Deep muscles: Popliteus + flexor hallucis longus, flexor digitorum longus + tibialis posterior
–> Tendons pass under medial malleolus flexor retinaculum (tarsal tunnel) to cause dorsiflexion of the ankle and toes

– All the posterior compartment is supplied by branches of the tibial nerve.

Neurovascular Status of lower Limb

The main neurovascular structures enter the lower limb through the femoral triangle:
– Bounded superiorly by inguinal ligament, Laterally medial border of Sartorius + medially by adductor longus.
– Lateral to medial: Femoral nerve –> Femoral Artery –> Femoral vein –> Femoral canal (space with lymphatics)

Arteries:
After the femoral artery has passed through, it gives profunda femoris and superficial femoral artery.
– Continues as popliteal artery before dividing into 3 branches, anterior + posterior tibial and peroneal artery.

Nerves:
– Femoral nerve (L2-4) is anterior and supplies quadriceps + Sartorius.

– Obturator nerve (L2-4) supplies adductors + medial thigh

– Sciatic nerve (L4-S3) is major nerve posterior which is composed of tibial + common fibular nerve.
–> Tibial branch supplies whole of posterior compartment of leg
–> Superficial branch of the common fibular nerve supplies lateral compartment of leg
–> Deep branch of the common fibular nerve supplies anterior compartment of leg