PROJECT SUMMARY
Femoroacetabular impingement syndrome (FAIS) is a common cause of hip pain and disability and a known
risk factor for hip osteoarthritis (OA). Patients with FAIS present with a loss of sphericity of the femoral head,
reduction in femoral-neck offset, and/or prominent acetabular wall. Patient symptoms as well as patterns of soft
tissue damage to hip cartilage and labrum (i.e., ‘chondrolabral’) tissues support the clinical theory that hip
pathoanatomy creates pathomechanics. Still, the presence of impingement deformities does not reliably predict
symptoms, soft tissue damage, or OA status. Earlier detection of structural and compositional changes to
cartilage and labrum would enhance clinical diagnostics and decision making for FAIS. Small, physiologic
changes in the water content of cartilage and associated changes in proteoglycan content and collagen density
– factors involved in early joint OA – can be evaluated by T1ρ and T2 mapping with quantitative MRI (qMRI).
Here, we propose an ancillary R21 study to interrogate relationships between hip anatomy, biomechanics,
and image-based measurements of cartilage and labrum ultrastructure provided by qMRI. We will incorporate
qMRI into our existing imaging workflow for the Parent R01. We will then leverage the statistical shape models
(SSM) and finite element (FE) modeling data provided by the parent R01 to study form-function relationships in
FAIS through two aims. Aim 1 will investigate links between hip morphology and chondrolabral tissue
ultrastructure by quantifying associations between spatial T1ρ and T2 maps of cartilage and labrum with a local
measure of the shape of proximal femur and acetabular bone shape as evaluated by a 3D statistical shape
model. Aim 2 will then investigate links between hip mechanics and chondrolabral tissue ultrastructure by
quantifying associations between spatial T1ρ and T2 maps with a local prediction of the stress and strain in the
cartilage and labrum as evaluated by patient-specific finite element models. We will test the hypothesis that
regions of greater bone deformity and elevated chondrolabral stress and strain as predicted by SSM and FE,
respectively, will coincide with regions of decreased proteoglycan content and loss of collagen organization, as
estimated by qMRI.
The ancillary R21 complements and leverages the parent R01 project in ways that will help us to identify
mechanisms underpinning chondrolabral damage and hip OA in patients with FAIS. To our knowledge, this will
be the first study to demonstrate the spatial correlation of T1ρ and T2 maps with 3D hip shape and chondrolabral
stresses/strains. This information will provide more direct evidence linking hip anatomy and biomechanics with
biochemical changes associated with OA. In the future, the developed framework could be expanded to develop
imaging biomarkers that predict hips at risk of degeneration and to evaluate the longitudinal effects of operative
or non-operative treatments for FAIS.
