Background Femoroacetabular impingement (FAI) is characterized by early pathologic contact of the proximal femur with the acetabulum. Pincer impingement is the acetabular cause of FAI.Whereas cam deformity seen as a flattening of the anterior contour of the head/neck junction or an osseous hump leading a decreased femoral head/neck offset. Patient with FAI presents with a hip or a trochanteric painusually in the sitting position or during or after activity. It might also be an important cause of hip osteoarthritis (OA).
Objectives Therefore in this study we evaluated the frequency of pistol-grip deformity (PGD), described as the most characteristic feature of cam-type FAI, in axial spondyloarthritis (axSpA) patients as a potential alternative cause of hip or trochanteric pain.
Methods A total 180 patients (107 [59%] male, mean age 41.9±12.8 years) with axSpA according to ASAS criteria and 198 patients (120 [61%] male, mean age 40.5±14.8 years) admitted to the emergency department (mostly due to trauma) and who had pelvic X-ray were included in the study.Patients with hip OA, hip prosthesis, acetabular protrusion or who have radiographs taken improper technique were excluded. An experienced radiologist assessed all anteroposterior pelvic radiographs. PGD was determined by demonstration of spherical or non spherical shape of femur head on AP pelvic radiography.
Results The axSpA group consists 135 ankylosing spondylitis and 45 non-radiographic axSpA patients. The mean duration of symptoms was 13.8±11.3 years in axSpA patients. Radiographic findings of cam abnormality (figure) were significantly more frequent in axSpA patients in comparison with control subjects (30/150 [20%] vs 17/193 [9%] and P=0.004). Cam-type radiographic abnormality was only present 2 female control subjects and none of female axSpA patients. FAI was significantly correlated with the presence of HLA-B27 (r=0.213 and P=0.048), smoking (r=0.194 and P=0.018), height (r=0.283 and P=0.001) and gender (r=0.443 and P<0.001).
Conclusions Our results showed that radiographic findings compatible with PGD were frequent in axSpA patients. In addition to repetitive injury tothe proximal femoral physis, new bone formation may be responsible for increased FAI in axSpA.In axSpA patients with hip or trochanteric pain, FAI may be kept in mind as an alternative explanation of the symptoms.
Disclosure of Interest None declared
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