Question: What is Quadrilateral Space Syndrome, and what ICD-9 code should I use? Georgia Subscriber Answer: Quadrilateral space syndrome (QSS) refers to the compression of the axillary nerve in the back of the patient's shoulder. Sometimes the compression of an artery can cause the symptoms in the same area, especially with overhead sports like throwing and swimming. You should report QSS using the symptom, which is shoulder pain (719.41, Pain in joint; shoulder region). -- Reader Questions and You Be the Coder were reviewed by Heidi Stout, CPC, CCS-P, director of orthopedic coding services at The Coding Network LLC; and Bill Mallon, MD, orthopedic surgeon and medical director at Triangle Orthopaedic Associates in Durham, N.C.