The Achilles tendon is the strongest tendon in the leg, and serves an important purpose by allowing the ankle to move up and down in a stable manner. This tendon begins in the calf as a combination of two different muscles, and attaches to the back of the heel bone. It can easily be felt through the skin, and can usually be seen bulging out of the skin as well. The Achilles tendon can become injured through both trauma and chronic stress, and unfortunately both of these occur commonly. When a force is applied to the foot that pushes it upward, the Achilles tendon can become strained or even tear, especially if the tendon is actively contracting downward at the same time. These types of injuries occur commonly in running sports such as basketball, football, track, and soccer. If the tendon does not outright tear, it will become inflamed and painful. The inflammation can be constantly renewed if the tissue is not supported, if the activity that caused it is continued, or if bone spurs on the back of the heel bone continually irritate the tendon fibers. Additionally, there is an area in the tendon a couple inches above the heel bone where the tendon has poor blood supply, and is weaker structurally. This area is much more likely to be injured and become inflamed, and is also more likely to rupture.
Achilles tendonitis pain can be felt as a sharp stab or a dull ache on the back of the heel. Bending the ankle upward or forcefully bending it downward can cause pain, as can simply walking. Sometimes the area behind the heel can become swollen, however this is not frequent and is typically associated with a rupture, as is bruising. Shoes that have a hard heel counter (the material that wraps around the heel) can irritate the heel tissue, as can gently bumping the back of the heel into something.
The Haglund’s deformity is a bone enlargement on the back of the heel, but is notably different from a spur. The top surface of the back of the heel bone is normally a rounded but generally flat surface that has nothing attached to it, unlike the back of the heel where the Achilles tendon attaches. In some people, this surface is rounded upward. Although this can be present from an early age, some people gradually develop the bump as the bone surface becomes irritated. This irritation can be due to high arches, in which the heel bone is angled steeply upward, delivering the top of the heel closer to the Achilles tendon which produces the irritation. Shoes with a hard heel liner can also cause the irritation, hence the name ‘pump bump‘. The bone surface eventually becomes enlarged enough to irritate the soft tissue covering the back of the heel above where the Achilles tendon attaches. Within this tissue are fibers associated with the Achilles tendon, as well as a pad of tissue called a bursal sac, which serves as a sort of pillow to separate the bone from the overlying soft tissue. The bursal sac can become inflamed and cause pain. The more it is irritated against the enlarged bone, the more pain is felt with activity or with shoes that rub against the bone.
Bone Spurs on the Back of the Heel (Posterior Heel Spur)
Spurs do indeed develop on the back of the heel bone, and often can be a source of pain. Spurs form for a variety of reasons, but usually develop in response to traction or pulling of the heel bone by the Achilles tendon. This is especially the case when there is a general tightening or lack of upward motion of the ankle, usually due to a tight Achilles tendon or calf muscle. The pulling force stimulates the outer layer of bone to calcify, forming a bone spur in the process. The Achilles tendon substance itself can also partially calcify where it attaches to the heel bone. People with flat feet are at greater risk for spurs on the back of the heel because the pulling force is greater in a flat foot where the heel bone excessively rotates outward. When viewed on an x-ray, the spur can look like a narrow spike of bone projecting outward and upward from the back of the heel bone. In actuality, it is more like a ledge running the width of the back of the heel bone. This bone has the potential to irritate the Achilles tendon, and sometimes can even fracture off partially from the heel bone, both resulting in pain. The presence of the spur itself does not mean that pain will always develop, as many patients with spurs on the back of their heel do not necessarily develop pain. However, the presence of a spur makes pain more possible, especially in situations of chronic stress to the Achilles tendon.