Shoulder bones, motion

Poppen N.K. and Walker P.S. 1976. Normal and abnormal motion of the shoulder. /. Bone Joint Surg. 58A 195. 

Three-dimensional reconstructions of CT and MR images can delineate precisely the spatial relationship between bones and musculotendinous structures and produce a good 3D visual presentation of biodynamic events of human joints. Rotational motion of a shoulder, knee flexion, other complex musculoskeletal motions and muscle contraction (Fig. 24.15) can be assessed, as well as the effect of muscle dysfunction and its relevance to the mechanics of joints (Totterman et al. 1998). This method is of great interest because many biomechanical studies are based on dramatically simplified anatomic models. 

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, and skeletal muscles. The articular ligaments and tendons are the main parts holding together the joint(s). hr respect to the movement, there are freely moveable, partially moveable, and immovable joints. Synovial joints, the freely moveable ones, allow for a large range of motion and encompass wrists, knees, ankles, shoulders, and hips. 

The bones of the true shoulder joint are the head of the humerus and the scapula, specifically the glenoid fossa located on its lateral surface beneath the acromion. The clavicle plays a significant role in the motion of the shoulder and is, therefore, considered the third bone of the shoulder girdle. 

Figure 12 represents a human body model with 39 bodies and 45 degrees of freedom. The degrees of freedom are distributed as follows 3 at the neck, 2 at each collar bone, 3 at each shoulder, 2 at each elbow, 2 at each wrist, 1 for finger motion on each hand, 2 at the waist, 3 at each hip, 1 at each knee and 3 at each foot. In addition, there are 6 degrees of freedom of the base body, which is taken to be the hips. The 3, 2 and 1 degrees of freedom motions at the joints have been represented with spherical, universal and revolute joints, respectively. For convenience, the model used for computation used only revolute joints. Universal joints were represented as two perpendicular revolute joints and spherical joints as three mutually perpendicular revolute joints. 

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