Just had a case where an employee had a shoulder injury on the job. Thought it was possible rotater cuff.
After an MRI it was a strained AC joint that showed signs of arthritis.
Apparently a strain to the AC joint has a pain that the patient will feel in the rotater cuff.
AC joint is where the scapula meets the clavical. Limit the strenious activity as much as possible. And if range of motion is limited I would go see a doctor.
Hope the pain subsides and you get back to your routine.
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Actually the AC (acromioclavicular) joint is where the acromion and the distal clavicle articulate, although weight of the scapula is felt via motion with the scapulothoracic joint. Based on what the OP described, I would suspect pain in the shoulder emanated from the RC, and not the AC joint. Pullups are notorious for supraspinatus tendonitis.