Ball and socket joint Ball and socket joint The ball and socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of axes, which have one common center. It enables the bone to move in many places (nearly all directions). An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator. Examples of this form of articulation are found in the hip, where the round head of
Hip femoral side, the distance between the head's cartilaginous rim and the capsular attachment at the base of the neck is constant, which leaves a wider extracapsular part of the neck at the back than at the front. The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement (second only to the shoulder) and yet support the weight of the body, arms and head. The capsule has two sets of fibers: longitudinal and circular. The hip joint is reinforced by four ligaments, of which three are extracapsular and one