Few studies have reported on the incidence of HO following hip arthroscopy. However, HO is an increasingly reported complication of arthroscopic treatment for femoroacetabular impingement(FAI). In a comparison of complications following arthroscopic treatment of FAI in 8 case-series, ectopic ossification occurred in up to 6% of cases and accounted for 10 of the 19 reported complications. Additionally, one recent study reported an HO incidence of 33% (5 out of 15 patients) following hip arthroscopy in patients not prophylaxed with NSAID therapy. In our experience, HO occurs at a comparable or higher rate of 10% in those undergoing this procedure. The formation of ectopic ossification is triggered as a result of muscle damage during introduction of hip portals and is potentially augmented by seeding of bone shavings in the soft tissues created during burring of the femoral neck.