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What is Anterior Shoulder Instability?

Anterior shoulder instability, also known as anterior glenohumeral instability, is a condition in which damage to the soft tissues or bone causes the head of the humerus (upper arm bone) to dislocate or sublux from the glenoid fossa, compromising the function of the shoulder. It is caused by trauma or injury to the glenohumeral joint in which the upper arm bone is dislodged from its usual position in the middle of the glenoid fossa, and there is no longer joint articulation. Anterior shoulder instability accounts for 95 percent of all acute traumatic shoulder dislocations.

Anatomy of the Shoulder

The shoulder joint (glenohumeral joint) is a ball and socket joint. A ball at the top of the upper arm bone (the humerus) fits neatly into a socket, called the glenoid, which is part of the shoulder blade (scapula). The labrum is a ring of fibrous cartilage surrounding the glenoid, which helps in stabilizing the shoulder joint. Tendons and ligaments around the shoulder joint provide additional strength and stability to the joint. 

Causes of Anterior Shoulder Instability

Some of the causes and risk factors of anterior shoulder instability include:

  • Dead-arm syndrome, which is often noted in repetitive overhead sports such as baseball, swimming, volleyball, or tennis
  • Bankart lesions, an injury of the anterior glenoid labrum
  • Humeral avulsion of the glenohumeral ligament (HAGL), an injury to the ligaments that join the upper arm bone to the glenoid
  • Rotator cuff muscle weakness
  • Hill-Sachs defect, an injury to the cartilage and bone of the humeral head

Signs and Symptoms of Anterior Shoulder Instability

Some of the signs and symptoms of anterior shoulder instability include:

  • Persistent glenohumeral joint pain
  • Shoulder stiffness
  • A sensation of grinding or popping in the shoulder joint
  • Numbness, tingling, or burning sensation
  • Tenderness in the glenohumeral joint
  • Swelling and bruising of the shoulder
  • Visible deformity and loss of function of the shoulder

Diagnosis of Anterior Shoulder Instability

Anterior shoulder instability is diagnosed with a review of your symptoms, medical history, and a physical examination of the shoulder where your doctor will assess the extent of injury by palpating the area to check for points of tenderness and checking the range of motion and strength of the shoulder. During examination, specific tests such as load and shift test; apprehension, relocation, and anterior release tests; and anterior drawer test may be ordered to assess the degree of shoulder instability. Imaging studies such as X-rays may be ordered to obtain additional information about the potential causes of the instability and to rule out other causes of shoulder pain. Additionally, CT scans and MRIs may also be ordered for a detailed evaluation of the bones and soft tissues of the shoulder joint.