Effects of Knee Flexion on Minimal Joint Space Width Increase in Knee Osteoarthritis Patients in the IMI-APPROACH Cohort

Purpose (the aim of the study): The minimal joint space width (mJSW) is an important parameter in knee osteoarthritis (OA) studies like the prospective IMI-APPROACH cohort. A decrease in radiological mJSW typically indicated cartilage loss in knee OA. However, some IMI-APPROACH patients show an increased mJSW over two years, possibly due to factors like cartilage swelling, cartilage tissue repair, measurement error, reduction of weight, meniscus extrusion, and knee positioning during acquisition of the x-ray. Statistical shape models (SSM) can determine positioning variations by quantifying anatomical shape variations of bone structures of a population. An SSM indicates contour variations of the knee that may reflect variations in bone shape, or indicate positioning variations during acquisitions, such as knee rotation or flexion. This study investigates whether positioning variations during acquisition of knee radiographs contribute to mJSW variations, and whether this led to falsely marked progressive patients.