Читать книгу Musculoskeletal Disorders - Sean Gallagher - Страница 111

Arthrokinematics describes the movements occurring between the joint surfaces, such as rolling, spinning, and gliding of joint surfaces. As such, joints can be divided into plane, hinge, saddle, condyloid, ball‐and‐socket, and pivot joints. Plane joints are characterized by opposing bony surfaces that are flat or nearly so. The arthrokinematics of a plane joint includes gliding and spinning or a combination thereof. Gliding refers to a translation of one surface with respect to another, whereas spinning refers to a clockwise or counterclockwise rotation of one surface with respect to another. Depending on the precise curvature of the surfaces of a plane joint, their orientation, and their constraints by soft‐tissue structures, the osteokinematics of plane joint movement ranges from uniaxial to triaxial. Examples of plane joints include the acromioclavicular joint, which is triaxial, and the vertebral zygopophyseal (facet) joints, which are uniaxial. Hinge joints are constrained to movement in one plane, usually sagittal, about one axis of rotation, usually mediolateral. The elbow joint is one example of a hinge joint. Saddle (sellar) joints are characterized by opposing surfaces that are concave and convex, but along opposite planes so that they are contoured to fit together. The osteokinematics of saddle joints are inconsistently described as either biaxial (motion about two primary axes in two planes) or triaxial. This inconsistency can be explained by the fact that the majority of motion typically occurs in two planes (usually flexion‐extension and abduction‐adduction), while there is a small amount of internal‐external rotation. The carpometacarpal joint of the thumb is an example of a saddle joint in which flexion‐adduction‐internal rotation combine to produce the action of opposition. Condyloid joints are composed a one nearly spherical convex surface opposing a shallow, nearly flat concave surface. These joints are considered biaxial owing to the predominance of movement about two axes and in two planes. The arthrokinematics during movement of condyloid joints are described by the “concave–convex rule,” which specifies that to maintain congruence of joint surfaces during bone movement, the convex condyloid component must roll in the direction of bony movement and glide in the opposite direction with respect to the concave component. Examples of condyloid joints include (a) the metacarpophalangeal joints of the fingers; (b) the knee joint, in which the distal femoral condyles articulate with the shallow, concave tibial plateaus; and (c) the atlanto‐occipital joint between the occipital condyles and the atlas. Ball and socket joints are distinguished by one bone with an ovoid or spherical convex surface that moves within a relatively deep concave surface. Ball and socket joints allow movement about all three axes and in all three planes of motion, flexion‐extension, abduction‐adduction, and internal‐external rotation. The coxofemoral (hip) and glenohumeral (shoulder) joints are examples of ball and socket joints. Lastly, pivot joints are characterized by one bone with a rounded process that moves within a sleeve or ring formed by the opposing bone. They permit rotation about a single axis and are, therefore, uniaxial joints. Examples include the proximal radioulnar and atlantoaxial joints.