Structure
The metatarsophalangeal joints (Articulationes metatarsophalangeales) are the joints located between the heads of the metatarsals and the corresponding base of the first limb of the toe (proximal phalanx, metatarsophalangeal phalanx). Since we have five toes on each foot, there are also five metatarsophalangeal joints on each foot, which are numbered from I to V in the anatomy. The socket of the metatarsophalangeal joint forms the proximal phalanx.
This is reinforced on the underside of the foot by a fibrocartilaginous ligament called the plantar ligament. This socket contains the head of the joint, which is the head of the metatarsal bone. However, since this head is larger than the intended socket, it protrudes over the socket towards the sole of the foot.
In the direction of the back of the foot, the metatarsophalangeal joint is covered by the so-called dorsal aponeurosis, a structure consisting of fibrous tracts originating from the tendons of the extensor muscles of the foot. On both sides, each metatarsophalangeal joint is supported by a collateral ligament. The metatarsophalangeal joints belong to the group of ball joints, which actually means that they have 6 degrees of freedom, i.e. they can move and rotate in any direction.
However, the metatarsophalangeal joints are limited in their range of motion, mainly due to the good security provided by the various ligaments. For example, “pulling up” (dorsiflexion) of the foot is only possible up to an angle of 70° in the active position and up to an angle of 90° in the passive position. Movement in the opposite direction, i.e. “front-to-bottom stretching” (extension) of the foot, can normally only be performed actively or passively up to an angle of about 50°.
Lateral movements of a metatarsophalangeal joint are initially quite possible in childhood, then decrease in circumference in the course of life, until they can hardly be accomplished in adulthood. In the relaxed position when standing, the joint is usually in a slight dorsiflexion. A malposition of the metatarsophalangeal joint of the big toe is often found, which is called hallux valgus.
Here, the metatarsophalangeal joint bends outwards, which is often caused or at least encouraged by incorrect footwear. This clinical picture is, however, in most cases only associated with minor symptoms and pain.
