The elbow has three main bones in it -- the humerus (upper arm) and two bones in the forearm. The forearm bones are the radius and the ulna. The radius has a flat, round disc-like top where it connects to the bottom of the humerus at the elbow. Next to the radial head is a bony shelf at the top of the ulna. This part of the ulnar bone is called the coronoid process.
A terrible triad injury consists of three parts. The head of the radius is broken. The coronoid process is also fractured. The elbow is dislocated and most often, the lateral collateral ligament (LCL) along the outside of the elbow is torn.
The word terrible is used because these injuries are very hard to treat successfully. The elbow dislocates repeatedly and is unstable. Post-traumatic arthritis is common.
The best way to treat terrible triad injuries remains a topic of debate among surgeons. Some suggest removing part or all of the radial head. Other say the radial head should be repaired along with the LCL. The radial head can also be replaced with a titanium implant. The coronoid fracture must be repaired as well. Screws or wires are used to hold the coronoid together.
Sometimes pins are used outside the arm that go through the bone to hold everything together until it heals. This is called external fixation.
All in all, the terrible triad injury is a complex elbow joint problem that often results in an unstable joint. Careful surgical management along with rehab is the key to a good outcome.