The joint space separates the joint surfaces. It contains synovial fluid that helps nourish, move, and protect the joints. When the joint space narrows or widens, there is a pathologic change in the joint.
What is the joint space?
Medicine distinguishes between unreal and real joints. In addition to cartilaginous bone joints, synchondroses and symphyses, inauthentic joints are connective tissue bone joints, syndesmoses and synsaroses. Unreal joints differ from real joints in their structure. In true joints, there is a gap between the ends of the bones that abut and interlock, called the joint space. Accordingly, the joint space is the gap-shaped cavity of the cartilaginous surfaces, which constitutes a part of the joint cavity and is considered a characteristic feature of diarthroses. The body has over 100 joints. A large number of them are among the true joints with fluid-filled joint cavity. Viscous synovial fluid is a required component of each joint space and is also called synovium. The substance in the joint space nourishes the bones and allows them to move. Joints such as the tarsal joint physiologically have multiple joint spaces.
Anatomy and structure
The joint space lies between the individual cartilage surfaces involved in a joint. The space between them is crevice-shaped, which explains its designation as a joint space. The joint cavity is the entire internal space of the joint enclosed within the joint capsule. The joint cavity is formed predominantly by the joint space and is filled with synovial fluid. This synovial fluid is of viscous consistency. It serves as a sliding film of the bones and in this way enables bone movements. The synovial fluid protects the articular cartilage during movements by down-regulating friction and thus reducing signs of wear. As it is composed of substances such as glucose, it also nourishes the joints. The volume of synovium in the joint space varies from joint to joint. In addition to joint spaces and synovium, intraarticular structures such as disci, ligaments, tendons, or fat bodies may be present in the joint cavity. In larger joints, the joint cavity as a whole is often associated with bursae.
Function and tasks
In functional anatomical terms, it is basically the joint space that allows a joint to move. Joints connect free bone ends together and give them a certain range of motion on different axes depending on the particular type of joint. In addition to extension, abduction, adduction, flexions and rotations, some joints of the body can perform pronations, supinations, nutations, oppositions, inclinations and repositions. The extent of movement depends on the type of joint. True joints with joint space, for example, may correspond to triaxial ball joints and thus be capable of flexion, extension, abduction, adduction, and external and internal rotation. Biaxial egg joints with joint gap are also true joints and realize, for example, flexion-extension movements or side-to-side movements. Also among the true joints with joint space are biaxial saddle joints with the ability to flex and extend as well as abduct and adduct. Uniaxial cylindrical joints are also true joints and carry a joint space. They can flex and extend. Uniaxial true joints are also the trunnion joints. Plane-only joints are static, but they have translational degrees of freedom. True bicondylar joints with joint gaps are again biaxial and perform, for example, external and internal rotations in addition to flexion and extension. The joint space is essentially involved in all of the above movements. It contains the synovial fluid, which acts as a lubricating film over the cartilage during the movements, reducing friction between the elements. Without the friction reduction of the synovium in the joint space, the joints would wear out after a very short time and become rigid in movement. In addition, without the supply of synovial fluid in the crevice, cartilage could not survive because the glucose it contains feeds it.
Diseases
The joint space of a joint is an important factor in radiographic diagnosis to evaluate a joint and any joint abnormalities.A widened joint space can, for example, indicate to the doctor an injury to the ligament structures or an effusion of the joint. In a joint effusion, fluid accumulates inside the joint. This condition is often the result of trauma or is associated with inflammation. For example, the causes of joint effusion can also be degenerative joint diseases such as osteoarthritis. In addition, gout, hemophilia and rheumatoid arthritis cause joint effusions. In addition, tumors are often associated with the appearance and related changes in the joint space. Thus, in addition to providing evidence of joint effusion, evaluation of the joint space also provides the physician with evidence of larger primary diseases in which the joint effusion may have occurred. In some cases, the radiograph also reveals a narrowed or even completely abolished joint space. Such a discovery is indicative of chronic polyarthritis or a degenerative disease such as osteoarthritis. Because the joint space separates the joint surfaces involved and definitely in need of contact, it tends to be small by nature. If the cartilage surfaces are in normal condition and do not bear calcifications, for example, the gap between healthy cartilages will appear much larger on an x-ray than the gap between degeneratively altered cartilage surfaces. When cartilage undergoes degenerative changes, the protective cartilage portions of the joint break down and the bony joint surfaces slip closer together. This phenomenon results in the joint space narrowing on the radiograph. Joint space narrowing is divided into two forms. Uniformly concentric joint space narrowing represents arthritis. In contrast, unevenly eccentric joint space narrowing occurs in osteoarthritis.
