About a month ago I was bouldering in the gym and fell with my left arm overhead and internally rotated (in a gaston position). I had been transferring my weight onto that hand on a roof and trying to hold a lock-off so that I could move my feet, but ended up rapidly loading my shoulder as I fell. I felt popping and had immediate pain and tenderness over my acromion. Over the next week, I was surprised to find that resisted testing of my rotator cuff was pain-free. I still had shoulder pain with horizontal adduction (active/resisted end range), reaching hand behind back, and lying on my opposite side or sitting prolonged without support. I asked a coworker to test my AC joint and I had pain and laxity upon testing of the AC ligaments (acromioclavicular only, conoid and trapezoid ligaments stable and pain-free). I have never heard of an AC joint traction/rotation injury, which I am assuming is what occurred. Has anyone else seen an AC joint injury from a climbing fall before, in themselves or a patient? Any insight into the mechanism of how this occurred?

Thank-you!