Lower Limb – Anatomy, Structure, Functions

Lower Limb – Anatomy, Structure, Functions

Lower limb consists of the thigh (the upper leg), the leg (the lower leg), and the foot. The thigh consists of a single bone, the femur. The leg consists of two long bones, the tibia and fibula, and the sesamoid bone, the patella, that serves as the knee cap.

Bones and Joints

Tibia

  • A medial, weight-bearing bone of the leg
  • Articulates with the femur and fibula proximally and the talus and fibula distally
  • Important landmarks:
    • Tibial condyles:
      • Horizontal proximal surfaces that articulate with the femoral condyles
      • Separated by the lateral and medial intercondylar tubercles
    • Tibial tuberosity:
      • The triangular, superior–anterior area where condyles merge
      • Site of attachment for the patellar tendon
    • Shaft: anterior, lateral, and posterior surfaces
    • Medial malleolus:
      • Distal projection
      • Articulates with the talus as part of the ankle

Fibula

  • The thin, lateral bone of the leg
  • Articulates with the tibia proximally and distally and with the talus distally
  • Important landmarks:
    • Head:
      • Serves as the site of attachment for ligaments of the knee
      • Articulates with the tibia
    • Neck:
      • Narrow
      • The common peroneal nerve wraps around it.
    • Shaft: medial, lateral, and posterior surfaces
    • Lateral malleolus:
      • Distal projection
      • Articulates with the talus as part of the ankle

Joints

  • Proximal tibiofibular joint
    • The arthrodial plane joint between the lateral tibial condyle and the head of the fibula
    • Stabilized by a sturdy capsule and multiple ligaments
  • Distal tibiofibular joint
    • Syndesmosis of the distal ends of the fibula and tibia
    • Stabilized by multiple ligaments and the interosseous membrane
  • Interosseous membrane: 
    • Fibrous tissue directed downward and laterally
    • Connects medial border of the fibula with the lateral border of the tibia
    • Stabilizes the leg
    • Contains an opening on the proximal region that allows for the passage of the anterior tibial vessels to the anterior compartment of the leg

Fascial Compartments

The leg is divided into 4 fascial compartments by the interosseous membrane and the anterior, posterior, and transverse intermuscular septa as follows:

  1. Anterior compartment:
    • Separated from the lateral compartment by the anterior septum
    • Separated from the deep posterior compartment by the interosseous membrane and the tibia
    • Contains 4 muscles:
      • Tibialis anterior
      • Extensor hallucis longus
      • Extensor digitorum longus
      • Peroneus Tertius
  2. Lateral compartment:
    • Separated from the anterior compartment by the anterior septum
    • Separated from the superficial posterior compartment by the transverse septum
    • Contains 2 muscles:
      • Peroneal brevis
      • Peroneal longus
  3. Superficial posterior compartment:
    • Separated from the deep posterior compartment by the posterior septum
    • Separated from the lateral compartment by the transverse septum
    • Contains 3 muscles:
      • Soleus
      • Gastrocnemius
      • Plantaris
  4. Deep posterior compartment:
    • Separated from the anterior compartment by the interosseous membrane and the tibia
    • Separated from the superficial posterior compartment by the posterior septum
    • Contains 4 muscles:
      • Popliteus
      • Tibialis posterior
      • Flexor digitorum longus
      • Flexor hallucis longus

Blood Supply

Arteries of the lower leg

A continuation of the popliteal artery supplies blood to the lower leg. The artery bifurcates at the lower margin of the popliteal fossa and sends branches to the anterior compartment, the anterior tibial artery, and the posterior and lateral compartments, forming the tibioperoneal trunk.

