Our daughter was hurt in a water skiing accident over the weekend. The doctor wants to inject a dye into her shoulder and do an MRI before doing surgery. We don’t want her exposed to these kinds of chemicals. What would a test like this really show?

Traumatic shoulder injuries can be very complex and difficult to diagnose. Yet without an accurate diagnosis, surgery can be incomplete. If there are unrecognized ligaments or cartilage torn, the patient may end up with continued painful symptoms even after surgery.

X-rays can show damage to the bone such as fractures or even bony avulsions. An avulsion means a small piece of the bone and whatever ligament or tendon it was attached to has pulled away from the main bone.

But an MRI is needed to show damage to soft tissue structures that might go undetected otherwise. Injecting a dye allows the surgeon to see if normal fluid in the joint has moved into areas where it shouldn’t be.

This is a sign that a ligament is torn. Based on the location of the tear, damage to specific ligaments can be identified. Changes in the normal shape of the soft tissues is also diagnostic of certain lesions.

For example, there is an overlap of tissue under the shoulder that allows the arm to move overhead smoothly. This is called the axillary pouch. Normally the axillary pouch is a U-shaped feature when seen on MRI. But when the inferior glenohumeral ligament is torn, this pouch becomes a J-shape.

The more information the surgeon can gather before operating, the better. A successful surgical procedure depends on reconstructing the shoulder by repairing all damaged tissue.