Haglund's Deformity: A bony enlargement on the back of the heel that can cause pain and swelling, often due to irritation from shoes. This condition is common and directly correlates with the described location of the protusion.

Bursitis: Inflammation of the bursae, fluid-filled sacs that cushion bones, tendons, and muscles near joints, can cause swelling and protusions, especially if the bursae near the heel are affected.
Bone Spur: A bony growth that can develop on the edge of any bone, including those in the heel, due to aging, injury, or conditions like arthritis, potentially causing protusions.
Plantar Fasciitis: While primarily causing pain under the heel, in severe cases, plantar fasciitis can lead to the development of a heel spur, which might be felt as a protusion.

Tumor (Benign or Malignant): Although rare, tumors such as osteochondromas (benign) or sarcomas (malignant) can present as protusions on the heel. Missing a diagnosis of a malignant tumor could have severe consequences.
Infection (Osteomyelitis or Soft Tissue): Infections of the bone or soft tissue near the heel can cause swelling and protusions, and if not treated promptly, can lead to serious complications.
Gout or Pseudogout: These conditions can cause sudden, severe joint pain and swelling, which might be perceived as a protusion, especially if a tophus (deposit of uric acid crystals) forms near the heel.

Ganglion Cyst: A noncancerous lump that can develop on the tendon or joint near the heel, though less common in this location.
Lipoma: A rare benign tumor composed of fat tissue that could potentially occur near the heel, causing a protusion.
Heel Pad Atrophy: A condition where the fat pad under the heel thins, potentially causing discomfort and the sensation of a protusion due to the loss of cushioning.