The kind of shoulder injury that would not show up in an X-ray are shoulder injuries with soft tissue damage.
Soft tissue shoulder injuries like rotator cuff tears for example don't show up on a standard X-ray because X-rays can only capture dense bone structures.
X-rays allow radiation to pass right through muscles, tendons, and cartilage and because of this, conditions like rotator cuff tears, labral tears, tendonitis, bursitis, frozen shoulder and ligament sprains will look normal on an X-ray.
Rotator cuff tears are damage or full ruptures to the muscles and tendons, which stabilize your shoulder joint.
Labral tears are rips in the ring of cartilage (the labrum) surrounding the socket.
Tendonitis, is inflammation of the tendons, like your biceps or rotator cuff tendons.
Bursitis, is swelling in the bursa, which are the small fluid filled sacs that reduce friction.
Frozen shoulder is a painful condition in which the capsule around the joint tightens up and restricts movement.
And ligament sprains are overstretched or torn ligaments that hold the joint together.
If the X-ray of your shoulder injury turns out to be normal, but you still feel pain, doctors will use other imaging tools to see the soft tissue.
These other imaging tools to diagnose your shoulder injury when an X-ray shows as normal, include MRI and Ultrasound.
MRI (Magnetic Resonance Imaging), uses magnets to create detailed views of both bone and soft tissue.
Ultrasound uses sound waves to check the tendons and movement in real time.