Calcaneus

The calcaneus, commonly referred to as the heel bone, is the largest and most posterior of the tarsal bones. It forms the foundation of the rearfoot and serves as the primary weight-bearing bone of the foot during standing and locomotion. The calcaneus articulates with the talus superiorly to form the subtalar joint and with the cuboid anteriorly as part of the midfoot. Its robust structure, numerous articular facets, and ligamentous and muscular attachments make it a crucial element in foot mechanics and gait.

Structure

The calcaneus is an irregularly shaped bone with a complex anatomy that includes prominent bony processes, grooves, and articular surfaces. Internally, it consists of a cancellous trabecular network enclosed by dense cortical bone. Its external features are adapted to transmit forces from the leg to the ground while accommodating muscular leverage and tendon passage.

Surfaces and Features

• Superior surface: Articulates with the talus at three distinct facets — anterior, middle, and posterior — separated by the sulcus calcanei.
• Inferior surface: Rough and irregular, contains the weight-bearing heel region that contacts the ground during heel strike.
• Anterior surface: Articulates with the cuboid bone at the calcaneocuboid joint.
• Posterior surface: Features the calcaneal tuberosity and medial/lateral processes, serves as the attachment for the Achilles tendon.
• Medial surface: Presents the sustentaculum tali, a horizontal shelf that supports the talus and serves as a ligament and tendon passage area.
• Lateral surface: Marked by the peroneal (fibular) trochlea, a bony ridge guiding the tendons of the fibularis muscles.

Location

The calcaneus is located in the posterior part of the foot, forming the heel. It lies inferior to the talus and posterior to the cuboid. The bone projects posteriorly beyond the ankle joint and contacts the ground during standing and ambulation.

• Superior: Talus (via subtalar joint)
• Anterior: Cuboid (via calcaneocuboid joint)
• Posterior: Skin and subcutaneous tissue of the heel pad
• Medial: Sustentaculum tali adjacent to the tarsal tunnel
• Lateral: Peroneal tendons pass along this side

Function

• Weight-bearing: Transmits body weight from the talus to the ground during heel strike and stance phase of gait
• Shock absorption: Cushions impact forces through its trabecular bone and overlying soft tissue
• Joint articulation: Facilitates inversion and eversion of the foot via subtalar joint movement
• Leverage: Provides a mechanical advantage for the triceps surae muscles during plantarflexion

Articulations

The calcaneus articulates with two bones:

Bone	Joint	Type
Talus	Subtalar joint	Synovial plane
Cuboid	Calcaneocuboid joint	Synovial saddle (modified)

Articular Facets

• Posterior facet: The largest; concave surface for articulation with the talus
• Middle facet: Located on the sustentaculum tali
• Anterior facet: Flat or convex, articulates with the anterior talus

The sulcus calcanei lies between the middle and posterior facets and combines with the talar sulcus to form the sinus tarsi, a channel for ligaments and neurovascular structures.

Ligament Attachments

The calcaneus anchors multiple ligaments that support the hindfoot and maintain arch integrity:

Ligament	Attachment Site	Function
Plantar calcaneonavicular (spring) ligament	Sustentaculum tali to navicular	Supports head of talus and medial arch
Long plantar ligament	Calcaneal tuberosity to bases of metatarsals	Stabilizes lateral arch
Short plantar (calcaneocuboid) ligament	Anterior calcaneus to cuboid	Supports calcaneocuboid joint
Interosseous talocalcaneal ligament	In sinus tarsi between talus and calcaneus	Stabilizes subtalar joint

Muscle Attachments

The calcaneus serves as an origin or insertion point for several muscles:

Muscle	Attachment	Function
Gastrocnemius	Via Achilles tendon to calcaneal tuberosity	Plantarflexion of foot
Soleus	Via Achilles tendon to calcaneal tuberosity	Plantarflexion
Plantaris	Variable insertion near medial tuberosity	Assists plantarflexion
Abductor hallucis	Medial process of calcaneal tuberosity	Abducts great toe
Abductor digiti minimi	Lateral process of tuberosity	Abducts little toe
Flexor digitorum brevis	Central calcaneal tuberosity	Flexes lateral four toes
Quadratus plantae	Medial and lateral calcaneus	Assists flexor digitorum longus

Blood Supply

The calcaneus is supplied by branches of the posterior tibial artery, peroneal (fibular) artery, and lateral plantar artery. These vessels form an extensive network around the bone, particularly near the tuberosity and sustentaculum tali.

• Posterior tibial artery: Primary supply to medial aspect
• Peroneal artery: Supplies lateral and posterior regions
• Lateral plantar artery: Supplies plantar surface

Nerve Supply

The calcaneus is innervated by sensory and motor branches of the:

• Medial calcaneal branches (tibial nerve): Innervate medial and plantar heel skin
• Lateral plantar nerve: Supplies muscles arising from lateral tuberosity
• Sural nerve: Provides cutaneous innervation to lateral heel

Ossification

The calcaneus ossifies from a primary center that appears during fetal development, along with a secondary center in the posterior tuberosity.

• Primary center appears: 5th–6th fetal month
• Secondary ossification center (calcaneal apophysis): Appears around age 6–8, fuses by age 14–16

Clinical Significance

• Calcaneal fractures: Commonly occur from high-energy axial loading (e.g., falls). Intra-articular types affect the subtalar joint and may require ORIF (open reduction internal fixation).
• Calcaneal apophysitis (Sever’s disease): Common in athletic children; due to repetitive stress on the secondary ossification center.
• Heel spur syndrome: Bony projection from the tuberosity associated with chronic plantar fasciitis; visible on lateral foot X-ray.
• Bursitis: Retrocalcaneal and subcutaneous bursae over the tuberosity may become inflamed from friction or overuse.
• Tarsal coalition: Congenital fusion between the calcaneus and talus or navicular limits motion and causes chronic pain or flatfoot deformity.

Imaging

• X-ray: Standard lateral, axial (Harris-Beath), and oblique views assess fracture patterns and alignment
• CT scan: Crucial for evaluating intra-articular fractures and sinus tarsi detail
• MRI: Used for soft tissue injuries, marrow edema, and chronic heel pain assessment
• Ultrasound: Helps visualize Achilles tendon insertion and retrocalcaneal bursae