At Slocum Center for Orthopedics & Sports Medicine, our shoulder specialists are experts in understanding how our shoulders function and operate. This is also referred to as shoulder physiology. The Slocum Center has been caring for shoulder injuries and conditions for more than four decades. For this reason, you know that your shoulder condition is in good hands—our shoulder team provides the highest level of care that's virtually unmatched in Eugene, the surrounding areas of Oregon, and throughout the Northwest.
The shoulder, a ball-and-socket joint, is made up of three bones: the upper arm bone (humerus), shoulder blade (scapula) and collarbone (clavicle). It has four "joints:" the sternoclavicular joint (SC joint), the acromioclavicular joint (AC joint), the glenohumerral joint (shoulder) and the articulation between the scapula and ribs.
The ball at the top end of the arm bone fits into the small socket (glenoid) of the shoulder blade forming the shoulder joint (glenohumeral joint). The socket of the glenoid is surrounded by a soft-tissue rim (labrum). A smooth, durable surface (articular cartilage) on the head of the arm bone and a thin inner lining (synovium) of the joint allow the smooth motion of the shoulder joint. The glenoid is small relative to the humeral head; much like a golf ball on a tee, giving the shoulder joint very limited inherent stability. The shoulder depends on soft tissues to keep it stable. These tissues are the ligaments and tendons including the rotator cuff.
The upper part of the shoulder blade (acromion) projects over the shoulder joint. One end of the collarbone (clavical) is joined with the shoulder blade by the acromioclavicular (AC) joint; the other end of the collarbone is joined with the breastbone (sternum) by the sternoclavicular joint.
The joint capsule allows the shoulder a wide range of motion while providing stability. The rotator cuff attaches the upper arm to the shoulder blade, covering the shoulder joint and joint capsule. The muscles attached to the rotator cuff enable individuals to lift the arm, reach overhead, and take part in activities such as throwing or swimming.