Intraoperative Fluoroscopic Imaging to Accurately Treat Cam Deformities: Correlation with 3D Computed Tomography

Abstract

In the diagnosis and surgical treatment of cam-type femoroacetabular impingement (FAI), three-dimensional (3D) imaging is the gold standard for detecting and defining femoral head-neck junction malformations. Although intraoperative fluoroscopy is used by many surgeons to evaluate and verify adequate correction of the deformity, a meaningful, systematic approach has not been well defined. The purposes of this study were (1) to correlate radial reformatted computed tomography (CT) scans with six defined intraoperative fluoroscopic views prior to surgical correction to determine if fluoroscopy could adequately depict cam deformity, and (2) to define the influence of femoral version on the clock-face location of the maximum cam deformity on these views. A consecutive series of 50 hips (48 patients) that underwent arthroscopic treatment for symptomatic FAI by a single surgeon were analyzed. Each patient underwent a CT scan and six consistent intraoperative fluoroscopy views: three views in hip extension (medial and lateral deformities) and three views in hip flexion of 50° (anterior and posterior deformities). The alpha angles of each of the fluoroscopic images were correlated with the radial reformatted CT using a 3D software program. Femoral version was also assessed on CT studies. Statistical analysis was performed with Student's t-test, with P < .05 defined as significant. Fifty-two percent of patients were male, average age of 28 years (range, 15-56 years). The maximum mean alpha angle was 65° (range, 37°–93°) and was located on the anteroposterior (AP) 30° external rotation (ER) fluoroscopy view. The mean clock-face positions of each of the fluoroscopy views (standardized to the right hip) were AP 30° internal rotation, 11:45; AP 0° (neutral) rotation, 12:30; AP 30° ER, 1:00; flexion/0° (neutral) rotation, 1:45; flexion/40° ER, 2:15; and flexion/60° ER, 2:45. Increased femoral anteversion (>20°) was associated with a significant change in the location of the maximum alpha angle (1:45 vs. 1:15; P = .002). The described six fluoroscopic views are helpful in localization and visualization of the typical cam deformity from 11:45 to 2:45 and can be utilized to reliably confirm a complete intraoperative resection of cam-type deformity in most patients. These views correlate with preoperative 3D imaging, and may be of even greater importance in the absence of preoperative 3D imaging.