Shoulder joint allows lifting, pushing and pulling by upper extremity. Strong ligaments, muscles and tendons support shoulder joint.
Skeletal System of Shoulder Joint
Shoulder Joint Includes Following Skeletal and Bones-
- Glenohumeral Joint.
- Acromio-Clavicular Joint.
Glenohumeral joint is formed by clavicle, scapula and humerus. Glenohumeral joint links humerus (bone of upper arm) and scapula. Glenohumeral joint is a ball and socket joint formed by humerus sitting on glenoid fossa of scapula. Smooth cartilages cover the surfaces of humerus and glenoid fossa. Most shoulder joint movements are around Glenohumeral joint.
A second joint of the shoulder is Acromio-Clavicular joint formed by the collar bone and acromion process of shoulder blade. Acromio-clavicular joint participates in circular rotation of shoulder joint.
3D Video of Shoulder Joint Anatomy: Glenohumeral, Acromio-Clavicular Joints
Cartilages of Shoulder Joint
Shoulder joint has cartilage, which covers glenoid socket. The cartilage is known as articular cartilage. Surface of cartilage is smooth that allows movements of humerus with least friction. The rim of the cartilage is known as labrum. Cartilage cushions glenoid socket and humerus. Labrum is shaped like a ring. Articulating cartilage creates a specific shape to accommodate semi ball shape head of humerus.
The Shoulder Labrum
Shoulder joint has a socket and a ball shaped head of humerus. Socket is circular in shape and rim of socket is made up of cartilage. The cartilaginous rim of the socket is known as shoulder labrum. Labrum provides a depth to shallow socket of shoulder joint thus providing stability. Tendons and ligaments are attached to labrum.
Shoulder Joint Capsule
Shoulder joint capsule encloses the ball and socket shoulder joint. Capsule surrounds and attaches to humerus, outer circumference of glomerular fossa or labrum, scapula and head of biceps. Capsule is made up of thin fibrous and areolar tissue. Joint capsule is strengthened by multiple ligaments and tendons of shoulder joint. Inner surface of capsule is covered by synovial membrane. Shoulder capsule supported by synovial membrane from inside and ligaments as well as tendons from outside maintains the appropriate tension to allow optimum shoulder joint movements. Loose capsule causes shoulder joint instability and tight capsule causes frozen shoulder.
Synovial membrane covers inside of the capsule. Synovial membrane secretes viscous fluid, which enables a smooth multi-directional movement with least friction.
Ligaments of Shoulder Joint
Ligament is a band of tough fibrous tissue. Ligaments connect and anchor the bones of shoulder joint. Tear or inflammation of ligament causes shoulder joint sprain.
- Coraco-humeral Ligament- This attaches the coracoid process of the scapula to the greater tubercle of the humerus.
- Glenohumeral Ligament- Three ligaments attaching the lesser tubercle of the humerus to lateral scapula-
- Superior Glenohumeral Ligament.
- Middle Glenohumeral Ligament.
- Inferior Glenohumeral Ligament.
- Semicircular humerus Ligament- 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.
- Coraco-acromial Ligament (CAL) - This Ligament anchors coracoid bone to acromion bone. Thickening or hypertrophy of the ligament causes Pinch Shoulder Syndrome.
- Transverse Humeral Ligament (THL) - This Ligament anchors or links long head of biceps to greater and lesser tubercle of humerus.
Muscles and Tendons of Shoulder Joint
Several muscles and tendon of these muscles support shoulder joint. Muscles end in tough fibrous tissue known as tendon. Tendon is thus attached to muscles at one end and bone at opposite end. Muscle contraction pulls the tendon and thus tendon pulls the bone of the joint where tendon is attached. The muscle contraction thus causes synchronized joint movement. Inflammation of tendon is known as tendonitis.
The List of Seven Muscles Supporting Shoulder Joint Is As Follows-
- Supraspinatous Muscle
- Infraspinatous Muscle
- Teres Minor Muscle
- Subscapularis Muscle
- Serratus anterior Muscle
- Subclavius Muscle
- Deltoid Muscle
Group of four muscles of the seven shoulder joint muscles are known as rotator cuff. Rotator cuff muscles hold head of humerus against glenoid fossa and prevent subluxation. Injury of any one of these muscle or tendon causes severe shoulder joint pain diagnosed as rotator cuff syndrome.
Rotator Cuff Is Formed By the Following Four Muscles and Its Tendon-
- Teres Minor
Shoulder Joint Bursa
Shoulder joint has several bursas between protecting ligaments and tendons. Bursa is situated between tendon and bone or ligament and bone or between tendon and ligament. Inflammation of bursa is known as bursitis. Most common bursitis observed is subacromial bursitis. Subacromial bursa is located between acromial bone and Coraco-acromial ligament.
Shoulder Joint Movements
Shoulder joint movement involves head of humerus rotating and sliding in smooth shallow glenoid fossa. Movement is known as ball and socket movements. Shallow glenoid fossa and loose capsule allows wide range of mobility. Coordinated shoulder joint movements in several directions helps to accomplish highest quality of sporting activities like baseball, football, tennis and basketball.
Following Are the Various Shoulder Joint Movements-
- Circular Movements or Arm Circumduction- Humerus rotates in the glenoid sockets in forward as well as backward spin accomplishing 360 degree rotation.
- Abduction- The upper arm is stretched outward from side of the body. The arm is in extension or flexed position at elbow joint.
- Adduction- Adduction brings the upper arm against the side of body. The arm is in extended or flexed position at elbow joint.
- Flexion- The upper arm is bent forward at shoulder joint, while arm is in extension or flexion at elbow joint.
- Extension- The upper arm is bent backward at shoulder joint, while arm is in extension or flexion at elbow joint.
- Internal Rotation- Internal rotation at shoulder joint is performed while arm is in extension or flexion at shoulder joint.