What Is the Anatomy of the Leg?
The structure of the leg begins with the skeleton. The large bones of the leg are the femur (thighbone) and the tibia and fibula of the shin. The patella (kneecap) is located in front of the knee joint where the femur and tibia meet. Smaller bones are in the feet and toes. Major joints of the leg include the hip, knee, and ankle, but the small joints in the feet and toes are important since they help support the body and cushion the force that is generated by walking and running.
Thick bands of tissue called ligaments stabilize the joints. The ends of a bone that make up part of a joint are covered with cartilage to help them glide through their range of motion and decrease the friction of bone rubbing on bone.
Muscles attach to bone and have tendons that stretch across a joint. When a muscle contracts, the joint moves. Major muscle groups that affect leg movement include the buttocks, the quadriceps (in the front of the thigh), the hamstrings (in the back of the thigh), and the gastrocnemius (in the back of the calf). There are other smaller muscles, including those in the foot, that help stabilize the multiple joints in the feet.
There are two sets of blood vessels in the leg. The arterial system delivers blood, rich with oxygen, from the heart. The aorta leaves the heart and descends into the abdomen, divides into the iliac arteries, and further splits into the femoral arteries at the level of the groin. The femoral artery runs along the back of the femur in the thigh, where at the back of the knee (the popliteal fossa) it begins branching into smaller and smaller arteries to supply the lower leg, feet, and toes with blood.
The venous system drains blood from the leg and returns it to the heart, allowing tissue like muscle to get rid of carbon dioxide and other waste products of metabolism. There are two sets of veins in the leg, the superficial and deep venous systems. The superficial system runs along the skin while the deep system is located deep within the muscles and along the bones. Blood drains from the superficial system to the deep system through connecting veins called perforators that prevent blood clots that occur in the superficial veins from entering the deep vein system and embolizing or traveling to the heart and lungs. The superficial and deep systems come together in the groin to form the femoral vein.
Nerves from the spinal cord supply information to the leg, transmitting signals from the brain that allow purposeful movement. They also return information or sensations to the brain. These include the sensations of pain, light touch, pressure, vibration, temperature, and position. As well, nerve impulses can flow from the legs to the spinal cord and back without going up into the brain. These nerve loops allow the health care professional to test deep tendon reflexes (when the knee or ankle are tapped with a hammer) to assess spinal cord function.
Illness and injury can affect any of these structures, causing inflammation, discomfort, and pain. More than one mechanism may occur at the same time to cause leg pain. Some examples include the following:
- People with poorly controlled diabetes may develop diabetic neuropathy, in which the nerves to the legs and feet malfunction. Symptoms may include pain and loss of sensation in the feet as well as a pins-and-needles or tingling sensation. Diabetes is also one of the risk factors for peripheral vascular disease, which may cause narrowing of arteries in the legs, decreasing blood flow to muscles. Lack of blood supply may cause exercise-induced (exertional) pain or claudication, in which muscles start to ache with activity because not enough oxygen-rich blood can be delivered. Intermittent claudication is the term used to refer to pain in the legs that occurs while walking due to peripheral artery disease (peripheral vascular disease). This pain usually gets better with rest. As arteries narrow over time, decreased activity will bring on increased pain.
- An injured muscle will cause pain because of inflammation and swelling, but it may also affect the balance of muscles surrounding a joint. If this imbalance persists, the joint may start to hurt because of chronic stress placed upon it.
- People with back problems due to arthritis or a ruptured disc may develop sciatica, or pain from the sciatic nerve that radiates down the leg. Sciatica may also be associated with numbness and/or tingling in the leg.