Synonym
USG, Articulatio talotarsalis
Definition
The lower ankle joint in combination with the upper ankle joint is the articulated connection between the two, allowing for optimal stability and great mobility. In contrast to the upper ankle joint, it has no direct contact to one of the lower leg bones, the joint surfaces are formed by three of the tarsal bones.
- Lower leg and
- Foot,
Ankle joints in general
The ankle joint is not a joint in the true sense of the word, but consists of two separate joints, which nevertheless form a functional unit. Together they allow for optimal mobility, but at the same time are stable enough to withstand the great forces exerted on them by body weight and the complexity of human movements.
Lower Ankle Joint – Anatomy
The USG lies below the upper ankle joint. Three of the tarsal bones participate with their joint surfaces in its formation. The lower ankle joint is divided into two joint cavities by two bone grooves, the so-called sinus tarsi.
In the back is the Articulatio subtalaris (subtalar joint). This is where the posterior joint surface of the talus and the calcaneus articulate. In front is the Articulatio talocalcaneonavicularis, where the head of the talus articulates not only with one joint surface, but with three structures. It has an articulated connection to the
- The talus forms the upper (proximal) joint body,
- The calcaneus (heel bone) and
- The scaphoid (Os naviculare) the lower (distal).
- Calcaneus, for
- Os naviculare and to the so-called
- Cup band (Ligamentum calcaneonaviculare plantar).
Ligamentous apparatus
Also the lower ankle joint is strengthened in its bony basic structure by ligaments. However, two of these ligaments do not have the typical ligament function in the sense of inhibition or stabilization, but are parts of the lower joint body. The acetabular ligament lies on the side of the sole of the foot (plantar) and serves the purpose of interlocking the calcaneus and the os naviculare, the main joint surfaces of the anterior part of the USG.
In addition, the acetabular ligament is considered important in shaping the arch of the foot. A portion of the fork ligament (Ligamentum bifurcatium) also serves to connect the calcaneus and the navicular bone. This firm connection between the calcaneus and the navicular bone is important because they do not have a bony connection to each other.
In addition to these ligaments, there are also ligaments in the USG that serve to inhibit undesirable movements. Some of the ligaments of the upper ankle joint also have an additional effect on the lower one. Thus, two parts of the Ligamentum deltoideum, the inner ligament of the OSG, are involved.
They keep pronation, i.e. the lifting of the lateral edge of the foot, within limits. The calcaneofibular ligament, which belongs to the outer ligament of the OSG, limits the opposite movement, supination, i.e. the lifting of the inner edge of the foot. In addition to these ligaments, the OSG is also secured by its own ligaments.
The Ligamentum talocalcaneum interosseum lies in the bony groove that divides the USG into two joint cavities. It connects the calcaneus with the talus and inhibits both pronation and supination of the foot. The Ligemantum talocalcaneum laterale serves to inhibit supination.
- Pars tibiocalcanea and
- Pars tibionavicularis
The USG is – analogous to the OSG – a hinge joint. However, its axis is different, so it supports other movements. Thus, the combination of both joints allows a large range of movement.
Two movements take place in the USG. An eversion of about 10 degrees and an inversion of about 20 degrees are possible. Strictly speaking, these two movements cannot be equated with pronation or supination, since these are movements that are not performed in the USG alone, but are the result of a combination of the extent of movement of the USG and the joints between the tarsal bones. Clinical reason: The USG is much less likely to suffer from injuries than the OSG.
- The Eversion (lifting of the lateral foot edge) and the
- Inversion (lifting the inner foot edge).
