Ankle Anatomy and Physiology

The human ankle is the joint created at the point where the tibia (the shin bone) and the fibula (the outer bone running from the knee to the ankle) meet the talus (the ankle bone). Running parallel to the tibia and fibula, behind the ankle, is the Achilles tendon. The talus is positioned above the calcaneus (heel bone). The joint created where these three bones meet is known as the synovial joint, a joint where the component parts function due to the presence of a viscous, fluid lubrication between the bones. The ankle is a structure where its function is a compromise between the greater flexibility and range of motion as found in joints such as the shoulder, and the less flexible and more limited range of motion found in the very stable joints, such as the pelvis.

The human ankle has a deceptively simple construction; understanding its strengths and its limitations is a critical component to efficient, stable human movement and athletic success.

The epiphysis, which is the surface of the ends of the tibia and fibula where the ankle is joined, are lined with a smooth cartilage that is 0.07-0.11 in (2-3 mm) thick. The bones and cartilage are contained within the synovial membrane cavity, the space surrounding the tibia, fibula, and talus, which creates a friction-reduced surface in the joint. The ankle is provided further support through the bursa, which are sealed fluid sacs positioned between the bones of the ankle. The propulsion necessary to walk, run, or jump is achieved in a combination of movements coordinated between the flexors located on the top of the foot, and the ligaments of the ankle, which connect the ankle bones. The ligaments, which have a somewhat elastic construction, radiate from the talus to each of the calcaneus, tibia, and fibula.

The ankle is required to bear forces of 1.5 times the body weight through walking; running, or jumping forces will exceed 3-4 times body weight. When additional twisting forces, referred to as torque, are generated through sport performance and are added to the regular weight-bearing stresses, the risk of ankle injury is pronounced. The majority of injuries involving the ankle and its related structures are sprains, a relatively straightforward and treatable condition; it is where the injury is either treated incorrectly, or where the athlete returns to training or competition too quickly, that the uncomplicated injury can escalate into a chronic problem.

Everyone has a natural foot strike: the manner in which the foot comes into contact with the walking or running surface. For over 80% of athletes, the natural motion is "pronation," in which the foot turns inwardly upon contact with the running surface; the less common "supination" is when the foot rolls outward. The manner and the degree to which the foot strikes the surface place pressure on the ankle.

The natural foot strike is mimicked in the mechanisms of the ankle sprain, referred to as inversion and eversion, which are circumstances created when the ankle becomes unstable. Inversion is the common result when an athlete seeks to change direction, or "cut" on the playing surface, and the ankle joint moves inwards as the forces are applied. Eversion utwards on movement being made. Both mechanisms result in the ligaments becoming strained. Inversion may also result when a player jumps or strides and lands on an unequal surface, such as another player's foot or a hole in the playing field. In a more serious circumstance, the ankle ligaments may become torn, requiring medical intervention.

A high ankle sprain is a condition usually caused by a force being applied to the leg above the ankle, causing a degree of rotation to occur in the lower leg above the ankle joint, while the foot remains planted to the surface. In this circumstance, the tibia and fibula become separated from where these bones meet the talus, causing the ligament that connects these bones to the talus to become strained.

The ankle may also be injured through damage to the Achilles tendon, either through irritation of the tendon fibers and sheath, referred to as Achilles tendonitis, or through a tear or rupture of the tendon fibers. These injuries are typically caused by either overuse, such as dramatically increased training levels in a short period, or through a sudden explosive motion that is not properly supported due to tight calf or quadriceps muscles.

Any of the bones that comprise the ankle joint may become fractured through a direct blow. In sports such as field hockey or soccer, the ankle is exposed to such traumas. In addition, the ankle can become dislocated, where the tibia/fibula and talus are forcibly separated. Further, the tibia or the fibula may sustain damage known as shin splints, a micro tear of thin muscle covering the shins, through overuse or poor fitting footwear.

The ankle is a joint that can be significantly protected from injury through a commitment to a specialized stretching program. In addition, many sports require athletes to either wear a brace (volleyball is a sport in which braces are a part of the competitive culture), or to tape the ankles in advance of training or competition.

The basic components of good ankle care include warm-up and cool-down practices involving ankle and lower leg stretches; stretching exercises (as a part of the over all fitness program); careful attention to the heel wear and the support in athletic shoes; and shoe fit, as an improper fit may cause the foot to strike the surface and cause inversion/eversion.

SEE ALSO Achilles tendonitis; Ankle sprains; Heel spurs; Lower leg anatomy.