| Fibrous joint | |
|---|---|
 Fibrous joints | |
| Details | |
| Identifiers | |
| Latin | articulatio fibrosa, junctura fibrosa |
| TA98 | A03.0.00.004 |
| TA2 | 1517 |
| FMA | 7492 |
| Anatomical terminology | |
Inanatomy,fibrous joints arejoints connected byfibrous tissue, consisting mainly ofcollagen. These are fixed joints wherebones are united by a layer of white fibrous tissue of varying thickness. In theskull, the joints between the bones are calledsutures. Such immovable joints are also referred to assynarthroses.
Most fibrous joints are also called "fixed" or "immovable". These joints have no joint cavity and are connected via fibrous connective tissue.
Asuture is a type of fibrous joint that is only found in the skull (cranial suture). The bones are bound together bySharpey's fibres. A tiny amount of movement is permitted at sutures, which contributes to thecompliance andelasticity of the skull.These joints aresynarthroses.[1] It is normal for many of the bones of the skull to remain unfused at birth. The fusion of the skull's bones before birth is known ascraniosynostosis. The term "fontanelle" is used to describe the resulting "soft spots". The relative positions of the bones continue to change during the life of the adult (though less rapidly), which can provide useful information inforensics andarchaeology. In old age, cranial sutures may ossify (turn to bone) completely.[3]The joints between the teeth and jaws (gomphoses) and the joint between the mandible and the cranium, thetemporomandibular joint, form the only non-sutured joints in the skull.
Most sutures are named for the bones they articulate, but some have special names of their own.
Asyndesmosis is a slightly mobile[4] fibrous joint in which bones such as the tibia and fibula are joined together by connective tissue. An example is the distal tibiofibular joint. Injuries to the ankle syndesmosis are commonly known as a "high ankle sprain". Although the syndesmosis is a joint, in the literature the term syndesmotic injury is used to describe injury of the syndesmotic ligaments. It comes from the Greek σύν,syn (meaning "with") and δεσμός,desmos (meaning "a band").[5] Syndesmosis sprains have received increasing recognition during recent years because of a heightened awareness of the mechanism, symptoms, and signs of injury.[6]
Diagnosis of syndesmosis injuries by physical examination is often straightforward. Physical examination findings that are often positive include the squeeze test and the external rotation test. Patients with high-grade syndesmosis injuries often cannot perform a single-leg heel raise. Patients report pain in varying degrees over the anterior and often posterior distal fibular joint.[7]
The severity of acute syndesmosis injury is rated from grade I to III by several authors. A grade I injury is a partial anteroinferior tibiofibular ligament tear, meaning the exorotation and squeeze tests are negative for this grade. Grade II injury is a complete anteroinferior tibiofibular ligament and inferior interosseous ligament tear, meaning that squeeze test and exorotation are positive. This results in the injury being stabilized with immobilization but not operatively stabilized. A grade III injury is a complete anteroinferior tibiofibular ligament tear including a (partial) interosseous ligament tear and deltoid ligament avulsion, meaning the joint is unstable and positive on the exorotation and squeeze tests. This grade requires operative stabilization.[8] If the syndesmosis is torn apart as result of bone fracture, surgeons will sometimes fix the relevant bones together with asyndesmotic screw, temporarily replacing the syndesmosis, or with atightrope fixation, which is calledsyndesmosis procedure.[9][10] The screw inhibits normal movement of the bones and, thereby, the corresponding joint(s). When the natural articulation is healed, the screw may be removed. The tightrope fixation with elastic fiberwire suture on the other hand allows physiologic motion of the ankle and may be permanent.
Agomphosis, also known as adentoalveolarsyndesmosis,[11] or 'peg and socket joint'[12] is a joint that binds theteeth to bonyteeth sockets in themaxillary bone andmandible. Gomphos is the Greek word for "bolt". The fibrous connection between a tooth and its socket is aperiodontal ligament. Specifically, the connection is made between the maxilla or mandible to the cementum of the tooth.
The motion of a gomphosis is minimal, though considerable movement can be achieved over time—the basis of using braces to realign teeth. The joint can be considered asynarthrosis.[13]
The gomphosis is the only joint-type in which a bone does not join another bone, as teeth are not technically bone. In modern, more anatomical, joint classification, the gomphosis is simply considered a fibrous joint because the tissue linking the structures is ligamentous. It has been suggested that this permanent soft-tissue attachment was a critical requisite in the evolution of the mammalian (synapsid)tusk.[14]
