Subchondral fatigue fracture of the femoral head with acetabular dysplasia treated by transposition osteotomy of the acetabulum: a case report

INTRODUCTION: Subchondral insufficiency fracture of the femoral head commonly occurs in older women with osteoporosis. However, subchondral fatigue fracture of the subchondral femoral head is rare. We present a rare case of fatigue fracture of the subchondral femoral head with acetabular dysplasia. CASE REPORT: The patient was a 16-year-old male, height 180 cm, weight 112 kg, and body mass index 34.6 kg/m2. Continuous right hip pain appeared after club activity of table tennis a month before admission to our department. Pain was observed on deep flexion of the right hip joint. The FADIR test was positive. X-ray images showed a depressed deformity of the right femoral head loading portion. In addition, the center-edge angle was 10° on the right and 21° on the left, tear drop distance was 12 mm on the right and 8 mm on the left, and bilateral acetabular dysplasia was noted. In magnetic resonance imaging, the T1-weighted image shows low-intensity signal and the T2-weighted image shows high-intensity signal, indicating a fatigue fracture of the femoral head with subchondral depression. Thus, transposition osteotomy of the acetabulum was performed in this case. Postoperatively, the depression portion showed gradual remodeling, and the patient returned to sports after 6 months. Because this patient was highly obese with acetabular dysplasia, a large shear force was applied to the loading portion of the femoral head relative to the acetabular rim. The femoral head was repeatedly forced, resulting in a fatigue fracture. We believe that the stress applied to the depressed portion was dispersed by the transposition osteotomy of the acetabulum, resulting in remodeling. CONCLUSION: This is the first report of the transposition osteotomy of the acetabulum for a subchondral fatigue fracture of the femoral head with acetabular dysplasia. Thus, this may serve as a reference in the management of such rare occurrences and pave the way for further understanding of this condition.