Bunion of Big Toe: Structure, Function & Diseases

The ball of the big toe is a functionally important area on the sole of the foot. It plays a significant role in the statics of the foot.

What is the ball of the big toe?

The ball of the big toe is an enlarged downward curved region on the inside of the sole of the foot in the area of the metatarsophalangeal joint. It is part of the ball of the toe as a whole, which impresses as a transverse bulge on the sole of the foot in the area of the forefoot, and represents the largest single region in this system. It is composed of 3 layers formed by different tissue structures. The solid framework in depth is formed by the bones belonging to the 1st metatarsal and the metatarsophalangeal phalanx. The middle layer consists of muscles and the outer one is formed by the skin and the subcutaneous fat pad with parts of the plantar aponeurosis. This creates a simultaneously soft, yet firm cushion structure that can absorb and distribute forces very well. The ball of the big toe represents a key strategic point for the arch of the foot. The longitudinal arch spans the inside of the sole of the foot as an arch from the heel to the ball of the big toe, just as the transverse arch ends there coming from the ball of the little toe.

Anatomy and structure

The metatarsophalangeal joint of the big toe is formed by the head of the first metatarsal and the base of the metatarsophalangeal joint. Two sesamoid bones are regularly found on the underside of the joint, completing the bony substructure. The next layer is three muscles that have their origins in the tarsal region or at the metatarsal bones, the M. adductor halucis (big toe puller), M. abductor halucis (big toe spreader)and the Musculus flexor halucis brevis (small big toe flexor). All three attach at the base of the great toe proximal phalanx. They run over one or both sesamoid bones in the area of the 1st metatarsal head, which on the one hand deflects them, but on the other hand also makes them jointly responsible for the arching of the big toe ball. Spanning this structure are the extensions of the plantar aponeurosis, a tendon plate on the sole of the foot that forms a firm yet soft network with the subcutaneous tissue and fat deposits that lie between the two layers. Together with the outer skin, which provides the closure to the outside, a thick layer of cushioning material is formed over the muscles and bones.

Function and tasks

The ball of the big toe, along with the ball of the little toe and the heel, is one of the 3 contact points of the arch structure of the foot, which plays an enormously important role in the statics of the foot and the stress on the joints above it. It is constructed in such a way that the load that arrives at the foot via the lower leg is buffered and distributed among many bones. This keeps the weight pressure of the individual parts low. The ball of the big toe is a key part of this system because it is involved in both arches and must bear a relatively large amount of load compared to other areas of the sole of the foot during walking and standing. It is also responsible for the absorption and transmission of foot movement. In the course of the rolling motion during walking, the force is transmitted from the heel via the outer edge of the sole of the foot to the ball of the little toe and finally to the ball of the big toe. From there, together with the big toe, the imprint of the foot for the swing leg phase then takes place. The structure with the soft tissue cushion as the outer layer forms an ideal cushioning system for this stress, which ensures that the pressure is not transferred too much to the sensitive bony structures. Through its connection with the plantar aponeurosis, the ball of the big toe is involved in the bracing system of the sole of the foot, which is of great importance for the stability of the longitudinal arch and also proportionally of the transverse arch. The adductor halucis muscle, in particular, reinforces the transverse arch in the distal (far from the body) region with its transverse fibers.

Diseases

Changes in arch construction affect the position of bones located in the ball of the big toe. Drop foot, a lowering of the longitudinal arch, causes the bearing surface under the sole of the foot to shift. As a result, other regions of the ball of the big toe come into the pressure zone and are overloaded. Painful irritations occur in the soft tissues or bones, mainly affecting the two sesamoid bones. Running athletes in particular complain more frequently of such complaints, which are referred to as sesamoiditis.Another long-term consequence of the changed joint position can be arthrosis, which leads to stiffening of the joint. This phenomenon is called hallux rigidus. It prevents the final phase of rolling and thus changes the gait pattern. The flattening of the transverse arch is called splayfoot because the metatarsals move away from each other. This is visible by an increased spreading of the toes. This particularly affects the first metatarsal, which can clearly move inward. On the one hand, the entire process leads to the fact that the main contact points are no longer located exclusively at the ball of the big toe and the ball of the small toe. The heads of the other metatarsal bones sink and also get into the pressure zone. The consequences are unpleasantly painful for these bones because they are not initially adapted to these loads. The ball of the big toe is basically relieved. However, the process is accompanied by a significant change in the static conditions. The displacement of the first metatarsal can have specific consequences for the metatarsophalangeal joint of the big toe. The joint position changes because the articular surface at the metatarsal head moves inward. This also changes the course of the flexor tendons that run across the joint. They slip outward and change their direction of pull so that they pull the big toe outward, resulting in hallux valgus. In extreme cases, this process can progress to the point where the big toe is pulled under the second toe and held there. Another consequence of bone displacement is the increase of pressure in the shoe on the inside of the ball of the big toe, causing a painful ganglion to develop. Wearing high-heeled shoes can accelerate the development of hallux valgus.