What is Posterior Shoulder Instability?
Posterior shoulder instability, also known as posterior glenohumeral instability, is a condition in which the head of the humerus (upper arm bone) dislocates or subluxes posteriorly from the glenoid (socket portion of the shoulder) as a result of significant trauma. A partial dislocation is referred to as a subluxation whereas a complete separation is referred to as a dislocation.
Posterior shoulder instability occurs when considerable force is applied through the arm when the arm is extended in front of the body, rupturing the shoulder capsule, ligaments, and labrum.
Posterior shoulder instability is commonly noted in athletes involved in high contact or overhead sports, such as American football, baseball, weightlifting, rugby, gymnastics, and people involved in heavy bench pressing. Posterior shoulder instability is far less common than anterior shoulder instability and accounts for only about 5 per cent of all shoulder instabilities.
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 stabilising the shoulder joint. Tendons and ligaments around the shoulder joint provide additional strength and stability to the joint.
Causes of Posterior Shoulder Instability
Some of the causes and risk factors of posterior shoulder instability include:
- Fall on an outstretched hand
- Proximal humeral fractures, especially lesser tuberosity and/or anatomical humeral neck fracture
- Reverse Hill-Sachs fracture, an impaction fracture of the anteromedial humeral head
- Reverse osseous Bankart fracture, a fracture of the posteroinferior rim of the glenoid
- Developmental anomalies, such as glenoid dysplasia, glenoid hypoplasia, and posterior glenoid rim deficiency
- Bennett lesion, a condition characterised by calcification of the posterior band of the inferior glenohumeral ligament
Signs and Symptoms of Posterior Shoulder Instability
Some of the signs and symptoms associated with posterior shoulder instability include:
- Posterior shoulder pain with activity
- Pain with adduction, flexion, as well as internal rotation of the arm
- Posterior rotator cuff weakness
- Stiffness and decreased range of motion
- Numbness, tingling, or burning sensation
- Painful clicking or catching in movements
- Tenderness on palpation of the posterior joint line
- Swelling and bruising of the shoulder
- Visible deformity and loss of function of the shoulder
Diagnosis of Posterior Shoulder Instability
Posterior 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 shoulder area to check for points of tenderness and prompting shoulder motion to check for range of motion and strength. During examination, specific diagnostic tests such as Posterior Load and Shift Test; Posterior Drawer Test; the Jerk test; the Kim Test; and Posterior Apprehension/Stress Test may be ordered to assess the degree of posterior instability. In addition to routine X-ray exams such as AP and lateral views to check for bony abnormalities, your doctor may specifically order an axillary lateral view as it provides the most diagnostic information for a posterior subluxation or dislocation. CT scans and MRIs may also be ordered for a detailed evaluation of the bone quality and morphology and to detect any soft tissue lesions that may be contributing to posterior shoulder instability.
Treatment for Posterior Shoulder Instability
The treatment options for posterior shoulder instability involve both conservative as well as surgical treatment.
- Closed reduction: Following a dislocation, your surgeon can often externally manipulate the shoulder joint, usually under anaesthesia, realigning it into proper position.
- Medications: Over-the-counter pain medications and NSAIDs can help reduce the pain and swelling. Steroidal injections may also be administered to decrease swelling.
- Rest: Rest the injured shoulder and avoid activities that require overhead motion. A sling may be worn for 2 weeks to facilitate healing.
- Ice: Ice packs should be applied to the affected area for 20 minutes every hour.
When conservative treatment options fail to relieve shoulder instability, your surgeon may recommend shoulder stabilisation surgery. Posterior shoulder stabilization surgery is performed to improve the stability and function of the shoulder joint and prevent recurrent dislocations. It can be performed arthroscopically or through open surgery, depending on your condition.
Arthroscopy is a surgical procedure in which an arthroscope, a small flexible tube with a light and video camera at the end, is inserted into a joint to evaluate and treat the condition. It is a minimally invasive surgery and is performed through two tiny incisions (portals), about half-inch in length, made around the joint area. Through one of the incisions, an arthroscope is passed. The camera attached to the arthroscope displays the images of the inside of the joint on the television monitor, which allows your surgeon to carry out the required repair accordingly through tiny surgical instruments that are passed through the other incisions.
Open surgery is mostly required to correct severe instability. During this surgery, a large surgical cut is made on the shoulder and the muscles under it are moved apart to obtain access to the joint capsule, labrum, and ligaments. These soft tissue structures are then reattached, tightened, or repaired accordingly depending on the extent of tissue injury and closed with sutures.
The surgery is followed by rehabilitation to restore range of motion and strength of the shoulder joint.