Origin Trajectory Branches Supply
Anterior tibial artery (accompanied by the deep peroneal nerve) Division of popliteal artery into the anterior tibial artery and tibiofibular trunk
  • Begins in the popliteal fossa
  • Enters anterior compartment through the upper opening of the interosseous membrane
  • Continues as the dorsalis pedis
  • Recurrent branches to knee joint anastomosis
  • Muscular branches
  • Medial and lateral malleolar branches
Anterior compartment of leg
Posterior tibial artery (accompanied by the tibial nerve) The terminal branch of the tibioperoneal trunk
  • Begins at the lower border of the popliteal fossa
  • Lies deep to the soleus muscle
  • Passes under the medial malleolus
  • Divides into medial and lateral plantar arteries
  • Circumflex branch to knee
  • Muscular branches
  • Medial malleolar and calcaneal branches
  • Posterior compartment of leg
  • Plantar aspect of the foot
Peroneal artery The terminal branch of tibioperoneal trunk
  • Begins at the lower border of the popliteal fossa
  • Travels along the medial border of the fibula
  • Divides into calcaneal branches
Muscular branches Lateral compartment and deep layer of the posterior compartment of leg

Veins of the lower leg

There are 2 venous drainage networks in the leg:

  • The deep venous branches unite to form the popliteal vein.
  • The superficial or saphenous veins are located in the subcutaneous tissue.
Origin Trajectory Tributaries Drainage
Great saphenous vein (accompanied by saphenous nerve) Continuation of medial end of dorsal venous arch of the foot
  • At ankle, passes anterior to medial malleolus
  • Ascends leg medially
  • Passes behind medial condyles of femur and tibia
  • Drains into saphenofemoral junction
  • Short saphenous vein
  • Superficial external pudendal vein
  • Superficial epigastric veins
  • Superficial circumflex iliac vein
  • Lateral femoral cutaneous vein
Anteromedial aspect of leg and plantar aspect of foot
Small saphenous vein (accompanied by sural nerve) Continuation of lateral end of dorsal venous arch of foot
  • At ankle, passes posterior to lateral malleolus
  • Ascends in midline of posterior leg
  • Drains into saphenopopliteal junction (variable)
Posterior aspect of leg

Deep veins of the leg:

  • Located deep to the deep fascia of the leg
  • Accompany the arteries of the leg of the same name:
    • Anterior tibial veins
    • Posterior tibial veins
    • Peroneal veins
  • Converge at the inferior border of popliteus muscle to form the popliteal vein
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Femur (The Thigh)

The femur—the bone of the upper leg—is the longest bone in the human body and one of the strongest.

Key Points

The femur is the longest bone in the human skeleton.

It functions in supporting the weight of the body and allowing motion of the leg.

The femur articulates proximally with the acetabulum of the pelvis forming the hip joint, and distally with the tibia and patella to form the knee joint.

Key Terms

condyle: A smooth prominence on a bone where it forms a joint with another bone.

The femur or thigh bone is found in the upper leg and is the longest bone in the body. The femur articulates proximally with the acetabulum of the pelvis to form the hip joint, and distally with the tibia and patella to form the knee joint.

Proximal

This is a drawing of the anterior surface of the femur with its parts labeled. In particular, it shows how the acetabulum of the pelvis forms the hip joint, and how with the tibia and patella form the knee joint.

Femur: The anterior surface of the femur with parts labeled

Proximally, the femur exhibits four key regions. The femoral head projects medially and superiorly and articulates with the acetabulum of the pelvis to form the hip joint. Immediately lateral to the head is the neck that connects the head with the shaft. It is narrower than the head to permit a greater range of movement at the hip joint.

Located superiorly on the main shaft, lateral to the joining of the neck, the greater trochanter is a projection to which the abductor and lateral rotator muscles of the leg attach.

Also located on the main shaft, but inferiorly to the neck joint, is the lesser trochanter. A much smaller projection than the greater trochanter, the psoas major and iliacus muscles attach here.

Shaft

The shaft descends in a slightly medial direction that is designed to bring the knees closer to the body’s center of gravity, increasing stability. Due to the widening of the female pelvis, this angle is greater in women and can lead to increased knee instability.

Two key features of the shaft are the proximal gluteal tuberosity to which the gluteus maximus attaches and the distal adductor tubercle to which the adductor Magnus attaches.

Distal

Distally, the femur exhibits five key regions. Two rounded regions, termed the medial and lateral condyles, articulate with the tibia at the most anterior projection of the patella.

Between the two condyles lies the intercondylar fossa, a depression in which key knee ligaments attach; this significantly strengthens the knee joint and protects it against torsional damage.

