Statistical shape modeling of cam femoroacetabular impingement

Abstract

Statistical shape modeling (SSM) was used to quantify 3D variation and morphologic differences between femurs with and without cam femoroacetabular impingement (FAI). 3D surfaces were generated from CT scans of femurs from 41 controls and 30 cam FAI patients. SSM correspondence particles were optimally positioned on each surface using a gradient descent energy function. Mean shapes for groups were defined. Morphological differences between group mean shapes and between the control mean and individual patients were calculated. Principal component analysis described anatomical variation. Among all femurs, the first six modes (or principal components) captured significant variations, which comprised 84% of cumulative variation. The first two modes, which described trochanteric height and femoral neck width, were significantly different between groups. The mean cam femur shape protruded above the control mean by a maximum of 3.3 mm with sustained protrusions of 2.5–3.0 mm along the anterolateral head-neck junction/distal anterior neck. SSM described variations in femoral morphology that corresponded well with areas prone to damage. Shape variation described by the first two modes may facilitate objective characterization of cam FAI deformities; variation beyond may be inherent population variance. SSM could characterize disease severity and guide surgical resection of bone.

Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

“…Because the focus was on cam-type FAI, we selected common recurring parameters of the proximal femur, as opposed to the acetabulum, postulated to describe characteristics of FAI. To fully understand the relationship among joint structures, clinical signs, and the role of acetabular orientation on joint kinematics, an extensive study of the morphological parameters associated with the acetabulum (eg, lateral center-edge angle and retroversion index) may be needed in the future along with a 3-D shape analysis of the cam deformity [20,21]. Because the cam morphology is statistically more prevalent in males [2,9,27], our sample population consisted of only male participants.…”

Cam deformity and the omega angle, a novel quantitative measurement of femoral head-neck morphology: a 3D CT gender analysis in asymptomatic subjects

“…More specifically, our results stress that the α°alone is not an appropriate parameter to define cam lesions and that thresholds should be redefined according to sex and cam location. In recent CT-based studies, 3D bone reconstructions of the proximal femur have been used to evaluate femoral head sphericity using α°measurements [12,34] and model fitting [56,57]. However, normative data is lacking on 3D CT morphology of the femoral head in asymptomatic individuals.…”

Computed tomography arthrography with traction in the human hip for three-dimensional reconstruction of cartilage and the acetabular labrum

“…Images can be used to measure cartilage thickness, 27,39 and thus evaluate the progression of hip OA or evaluate the integrity of the cartilage prior to surgery. Images can also be used for translational research, including reconstruction into three-dimensional models to measure hip morphometrics 20,40 and estimation of the mechanical forces applied to the cartilage and labrum to study the origins of hip OA. 21–23,37 For biomechanical models, the entire articulating surface must be visible as accurate representations of hip cartilage geometry are required to obtain realistic predictions of hip joint contact mechanics.…”