Anterior Glenohumeral Instability - Pathophysiology, and Management

Introduction

One of the most complex and largest joints in the body, due to its wide range of motion, is the glenohumeral joint, which is surrounded by various ligaments and muscles which provide stability. Shoulder movement is possible mainly due to the coordinated articulation of four joints, which constitute the shoulder girdle, namely; the glenohumeral joint, sternoclavicular joint, acromioclavicular joint, and scapulothoracic joints. The glenohumeral joint (shoulder joint) is a ball and socket joint that includes the humeral head (top portion of the bone of the upper arm) which articulates in the glenoid fossa of the scapula (shoulder blade). The glenoid fossa is a shallow and narrow cavity that offers minimal support to the humeral head; thereby, the joint's stability is contributed by the integrity of the soft tissues and rotator cuff muscles, and the glenoid labrum.

What Is Anterior Glenohumeral Instability?

A condition in which the humeral head dislocates or sub lux` from its socket or the glenoid fossa due to soft tissue damage or a bony insult leading to instability and loss of function is anterior glenohumeral instability. It is mainly seen in males than females, affecting primarily young and active individuals like athletes and sportspersons. It is the most common joint in the body to be dislocated and may be associated with neurological involvement. Anterior glenohumeral instability contributes to the majority of acute shoulder injuries.

What Are the Types of Shoulder Instability?

Shoulder instability can occur due to various reasons:

• Dislocation: A complete loss of humeral head articulation in the glenoid fossa due to acute trauma, which pushes the humeral head out of the glenoid fossa. The joint capsule, ligaments, and labrum are torn, stretched, or detached from the bone.

• Subluxation: A partial loss of articulation of the humeral head and is symptomatic and involves damage to the supporting soft tissues, mainly caused due to repeated trauma.

• Laxity: A partial loss of glenohumeral articulation, but the patient is asymptomatic, is termed as laxity, which may also be caused by repeated injuries.

• Labral Tear: Tearing or peeling away of the labrum from the glenoid, usually due to trauma or repeated trauma, can also result in shoulder instability.

Shoulder injuries are of three types:

• Anterior Instability: It is the common type of glenohumeral instability, also known as Dead arm syndrome; it occurs in young individuals below 25 years of age; it is caused due to severe trauma, sports injuries, or due to overuse of muscles leading to dislocation or subluxation. Anterior dislocations occur when the shoulder is in the abduction and external rotation, which is the classic position for instability. It may also be associated with muscle tears and nerve injuries, resulting in numbness or tingling sensation.

• Posterior Instability: It is associated with trauma but may also occur as a result of electric shock or seizures, characterized by loss of external rotation. It can also be caused due to muscle weakness, which results from repeated trauma or muscle overuse. A subluxation can occur when the arm is forwardly flexed, adducted, and internally rotated.

• Multidirectional Instability: It is seen in individuals with congenital generalized hyperlaxity of joints and muscle weakness or can also occur due to overuse of muscles or injury to the rotator cuff muscles, which cause subluxation.

What Are the Causes of Anterior Glenohumeral Instability?

Anterior glenohumeral instability is seen in young males around the age of 16 to 20 years and in elderly individuals around the age of 60 to 70 years. Some of the causes include:

• Severe injuries due to vehicle accidents, military injuries, and sports injuries are seen in overhead sports like volleyball, baseball, tennis, polo, swimming, etc.

• Weakness or fractures in the surrounding ligaments or joint capsule or rotator cuff muscles.

• Repeated subluxations or injuries, or overuse of the muscles, lead to damage of the connective tissue, glenoid labrum, and scapula, called the Bankart lesion. Damage to the head of the humerus bone due to trauma called Hill Sachs lesion.

• Congenital absence of glenoid or deformities of the humerus bone or generalized laxity of the joints.

• Shoulder instability can also be associated with Ehlers-Danlos syndrome, Marfan syndrome, collagen disorders, etc.

What Are the Signs and Symptoms of Anterior Glenohumeral Instability?

Signs and symptoms are

• Soft tissue injuries, skin abrasions, and bleeding in case of acute trauma.

• Severe shoulder pain increases physical activity.

• Tenderness of the area on palpation.

