Informed consent was obtained from the patient for the use of all images and publication of this report before the beginning of this project. A 20-year-old basketball player presented with a 2-year duration of the left groin pain after a basketball-related injury. The pain was aggravated by athletic activity and prolonged sitting. Physical examination of the left hip showed pain with hip external rotation at 40  and internal rotation at 10 . Radiographs showed a lateral center-edge angle of 36  and an alpha angle of 83  on the anterior-posterior (AP) and 72  on the frog view (Fig. 1 and 2). Due to continued disability and failure of conservative management, the patient underwent hip arthroscopy.
Intraoperative findings included chondral detachment at the chondrolabral junction in zone 3 and an adjacent partial labral tear. These were treated with chondroplasty, microfracture, acetabular osteoplasty and labral repair followed by osteoplasty of the femoral head-neck junction. No HO prophylaxis was given. Follow-up radiographs at 3 months after the left hip arthroscopy showed Grade 3 HO on the left side (Fig. 3 and 4). On the 2nd post-operative visit (following 6 weeks of non-weight bearing rehabilitation) the patient complained of contralateral (right-sided) hip pain.
At 6 months, the patient returned his regular basketball activity with no left hip pain. Left hip external rotation and internal rotation improved to 60  and 30  respectively. However, in the right hip, the patient had a positive impingement test with pain on flexion, adduction, and internal rotation and flexion, abduction, and external rotation. AP radiographs showed a lateral center-edge angle of 30  and an alpha angle of 84  in the right hip. Due to continued symptoms on the right side 1 year after the left hip arthroscopy and failure to respond to conservative management the patient underwent right hip arthroscopy. Acetabular osteoplasty and labral repair were followed by osteoplasty of the femoral head-neck junction. Subsequently, HO prophylaxis was initiated with NSAID treatment (Etodolac) 600 mg/day for 14 days. Follow-up radiographs at 3 months after the right hip arthroscopy showed no HO (Grade 0) (Figure 5).
Before the right hip arthroscopy, the patient presented with a modified Harris Hip Score (mHHS) of 95.7, furthermore, he presented with an SF-12 score of 52 Physical Component Score (PCS) and 39 Mental Component Score (MCS). He described his "General Activity Level" to be 90% of normal. An 18-month postoperatively, the patient reported an mHHS of 100. His SF-12 scores improved to 56 (PCS) and 57 (MCS). His "General Activity Level" was increased to 100% postoperatively and he returned to play basketball professionally.