The clinical utility of imaging in osteoarthritis and its importance in future prediction of total hip replacement; a nested case-control study within the AGES-Reykjavik cohort

Current guidelines are split on the role that imaging has in the clinical assessment of osteoarthritis (OA), yet clinical CT imaging has now revealed how a 3D approach can improve prediction of TH replacement (THR) over 2D measures alone. We applied 2D grading and measurement along with 3D cortical bone mapping to ordinary clinical CT imaging of the pelvis in a cohort of healthy older people, aiming to discover which of these features had clinical utility in predicting THR within 8 yr and which were related to baseline hip pain. Using a nested case-control design in the Age, Gene/Environment Susceptibility-Reykjavik (AGES-Reykjavik) study, 74 future THR cases were age and sex-matched with 184 controls from the cohort (age 74 +/- 5 yr). Baseline assessment involved a validated hip pain questionnaire and pelvic CT. The following were performance-tested using receiver operating characteristics analysis and clinical utility index: (1) hip pain, (2) Kellgren and Lawrence grade (K&L grade), (3) minimum joint space width, and (4) 3D cortical bone thickness (CTh). The clinical utility index for prediction of future THR from baseline pain was poor at 0.28, with the inclusion of imaging improving this to 0.79 (K&L grade) and 0.82 (3D CTh). Self-reported hip pain at baseline was also a poor-to-marginal predictor of THR (AUC = 0.63), but 3D cortical thickening at the femoral head was predictive of future THR (0.81). Having radiographic OA strongly predicted THR irrespective of hip pain (0.85). Combining hip pain, K&L grade, and 3D CTh gave optimal prediction (0.88). Ascertainment bias may have occurred, if primary care physicians requested their own radiographs of their patients' hips. Imaging features from standard clinical CT identifies patients at high risk of progression to surgery for OA, regardless of baseline pain.Hip osteoarthritis (OA) is a common and debilitating degenerative joint disease that often results in chronic pain and disability affecting individual's quality of life and potentially leading to other conditions, such as obesity, diabetes, and cardiovascular disease. Early diagnosis and staging of arthritis offers the opportunity to tailor treatment plans to an individual patient's circumstances, particularly helping the general practitioner decide who to refer for hospital surgeons to consider definitive replacement of the arthritic hip joint. Our study shows that timely hip X-ray measurements, whether they are standard front-to-back X-rays or more complex 3D scans of older, healthy people with hip pain would greatly increase the general practitioners' ability to predict those patients who will require future hip replacement for severe OA. Conversely, the same simple image results would allow the general practitioner to reassure most patients with hip pain that they will not require surgery for severe OA in the coming years. We suspect that in Iceland, where this work was done, doctors and nurses already follow these simple principles so we now suggest looking at outcomes in a country, such as the United Kingdom, where general practitioners are strongly advised by national guidelines not to ask for X-rays in their patients.