The heel bone or calcaneus is the rearmost and also the largest foot bone. It gives the foot stability and is the attachment point for the Achilles tendon, for the most important calf muscles and for the tendon plate underneath the foot, as well as for several muscles in the sole of the foot. The rearmost part of the calcaneus forms the bony base for the heel, which is used to transfer compressive forces coming from above to the ground.
What is the calcaneus?
The calcaneus, or heel bone, is the largest and rearmost tarsal bone of a total of 26 foot bones. It lies somewhat laterally offset inward and fulfills a variety of complex functions. The bone, which appears almost cuboid in shape, serves as an attachment point for the Achilles tendon and the most important calf muscles as well as the tendon plate of the sole of the foot and several other ligaments and muscles under the foot. It therefore has an enormously important position for the statics of the foot. On the upper side, the calcaneus is connected to the ankle bone (talus) and absorbs its forces, which can be considerable during walking, jumping and running. The calcaneus transmits the enormous compressive forces to the ground. In order not to collapse, it must meet high strength requirements. Towards the front, towards the toes, the calcaneus maintains the tension of the arch of the foot and therefore supports itself on the cuboid bone, to which it is connected by an articular surface.
Anatomy and structure
The calcaneus is composed of bone mass and bears specially shaped projections and articular surfaces to perform its multiple functions. Three articular surfaces are formed on the superior aspect of the calcaneus, the middle of which is located on a process called the sustentaculum tali. It provides the connection to the talus (ankle bone). A broad tendon groove can be seen on the plantar side. The connection to the cuboid bone (Os cuboideum), which lies in front of the calcaneus, is established by another articular surface. The posterior part of the calcaneus, which can be seen from the outside, is formed as a hump (tuber calcanei), which serves as an attachment point for the Achilles tendon (tendo calcaneus), the twin calf muscles and the clod muscle on the upper side. On the lower side, two bumps are formed to which the tendon plate of the sole of the foot and several muscles are attached, through which the movement of the individual toes can be controlled. Other bony protuberances and grooves serve as protection and guide channels for numerous other tendons and muscle.
Function and tasks
The calcaneus performs a variety of complex tasks and functions. The upright gait of humans requires differentiated movement patterns of the foot, for which a total of 26 foot bones, including the phalanges, are available. The calcaneus plays a major role in absorbing pressure, shear and twisting forces. The main compressive forces occur during running and especially during jumps from great heights. The calcaneus absorbs the forces and transmits them to the ground without collapsing. Shear and twisting forces occur when the attached muscles and ligaments are stressed, such as during running and jumping and during climbing when the toes are loaded. The calcaneus also plays an important role in maintaining tension on the longitudinal arch of the foot.
Diseases and ailments
The most common complaints associated with the calcaneus arise from a bony lower or upper heel spur (calcaneal spur) in the attachment area of the Achilles tendon (upper spur) or plantar tendon plate (lower spur). Painful irritation and inflammation of the affected tendon insertions can occur and cause considerable discomfort. Typical symptoms are morning onset pain that diminishes with movement. In this context, a total rupture of the Achilles tendon as well as bursitis and Haglund’s syndrome or Haglund’s exostosis (ganglion) should also be mentioned. Similar complaints can also be caused by osteoarthritis at the articular surfaces of the calcaneus. Rather rarely, the calcaneus may be subject to fracture by direct violent impact or fatigue, such as a fall from a height of several meters and landing unbraked directly on the heel. Calcaneal fractures are usually so-called comminuted fractures that require surgical treatment (plates and nailing).Congenital deformities of the foot and unsuitable footwear worn over a long period of time can contribute to gradually increasing pain in the calcaneal region. Furthermore, primary tumors – originating directly from the bone cells – or secondary cancerous tumors (daughter carcinomas) rarely form in the area of the calcaneus. Just as rarely, bone cysts filled with tissue fluid develop directly in the calcaneus. They are usually benign, but may cause discomfort when pressure is applied to the calcaneus, i.e., discomfort when walking. Stinging pain when walking can be caused by so-called plantar warts under the sole of the foot. Plantar warts form thorn-like projections that cause a stabbing pain when walking.
