![]() ![]() The third type of action, rolling, may also occur at the glenohumeral joint. In this circumstance, the contact point on the glenoid is moving, while that for the humerus remains the same. At the extremes of motion, and certainly in unstable joints, glenohumeral translations occur. Sliding is pure translation of the humeral head on the articular surface of the glenoid. Spinning occurs when the contact point on the glenoid remains the same while the humeral head contact point is changing. The three motions that best describe shoulder function are spinning, sliding, and rolling. In the glenohumeral joint, as in all diarthrodial joints, six degrees of freedom are present, three translational and three rotational. Arm abduction has an arc of motion of approximately 0–180°, flexion and extension is approximately 180°, and internal and external rotation is approximately 150°. Shoulder motion can be broken down into three planes of motion: abduction and adduction in the coronal plane, flexion and extension in the sagittal plane, and rotation about the long axis of the humerus. ![]() The sternoclavicular and acromioclavicular joints move at the extremes of motion. Abduction in the scapular plane is created by both joints in a movement termed “scapulohumeral rhythm.” Shoulder abduction in the scapular plane is described in a 2:1 ratio between glenohumeral and scapulothoracic motion, with some variation in the first 30° of abduction (Fig. Shoulder motion is comprised of many joints, primarily the glenohumeral and scapulothoracic joints. ![]() This is provided by the intricate and complex coordinated interplay of the active and passive stabilizers of the shoulder. This unique function is essential at the shoulder to enable the hand to be placed in the multitude of positions required in everyday life. The shoulder provides the greatest range of motion of any joint in the body, but the trade-off is the propensity for instability. ![]()
0 Comments
Leave a Reply. |