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Glenohumeral Joint - is responsible for the common/normal movements of the shoulder.
Bones: Scapula and humerus.
Cartilage: There is articular cartilage that is between the bones and a capsule that covers the connection. There are also several Bursae, which are fluid filled sacs that roll over the joint and lubricate it.
Ligaments: The glenohumeral ligaments stabilize the head of the humerus. The coroacohumeral ligament supports the cartilage capsule. The coracoacromial ligament connects two portions of the scapula (not connecting to the humerus) but stretches over it preventing displacement of the joint.
Muscles: Rotator cuff is a group of muscles that run along the front and back of the scapula and connect to the head of the humerus, they provide stability and allow the upper arm (humerus). The deltoid is the main muscle for frontal abduction of the arm (moving the arm up to the side of the body). The pectoralis major adducts the humerus horizontally towards the other shoulder (this is how a pushup mostly works). The latissimus dorsi abducts the humerus horizontally away from the the other should (in a backwards direction). Note that there are more muscles dealing with shoulder movement but these are the some of the major ones.
Joint type: Ball and socket.
Mechanics: Most all of the muscular attachments at this joint pull at the head of the humerus which mechanically produces a lot of power. When the head of the humerus is pulled to rotate slightly the other end of the humerus must rotate at the same time, but it travels a greater distance due to the length of the humerus and therefore has a greater speed. This becomes a main mechanic of swinging strikes like hammer fist or chop and especially elbow strikes.
Range of motion: Rotator cuff allows for rotation of the humerus close to 90 degrees towards and away from the body. When the deltoid contracts (abducting the arm away from the body, to the side) the scapula stays in place only for the first roughly 30 degrees of motion, the other roughly 90 degrees of the humerus the scapula must rotate to compensate for the movement, this motion is stabilized by the trapizoid and the serratus anterior. Note that this joint alone can not pull the humerus above the head. The pectoralis major is able to pull the humerus horizontally towards other other shoulder (from being in line with the body) at about 120 degrees. The latissimus dorsi is able to pull the humerus backwards at about 70 degrees.
Injury: The shoulder is the most mobile joint in the body and therefore is the most unstable and likely to be dislocated and is the most common dislocation.
Manipulation: This joint is highly mobile and hard to be singled out but most maneuvers that lock up the arm can then then be followed up with enough force to the shoulder to dislocate it. A bursting maneuver, simultaneously blocking and striking, an outside attack; blocking at the forearm and striking with the heel of the hand to the should will also likely dislocate it and at the least off kilter's their momentum and causes impact stress to the joint.
For information on additional joints please refer back to the Joints page.
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