The shoulder is one of the most complex parts of the human anatomy. Though basically nothing more than a ball and socket joint created by the intersection of the humerus (upper arm bone) and scapula (shoulder blade), evolution has transformed the human shoulder into an intricate fulcrum and lever that allows us to do everything from swing a baseball bat to paint a wall. This evolution, which began when mankind first stood on two legs, allows the shoulder to move in all planes and also rotate simultaneously. In the animal world, only primates share this amazing ability.



Four muscles hold the shoulder together and support these actions. Together they are called the rotator cuff. Additional muscles like the pectoralis, deltoids and trapezius surround the shoulder to provide additional strength, stability and motion. The shoulder joint itself contains a bursa, or fluid-filled sac that reduces friction between the moving parts. If not for the bursa, the shoulder would wear out before we were thirty!

Even then, stressful activities involving repetitive motion – like swimming, tennis, pitching, batting and weight lifting – can cause significant shoulder injuries, even among the young and fit. As we age, even simple tasks like painting, hanging curtains or gardening can cause problems. In 2003, approximately one in every twenty adults went to a doctor's office or a hospital emergency room for shoulder injuries ranging from a rotator cuff injury, which can cause permanent loss of range of motion, to a dislocated shoulder, which can become chronic.

Orthopedic surgeons, whose job it is to repair these injuries, use anatomical models to explain shoulder-related problems to their patients. One of the simplest yet best teaching models is the functional joint model, which shows both the anatomy and the mechanics of the shoulder. Life-sized and fully flexible, this model consists of the shoulder blade, the collar bone, the upper portion of the humerus and all attendant ligaments. It can be used to demonstrate the full range of motion of which the shoulder joint is capable, including abduction, adduction, anteversion and retroversion.

An even more detailed model, showing the upper humerus, clavicle and scapula also displays the musculature of the rotator cuff and the origin (red) and attachment points (blue) of the large shoulder muscles. The muscles - subscapularis, supraspinatus, infraspinatus and teres minor – can be detached for more detailed explanation, and, once detached, all the movements of the shoulder joint mentioned in the above paragraph can be fully demonstrated.

The most complex model has an exclusive, removable ligament system which allows physicians and surgeons to display each bone, ligament and cartilaginous structure of the shoulder. The ligaments, made of a durable, elastic polymer, provide years of trouble-free demonstration, and the entire model comes on a removable stand.

Being able to use anatomical models to demonstrate the amazing ability of the shoulder to move in 360 degrees of rotation through all planes of the body is a boon to orthopedists, physicians, surgeons, teaching professionals and sports medicine practitioners. The latter, in particular, will find these models an endless source of instruction, and caution, to their teams as players get larger, contact sports more dangerous, and the costs of injuries more unaffordable, both in terms of money and time lost.