By: Terry R. Yochum, DC, DACBR, Fellow, ACCR and Michael S. Barry, DC, DACBR
What is this unusual lesion of the ischium? Does this patient need to be referred
Figure 1 Diagnosis: Rider’s bone (avulsion of the secondary growth center for the ischial tuberosity).
This type of fracture represents an avulsion of the secondary growth center (apophysis) for the ischial tuberosity as the result of a forceful contraction of the hamstring group of muscles. These can be acute or chronic injuries and are frequently bilateral. With healing, an unexplained 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 hyperemia upon the ischial apophysis. Occasionally, the avulsed ischial apophysis may assume a size larger than the parent ischium. This large overgrowth can be confused with an osteochondroma. Usually, the patient’s history of 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 encouraging. 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.”
- Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 2nd ed. Baltimore: Williams & Wilkins, 1996. 710.
- Phillips CD, Pope TL, Jones JE, et al. Non-traumatic avulsion of the lesser trochanter: a pathognomonic sign of metastatic disease? Skeletal Radiol 1988; 17:106.
About the Authors
Dr. Terry R. Yochum is a second generation Chiropractor and a cum laude graduate of the National College of Chiropractic, where he subsequently completed his radiology specialty. He is a Diplomate of the American Chiropractic Board of Radiology and served as its vice-president and president for seven years (1983–1990).
Dr. Michael S. Barry is a 1988 cum laude graduate of Palmer College of Chiropractic. He completed a three-year radiology residency at Logan College of Chiropractic following two years of clinical practice in Las Vegas, Nevada. He received his diplomate in radiology from the American Chiropractic Board of Radiology in 1992.