Pain at the back of the shoulder can be due to many causes, including rotator cuff tendonitis, shoulder arthritis, and referred pain from the neck. However, a rare cause of pain at the back of the shoulder is quadrilateral space syndrome. So, what is quadrilateral space syndrome, how do we diagnose it, and what do we do?
What is the Quadrilateral space?
The quadrilateral space is located at the back and below the shoulder joint. It is situated between two muscles, teres minor and teres major. The space contains the axillary nerve and an artery, which supply the shoulder joint and muscles. Pressure in this space leads to the trapping of the Axillary nerve.
Quadrilateral space syndrome causes
Causes of trapping of the axillary nerve in the quadrilateral space include:
- fibrous bands or muscle swelling in the space
- Paralabral cysts from the lower part of the labrum of the shoulder
- growth, such as tumours
- overhead or throwing athletes. We think that repeated movement of the shoulder into the cocking position leads to narrowing of the space.
In general, this syndrome produces pain in the back of the shoulder. Often, pain occurs when moving the shoulder into the cocking position during a throw. Sometimes, we can see wasting or atrophy of the muscles at the back of the shoulder. Also, people can report pins and needles or numbness in the upper arm.
When examing a shoulder, we often find point tenderness in the quadrilateral space and weakness and wasting of the deltoid and the muscles behind the shoulder.
Other causes of shoulder muscle atrophy
Not all muscle atrophy in the shoulder is due to quadrilateral space syndrome. In general, other common causes of shoulder pain and muscle atrophy include brachial neuritis, suprascapular nerve compression at the back of the shoulder, thoracic outlet obstruction, and nerve compression from the neck.
Quadrilateral space syndrome radiology
Often, an MRI scan of the shoulder is the most helpful investigation. Often, we see swelling and wasting of the teres minor muscle. Sometimes, paralabral cysts from the inferior labrum are seen compressing the space.
Finally, in complex cases where the diagnosis is uncertain, we think a diagnostic local anaesthetic block can be helpful to confirm a diagnosis.
Quadrilateral space syndrome treatment
In general, treatment depends on the cause of the trapping.
Firstly, in mild cases with a normal MRI, physical therapy can improve pain and function after a few months. Sometimes an ultrasound-guided cortisone injection can be directed next to the axillary nerve. Also, we can aspirate a paralabral cyst to reduce pressure on the nerve.
Finally, for more severe symptoms or cases due to an apparent compression (such as a paralabral cyst), surgical decompression and labrum repair are needed.
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