Femoroacetabular Impingement (FAI) was associated with anterior hip pain and premature osteoarthritis in young patients[1,2]. Pincer-type FAI was described as an early osseous conflict of a prominent acetabular rim with the proximal femur[1,2]. Pincer-type FAI can be caused by global acetabular overcoverage or focal prominent overgrowth of the anterior acetabular wall[3]. Acetabular retroversion is an additional cause for pincer-type FAI[4,5]. Initially, the surgical treatment for pincer-type FAI due to acetabular retroversion was acetabular rim trimming during hip arthroscopy[3] or open hip preservation surgery. MR-based three-dimensional (3D) analysis of the size of the lunate surface showed increased acetabular size in protrusio patients[7] but not for acetabular retroversion. Decreased pelvic incidence was associated with pincer-type FAI[8], however the hip spine relation is unclear. Interestingly, some FAI patients reported hip pain as well as low back pain[9].

Pincer-type femoroacetabular impingement (FAI) and acetabular retroversion(AR) were associated with decreased pelvic incidence(PI) and sacral slope(SS). But the hip-spine relation and sagittal balance for these patients are unclear.Therefore, we investigated (1)Frequency of patients with PI<40° (2)Frequency of patients with SS<35° and (3) what types of SS (Type 1-4) are associated with AR and hip dysplasia.