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1. Describe the main muscle groups or muscle compartments of the lower limb.

The lower limb is specialized for bipedal locomotion. It is connected to the trunk via the sacro-iliac (SI) joints – the hip bones (coxal bones) articulate with the sacrum. The hip bones together with the sacrum and coccyx form the bony pelvis. Some of the muscles that act on the lower limb arise from the bony pelvis and the inferior part of the vertebral column; consequently, it is customary to include these transitional regions when describing the lower limb.

• Hip

  • Gluteal region

• Thigh

  • Anterior compartment

  • Medial (adductor) compartment

  • Posterior compartment

• Leg

  • Anterior (extensor) compartment

  • Lateral compartment

  • Posterior compartment (superficial & deep)

• Foot

  • Plantar region

  • Dorsal region

2. Understand the details (attachments, actions, innervation, blood supply, etc.) regarding the compartments of the thigh and leg.

Click here to download the PDF version of all individual muscle tables. 

Click here to download the PDF of a comprehensive muscle table. 

*Students are only responsible for muscles discussed in the main text of the learning objectives and list of structures

Anterior compartment of thigh generalizations

• Muscles (follow links for specifics of each muscle; some of these muscles extend superior to thigh)

  • Iliopsoas m.

  • Sartorius m.

  • Rectus femoris m.

  • Vastus lateralis m.

  • Vastus medialis m.

  • Vastus intermedius m.

• Joints crossed

  • Hip and/or knee joints

• Innervation

  • Mostly femoral n.

• Blood supply

  • Femoral a.

• General actions

  • Flexion of hip joint

  • Extension of knee joint

Medial compartment of thigh generalizations

• Muscles

  • Gracilis m.

  • Adductor longus m.

  • Adductor brevis m.

  • Adductor magnus m.

• Joints crossed

  • Hip joint, mostly

• Innervation

  • Obturator n.

• Blood supply

  • Deep artery of thigh & obturator a.

• General actions

  • Adduction of hip joint

  • Synergist for gait & posture

Posterior compartment of thigh generalizations

• Muscles

  • Biceps femoris m.

  • Semimembranosus m.

  • Semitendinosus m.

• Joints crossed

  • Hip joint

  • Knee joint

• Innervation

  • Sciatic n., tibial division - mostly

• Blood supply

  • Deep artery of thigh

• Actions

  • Extension of hip joint

  • Flexion of knee joint

Anterior compartment of leg generalizations

• Muscles

  • Tibialis anterior m.

  • Extensor digitorum longus m.

  • Extensor hallucis longus m.

• Joints crossed

  • Talocrural joint

  • Subtalar and transverse tarsal joints

  • Interphalangeal joints

• Innervation

  • Deep fibular (peroneal) n.

• Blood supply

  • Anterior tibial a.

• Actions

  • Dorsiflexion of talocrural joint

  • Inversion of subtalar & transverse tarsal joints

  • Extension of interphalangeal joints

Lateral compartment of leg generalizations

• Muscles

  • Fibularis longus m.

  • Fibularis brevis m.

• Joints crossed

  • Talocrural joint

  • Subtalar & transverse tarsal joints

• Innervation

  • Superficial fibular (peroneal) n.

• Blood supply

  • Anterior tibial a.

• Actions

  • Eversion of subtalar & transverse tarsal joints

  • Plantarflexion of talocrural joint

Posterior compartment of leg generalizations

• Muscles

  • Superficial

    • Gastrocnemius m.

    • Soleus m.

  • Deep

    • Flexor hallucis longus, Flexor digitorum longus, Tibialis posterior (not discussed)

• Joints crossed

  • Talocrural

  • Knee joint

  • Deep muscles - foot joints

• Innervation

  • Tibial n.

• Blood supply

  • Posterior tibial a.

• Actions

  • Plantarflexion of talocrural joint

3. Describe the cutaneous innervation of the lower limb.

The cutaneous innervation of the lower limb is almost exclusively derived from the lumbar (L1-L4) and sacral (L4-S4) plexuses. Lumbar plexus branches innervate the superior thigh region and the majority of the anterior lower limb. Sacral plexus branches innervate the majority of the posterior lower limb. These cutaneous nerves are derived from larger, source branches, including femoral, obturator, common fibular, and tibial nerves. The sural n. is a cutaneous nerve that has contributions from both the tibial & common fibular nn.

See the images below for a peripheral cutaneous nerve maps of the lower limb.

4. Describe the deep fascia of the lower limb, and give an example of a specialization of this fascia.

The deep fascia of the limbs envelopes the muscles and separates the muscles into compartments associated with each segment of the limb. The muscles are “collected” into compartments or groups of muscle by portions of deep fascia, and typically separated by intermuscular septa.

The deep fascia of the lower limb has many functions, but of particular importance is resistance of excessive muscle expansion during contraction. This allows the muscles to compress the veins, and assists venous valves in directing blood flow towards the heart.

