Validity of the alpha angle measurement on plain radiographs in the evaluation of cam-type femoroacetabular impingement.
BACKGROUND
Cam-type femoroacetabular impingement is secondary to lack of concavity at the anterosuperior femoral head-neck junction, resulting in reduced femoral head-neck offset and femoral head asphericity. This morphologic deformity can be detected by MRI and plain radiographs and quantified using the alpha angle.


OBJECTIVE
We evaluated the accuracy and reproducibility of plain radiography in the diagnosis of cam-type deformity.


METHODS
Sixty-eight patients (37 females, 31 males) with a mean age of 38 years (range, 17-60 years) were treated for intraarticular hip pathology with 43 hips having cam-type femoroacetabular impingement and 25 having isolated labral tears. All patients had alpha angle measurements made on plain radiographs (AP pelvis, crosstable lateral, Dunn view) and multiplanar MRI using an alpha angle of more than 50.5° as the gold standard.


RESULTS
The Dunn view had a sensitivity of 91%, specificity of 88%, positive predictive value of 93%, negative predictive value of 84%, and accuracy of 90% for diagnosing the cam deformity associated with femoroacetabular impingement. The Pearson correlation coefficients between the MRI and plain radiography values were 0.702, 0.552, and 0.349 for the Dunn, crosstable lateral, and AP views, respectively.


CONCLUSIONS
Our observations validate the clinical use of the Dunn view in the evaluation of the femoral head-neck contour in cam-type femoroacetabular impingement.


METHODS
Level I, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
Division of Orthopaedic Surgery, The Ottawa Hospital - General Campus, 501 Smyth Road, CCW 1446, Box 502, Ottawa, ON K1H 8L6, Canada.
Cefin
C
Barton
Matias J
MJ
Salineros
Kawan S
KS
Rakhra
Paul E
PE
Beaulé
D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D000328:Adult; D001175:Arthrography / Q000379:methods*; D005189:False Positive Reactions; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D006617:Hip Dislocation / Q000000981:diagnostic imaging* / Q000601:surgery; D025981:Hip Injuries / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult