ePoster #814 - ISHA Annual Scientific Meeting 2016

Comparison of MRI, CT, Dunn 45, And Dunn 90 Alpha Angle Measurements In Femoroacetabular Impingement

Joshua David Harris, MD, Houston, TX UNITED STATES
Kevin Smith, MD, Houston, TX UNITED STATES
Brayden J. Gerrie, BS, Houston, TX UNITED STATES
David M Lintner, MD, Houston, TX UNITED STATES
Patrick C. McCulloch, MD, Houston, TX UNITED STATES

Houston Methodist Orthopedics & Sports Medicine, Houston, TX, UNITED STATES

FDA Status Not Applicable

Summary: In patients with symptomatic femoroacetabular impingement, the Dunn 45-degree plain radiograph yielded a significantly higher alpha angle than the Dunn 90-degree plain radiograph, axial oblique MRI, and axial oblique CT, concluding that the Dunn 45 is the most sensitive two-dimensional evaluation of three-dimensional cam morphology.

PURPOSE: To determine if a significant difference existed among alpha angle measurements between four imaging techniques, axial oblique CT and MRI, Dunn 45° and Dunn 90° plain radiographs, in patients with symptomatic cam femoroacetabular impingement (FAI) and labral tear. METHODS: A single-surgeon prospective radiographic analysis of consecutive non-arthritic and non-dysplastic patients with symptomatic FAI and labral tears who underwent surgery was performed. Alpha angle was measured using standard techniques as described by Notzli. Cam morphology was defined via alpha angle of 50.5 degrees. Group comparisons were made using ANOVA and chi-squared. Sample size calculation was performed prior to study enrollment. RESULTS: Thirty-one subjects (16 female; 33.5 +/- 10.5 years mean age) were included. There was a significant difference in alpha angle measurements between all four imaging techniques (F [3,120] = 8.144; p<0.001), with the Dunn 45° view (66.3+/-11.4°) significantly greater than all three other techniques (Dunn 90° [57.5+/-10.7°; p=0.015], MRI [53.3+/-11.5°; p<0.001], and CT (54.9+/-11.6°; p=0.001). There was no significant difference in alpha angle between Dunn 90°, MRI, and CT. There was a significant difference in the number of hips with cam morphology between imaging techniques (?2 9.4; p=0.025). CONCLUSIONS: The Dunn 45° radiograph yielded a significantly higher alpha angle than Dunn 90°, axial oblique MRI, and CT imaging modalities. Use of the Dunn 90° or axial oblique MRI or CT as the threshold for cam osteoplasty may result in untreated symptomatic cam FAI. The authors recommend the Dunn 45° radiograph as the most sensitive evaluation of cam morphology. LEVEL OF EVIDENCE: II (Diagnostic; Consecutive patients, consistently applied reference standard)