HISTORY: An 11-year-old baseball pitcher sustained a right elbow injury while pitching in the first inning. He had pitched all season without difficulty. After feeling well during his normal warm-up, on the 15th pitch, he felt a pop in his elbow during the acceleration phase. He developed pain and swelling in the right elbow immediately and was unable to continue pitching. He was seen the following day where he had limited range of motion of his right elbow secondary to pain and swelling. PHYSICAL EXAMINATION: Positive effusion, no ecchymosis. Tenderness over the medial epicondyle and flexor/pronator mass. 10 degrees to 80 degrees, active; 0 degrees to 90 degrees, passive. Severely tender medially with minimal valgus stress. Neurovascular exam was normal. DIFFERENTIAL DIAGNOSIS: Osteochondritis dissecans Panner's disease Flexor/pronator common tendon avulsion Medial epicondyle avulsion fracture UCL tear Medial epicondyle apophysitis TEST AND RESULTS: AP, lat at 90 degrees flexion and oblique radiographs: Small eggshell fleck of bone from medial epicondyle, ossification center unfused. No joint effusion seen. MRI: Medial epicondyle avulsion with 2 mm gap. Common flexor and UCL origins intact on the avulsed fragment. Radial collateral ligament intact. FINAL WORKING DIAGNOSIS: UCL avulsion fraction of the medial epicondyle TREATMENT AND OUTCOMES: Immobilization in posterior splint with no throwing activities. Operative repair of avulsed UCl performed 14 days post injury.Complete avulsion of UCL with small eggshell of cortical bone from the medial epicondyle with 4 mm displacement.Follow-up: Ten days post-op, patient was doing well. ROM was 20 – 100 degrees with full supination and pronation. Ulnar nerve function was intact. Repeat AP, lat and oblique radiographs at 10 days, six weeks and 12 weeks showed healing of avulsion fragment of cortical bone to medial epicondyle. Rehabilitation: Immediately post-op: Patient was placed in a splint at 60 degrees flexion. Ten days post-op: The patient started a home program of elbow flexion and extension isometrics at 60 degrees with gentle hand exercises. One month post-op: Gentle concentric exercises were initiated. Six weeks post-op: Patient was advanced to elbow flexion and extension between 0 and 145 degrees, out of splint. Splint was discontinued except at school. No sports participation. Two months post-op: Discontinuation of brace at all times. PREs, shoulder and scapular stabilization exercises were advanced. Ten weeks post-op: Functional exercises; reactive, oscillating blade device; the upper body cycle and tricep PREs were added. Twelve weeks post-operation: Light batting practice.