'Normal' Abnormalities in Our Knees
Article Review: Structural abnormalities detected by knee magnetic resonance imaging are common in middle-aged subjects with and without risk factors for osteoarthritis.
Kumm et al.
Published in Acta Orthopaedica, October 2018, 89(5):535-540
Modern medical imaging techniques such as MRI (magnetic resonance imaging) allow us to see the structures and tissues within our bodies in an extraordinary amount of detail. This can be incredibly useful to medical specialists, helping them to make good decisions about patient care. But, as we discussed here (Ignorance Might Be Bliss When it Comes to Medical Scans), these highly detailed and readily available scans can lead to premature, unnecessary and unhelpful diagnosis of normal age-related changes that are not actually a problem. A good example of this was highlighted in a 2018 article by Jaanika Kumm looking at the use of MRI in diagnosing knee osteoarthritis (OA).
Kumm and colleagues recruited 340 ‘normal’ subjects aged 45-55. These people had no pain, stiffness or swelling in their knees, and had no evidence of OA on X-ray. They were separated into two groups, either with or without risk factors for osteoarthritis (such as obesity, previous knee trauma, previous knee surgery, family history and repetitive knee bending). Every subject had MRI scans of their knees at 2 year intervals over a 6-year period. Their scans were reviewed for signs of OA, including bone spurs (osteophytes), cartilage damage, cysts, meniscal tears, inflammation of the joint lining, swelling, or ligament abnormalities. The same radiologist reviewed all the images, without any knowledge of which group the subject was in.
What did they find? In the group with pain-free knees and some OA risk factors, 96% of the subjects had at least one ‘abnormality’ on MRI, most commonly cartilage damage (82% of subjects). In the group with pain-free knees and no risk factors for OA, 87% of subjects had at least one ‘abnormality’ on MRI. Again, the most common was cartilage damage (67%).
In short, almost all people aged between 45 and 55 years will have some MRI sign of ‘abnormality’ in their knee joints, despite having no symptoms, and regardless of whether or not they have risk factors for osteoarthritis. This fact could be interpreted in at least 2 different ways:
Maybe almost all people are developing knee osteoarthritis by the age of 45-55, and an MRI is sensitive enough to pick it up, unlike an X-ray. But, if there is no pain, does this information help us?
Or
The ‘abnormalities’ used to diagnose the presence of OA should actually be considered ‘normalities’- a simple sign of normal age-related knee joint change, rather than a necessary sign of developing osteoarthritis.
This article provides more evidence for the growing consensus that the disease of osteoarthritis is better understood as a spectrum, ranging from; normal age-related joint changes to diagnosable OA to severe degenerative changes. It also confirms that in fact there is no correlation between where a person sits on this OA spectrum and their individual symptoms.