Shoulder Joint or Glenohumeral Joint: Structure, Function, Movements, Muscles

Shoulder joint is a ball and socket joint also known as ‘Glenohumeral Joint”. The joint is formed by three skeletal bones and supported by several ligament and muscles. Synovial membrane covers the inner surface of the joint. Acromio-clavicular joint between lateral (outer) end of clavicle and acromion bone of scapula is also considered as a subsection of shoulder joint.

The proximal end (near shoulder joint) of the humerus is identified as head of the humerus, which is shaped like a ball known as head of humerus. Head of the humerus is larger in size than socket of the shoulder joint. The head rests over the socket known as glenoid. The contact between the bones is stabilized by a capsular rim consisting of thick band of fibrous tissue known as labrum. Rim enlarges the area of socket to accommodate the head of humerus. Rim also allows the strong band of outer surface for the ligaments to anchor to form a rotator cuff.

Shoulder joint is formed by following three bones:

• Clavicle or Collarbone
• Scapula or Shoulder Blade
• Humerus or Upper Arm Bone

Shoulder joint allows the most efficient use of upper extremities in almost all direction.

Shoulder Joint allows following movements of upper extremity-

• Flexion
• Extension
• Lateral Rotation- Upper arm is turned outward at shoulder joint.
• Medial Rotation- Upper arm is turned inward at shoulder joint.
• Abduction- Arm is stretched away from the body and placed against the head.
• Adduction- Arm is at rest position against side of the body
• Circular rotation of upper extremity
• Scapular elevation
• Scapular depression

The proximal end of the humerus near shoulder joint is shaped like a bony round ball attached to the shaft of the humerus. Ball like structure of the humerus fits in the socket of the scapula. Hollow socket is also known as “Glenoid”. Socket is the outermost part of the scapula. The shoulder joint is supported by a rotator cuff.

Movement of shoulder joint is extremely proficient. The upper extremity has a wide range of movements anchored around shoulder joint. An efficient movement of upper arm in various directions allows athletes to participate in various sports. Outstretched arm can protect body from injury during accidental fall or emergency situation. Joint efficiency is depended on least resistant rotating movements of head of humerus within stationary smooth least resistance sockets of scapula. Arm movement is further facilitated by the ability of the scapula itself to slide along the rib cage.

Shoulder joint is supported by joint capsule made up of ligaments, tendon, bursa and muscles.

Ligaments are band of tough fibrous tissue that links and anchors ends or sides of the bones to maintain the link and stability of the joint.

Following are the ligaments associated with shoulder joint-

Coracoacromion Ligaments– links coracoid bone to acromion bone.

Glenohumeral Ligaments (GHL)– forms the joint capsule, surrounds the joint from all sides. GHL is composed of group of ligaments that anchors the humerus to glenoid. GHL is the main capsule that encloses head of humerus in socket of scapula. GHL is made up of three ligaments called superior GHL, Middle GHL and Inferior GHL.

Coraco-Clavicular Ligament– Ligament is small and strong, and helps to anchor scapula to lateral (outer) end of clavicle.

Transverse Humeral Ligament- Ligament holds the tendons of the long head of biceps to the humerus.

Tendons are the thick bundle of tough fibrous tissue like ligaments. Tendons are located between end of muscle mass and bone. Tendon is continuation of muscle fibers as fibrous bundle, which anchors muscle to the bone

List of tendons associated with shoulder joint are as follows-

• Supraspinatus Tendon
• Subscapulais Tendon
• Infraspinous Tendon
• Teres Minor tendon
• Long Head of Biceps

Serratus anterior, subclavius, pectoralis minor, sternocleidomastoid, rhomboid major, rhomboid minor, trapezius and deltoid muscles are the muscles that support shoulder joint.

Head of humerus and socket of scapula (Glenoid) held together by thick fibrous joint capsule. The capsule is reinforced and supported by muscles and tendons spread around the rim of the joint. The group of muscles and tendon supporting the shoulder joint is known as rotator cuff.

Shoulder joint has two cartilages covering head of humerus and glenoid cavity (socket) of scapula. Surface of cartilage is smooth and allows glide and movements in all the directions.

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• Shoulder Injuries From Lifting Weights
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