Quadrilateral Space Syndrome

R posterior arm picture by Mickeymed.com

I treated an 11year old girl recently with pain in her quadrilateral space. What space you may ask? The quadrilateral (or quadrangular) space is a tiny window or space that the axillary nerve and other blood vessels (posterior circumflex humeral artery) exit from the shoulder to the back of the arm. It's boundaries are teres minor on top, the humerus (arm bone) on the right, teres major below and the long head of triceps on the left. The axillary nerve supplies the deltoids and the teres minor muscles. 

Picture from Clinical Anatomy & Op Surgery

This young patient plays softball for her school and is her team's first choice pitcher. Softball pitching is different as the ball is thrown to the batter using an underhand motion. The goal while pitching is similar to baseball, to get the batters out by strikes or preventing them from reaching base. 

Injury or compression in the quadrilateral space often leads to pain, numbness in the posterior shoulder/ arm and/ or weakness in those areas.

This condition is much more common in young athletes participating in arm over head sports like swimming, throwing and volleyball in their dominant hand. But she did do many overhead throws prior to having this pain in her posterior shoulder and arm. In addition, her coach also started her on a weight training program in the upper body and arms.

Injury or compression in the quadrilateral space often leads to pain, numbness in the posterior shoulder/ arm and/ or weakness in those areas. There is often tenderness in the quadrilateral space on palpation. 

My patient also had some paresthesia (numbness, tingling sensations) on the outer shoulder and elbow when I checked her upper limb tension test. Her shoulder external rotation strength was also noticeably weaker on her thowing arm, which should not be the case.

Once we determined the cause, treatment was easy as we simply had to 'widen' the quadrilateral space while also addressing the overhead throwing overuse and the sudden increase in weight training. A simple phone call to her coach,who happened to be a previous national pitcher and patient of mine solved that.

Reference

Pocellini G, Brigo A, Novi M et al (2025). Different Patterns Of Neurogenic Quadrilateral Space Syndrome: A Case Series Of Undefinied Posterior Shoulder Pain. J Orthop Trauma. 26(1). DOI: 10.1186/s10195-024-00813-y.