• Restricted movement and stiffness of the shoulder.

• Presence of swelling and bruises.

• Tingling or burning sensation, or numbness in case of severe injuries

• Sensation or episodes of giving way or instability during certain shoulder movements like reaching the back or above the shoulder height.

• Popping or grinding sound on joint movement.

How Is Anterior Glenohumeral Instability Diagnosed?

A complete history of the patient is taken, followed by a physical examination to determine the range of motion and strength of the joint. Shoulder stability tests are performed, such as

Load and Shift Test: The patient is asked to lie in a supine position with the shoulder relaxed. The examiner then places both hands around the patient's upper arm, loads the humeral head against the glenoid fossa, and shifts the humeral head anteriorly and posteriorly. If the shift is between 25 to 50 percent, it is a grade I, more than 50 percent with spontaneous reduction is a grade II, and more than 50 percent shift without spontaneous reduction is gradeIII instability.

Apprehension Test: The patient is asked to sit, and the examiner applies abduction and external rotation stress on the joint; the test is positive if the patient shows apprehension by fearing that the shoulder will slip out of place.

Sulcus Sign Test: The patient is asked to sit, and the examiner applies caudal traction to displace the humerus bone inferiorly; the presence of inferior displacement shows sulcus sign positive and confirms multidirectional instability.

Radiological investigations include

• X-Ray: It is recommended to rule out fractures with an anterior-posterior view with both internal and external rotation. The axillary view is recommended as it shows the position of the humeral head in the glenoid fossa, and also the Westpoint view, which gives a view of the glenoid rim.

• Computed Tomography (CT Scan): It helps evaluate bone abnormalities and bone loss and is recommended for patients who cannot undergo an MRI Scan.

• Magnetic Resonance Imaging (MRI): To determine soft tissue injuries like a labral tear and bone loss and advised in cases of chronic subluxations, as it provides the view of all the shoulder structures.

• MR Arthrogram: It is more advanced than MRI scans and increases the sensitivity and specificity for detecting soft tissue injuries.

How Can Anterior Glenohumeral Instability Be Managed?

Anterior glenohumeral instability can be managed by nonoperative and operative methods.

Nonoperative methods include

• Analgesics like nonsteroidal anti-inflammatory drugs or steroidal injections can be administered to relieve pain and swelling. Resting the injured shoulder by avoiding physical activities.

• Acute reduction and immobilization, followed by physical therapy. Meperidine or benzodiazepines are given before facilitating reduction. Modified Kocher or Stimson method is performed, following which the arm is mobilized for two to six weeks.

Shoulder stabilization surgery is performed to improve the strength and stability of the joint, restore function, and prevent recurrent subluxations. Operative methods include:

• Arthroscopic surgery is recommended in cases of first-time injury causing dislocation, less than 20 to 25 percent bone loss, and in cases of patients less than 25 years of age to prevent recurrence and arthritis. Incisions are made, about half an inch in length, and an arthroscopic device is inserted, the repair is done, and the structures are reattached, followed by rehabilitation.

• Open Bankart repair is indicated in cases of failure of arthroscopic surgery or in severe cases of instability. An incision is made by the anterior shoulder approach, and the capsule and ligaments are exposed. Repair is then done, and the structures are reattached and sutured with simple sutures or metal or absorbable plastic anchors, which remain permanently and stabilize the joint. Surgery is followed by immobilization with the cast for four to six weeks and rest.

• Surgery is followed by physical therapy and rehabilitation by a range of motion exercises to strengthen the muscles and stabilize the joint.

What Are the Complications of Anterior Glenohumeral Instability?

Some of the major complications include

• Permanent damage to the nerves and blood vessels.

• Recurrence of complete or partial dislocation.

• Inflammation of the shoulder joints.

• The stiffness of the shoulder may hamper daily activities.

Conclusion

Anterior glenohumeral instability is a condition in which the humeral head is dislocated from the glenoid fossa, resulting in severe pain and stiffness of the shoulder joint. It is mainly associated with trauma or sports injuries, and neurological involvement can cause loss of sensation. It is treated by closed reduction and immobilization, and severe dislocations are managed by surgical management and rehabilitation.