Skeletal Radiol DOI 10.1007/s00256-006-0150-0 CASE REPORT Kevin P. Banks David E. Grayson Received: 10 August 2005 Revised: 22 September 2005 # ISS 2006 Acetabular retroversion as a rare cause of chronic hip pain: recognition of the “figure-eight” sign Abstract While well-recognized in the orthopedic literature as a cause of chronic hip pain, acetabular retrover- sion has not been specifically described in the radiologic literature. Acetabular retroversion represents a particular form of hip dysplasia char- acterized by abnormal posterolateral orientation of the acetabulum. This pathophysiology predisposes the individual to subsequent anterior impingement of the femoral neck upon the anterior acetabular margin and fibrous labrum. Without treat- ment, cases may progress to damage of the anterior labrum and cartilage, with eventual early onset of osteoar- thritic disease. This impinging condi- tion has been described as occurring in isolation or as part of a complex dysplasia. We describe two cases of acetabular retroversion diagnosed by conventional radiographic evaluation of the pelvis, one in isolation and one occurring in the setting of a larger congenital syndrome. These cases illustrate the utility of the “figure- eight” sign in identifying abnormal- ities of acetabular version and thus assisting clinicians in properly identifying these individuals so that appropriate therapy may be instituted. Keywords Acetabular retroversion . Acetabular dysplasia . Chronic hip pain . Congenital dysplasia of the hip . Radiographs Introduction The acetabulum is normally oriented in the caudolateral direction with mild angulation anteriorly (Fig. 1). The normal acetabular anteversion typically ranges from 12° to 16.5° [1]. While congenital abnormalities of the hip are not uncommon, acetabular retroversion is an under-reported variety of hip dysplasia that often does not present until the 2nd or 3rd decade of life, with an insidious onset of nonspecific symptoms, making for an elusive clinical diagnosis with resultant improper treatment for other presumed causes of the individual’ s symptoms. Case report The first individual was a 20-year-old male with Trisomy 10-mosaicism manifested by mental retardation, dimin- ished growth, a ventricular septal defect, and multiple skeletal abnormalities to include severe scoliosis. At a routine orthopedic follow-up, the patient’ s mother com- plained that the young man suffered from chronic right hip pain. Physical exam was unrevealing, and a routine hip series was obtained, to include an anterior–posterior view of the pelvis. This radiographic view showed abnormal overlap of the anterior and posterior margins of the acetabulum, resulting in a “figure-eight” appearance char- acteristic of acetabular retroversion (Fig. 2a and b). Given the patient’ s extensive co-morbidities, the parents declined surgical therapy and chose symptomatic treatment for his hip pain. The second individual was a 19-year-old male military basic trainee who complained of a 2-month history of bilateral hip pain unresponsive to analgesics. Physical exam was significant for pain during passive hip flexion and adduction, with an associated decreased range of K. P. Banks (*) Department of Radiology, Brooke Army Medical Center, 3851 Roger Brooke Drive, Fort Sam Houston, TX 78234, USA e-mail: Kevin.Banks@CEN.AMEDD. ARMY.MIL Tel.: +1-210-9163290 Fax: +1-210-9161967 D. E. Grayson Department of Radiology, Wilford Hall Medical Center, 2200 Bergquist Drive, Suite #1 , Lackland Air Force Base, TX 78236, USA Accepted: 23 September 2005 Published online: 20 May 2006 (2007) 36: S108–S111