Calcaneus
Short bone; part of the appendicular skeleton within the tarsal group. · Located in the hindfoot, inferior to the talus and posterior to the cuboid. It forms the skeletal foundation of the heel.
Also known as: Heel bone
Classification
Short bone; part of the appendicular skeleton within the tarsal group.
Location
Located in the hindfoot, inferior to the talus and posterior to the cuboid. It forms the skeletal foundation of the heel.
Origin
Endochondral ossification. It has a primary center appearing at month 5-6 of fetal life and a secondary center at the posterior epiphysis that appears around age 6-8 and fuses by age 14-16.
Dimensions
The largest of the tarsal bones. In adults, it typically measures 7-9 cm in length. This specimen appears to be from a fully developed adult based on the presence of sharp landmarks and fused tuberosities.
Description
The calcaneus is the powerhouse of the hindfoot, acting as a massive lever for the calf muscles and providing the primary contact point during the human walking cycle.
Key Features
Sustentaculum tali (medial shelf), Calcaneal tuberosity (posterior projection), and the deep Calcaneal sulcus.
Anatomical Description
Large, rectangular, and robust bone. Features include the calcaneal tuberosity posteriorly, the sustentaculum tali (a shelf-like projection medially), the peroneal tubercle laterally, and three articular surfaces on the superior aspect for the talus.
Dimensions & Proportions
The largest of the tarsal bones. In adults, it typically measures 7-9 cm in length. This specimen appears to be from a fully developed adult based on the presence of sharp landmarks and fused tuberosities.
Surface Features
Characterized by a rough posterior tuberosity for the Achilles tendon, a deep sulcus calcanei that forms the floor of the tarsal sinus, and a smooth medial projection (sustentaculum tali). The lateral surface is relatively flat with a small peroneal tubercle.
Articulations
Articulates superiorly with the talus (forming the subtalar joint) and anteriorly with the cuboid bone (calcaneocuboid joint).
Muscle Attachments
Insertion site for the Gastrocnemius and Soleus (via the Achilles tendon) on the posterior tuberosity. Origin for the Abductor hallucis, Extensor digitorum brevis, and Quadratus plantae.
Blood Supply
Principal supply from the posterior tibial artery and the peroneal (fibular) artery, which form an anastomotic network around the heel.
Developmental Origin
Endochondral ossification. It has a primary center appearing at month 5-6 of fetal life and a secondary center at the posterior epiphysis that appears around age 6-8 and fuses by age 14-16.
Clinical Significance
Commonly fractured in 'Don Juan' or 'Lover's' fractures (falls from height). Changes in Boehler's angle on X-ray are used to assess fracture severity. It is also the site of plantar fasciitis and heel spurs.
Age & Sex Determination
Sex determination can be estimated via the 'Calcaneal Index' (length/width ratios), though it is less diagnostic than the pelvis. Age is estimated in subadults by the fusion of the posterior epiphysis.
Forensic Importance
Because of its high density, it often survives fire or extreme decomposition, making it useful for stature estimation using specialized regression formulas.
Comparative Anatomy
In digitigrade mammals (like dogs/cats), the calcaneus is elevated and forms the 'hock.' In humans, its size and robusticity are adaptations for full bipedalism and heel-strike gait.
Evolutionary History
Evolved from a more slender tarsal element in early tetrapods to a massive, weight-bearing lever in hominids to facilitate bipedal locomotion and upright balance.
Imaging Characteristics
Easily visualized on lateral and axial (Harris) X-ray views. Boehler's angle (normally 20-40 degrees) is a primary radiographic landmark.
Pathological Conditions
Haglund's deformity ('pump bump'), Sever's disease (calcaneal apophysitis in children), and Paget's disease.
Surgical Relevance
Open Reduction Internal Fixation (ORIF) is common for intra-articular fractures. The 'lateral extensile approach' is a standard surgical pathway, though it risks the sural nerve.
Similar Bones
Talus: Distinguishable by its smooth, rounded trochlea (dome) and lack of a large posterior tuberosity. Cuboid: Much smaller and more cube-shaped without a long posterior lever arm.
Interesting Facts
The calcaneus must withstand forces several times the body's weight during running. It is the first tarsal bone to begin ossifying during fetal development.
Photography Tips
Capture the medial view to show the sustentaculum tali and the superior view to show the three articular facets for the talus. Use a scale bar to indicate robusticity.