A 19-year-old athlete complains of pain and swelling of the anterior pretibial area of his right lower leg. He hopes to win a football or track scholarship to college and is concerned because his symptoms are impairing his performance.
History. The symptoms started about 6 months earlier when he experienced "shin splints" during the spring track season. He specialized in the 100- and 200-meter dashes. After the season ended, the pain and swelling began to resolve; however, these symptoms returned during football workouts in the fall.
When he made sharp cuts on the field or accelerated quickly, the pain increased. He was told by the coach that the injury was a bruise and was advised to continue practice. With the regular exertion of practice and the season's games, the symptomatic area became more swollen. He now experiences pain with simple weight bearing.
There is no history of redness at or drainage from the site, joint pain, fever, or generalized leg edema. Although he plays running back and is tackled frequently, he has had no penetrating or other leg injury except for the usual bruises.
Examination. The patient is muscular and well built. Pulse rate is 60 beats per minute; respiration rate, 18 breaths per minute; blood pressure, 110/80 mm Hg. The only abnormalities noted are a tender 3 X 4-cm slightly rubbery soft tissue mass overlying the lateral aspect of the middle of the right tibial shaft, and a discrete bony nodule or prominence on the anterolateral tibial surface. The patient rates the pain as 6 on a scale of 1 to 10. There is no fluctuation, erythema, or drainage. Knee and ankle joints are normal. No inguinal adenopathy is noted, and the neurovascular status of both lower legs is normal for his age and level of conditioning.
Anteroposterior and lateral plain radiographic views of the tibia are ordered.
What do the films show—and to what diagnosis do these findings point in light of the patient's history?