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Anterior & Posterior Shoulder Instability – Causes, symptoms, and treatment

The shoulder joint, called the glenohumeral joint, has a ball and socket joint mechanism. The upper arm bone, known as the humerus, has a ball-shaped bone at the top that fits into a socket called the glenoid, which is attached to the shoulder blade (scapula). The labrum provides stability to the shoulder joint by surrounding the glenoid with fibrous cartilage. The shoulder joint is strengthened and stabilised by the tendons and ligaments surrounding it.

The shoulder is the most mobile joint in your body, which makes it prone to various shoulder problems, and shoulder instability is one of them. It is classified as follows:

Anterior Shoulder Instability

Anterior shoulder instability (anterior glenohumeral instability) occurs due to injury to soft tissues or bones of the humeral head (upper arm bone). It happens when the humeral head is displaced from its natural position in the middle of the glenoid cavity due to trauma or injury and when the joint ceases to articulate. This impairs shoulder function and may lead to anterior shoulder dislocation or subluxation from the glenoid fossa.

A majority of acute traumatic shoulder dislocations occur because of anterior shoulder instability.

What is Posterior Shoulder Instability?

Posterior shoulder instability (posterior glenohumeral instability) occurs due to trauma in which the humerus head is dislocated or subluxated posteriorly from the glenoid socket. A subluxation means partial dislocation, and complete separation is called a dislocation.

Posterior shoulder instability develops due to the rupture of the shoulder capsule, ligaments, and labrum when a significant amount of force is applied through the arm while extending it in front of the body. 

Posterior shoulder instability is more common in athletes who play sports like football, baseball, badminton, gymnastics, and people who lift heavy weights, perform repetitive overhead actions, etc. About 5% of all shoulder injuries are caused by posterior shoulder instability, which is much less common than anterior shoulder instability.

Causes of Anterior Shoulder Instability

Anterior shoulder instability has several causes and risk factors, including:

  • Bankart lesions
  • Humeral avulsion of the glenohumeral ligament (HAGL)
  • Weak rotator cuff muscles
  • Hill-Sachs defect 

Anterior Shoulder Instability Signs and Symptoms 

The following signs and symptoms characterise anterior shoulder instability:

  • Persistent joint pain
  • Stiffness in the shoulder 
  • A grinding sensation 
  • A feeling that your shoulder joint is popping out
  • Numbness, tingling, or burning sensations
  • Tenderness in the humeral joint
  • Swelling and bruising of the joint
  • Loss of shoulder functions
  • Visible deformity 

Causes of Posterior Shoulder Instability

Posterior shoulder instability has several causes and risk factors, including:

  • Proximal humeral fractures
  • Reverse Hill-Sachs fracture
  • Reverse osseous Bankart fracture
  • Falling on an outstretched arm
  • Seizures
  • Electrocution
  • Developmental disorders like glenoid dysplasia or hypoplasia and deficiency of posterior glenoid
  • Bennett lesion 

Signs and Symptoms of Posterior Shoulder Instability

The following signs and symptoms characterise posterior shoulder instability:

  • While performing activities, you may experience pain in the posterior shoulder
  • There is pain in the arm when it is adducted, flexed, and rotated internally
  • Weakness in the rotator cuff 
  • Shoulder stiffness
  • Reduced range of motion
  • Numbness, tingling, or burning sensations
  • Movements that are painful or catchy
  • A tender feeling can be felt when palpating the posterior joint line
  • Shoulder swelling and bruising 
  • Loss of shoulder functions
  • Visible deformity

Treatment for Shoulder Instability

Both conservative and surgical treatment options are available for shoulder instability.

Conservative Treatment

Closed reduction: when the shoulder is dislocated, external manipulation of the shoulder joint is often performed under anaesthesia to realign the joint properly. Depending on the severity of the dislocation, surgical intervention may be performed to restore the normal functions of the shoulder.

Medications: Pain and swelling can be managed with OTC pain medications and NSAIDs. In some cases, steroid injections may be injected directly into the joint to reduce swelling.

Rest: Avoid overhead motions and rest the damaged shoulder. It is recommended to wear a sling for at least two weeks to aid in the healing process.

Ice: An ice pack should be applied every hour for 15 – 20 minutes to the affected area. It helps in the reduction of swelling and pain.

Surgical Treatment

Should conservative treatment options not successfully relieve shoulder instability, you may be recommended shoulder stabilisation surgery. A shoulder stabilisation procedure improves the function and stability of the joint and prevents recurrent dislocations. Based on your condition, arthroscopic surgery or open surgery may be performed.

Arthroscopy: It is a minimally invasive surgical procedure in which a small incision is made, and an arthroscope, a flexible, light- and video-equipped tube, is inserted into the damaged shoulder joint to diagnose, treat, and evaluate the condition. This surgery requires making two tiny incisions (about half-inch) around the joint area. An arthroscope is passed through one of the incisions and some surgical tools through the other incision. 

By sending the camera-headed arthroscopy through the incisions, your surgeon can view the inside of the joint and perform necessary repairs. 

Open surgery: Most often, it is performed to treat severe instability. During the operation, a large incision is made on the damaged shoulder, and the muscles are shifted aside to access internal parts like the joint capsule, labrum, and ligaments. Depending on the extent of tissue injury, these structures will be reattached, tightened, or repaired and sutured.

Following surgery, a rehabilitation program is necessary to strengthen and regain the range of motion in the shoulder joint.

If you’re having any shoulder problems, Dr Chandra Sekhar and his staff of shoulder experts can help you out with treating various shoulder problems, including severe shoulder instability. For more information about treatment, please call +91 99595 88389.

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