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Fibrocystic changes at anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement.

PURPOSE
To retrospectively evaluate if there is an association between juxta-articular fibrocystic changes at the anterosuperior femoral neck and femoroacetabular impingement (FAI).


MATERIALS AND METHODS
The institutional review board approved this study and did not require informed patient consent. An orthopedic surgeon and a radiologist in consensus retrospectively reviewed the anteroposterior (AP) pelvic radiographs of 117 hips with FAI and compared these images with the AP radiographs of a control group of 132 hips with developmental dysplasia (DD) to determine the prevalence of juxta-articular fibrocystic changes at the anterosuperior femoral neck. Criteria for juxta-articular fibrocystic changes at the anterosuperior femoral neck were location close to the physis and a diameter (of the fibrocystic change) of greater than 3 mm. The sensitivity and specificity of AP pelvic radiography in the detection of these fibrocystic changes were calculated by using an additional 61 hips with FAI and on the basis of findings at magnetic resonance (MR) arthrography, which was routinely performed for assessment of FAI. In 24 patients who underwent joint-preserving surgery for FAI, the fibrocystic changes were localized intraoperatively and the spatial relation of the region of these changes to the area of FAI was identified. Joint-preserving surgery consisted of anterior surgical dislocation of the hip with osteochondroplasty of the proximal femur and/or the acetabular rim to improve the impingement-free range of hip motion. For statistical comparisons, nonparametric tests were performed.


RESULTS
Fibrocystic changes were identified on the AP radiographs of 39 (33%) of the 117 FAI-affected hips and on none of the radiographs of the 132 DD-affected hips. According to MR arthrogram findings, the sensitivity, specificity, and positive and negative predictive values of AP pelvic radiography were 64%, 93%, 91%, and 71%, respectively. The mean diameter of the juxta-articular fibrocystic changes was 5 mm (range, 3-15 mm); smaller lesions were more prevalent. Dynamic MR imaging with the hip flexed and intraoperative observations revealed a close spatial relationship between the region of the fibrocystic changes at the anterosuperior femoral neck and the acetabular rim.


CONCLUSION
The high prevalence of juxta-articular fibrocystic changes at the anterosuperior femoral neck and their spatial relation to the impingement site suggest an association and possible causal relationship between these alterations and FAI.