The Achilles tendon is the largest tendon in the body. It connects the upper calf muscles to the back of the heel bone. Achilles tendinitis is an injury to this tendon that causes pain in the back of the leg. Typically this injury results from inflammation of the surrounding sheath (paratenonitis), degeneration within the tendon (tendinosis), or a combination of the two.

The Achilles tendon is the largest tendon in your body. It connects the upper calf muscles to the back of the heel bone. Achilles tendinosis is a condition in which the Achilles tendon degenerates and becomes inflamed. Sometimes, it may also be called Achilles tendinitis. If you have Achilles tendinosis, your tendon can swell and become painful. This condition is common in athletes, runners, and people who have calf tightness. Achilles tendinosis may occur in the middle of the tendon (known as midsubstance Achilles tendinosis) or at the point where the tendon connects to the heel bone (known as insertional Achilles tendinosis).

The ankle is made up of three bones:

• the tibia (shin bone), which forms the inside, front, and back of the ankle
• the fibula, which forms the outside of the ankle
• the talus, a small bone that sits between the tibia and fibula and the heel bone

The ends of these bones are called malleoli. The tibia has a medial (inside) malleoli and a posterior malleoli. The fibula forms the lateral (outside) malleoli.

An ankle sprain refers to tearing of the ligaments of the ankle. The most common ankle sprain occurs on the lateral (outside) part of the ankle. There's a good chance that while playing sports as a child or stepping on an uneven surface as an adult you sprained your ankle—some 25,000 people do it every day. It can happen in the setting of an ankle fracture (i.e., when the bones of the ankle also break). Most commonly, however, it occurs in isolation.

The pain and stiffness you feel in your feet and ankles as you age could be arthritis. If left untreated, this nagging pain can get worse over time, eventually making it difficult to walk even short distances. Severe arthritis can restrict your mobility, but with proper treatment, you can minimize the pain and maximize your quality of life.

Arthritis is a broad term for a number of conditions that destroy the workings of a normal joint. Arthritis may occur in your back, neck, hips, knees, shoulders or hands, as well as your feet and ankles. Almost half of people in their 60s and 70s have arthritis of the foot and/or ankle, but not all of them have symptoms.

Chronic lateral ankle pain is recurring pain on the outer side of the ankle that often develops after an injury such as a sprained ankle. However, several other conditions also may cause chronic ankle pain.

The high ankle ligaments are located above the ankle, as opposed to the more commonly injured ligaments on the outside of the ankle. These high ankle ligaments connect the tibia to the fibula. It is important to have stability between the tibia and fibula at this level because walking and running place a tremendous amount of force at this junction.

A high ankle sprain occurs when there is tearing and damage to the high ankle ligaments. These injuries are much less common than a traditional ankle sprain. 

Insertional Achilles tendinitis is a degeneration of the fibers of the Achilles tendon directly at its insertion into the heel bone. It may be associated with inflammation of a bursa or tendon sheath in the same area. 

Osteochondral lesions, sometimes called osteochondritis dessicans or osteochondral fractures, are injuries to the talus (the bottom bone of the ankle joint) that involve both the bone and the overlying cartilage. These injuries may include softening of the cartilage layers, cyst-like lesions within the bone below the cartilage, or fracture of the cartilage and bone layers. Throughout this article, these injuries will be referred to as osteochondral lesions of the talus (OLT).

The peroneal tendons run on the outside of the ankle just behind the bone called the fibula. Peroneal tendinosis is enlargement and thickening with swelling of these tendons. This usually occurs with overuse, such as a repetitive activity that irritates the tendon over long periods of time. 

The tibia (shin bone) and the fibula are the bones of the lower leg. Pilon fractures are injuries that occur at the lower end of the tibia and involve the weightbearing surface of the ankle joint. The fibula also may be broken. These injuries were first described more than 100 years ago and remain one of the most challenging problems for orthopaedic surgeons to treat. Common causes of pilon fractures are falls from a height and car accidents.

A talus fracture is a broken ankle bone. The talus is the bone in the back of the foot that connects the leg and the foot. It joins with the two leg bones (tibia and fibula) to form the ankle joint and allows for upward and downward motion of the ankle.

The talus (ankle bone) sits within the ankle mortise or hinge, which is made up of the two leg bones, the tibia and fibula. There are three joints:

• the ankle, which allows the up-and-down motion of the foot with the leg
• the subtalar joint, which allows for side-to-side movement
• the talonavicular joint, which has a complicated biomechanical function that controls flexibility of the foot and the arch of the foot.

The talus has no muscular attachments and is mostly covered with cartilage, which makes injuries difficult to heal.