Interaction between the joints in the shoulder mechanism: the function of the costoclavicular, conoid and trapezoid ligaments.

By developing a measurement method based on the palpation of bony landmarks, the three-dimensional positions of the scapula and clavicle can be measured at several angles of humerus elevation. An analysis of these measurements shows the interaction between all joints of the shoulder mechanism. With the help of a biomechanical shoulder model the role of some of the extracapsular ligaments in the motion pattern of scapula and clavicle can be derived. In addition, the interaction between the rotations in the acromioclavicular and sternoclavicular joints is shown, and the possible implications for the treatment of joint problems in the shoulder are discussed.