What is Shoulder Subluxation?
A shoulder subluxation is a partial or incomplete dislocation of the shoulder joint. In this condition, the upper arm bone (humeral head) moves slightly out of its socket (glenoid fossa), but still touches it. This usually happens due to weakness in the rotator cuff muscles (muscles that keep your shoulder joint stable) or looseness of the shoulder ligaments (tissues that connect bones). When this happens, the upper arm bone can easily slip out of its socket, causing the shoulder to partially dislocate.
What Causes Shoulder Subluxation?
The reasons for shoulder dislocations can be categorized into three types: those caused by trauma, those that are not caused by trauma, and those that are due to problems with the muscles or nerves. People who are active, like young people or boxers, are more likely to experience dislocations caused by trauma. However, even non-contact sports that involve a lot of shoulder movements, like throwing, can also cause the shoulder to dislocate.
For the non-traumatic type, there could be several factors. The patient might have poor control of their shoulder muscles or they may have damage to the tendons or ligaments that help keep the shoulder in place.
There are two types of shoulder instability which can be defined as TUBS syndrome and AMBRI syndrome. TUBS syndrome relates to traumatic injuries resulting in shoulder dislocations on one side which frequently need surgery to fix. On the other hand, AMBRI syndrome describes atraumatic, multidirectional, and bilateral shoulder dislocations, usually treated with physiotherapy and sometimes requiring a certain kind of surgery.
Diseases affecting the muscles and nerves, such as stroke, cerebral palsy, and brachial plexus injury (a nerve injury in your shoulder), can also cause shoulder dislocations.
Risk Factors and Frequency for Shoulder Subluxation
There aren’t many studies that examine shoulder subluxation, which is when your shoulder slips out of place. Most of the research concentrates on shoulder dislocations, where the shoulder comes out of the socket completely.
A study of athletes in U.S. military academies found that most sports-related shoulder issues (84.6%) were subluxations, with only 15.4% being dislocations. Among those who experienced subluxation, about half were having the issue for the first time, while the rest had recurrent subluxations.
In cases of shoulder subluxation not caused by injury or trauma, it was reported in a study from Japan that this issue affected 3.9% of people with shoulder disabilities. Also, irrespective of the cause, younger people are at a higher risk of shoulder dislocation.
It’s also important to note that shoulder subluxation is a common problem among stroke patients; with reports indicating that anywhere from 17% to 81% of stroke patients have experienced this issue.
Signs and Symptoms of Shoulder Subluxation
Patients experiencing shoulder instability often have symptoms like stiffness, slight pain, and feeling of unsteadiness in the shoulder. Other factors to consider include prior dislocations, how the shoulder was moving during any injury, and whether there’s a family history of shoulder instability.
When it comes to stroke patients who can’t move one side of their body (hemiplegia), pain and shoulder dislocation can occur at the same time, but they aren’t always related. Also, after a shoulder dislocation, some patients can’t move the affected shoulder as much as they used to.
A physical examination is performed to detect any subluxation, or partial dislocation, of the shoulder. This is done by feeling the joint between the shoulder and arm (the glenohumeral joint). Measuring the distance from the shoulder blade to the upper arm bone using fingers, a caliper, or a tape can indicate the severity of the subluxation. It’s crucial to compare this with the other shoulder to make a correct diagnosis. The shape of the shoulders, movement range, and tests for motor and sensory function can help identify the reason for shoulder subluxation.
Different tests like the load and shift, drawer, sulcus, hyperabduction, and push-and-pull tests can help check the looseness of the shoulder. The apprehension and relocation test is specifically for examining instability in the front part of the shoulder.
For stroke patients who have both shoulder dislocation and pain, a physical examination can help identify if the pain is due to strained muscles/tendons in the rotator cuff, inflammation in the joint at the top of the shoulder, or pinching of the space above the shoulder joint.
Testing for Shoulder Subluxation
If you’ve suffered a traumatic shoulder subluxation, or partial dislocation, your doctor will likely order a few x-rays from different angles to assess the damage to both your shoulder and surrounding areas. They might also use a diagnostic ultrasound or MRI to get a more detailed look at any soft tissue injuries, such as a torn labrum, which is a type of cartilage in your shoulder. For more severe cases, such as a full dislocation, a CT scan is commonly used to check for fractures that may not be clearly seen in an x-ray, or to get a close look at any confirmed fractures.
For non-traumatic shoulder subluxations, x-rays can be used to look at how the ball of the upper arm bone, or humerus, has shifted in relation to the socket, or glenoid. This can help find any bone abnormalities that could be causing shoulder instability. While, in most cases, other tests like stress x-rays, arthrography (an x-ray of a joint after injection of a contrast medium), MRI or arthroscopy (a minimally invasive surgical procedure) aren’t required unless a specific underlying issue is suspected.
