Uneven collarbone/ tingling down left arm starting around 6 months ago, by stretching in the morning i had felt a pop in my sternum as you would if you were to "pop your knuckles" and it started out initially feeling good after it had popped. earlier toni

The : The prominence of the sternoclavicular joint is more likely than not arthritic in nature. If there is any concern with increased pain or deformity you should have x-rays taken. Numbness going down the arm is likely associated with either a pinched nerve in your neck or at the level of your shoulder in what we call the brachial plexus. Management really depends on the level of symptoms.

PossibleTOS : Need neurological exam and likely ncv/emg test. Thoracic outlet syndrome is possible.