Osteochondritis Dissecans of the Capitellum

Osteochondritis dissecans (OCD) of the capitellum is when a small patch of bone and cartilage on the outer side of your elbow joint loses its blood supply, dies, and can break loose into the joint. The patch sits on the bump at the end of your upper-arm bone — the capitellum — where the elbow rotates. It mostly hits young throwers (especially baseball players) and gymnasts between 10 and 17, when the same compressive, twisting load on the elbow happens over and over. Catching it early matters — once the fragment breaks free, you can lose cartilage permanently and develop arthritis decades earlier than you should.

• Outer elbow pain during throwing or weight-bearing — the ache sits on the outside of your elbow and flares with the specific motion that loads the capitellum (pitching, handstands, push-ups).
• Loss of full extension — your arm won't straighten all the way, especially after activity.
• Catching or locking — if the fragment has broken loose into the joint, the elbow may catch mid-motion or lock in one position until you wiggle it free.
• Activity-related swelling — mild puffiness on the outer side of the elbow after practice or competition.

A young athlete with pain and swelling on the outer side of the elbow — and an arm that won't fully straighten — is the classic picture. X-rays may show a dim spot on the capitellum where the bone has lost its density. An MRI answers the key question — is the fragment still stuck down or floating loose? Bright fluid tracking behind it on the scan means unstable. A CT scan with contrast (CT arthrography) maps the fragment in detail before surgery.

Surgery comes in when the fragment is loose, when there's already a piece floating around inside the joint, or when months of rest haven't healed the lesion.

External patient-education references and related OSI pages for additional background:

• Britannica — Joint (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language