Calcaneus

an irregular quadrangular bone of the heel or hindfoot, articulating with other tarsal bones (talus, navicular and cuboid bones). Other names for this bone are os calcis and heel bone.

Important tendons, aponeuroses and bursae are located about the calcaneus, including the Achilles tendon, the plantar aponeurosis, the retrocalcaneal bursa and the preachilles fat pad. Also, see calcaneus.

2. Pathology

Ossification of the calcaneal apophysis may produce radiographic appearances that may be mistaken for abnormalities. This apophysis may develop from multiple centres of ossification; the increased density and fragmentation on radiographs simulate a pathologic condition.

Abnormal positions of the calcaneus may occur in various foot deformities. The normal alignment of the foot is inferred from the information on radiographs using primarily the relationship of the talus and calcaneus. In hindfoot valgus deformity the calcaneus is abducted, leading to a decrease in the plantar support on the anterior portion of the talus, In hindfoot varus deformity the anterior end of the calcaneus is adducted, with the talus and calcaneus being more parallel to each other than normally. In hindfoot equinus deformity the calcaneus is flexed in a plantar direction, whereas in calcaneal hindfoot deformity it is dorsiflexed. Clubfoot is a combination of equinovarus foot deformithy and hindfoot varus deformity.

The calcaneus is the most common site of tarsal fracture. These injuries can be classified broadly into intra-articular and extraarticular fractures; intra-articular generally have a poorer prognosis because of displacement of fragments. In neuropathic osteoarthropathy, calcaneal fragmentation also is typical. Fractures of the calcaneus may occur as a complication of osteoarthropathy, calcaneal fragmentation also is typical. Fractures of the calcaneus may occur as a complication of osteoarthritis in one or both subtalar joints. Although fractures of the calcaneus usually can be diagnosed accurately by routine radiographs, especially if attention is paid to Boehlers angle, CT displays the extent of injury ideally.

In addition, avulsion of a portion of the calcaneus may follow exaggeraged pull of the Achilles tendon or accompany cruciate ligament injuries and spinal trauma. In children, identification of avulsion injuries may be difficult owing to the presence of unossified portions of the immature skeleton (Fig.1).

Retrocalcaneal bursitis, such as it occurs in rheumatoid arthritis, psoriatic arthritis, Reiter's syndrome, ankylosing spondylitis, and Haglund's syndrome, leads to erosions of the calcaneus at one or more sites. A soft tissue mass also may be observed on the posterosuperior aspect of the calcaneus.

Plantar or posterior enthesophytes may develop on the calcaneus in certain diseases, including rheumatoid arhtritis, ankylosing spondylitis, psoriatic arthritis, Reiter's syndrome, and diffuse idiopathic skeletal hyperostosis.

Miscellaneous other conditions also may affect the calcaneus, including Paget's disease (Fig.2) and intraosseous lipoma (Fig.3).

DR/RB