Evaluation of Cam Deformity on 3-Dimensional Computed Tomography With the Best-Fit Sphere Technique and the Alpha Angle Marking Method

Abstract

Background: Three-dimensional computed tomography (3D-CT) is commonly used for the evaluation of cam deformity; however, it does not display the cam border directly. Purpose: To compare the efficacy of the best-fit sphere (BFS) method and the alpha angle marking (AAM) method in 3D-CT evaluation for the cam border. Study Design: Cohort study (Diagnosis); Level of evidence, 3. Methods: Twenty-six cases of cam deformity, confirmed during hip arthroscopy, were included in this study. All patients underwent a CT scan before surgery. Using multiplanar reconstruction, we obtained reformatted CT images of oblique axial, oblique coronal, and radial views. The alpha angle and femoral head-neck offset ratio (hnoR) were measured on the reformatted CT images. The cam area on 3D-CT was displayed in 4 different ways: by importing the markers from the reformatted CT images of the oblique axial view (cam-oa), the oblique coronal view (cam-oc), or the radial view (cam-r) using the AAM method, or by using the BFS method (cam-bfs). The sizes and locations of the displayed cams were compared. Results: All hips in this study had an alpha angle greater than 60° and an hnoR smaller than 0.17. The radial view measured a larger alpha angle and smaller hnoR than the oblique axial and coronal views ( P < .05). The areas of cam-oa, cam-oc, cam-r, and cam-bfs were 161.47 ± 27.96, 89.78 ± 19.23, 241.73 ± 34.55, and 329.75 ± 42.73 mm2, respectively, and their medial-to-lateral ranges along the acetabulum (clockface referents) were 12:30 to 03:00, 11:30 to 01:30, 11:30 to 03:00, and 11:00 to 03:30, respectively. Among the 4 displays, cam-bfs had the largest area and medial-to-lateral range ( P < .05), and cam-r had the second largest area and range ( P < .05). No significant difference in the mean distances from the acetabular rim to the superior border was detected among the 4 displays ( P > .05). Conclusion: The cam area displayed by the BFS method on 3D-CT was larger than those evaluated by the AAM method. In the reformatted CT, the sizes and locations of cam deformity differed among the oblique axial, oblique coronal, and radial views, with the radial view showing the greatest area.

Three-Dimensional Quantification of Cam Resection Using MRI Bone Models: A Comparison of 2 Techniques

“…These results are comparable to the metrics of cam morphology obtained using alternative techniques. 12 , 25 , 28 Kang et al 28 used a BFS method to describe cam morphology in 5 patients and reported a mean deformity height ranging from 0.78 to 2.65 mm. In a series of 26 patients with cam deformity, Cong et al 12 used the BFS method to quantify cam surface area and cited a mean area of 329.75 ± 42.7 mm.…”

“… 12 , 25 , 28 Kang et al 28 used a BFS method to describe cam morphology in 5 patients and reported a mean deformity height ranging from 0.78 to 2.65 mm. In a series of 26 patients with cam deformity, Cong et al 12 used the BFS method to quantify cam surface area and cited a mean area of 329.75 ± 42.7 mm. 2 Harris et al 25 used statistical shape modeling on CT-based 3D bone models between patients with FAIS and control participants to evaluate morphologic differences.…”

“… 37 , 47 In 2013, Kang et al 28 described the use of the best-fit sphere alpha angle (BFS-AA) method to characterize the size and location of cam deformity, demonstrating that 3D computed tomography (CT) could be used to define the boundaries of the cam deformity. Cong et al 12 evaluated the relationship of cam deformity between the best-fit sphere (BFS) method on 3D CT and reformatted oblique axial, oblique coronal, and radial views. The authors reported that the cam area displayed using the BFS method was greater than that evaluated on reformatted CT images, with the radial view demonstrating the greatest area among the sequences.…”

“… 3 , 6 , 18 , 32 , 33 Given the complex 3D morphology associated with cam-type FAIS, multiple 2D views are necessary to accurately evaluate cam morphology in the assessment of patients with hip pain secondary to FAIS. 12 , 36 , 52 Increased accessibility of 1.5-T MRI scanners and advancements in imaging techniques have allowed for increased utility of MRI in the clinical setting, thereby eliminating the need for radiation exposure. Additionally, the ability to use MRI to assess soft tissue and bony anatomy has streamlined the preoperative workup by reducing the need for multiple diagnostic tests, with the added benefit of reducing cost.…”

The Modified Longitudinal Capsulotomy by Outside-In Approach in Hip Arthroscopy for Femoroplasty and Acetabular Labrum Repair—A Cohort Study

“…Clinically, patients with symptom for more than 6 months, failure of conservative therapy and positive finding of labral tear on MRI were considered to be the indications of surgery. The surgical treatment of FAI was femoroplasty and/or acetabuloplasty under hip arthroscopy, to correct the osteophyte of cam deformity and/or pincer deformity, as well as repair the torn labrum [ 2 ]. However, only surgeons with high arthroscopic experience could product the hip arthroscopy, due to the hip’s deep location, narrow joint space and high curvature of joint surface, which leading to a very limited arthroscopic view [ 3 ].…”