This 60 year old male patient presents with low back pain and sciatica. He relates a history of playing high school football where he went to punt the ball and missed the ball with a defensive player running under his leg causing him to further extend his leg. He developed immediate pain in his buttocks.
Diagnosis – Rider’s Bone (Ischial Tuberosity Avulsion)
Note the extensive bone production seen inferior to the lateral aspect of the left ischial tuberosity. This represents an avulsion of the secondary growth center (apophysis) for the ischial tuberosity as a result of the forceful contraction of the hamstring while trying to kick the football.
These can be acute or chronic injuries or frequently bilateral. With healing, overgrowth of the avulsed apophysis occurs, often leaving a wide radiolucent gap between the avulsed fragment and the parent ischium. This overgrowth may be the effect of increased blood flow to the ischial apophysis.
Occasionally the involved ischial apophysis may assume a size larger than the parent ischium. This large overgrowth could be confused with an osteochondroma if attached to the bone. The patient’s history of a previous severe hamstring injury and the fact that the lesion is asymptomatic secures the proper diagnosis. Reduction in hip mobility is common and surgical intervention has not been encouraged. These fractures are seen most commonly in cheerleaders and hurdlers. Since chronic stress often produces this lesion in horseback riders the residual bony fragment has been called “Rider’s Bone”.