For a hemiplegic shoulder subluxation, which is a common in stroke patients who lose muscle control in the upper arm, x-rays can be used to monitor the effectiveness of treatment or to check if the partial dislocation is progressing over time. However, a simple physical exam of the shoulder can also accurately assess the subluxication. It’s also good to remember that unnecessary x-rays should be avoided. Additionally, an ultrasound can help figure out the causes of shoulder pain with subluxation, such as tendinosis (the inflammation of a tendon) in the bicep or supraspinatus muscles in the shoulder, and impingement, which is when the rotator cuff rubs on the shoulder blade.
Treatment Options for Shoulder Subluxation
If you have a traumatic shoulder subluxation, which is a partial dislocation of your shoulder, immediate treatments typically include applying ice to reduce swelling, avoiding certain positions that could lead to another subluxation, and wearing an arm sling to protect the shoulder. Doctors might prescribe painkillers or anti-inflammatory drugs to manage the pain. They will also recommend starting range of motion exercises for the upper arm and shoulder as soon as possible, as well as exercises to strengthen the muscles in the shoulder and improve your control of shoulder movements.
For those with atraumatic shoulder subluxation, where the shoulder partially dislocates without injury, the focus of treatment is to regain function in the shoulder. This involves strengthening exercises for the rotator cuff, deltoid, and the muscles that give stability to the shoulder. Modifying your usual activities to accommodate for the shoulder condition is also suggested.
In patients who have had a stroke and experience a partial dislocation of the shoulder, treatments like functional electrical stimulation can be effective in reducing the subluxation if used in the early stages. Special shoulder supports or orthoses are also used to reduce the subluxation. Properly supporting the affected limb is crucial in preventing further subluxation in these patients. Pain management treatments can involve cooling the area, sound wave therapy, electrical stimulation, or applying moist heat.
Surgery might be considered for young or active individuals with recurring shoulder subluxations. This option is usually considered if non-surgical treatments have not worked. Surgery might also be necessary if the dislocation is irreducible, if the shoulder is unstable after the dislocation has been corrected, or if there is significant damage to the structures of the shoulder. Open surgery or arthroscopic surgery, which is less invasive and involves smaller incisions, can be used depending on the specific condition of the shoulder.
In comparing the two types of surgery, arthroscopic surgery is just as effective as open surgery in improving shoulder stability, and it usually involves a shorter operation time and hospital stay, fewer complications, less cost, and smaller scars. However, the success of arthroscopic surgery heavily relies on the surgeon’s experience and whether or not there is a bony defect in the shoulder.
What else can Shoulder Subluxation be?
When a patient has their shoulder slightly dislocated, or “subluxed,” doctors will often check for certain other conditions that can cause similar symptoms. These conditions can include:
- Bicipital tendinopathy (a painful inflammation of the tendon in the upper arm)
- Acromioclavicular joint injury (damage to the joint at the top of the shoulder)
- Rotator cuff injuries (damage to the group of muscles and tendons that stabilize the shoulder)
In situations where the shoulder subluxation was caused by a trauma or injury, doctors will also look at other non-traumatic factors that might have made the shoulder more vulnerable to being dislocated in the first place.
On the other hand, if a patient has a “hemiplegic” shoulder subluxation, which means they’ve lost some functional use of their arm due to minor paralysis, doctors will consider other conditions that can cause shoulder pain. These include:
- Complex regional pain syndrome (a chronic pain condition)
- Rotator cuff tendinopathy
- Shoulder girdle muscle spasticity (an abnormal increase in muscle tension)
In addition, some other potential conditions doctors may need to take into account can include:
- Glenoid labrum tear (a break in the ring of cartilage around the shoulder socket)
- Acromioclavicular joint injury
- Clavicle fractures (a break in the collarbone)
- Shoulder dislocation
- Swimmer’s shoulder (a condition common in swimmers caused by the overuse of shoulder tendons and ligaments)
- Bicipital tendonitis
- Rotator cuff injury
What to expect with Shoulder Subluxation
If a shoulder is dislocated due to an injury, there’s a higher chance of it happening again, especially in younger individuals. However, if these patients understand their condition and adapt their daily actions accordingly, they have a good chance of fully recovering. Resting the shoulder for 3 to 4 weeks doesn’t seem to impact the recovery rate, and mild movement can be started immediately.
Also, having a fracture in the humeral head (which is the top part of the arm bone) and the intensity of physical activities don’t seem to increase the likelihood of recurrent shoulder dislocations. However, it’s important to note that after surgery for shoulder instability, between 12% to 62% of patients can develop shoulder arthritis.
In cases where a shoulder dislocation happens without a prior injury, and there are no fractures or labrum injuries (damage to the rim of the shoulder socket), about 20% of patients recover spontaneously.
For those who suffer a stroke and become partially paralyzed, their level of arm weakness and motor function, according to a scale known as Brunnstrom’s arm motor stages, can predict whether they will experience shoulder dislocations. But, it has been observed that shoulder dislocation can reduce spontaneously in stroke patients who show significant recovery of their motor functions.
