The Kinematics of the Hip Joint with Femoroacetabular Impingement May Be Affected by the Thickness of the Articular Cartilage

The abnormalities in the shape and orientation of the femoral head and neck or the acetabulum are important morphological characteristics of femoroacetabular impingement (FAI). Concerns exist about the effect of damaged cartilage on the kinematics of the affected hip joint. The current study is aiming to track the motion of a femur bearing a cam deformity, with healthy or damaged articular cartilage. This may prove useful in understanding the changes occurring in a hip joint with cam-type FAI, as arthritis develops and progresses. A three-dimensional (3D) model of the left hip joint of a male patient diagnosed with FAI was obtained from pre-operative Computerised Tomography (CT) data using density segmentation techniques in Mimics 13.1 (Materialise NV). The kinematics of FAI was analysed in Abaqus 6.9 (Simulia Dassault Systems) using a finite element method. The translation and rotation parameters were defined in a single step for each one of three cases: healthy cartilage, 2mm (one-sided thinning) and 4mm (two-sided thinning) worn-out articular cartilage. As the acetabulum and femur came into contact, the penetrations were detected and the contact constraints were applied according to the penalty constraint enforcement method. The results of the analysis showed that thinning of the cartilage at the hip joint adversely affects impingement, as range of motion was decreased with progressive thinning of the articular cartilage.