Finally, the two epicondyles, the medial and lateral, lie immediately proximal to the condyles; they are also regions where key internal knee ligaments attach.

Patella (The Knee)

The patella (knee cap) is the bone between the fibula and femur.

Key Points

The primary functions of the patella are to enhance leg extension and protect the joint of the knee.

The patella is a bone embedded within a tendon. This means it is a sesamoid bone.

Key Terms

patella: A sesamoid bone found in the knee, commonly known as the knee cap.

sesamoid: A bone embedded within a tendon.

The patella or knee cap is the bone between the fibula and femur. Each leg has a patella to protect its knee joint. The patella serves two functions:

  1. To protect the knee from physical trauma.
  2. To enhance the leverage that the quadriceps tendon can exert on the femur, thereby increasing muscle efficiency.

The apex of the patella faces inferiorly and connects to the tibia tuberosity through the patella ligament that attaches to the anterior surface. The base of the patella faces superiorly and is the attachment point for the quadriceps tendon.

The posterior surface of the patella contains the medial and lateral facets that articulate with the condyles of the femur. The lower posterior region of the patella has vascular canaliculi, small channels within the bone, which form the infrapatellar fat pad.

This illustration of the knee joint shows the position of the patella relative to the articulation of the femur and the tibia.

Knee Joint: This image shows the position of the patella relative to the articulation of the femur and the tibia.

Tibia and Fibula (The Leg)

The tibia and the smaller fibula bones comprise the lower leg and articulate at the knee and ankle.

Key Points

The tibia is more commonly called the shinbone. It is located between the ankle and the patella.

The fibula is a long, thin bone also located between the ankle and the patella. It runs parallel to the tibia.

Like the femur, the tibia bears much of the body’s weight and plays an essential role in movement and locomotion. The fibula, along with the tibia and the tarsals, forms the ankle.

Key Terms

tibia: The inner and usually the larger of the two bones of the lower leg.

fibula: The smaller of the two bones in the lower leg, the calf bone.

The tibia and fibula are the two bones of the lower leg. The tibia is located medially to the fibula and is much larger. Both are bound together with the interosseous membrane.

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The Tibia

This is a drawing that shows the tibia and fibula in anatomical position with other parts of the leg labeled.

The leg: Tibia and fibula in anatomical position with parts labeled.

The tibia, or shin bone, spans the lower leg, articulating proximally with the femur and patella at the knee joint, and distally with the tarsal bones, to form the ankle joint. It is the major weight-bearing bone of the lower leg.

Proximally, there are five key features of the tibia:

  • It widens and forms two condyles —the lateral and medial—that articulate with the condyles of the femur.
  • Between the two condyles is the intercondylar fossa, a small grove, into which two intercondylar tubercles sit. Numerous internal ligaments of the knee joint attach to these tubercles and strengthen it significantly.
  • On the anterior surface of the proximal region and inferiorly to the condyles is the tibial tuberosity to which the patella ligament attaches.
  • The shaft of the tibia is triangular and the soleus muscle, which gives the calf its characteristic shape, originates on the posterior surface.
  • Distally, the tibia also widens to aid with weight-bearing and it displays two key features. The medial malleolus is a bony projection that articulates with the tarsal bones to form the ankle joint. Laterally, there is the fibular notch that articulates with the fibula.

The Fibula

The fibula also spans the lower leg, although proximally it does not articulate with the femur or patella. It serves more as an attachment point for muscles rather than a weight-bearing bone.

Proximally, the fibula head articulates with the lateral condyle of the tibia, and the biceps femoris attaches to the fibula head. As with the tibia, the shaft of the fibula is triangular and numerus muscles are involved in the extension and flexion of the foot. These muscles originate from the fibula’s surface and include the extensor digitorum longus, soleus, and flexor hallucis longus, among others.

Distally, the fibula forms the lateral malleolus, which is more prominent than the medial malleolus of the tibia. It also articulates with the tarsal bones to form the ankle joint.

Tarsals, Metatarsals, and Phalanges (The Foot)

The human ankle and foot bones include tarsals (ankle), metatarsals (middle bones), and phalanges (toes).

Key Points

The human foot contains 26 bones.

