The variation of pelvis in unilateral Crowe type IV developmental dysplasia of the hip

Abstract BackgroundThe whole pelvic morphology is very common in developmental dysplasia of the hip (DDH). The abnormalities may influence the pelvic landmarks, and then misguide the surgeon’s preoperative plan. The purpose of this study was to investigate the variation of pelvis in unilateral Crowe type IV DDH and analyze the reliability of pelvic landmarks.MethodsWe received preoperative anteroposterior pelvic radiographs examined for 89 adult patients with unilateral Crowe type IV DDH at our institution between September 2008 and May 2019. 48 patients without a false acetabulum was type IVA and 41 with a false acetabulum was type IVB. The heights of the ilium, acetabulum and ischium areas in affected and unaffected sides were measured, the discrepancies of bilateral iliac crest, inferior sacroiliac articulation, teardrop and ischial tuberosity on the bisector of the pelvis were also measured.ResultsThe mean heights of the ilium, acetabulum, ischium areas in the affected side were 74.4 mm, 88.6 mm and 37.0 mm, respectively, in type IVA group and 77.7 mm, 83.5 mm and 37.8 mm, respectively, in type IVB group. The heights in the unaffected side were 82.1 mm, 84.6 mm and 43.8 mm, respectively, in type IVA group and 84.6 mm, 82.0 mm and 44.0 mm, respectively, in type IVB group. The discrepancies of bilateral iliac crest, inferior sacroiliac articulation, teardrop and ischial tuberosity on the line of the bisector of the pelvis were 6.7 mm, 4.4 mm, 2.7 mm and 6.1 mm, respectively.ConclusionsThe pelvic asymmetry was a common occurrence in adults unilateral Crowe type IV DDH. Furthermore, it should be reliable to use teardrop as pelvic landmark to balance leg length discrepancy in preoperative planning.