Name = PAGENAME
Latin = articulatio humeri
GraySubject = 81
GrayPage = 313
Caption = Diagram of the human shoulder joint
Caption2 = Capsule of shoulder-joint (distended). Anterior aspect.
Width = 300
DorlandsPre = a_64
DorlandsSuf = 12161240
human anatomy, the shoulder joint comprises the part of the body where the humerusattaches to the scapula. [EMedicineDictionary|Shoulder+joint] The shoulder refers to the group of structures in the region of the joint. [EMedicineDictionary|Shoulder]
It is made up of three bones: the
clavicle(collarbone), the scapula(shoulder blade), and the humerus(upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The shoulder must be flexible for the wide range of motion required in the arms and hands and also strong enough to allow for actions such as lifting, pushing and pulling. The compromise between these two functions results in a large number of shoulder problemsnot faced by other joints such as the hip.
Joints of the shoulder
There are three
joints of the shoulder: The glenohumeral, acromioclavicular, and the sternoclavicularjoints.
glenohumeral jointis the main joint of the shoulder and the generic term "shoulder joint" usually refers to it. It is a ball and socket jointthat allows the arm to rotate in a circular fashion or to hinge out and up away from the body. It is formed by the articulation between the head of the humerus and the lateral scapula. The "ball" of the joint is the rounded, medial anterior surface of the humerus and the "socket" is formed by the glenoid fossa, the dish-shaped portion of the lateral scapula. The shallowness of the fossa and relatively loose connections between the shoulder and the rest of the body allows the arm to have tremendous mobility, at the expense of being much easier to dislocate than most other joints in the body.
The capsule is a soft tissue envelope that encircles the glenohumeral joint and attaches to the
scapula, humerus, and head of the biceps. It is lined by a thin, smooth synovial membrane. This capsule is strengthened by the coracohumeral ligament which attaches the coracoid process of the scapula to the greater tubercle of the humerus. There are also three other ligaments attaching the lesser tubercle of the humerus to lateral scapula and are collectively called the glenohumeral ligaments.
There is also a
ligamentcalled semicirculare humeri which is a transversal band between the posterior sides of the tuberculum minus and majus of the humerus. This band is one of the most important strengthening ligaments of the joint capsule.
The acromioclavicular (AC) joint is located between the
acromionprocess of the scapula (part of the scapula that forms the highest point of the shoulder) and the distal end of the clavicle.
The capsule of this joint is reinforced by the coracoclavicular ligament between the scapula and clavicle at the point of articulation. The coracoclavicular ligament in further detail is created by the conoid ligament, medial from the coracoid process of the scapula and inserts on the conoid tubercle of the clavicle. Lateral to the conoid ligament is the trapezoid ligament, which runs from the coracoid process of the scapula to the trapezoid line of the clavicle. One more ligament, the coracoacromial ligament, running from the coracoid process to the acromion of the scapula contributes to the integrity of the acromioclavicular joint.
The sternoclavicular occurs at the medial end of the clavicle with the
manubriumor top most portion of the sternum. The clavicle is triangular and rounded and the manubrium is convex the two bones articulate. The joint consists of a tight capsule and complete intra-articular disc which ensures stability of the joint. The costoclavicular ligament is the main limitation to movement, therefore, the main stabiliser of the joint. A fibrocartilaginous disc present at the joint increases the range of movement. Sternoclavicular subluxation is rare, however can be caused by direct trauma.
Movements of the shoulder
The muscles and joints of the shoulder allow it to move through a remarkable
range of motion, making it the most mobile joint in the human body. The shoulder can abduct, adduct (such as during the shoulder fly), rotate, be raised in front of and behind the torsoand move through a full 360° in the sagittal plane. This tremendous range of motion also makes the shoulder extremely unstable, far more prone to dislocation and injury than other joints.
The muscles that are responsible for movement in the shoulder attach to the scapula, humerus, and clavicle. The muscles that surround the shoulder form the shoulder cap and
rotator cuffis a structure composed of tendons that, with associated muscles (supraspinatus, infraspinatus, teres minor and subscapularis), holds the ball at the top of the humerus in the glenoid socket and provideoulder joint. The tendons of the rotator cuff muscles also connect to the capsule of the glenohumeral joint.
Two filmy sac-like structures called bursae permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.
Measurement of shoulder loads
For understanding normal and pathologic shoulder function knowledge of forces in the glenohumeral joint is essential. It forms the basis for performing fracture treatment or joint replacement surgery, for optimizing implant design and fixation and for improving and verifying analytical biomechanical models of the shoulder. With instrumented shoulder implants developed at the "Julius Wolff Institut" (Charité Berlin) the joint contact forces and moments can be measured in vivo [In vivo measurements of shoulder load with instrumented shoulder implants, [http://jwi.charite.de/en/research/instrumented_implants/shoulder_joint/ Julius Wolff Institut] , Charité - Universitätsmedizin Berlin] during different activities.
Rotator cuff tear
Chip on shoulder
* [http://chrisevans3d.com/research.htm Video of the shoulder carriage in motion]
* [http://www.niams.nih.gov/hi/topics/shoulderprobs/shoulderqa.htm NIH (article includes text from this source)]
* [http://surgery-sugery.com/Arhtroscopic-Shoulder-Surgery.php Video of shoulder surgery, showing interior anatomy of shoulder]
Wikimedia Foundation. 2010.