Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Skeleton
Classification of Joints

Joints are classified according to their Structure, the number of articulating bones, the shape of their articular surfaces, and the number of rotation axes. Based on the number of bones involved, joints are divided into simple and compound.

Simple joints are formed by two bones (for example, the shoulder and hip joints). Compound joints involve three or more bones (for example, the elbow and knee joints).

Complex and combined joints are also distinguished. Complex joints feature a cartilaginous disc or meniscus (cartilaginous plates of various shapes and thicknesses) located between the articulating bones, which divides the joint cavity into two compartments (for example, the sternoclavicular and knee joints). Discs or menisci compensate for the incongruity of the articulating bone surfaces.

A combined joint consists of two anatomically isolated joints that function together (for example, the right and left temporomandibular joints).

Based on the shape of their articular surfaces and the number of rotation axes, joints are classified as uniaxial, biaxial, and multiaxial (Fig. 18). The shape of a joint determines its number of rotation axes. Cylindrical joints and their variants (hinge and pivot joints) have a single axis. These are Uniaxial joints, such as the proximal and distal radioulnar joints. Biaxial joints have two rotation axes. These include ellipsoid, condyloid, and saddle joints, such as the radiocarpal and atlanto-occipital joints, and the joint at the Base of the thumb. Ball-and-socket joints possess three axes of movement. These are triaxial, or multiaxial, joints (for example, the shoulder joint). In ball-and-socket joints, movements can occur around a multitude of axes. Plane joints are also categorized under ball-and-socket joints, as their articular surface can be viewed as a small segment of a large sphere.

Joint mobility, as well as the range and direction of movements, depends on The structure of the articulating surfaces (their size, shape, and curvature). Movements in joints occur around various axes: transverse (frontal), anteroposterior (sagittal), and longitudinal (along the articulating bones). Flexion and extension take place around the frontal axis, abduction (away from the trunk) and adduction (toward the trunk) around the sagittal axis, and rotation around the longitudinal axis. The range of motion in joints depends on the angular difference between the articular surfaces, expressed in degrees. The range of motion is also influenced by the tension of the Joint Capsule, the number and arrangement of ligaments, and the Muscles acting upon the joints, which can restrain or limit joint movement.

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Fig. 18. Articular surfaces. Joints:

A — hinge; B — ellipsoid; C — saddle; D — ball-and-socket