Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study)

Denne viser hvordan det vi ser på MRI av kne som ofte ansees som medisinske funn egentlig er aldringstegn og helt normale, og med svært liten relasjon til smerte. Den viser også at det er lite sammenheng mellom BMI (fedme) og artrose sett på MRI.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3430365/

The higher the age, the higher the prevalence of all types of abnormalities detectable by MRI. There were no significant differences in the prevalence of any of the features between BMI groups. The prevalence of at least one type of pathology (“any abnormality”) was high in both painful (90-97%, depending on pain definition) and painless (86-88%) knees.

MRI shows lesions in the tibiofemoral joint in most middle aged and elderly people in whom knee radiographs do not show any features of osteoarthritis, regardless of pain.

Fig 2 Knee with multiple abnormalities on MRI indicating early stage osteoarthritis despite lack of radiographic osteoarthritis. A: coronal fat suppressed proton density weighted image shows several features of early OA detectable only by MRI. White arrowhead shows focal full thickness cartilage defect at central weight bearing part of medial femur. In addition there is adjacent subchondral bone marrow lesion presenting as area of ill defined hyperintensity (arrows). Black arrowheads show meniscal extrusion at medial joint line causing bulging of neighbouring medial collateral ligament (no arrow). B: sagittal proton density weighted image shows isolated degenerative horizontal oblique tear of posterior horn of medial meniscus extending to undersurface of meniscus adjacent to posterior tibial surface (arrows). No associated cartilage damage or subchondral bony alterations are seen

Discussion

We found that MRI detected features of osteoarthritis are highly prevalent in the tibiofemoral joint of knees that did not have any radiographic features of osteoarthritis in participants both with and without knee pain. Nearly 90% of our participants had at least one feature of osteoarthritis on MRI. Osteophytes were the most common, followed by cartilage damage and bone marrow lesions. In general, the older the age group, the higher the prevalence of features of osteoarthritis, although differences among age groups were not significant for synovitis and effusion and of borderline significance for ligamentous lesions and bone marrow lesions. Only meniscal lesions were more prevalent in men than women. No significant differences were observed for any type of lesions by BMI.

Our data showed that the prevalence of these MRI detected features is high irrespective of the knee pain status. When we compared the prevalence of MRI abnormalities in knees in people with and without pain, there were two trends. Firstly, and most importantly, the prevalence of MRI findings was extremely high in those without pain, suggesting that using MRI as a diagnostic test for people with normal knee radiographs in this age group would have poor specificity. Secondly, the prevalence of findings was modestly higher in those with pain than in those without, with the difference sometimes reaching significance. These differences, however, were not particularly informative—for example, the highest prevalence of MRI abnormalities was actually in those with mild pain rather than moderate or severe pain.

We did not find high BMI to be associated with higher prevalence of MRI features overall compared with low BMI, but rather that these MRI abnormalities were equally highly prevalent in all BMI groups. We speculate that BMI is important for progression of later stages of osteoarthritis, but potentially age is a much more relevant trigger of early stages of osteoarthritis.

It is important for the clinical community to recognise that findings that would be interpreted as abnormal and suggestive of disease are in fact present in most knees without any pain, even when different definitions of pain are used. That means that the clinical significance of these MRI findings is questionable. The same message has been reported for radiographic findings in patients with low back pain (similar highly prevalent abnormalities were seen in those without low back pain), and this led to discouraging radiographic evaluations in those with low back pain.35

Conclusions

Changes indicative of osteoarthritis are commonly present in the knees of most people aged 50 and over who have no radiographic evidence of tibiofemoral osteoarthritis. Osteophytes, cartilage damage, and bone marrow lesions are especially common among middle aged and older people. These features are common in knees with pain and in those that are painless and can potentially represent pre-radiographic or early stage osteoarthritis. A longitudinal study is needed to determine what proportion of people without radiographic osteoarthritis but with MRI abnormalities subsequently develop radiographic osteoarthritis.

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