The deep fascia of the lower limb is called the fascia lata in the thigh and crural fascia in the leg. In specific areas, this fascia is thickened and serves specialized functions. Important examples in the lower limb are:

• • iliotibial (IT) tract/band: a thickening of the fascia lata that stretches from the lateral side of the crest of the ilium to attach to the lateral condyle of the tibia.

  • retinacula of the patella: thickened/reinforced portions of the crural fascia from the patella to the medial and lateral condyles of the tibia and the head of the fibula.

The lower limb, due to typically tight closure of the fascial compartments, are more susceptible to compartment syndromes. Compartment syndromes can be caused by trauma to any structures within the compartment, which may lead to inflammation, hemorrhage, and edema. This can lead to entrapment or compression of structures within. The anterior leg compartment is particularly susceptible to this type of syndrome.

5. Describe the primary venous drainage of the lower limb.

The veins in the lower limbs have numerous valves to allow for proper directional flow (towards the heart), working against gravitational pull.

Veins are divided into superficial (located in subcutaneous tissue) and deep (accompanying arteries). Superficial veins of lower limbs always drain into deep veins by means of perforating veins.

There are two main superficial veins of the lower limbs:

• • The great saphenous vein is formed by the union of the dorsal venous arch of the foot and the dorsal vein of 1st digit, and drains into the femoral v. It can be located anterior to the medial malleolus of the tibia during surgeries.

  • The small (short; lesser) saphenous vein is formed by the coalescence of the dorsal venous arch of the foot and the dorsal vein of the 5th digit, and drains into the popliteal v. It is accessible posterior to the lateral malleolus of the fibula.

As mentioned above, deep veins of the lower limb accompany arteries and are often have similar names. These are the major (largest) veins of the lower limb. These veins (which often are paired - venae comitantes) are often packaged with the arteries within a vascular sheath.

Competency of venous valves are vital in directing blood flow in the proper direction. If competency has been compromised (potentially due to rotation or dilation), veins may become varicose. Varicose veins present as a dilated vein with valves that do not close - allowing blood to flow away from the heart.

6. Describe the primary arterial supply of the lower limb.

The primary blood supply to the lower limb is via the femoral a., a continuation of the external iliac a. beyond the inguinal ligament. The femoral a. is proximally located in the femoral triangle.

The boundaries of the femoral triangle are:

• • Inguinal ligament (superior)

  • Sartorius m. (lateral)

  • Adductor longus m. (medial)

  • Iliopsoas m. & Pectineus m. (posterior/deep)

Femoral neurovasculature lie in this triangular space as they enter the lower limb. The relationship of the neurovascular structures is important when accessing the vasculature – medial to lateral: femoral Vein, femoral Artery, femoral Nerve (VAN). Understanding this organization is of importance when trying to locate the femoral vein for cannulation. It is easily located by palpating the pulsations of the femoral artery (femoral pulse) and moving medially.

The femoral a. supplies the entire lower limb.

As the artery nears the distal end of the femoral triangle, it gives off the deep artery of thigh, which dives deep into the thigh muscles and runs medial to the femur to supply the deep muscles. It sends branches that perforate through the deep adductor muscles to supply the posterior compartment of the thigh. The deep artery of thigh terminates in the thigh.

The femoral a., on the other hand, continues through the anterior and medial thigh. As it nears the knee, it passes through a hiatus in an adductor muscle to relocate on the posterior surface of the distal femur. At this point it is behind the knee in the popliteal fossa and its name changes to popliteal a. The popliteal a. gives off numerous branches that supply the knee joint and form a complex anastomosis around this area.

The popliteal a. continues through the popliteal fossa to enter the leg. As it does, it splits into the anterior tibial a. and the posterior tibial a.

The anterior tibial artery passes through a space between the tibia and fibula just above the superior edge of the interosseous membrane to course down the leg on the anterior surface of the interosseous membrane. It supplies the anterior leg muscles. It passes across the dorsal ankle to run onto the dorsum of the foot as the dorsalis pedis a.

At the proximal leg, the posterior tibial a. gives off a lateral branch, the fibular (peroneal) a., which is a minor supply to the lateral compartment leg muscles (anterior tibial a. is the major supply). The posterior tibial artery continues down the posterior leg to supply the superficial and deep groups of posterior leg muscles. It courses around and behind the medial malleolus with the tendons of the deep posterior leg muscles to enter the plantar region of the foot. Here it splits into medial & lateral plantar aa. that connect to form the plantar arch at the metatarsal portion of the foot.

7. Describe the lymphatic drainage of the lower limb.

The majority of lymph in the lower limbs drains via lymph vessels and nodes that are associated with the superficial veins of the lower limb, in particular the greater & small saphenous veins. The lymph associated with the greater saphenous vein typically drains into the superficial inguinal lymph nodes, which either enters the external iliac lymph nodes or deep inguinal lymph nodes. The lymph associated with the small saphenous vein typically drains into the popliteal lymph nodes.

In terms of directionality of lymph associated with deep veins, it typically proceeds in this manner:

Popliteal lymph nodes → Deep inguinal lymph nodes → External iliac lymph nodes → Common iliac lymph nodes → Lumbar lymphatic trunks