The foot can be subdivided into tarsals, metatarsals, and phalanges.

Key Terms

phalange: A bone within the digit.

metatarsal: A bone from the center of the foot that articulates with the tarsals and phalanges.

tarsal: A bone forming part of the ankle or heel.

The foot contains 26 bones that are divided into three regions: the tarsals (or ankle and heel), the metatarsals (forming the sole of the foot), and the phalanges (forming the digits). While sharing a similar underlying structure with the hand, the foot is visibly and structurally different to account for its greater load-bearing and locomotive duties, and reduced fine movements.

This drawing of the foot shows how it contains the proximal tarsals that form the ankle and heel; intermediate metatarsals; and the distal phalanges that form the toes.

The Foot: The foot contains the proximal tarsals that form the ankle and heel; intermediate metatarsals; and the distal phalanges that form the toes.

Tarsals

The tarsal bones of the foot are organized into three rows: proximal, intermediate, and distal. The proximal row contains the talus, which is the most superior of the tarsals and articulates with the tibia and fibula to form the ankle joint. The talus is responsible for transmitting forces from the tibia to the heel and acts as an attachment point for numerous ligaments that strengthen the ankle joint.

The calcaneus is the thickest tarsal and forms the heel of the foot. It articulates with the talus superiorly and anteriorly with the cuboid of the distal group. Posteriorly the calcaneal tuberosity is the attachment point for the Achilles tendon.

The intermediate group contains only the navicular bone, which articulates with all of the tarsals—with the exception of the calcaneus. The navicular bone plays a key role in maintaining the medial longitudinal arch of the foot.

There are four distal tarsals: the lateral cuboid and the three cuneiforms, located medially. The distal tarsals articulate with the metatarsals and also maintain the transverse arch of the foot.

Metatarsals

The foot contains five metatarsals that are numbered I–V, moving medial to lateral, big toe to little toe. Each metatarsal consists of a head, shaft, and base.

The proximal base articulates with the cuboid bones, and distally with the proximal phalanges, and each metatarsal also articulates laterally with adjacent metatarsals. The interossei of the foot originate from the shafts of the metatarsals.

Phalanges

The digits are named in a similar fashion to the metatarsals, medial to lateral from the big toe. With the exception of the big toe, each digit contains a proximal, intermediate, and distal phalange; the big toe lacks an intermediate phalange. The length of the phalanges decreases distally.

Arches of the Feet

The arches of the foot are formed by the tarsal and metatarsal bones; they dissipate impact forces and store energy for the subsequent step.

Key Points

The arches of the foot are formed by the tarsal and metatarsal bones and strengthened by ligaments and tendons. They allow the foot to support the weight of the body in the erect posture with the least weight.

The slight mobility of the arches when weight is applied to and removed from the foot makes walking and running more economical in terms of energy.

The longitudinal arch of the foot can be broken down into several smaller arches. The main arches are the antero- posterior arches, which may, for descriptive purposes, be regarded as divisible into two types—a medial and a lateral.

The two longitudinal arches serve as pillars for the transverse arch that runs obliquely across the tarsometatarsal joints.

Key Terms

arches of the foot: The area of the foot formed by the tarsal and metatarsal bones and strengthened by ligaments and tendons. They allow the foot to support the weight of the body in the erect posture with the least weight.

Arches of the Foot

This is a drawing of the arches of the foot. It depicts a skeleton of a foot shown from its lateral aspect. 

Arches of the Foot: Skeleton of foot. Lateral aspect.

The arches of the foot are formed by the tarsal and metatarsal bones. Strengthened by ligaments and tendons, the elastic properties of arches allow the foot to act as a spring, dissipating impact forces and storing energy to be transferred into the subsequent step improving locomotion.

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The two longitudinal arches and a transverse arch are maintained by the interlocking shapes of the foot bones, strong ligaments, and pulling muscles during activity. The slight mobility of these arches when weight is applied to and removed from the foot makes walking and running more economical in terms of energy.

Excessive strain on the tendons and ligaments of the feet can result in fallen arches or flat feet.

Longitudinal Arches

The longitudinal arch of the foot can be broken down into several smaller arches. The main arches are the anteroposterior arches, which may, for descriptive purposes, be regarded as divisible into two types—a medial and a lateral.

