Ptosis of the hip: a new radiographic finding in patients undergoing femoroacetabular osteoplasty.

Ptosis is a newly described phenomenon appearing on AP radiographs of patients undergoing femoroacetabular osteoplasty (FAO), and refers to a reverse break down in Shenton's Line. Thorough characterization of this phenomenon is needed to better understand the hip morphology and pathologic ramifications. Our goal was to define the radiographic hip parameters accompanying a break down in Shenton's Line and to determine how these values compare with standard values in normal hips. Using two independent readers, we retrospectively reviewed the medical records and preoperative supine radiographs of 630 patients (1260 hips) who underwent FAO by a single surgeon between 2003 and 2016. Prevalence of hip pathology and 28 radiographic parameters in ptosis hips was measured, as well as a comparison between unilateral ptosis hips and contralateral normal hips. Of the 53 patients (106 hips) who fulfilled the criteria for the study, 94 hips had a Shenton's Line break down of at least 5 mm. Sixty-nine percent of ptosis hips had femoroacetabular impingement (FAI), 70.2% had coxa profunda, and 52.1% had partial joint space narrowing. Ptosis hips had 1.05 mm less lateral subluxation ( P = 0.012), 2.28° larger Center-edge angle ( P = 0.046), 2.59° smaller Sharp angle ( P = 0.011) and 2.49% smaller extrusion index ( P = 0.016) compared with contralateral normal hips. FAI is prevalent in patients with a positive ptosis sign. The high prevalence of partial joint space narrowing could suggest eventual osteoarthritis. We believe our results demonstrate the importance of further investigation of a positive ptosis sign on AP pelvic radiographs.