AN INTEGRATED, MULTIMODAL IMAGING APPROACH TO ASSESS FUNCTIONAL JOINT PATHOMECHANICS, PATHOPHYSIOLOGY AND STRUCTURAL CHANGES IN EARLY-STAGE KNEE OSTEOARTHRITIS

Abstract

INTRODUCTION

Joint pathomechanics is considered one of the key etiological factors in OA genesis and progression. Numerous studies have assessed joint biomechanics in advanced stages of OA, mainly in the knee. However, little is known about its role in the onset and progression in earlier stages of OA and specifically how cartilage loading relates to OA-related structural features. This is partly due to limitations of conventional optical motion capture (OMC) systems, with measurement errors that often exceed the subtle changes in movement patterns to be expected in early-stage OA. Hence, OMC-based studies in early OA often report inconclusive or conflicting results. Fluoroscopy is an imaging technique that, combined with a 3D bone model, can be used to very accurately assess 3D bone orientations during weight-bearing functional tasks, thereby overcoming the limitations of OMC. Additionally, novel combination of sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) with MRI can be used to assess pathophysiology (i.e. subchondral bone metabolism and cartilage composition) and structural changes. A unique combination of these complementary technologies could elucidate their relationship in early-stage OA.

OBJECTIVE

We aim to develop an integrated, multimodal imaging-based approach to assess joint pathomechanics, pathophysiology and structural changes. By using high-fidelity biomechanical and PET/MRI measurements, we intent to gain insight into the relationship between cartilage load, bone metabolism and structural changes in early stages of knee OA.

METHODS

We are establishing a beyond state-of-the-art biomechanics lab at our institution, combining a monoplanar fluoroscopy setup with a conventional OMC system including an instrumented treadmill. We will use intensity-based image registration to estimate 3D-bone positions from fluoroscopy, using MR images (multi-echo gradient-echo sequence) that we will convert to a pseudo-CT. These methods will provide us highly accurate joint kinematics, from which joint contact forces, cartilage load distributions and cartilage stress and strain can be derived by using personalized musculoskeletal and finite-element models. Our MRI protocol additionally facilitates semi-quantitative evaluation of OA-related structural features using the MRI Osteoarthritis Knee Score (MOAKS), assessment of cartilage composition (T1-rho and T2-mapping) and quantitative assessment of synovitis (dynamic contrast enhanced imaging). This will be combined with dynamic ¹⁸F-NaF PET-imaging to quantitatively evaluate subchondral bone metabolism.

RESULTS

We have developed a PET/MRI protocol and are developing our fluoroscopy processing workflow. With these methods we will start our clinical studies in the summer of 2024 involving ACL-reconstructed individuals and overweight individuals with early-stage symptomatic knee OA

CONCLUSIONS

By utilizing imaging techniques including fluoroscopy and PET/MRI, we will be able to measure joint biomechanics accurately and precisely during gait and other functional tasks in individuals with early-stage knee OA. By combining high-fidelity pathomechanical measurements with high-fidelity pathophysiological and structural measurements, we aim to elucidate the relationship between cartilage loading, bone metabolism and structural features in early stages of knee OA.