Medial Arch

This is a drawing of the arches of the foot. It depicts a skeleton of a foot shown from its medial aspect. 

Arches of Foot: Skeleton of foot. Medial aspect.

As can be examined in a footprint, the medial longitudinal arch curves above the ground. It is made by the calcaneus, the talus, the navicular, the three cuneiforms, and the first, second, and third metatarsals.

Its summit is at the superior articular surface of the talus. Its two extremities or piers, on which it rests in standing, are the tuberosity on the plantar surface of the calcaneus posteriorly, and the heads of the first, second, and third metatarsal bones anteriorly.

The chief characteristic of this arch is its elasticity, due to its height and to the number of small joints between its component parts. Its weakest part (i.e., the part most liable to yield from too much pressure) is the joint between the talus and navicular, but this portion is braced by the plantar calcaneonavicular ligament, also called the spring ligament, which is elastic and is thus able to quickly restore the arch to its original condition when the disturbing force is removed.

The ligament is strengthened medially by blending with the deltoid ligament of the ankle joint and is supported inferiorly by the tendon of the tibialis posterior, which is spread out in a fan-shaped insertion and prevents undue tension of the ligament or such an amount of stretching as would permanently elongate it.

The arch is further supported by the plantar aponeurosis, by the small muscles in the sole of the foot, by the tendons of the peroneus longus and the tibialis anterior and posterior, and by the ligaments of all the articulations involved.

Lateral Arch

In contrast, the lateral longitudinal arch is very low. It is composed of the calcaneus, the cuboid, and the fourth and fifth metatarsals.

Its summit is at the talocalcaneal articulation, and its chief joint is the calcaneocuboid, which possesses a special mechanism for locking and allows only a limited movement. The most marked features of this arch are its solidity and its slight elevation.

Two strong ligaments—the long plantar and the plantar calcaneocuboid—the extensor tendons, and the short muscles of the little toe preserve its integrity.

Fundamental Longitudinal Arch

While these medial and lateral arches may be readily demonstrated as the component anteroposterior arches of the foot, the fundamental longitudinal arch is contributed to by both and consists of the calcaneus, cuboid, third cuneiform, and third metatarsal: all the other bones of the foot may be removed without destroying this arch.

Transversal Arches

In addition to the longitudinal arches, the foot presents a series of transverse arches. The arches are complete at the posterior part of the metatarsus and the anterior part of the tarsus, but in the middle of the tarsus, they present more of the characteristics of concavities.

These are directed downward and medially so that when the medial borders of the feet are placed in apposition, a complete tarsal dome is formed. The transverse arches are strengthened by the interosseous, plantar, and dorsal ligaments; by the short muscles of the first and fifth toes (especially the transverse head of the adductor hallucis), and by the peroneus longus, whose tendon stretches between the piers of the arches.

Innervation

The sensory and motor innervation to the lower limb is supplied by the lumbosacral plexus (L1–S4).

  • Sciatic nerve: biggest and longest nerve from the lumbosacral plexus; gives off many branches and divides into the tibial nerve and the common peroneal nerve
    • Tibial nerve: provides motor function to the posterior compartment in the leg and multiple sensory branches to the entire leg (sural, medial calcaneal, and medial and lateral plantar nerves); passes inferior and posterior to the medial malleolus in the ankle, through the tarsal tunnel.
      • Sural nerve: sensory supply to the skin over the posterolateral aspect of the distal third of the leg and lateral border of the foot
    • Common peroneal nerve (common fibular nerve): provides motor function to the short head of the biceps femoris, then bifurcates into two branches:
      • Deep peroneal (fibular) nerve: terminal branch of the common peroneal nerve, provides motor function to the anterior compartment and sensory supply to the 1st interdigital space of the foot
      • Superficial peroneal (fibular) nerve: terminal branch of the common peroneal nerve, provides motor function to the lateral compartment and sensory supply to the lower anterior aspect of the leg and dorsum of the foot
  • Saphenous nerve: branch of the femoral nerve, arises from the femoral triangle, pure sensory function to the skin over the medial half of the leg

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