The diagnosis of osteoarthritis is generally made through a comprehensive clinical assessment - with imaging studies being used to confirm the diagnosis. The value of simple x-rays are often overlooked as patients assume that they need more sophisticated imaging modalities (MRI) and that x-rays only show “broken bones”. Obtaining adequate x-ray views is important. For example, failing to get a skyline (patella) view or weight-bearing view may mean that important changes are missed.
The hallmarks of osteoarthritis are joint space narrowing, sclerosis, and osteophytosis. If these findings are not present, another diagnosis should be considered. The joint space narrowing seen in osteoarthritis is usually asymmetric - in contrast to the joint space narrowing in other arthritides which is usually symmetric. Sclerosis usually occurs at joint margins and may be associated with marginal osteophytes or lipping. These two findings may not be seen when a patient is also osteoporotic.
While x-rays are a very useful test it is important to recognise that they have some limitations. Firstly the majority of patients who have x-ray signs of osteoarthritis do not have symptoms. As a result, it is important to clearly explain to patients that the presence of x-ray changes are not necessarily a barrier to them getting better. They may also be of no significance and do not necessarily mean that the patient will go on to develop symptoms. Do not B.A.R.F (brainlessly apply radiological findings)! X-rays also lack the sensitivity of other imaging studies. For example, this month’s radiology case shows an MRI image from a patient with medial compartment osteoarthritis. This 49-year-old woman presented with medial knee pain and a normal x-ray (even with the benefit of hindsight). Her MRI scan, however, showed significant full-thickness articular cartilage loss. In cases where a patient has symptoms and signs that are suggestive of osteoarthritis (but a normal x-ray) a specialist referral or high-tech imaging should be considered. MRI is generally the best next test. Ultrasound imaging is almost never helpful (as the problem is intra-articular).