Hi there,
The symptoms you are describing could be due to a problem with the nerves but sounds more likely to be a musculoskeletal problem (a problem with the muscles, bones and joints.) Sounds like you maybe damaged the rotator cuffs in your shoulder if the joint locks and the grinding you describe could be "crepitus" which is caused by the joints moving off one another. Another reason to get this checked out as osteoarthritis can occur after an injury to the shoulder so I would see a doctor about this. The treatments they suggest could be anything from physiotherapy, muscle relaxants or steroid injections. As you haven't mentioned any problems with numbness/tingling or weakness in your shoulder, it does not sounds like a nerve problem.
Hope this helped.