You’ll need to see an orthopedic surgeon to find out for sure. Being able to point to the pain with one finger suggests a local problem in one of the soft tissue structures along the front of the shoulder. This could be a tendinitis or acromioclavicular (AC) joint problem. Shoulder pain can also be referred from one of many other structures including the neck, heart, chest, kidney, or stomach.
The doctor will take a history and examine you first before deciding if X-rays or other imaging studies would offer helpful information. Your symptoms especially when it hurts and how you move help the physician tell what’s wrong. He or she will also palpate (feel) different structures to see what’s hurting.
The AC joint (acromioclavicular) occurs where the outer end of the collarbone meets up with the curved acromion coming around from the shoulder blade. This is a common area of injury and instability with young people and degenerative changes in older folks.
Sometimes an injection of a local numbing agent is helpful. Lidocaine and a steroid mixed together and injected into the AC joint can rule out or verify the joint as the source of pain.
There are many clinical tests the doctor can use to find out what’s wrong. Early diagnosis and treatment may help prevent further problems later.