SULCUS SIGN FOR INFERIOR SHOULDER INSTABILITY With the Sulcus Sign, you are able to assess inferior shoulder instability. By longitudinal traction directly above the elbow, you will be able to (sub)luxate the patient's unstable shoulder and see a "sulcus" under the roof of the acromion, where the humeral head shoulder normally sits. P.S. There are no studies that have evaluated the tests' diagnostic accuracy to our knowledge | Physiotutors