Lower Leg Anatomy

The lower leg is a remarkable structure, where each of its sophisticated components must work in harmony with the adjacent mechanisms to achieve support for the body or movement. No portion of the lower leg anatomy is capable of independent physical action.

The lower leg anatomy is composed of five distinct parts: the knee joint, the shin, the calf, the ankle, and the foot. In terms of the general functions of the lower leg, all movement is initiated by either a flexion or an extension of the knee joint. Either movement will stimulate a corresponding action on the part of the calf muscles and the attached Achilles tendon. These structures are themselves attached to the flexor and extension muscles of the ankle and the foot, which govern how the foot will be moved. The entire process of knee action to foot position is not a continuum, progressing down the lower leg. It is an integrated, system-wide response to a stimulus transmitted by the brain to the central nervous system and simultaneously received at the nerve endings in the muscles of the lower leg.

When the lower leg components respond in harmony to the direction of the nervous system to achieve the desired physical movement, all components must be functioning properly. When one of the lower leg anatomical parts is not capable of a proper response, the entire structure is compromised.

The knee joint is the hinge mechanism that initiates the propulsion of the lower leg. A flex of the hinge, powered by the hamstring and quadriceps muscles of the upper leg, will bring the other parts of the lower leg upward. The skeletal components of the knee joint are the protective patella, or kneecap, the femur, or thigh bone, connected at the joint to the tibia, the shin bone, and the fibula, which are the long bones of the lower leg. The integrity of the knee joint is secured by the sets of ligaments connecting the three bones, as well as through the stabilizing effect of knee cartilage.

The tibia and the fibula are commonly treated as a single skeletal structure. While neither bone is capable of independent movement, the chief function of these bones is in the formation of the knee and the various ankle joints, as well as providing support over a significant anatomical distance the tibia (the shin bone), relative to the overall body height, can range in length from approximately 10 in to over 20 in (25-50 cm) in healthy adults. The shin is covered with a very thin tissue that represents the limited cushion between the surface of the tibia and the skin. The most common ailment involving the shin is medial tibial stress syndrome, or shin splints, caused by the stresses of either poor running mechanics or overuse directed into the tissue adjacent to the tibia.

The tibia and the fibula provide support for both the calf muscles and the Achilles tendon. The calf muscles are a two-part structure, the larger gastrocnemius and the underlying soleus muscle. These are connected to the knee joint at one end, and through the Achilles tendon are joined to the calcaneus, the heel bone. The calf muscles and the Achilles working in concert link the flexing and extending motions of the knee to the movements of the ankle and the foot.

The ankle joint is created at the junction of the tibia, fibula, and the talus, the ankle bone. There are three separate joints formed by these three bones, all of which are secured by a protective structure known as the synovial capsule, which encloses the joint in a fluid that both protects and lubricates the joint. The three bones are connected by way of three separate sets of ankle ligaments. The structure of the joint and the manner in which its ligaments are arranged permits the ankle to be rotated, flexed, and extended in all directions.

The ankle is attached to the bones of the foot at the talus, which is positioned above the calcaneus, the largest of the bones of the foot. It is the heel that absorbs a significant degree of force in every movement made through the lower leg. The ankle and the foot skeleton are comprised of 26 different bones, many of which are small, but are secured through the sophisticated structure of the foot anatomy. In addition to its bone structure, the arch of the foot is secured through the plantar, which extends from the heel to the forefoot, often referred to as the ball of the foot. The metatarsal bones are the five structures extending from the ankle to the toes, or phalanges, which extend from the base of the metatarsalphalangeal joint. Each toe is secured by its own set of ligaments; movement of the toes in relation to the rest of the structure of the foot is achieved through a complex system of tendons and small muscles on the top, the sole, and the sides of each foot.

see also Ankle anatomy and physiology; Foot: Anatomy and physiology; Knee: Anatomy and physiology.