Knee pain is a common complaint among middle-aged patients and, although not the only cause, many cases trace their source back to osteoarthritis or some other type of degenerative joint disease. The use of MRI scans to diagnose knee pain is increasing, but many of the changes caused by degenerative diseases can appear on X-rays as well. A group of researchers sought to find which of the two is the best screening tool for knee pain. Their findings seem to suggest that X-rays (radiographs) have a useful role to play in helping those who wouldn’t be helped by an MRI, but it isn’t clear how they draw that conclusion and the math gets a bit murky.
In Brief: Study Format and Findings
The study design was relatively simple. Patients with knee pain were followed to see if they got a MRI or X-ray done prior to being referred to an orthopedic specialist. The rate of scans and whether they influenced treatment recommendations was observed. These are the findings:
- Of 599 patients, 22% (130) had pre-referral MRI scans
- Of this 130, 13% (17) had weight-bearing radiographs as well
- Of those who had MRI, 22 (17%) had results which showed over 50% loss of joint space (deterioration from arthritis)
- 62 (48%) of the pre-referral MRI did not appear to contribute to treatment recommendations
- Among the patients with MRI and weight-bearing radiographs showing over 50% loss of joint space, the MRI was considered unnecessary 95% of the time
- Based on the above, the researchers concluded that many pre-referral MRI did not contribute to clinical decision-making and that weight-bearing radiographs could help identify patients in whom MRI would not be helpful
The study was looking at patients who were presenting to an orthopedic surgical clinic, where the main determinant of whether to get surgery is loss of joint space.
And Now: Confusion
Now, one thing that is missing from the findings, which would be really helpful for figuring out the researchers’ reasoning, is that there is no mention of how many people had both MRI and weight-bearing radiographs showing over 50% space loss. This is important since one of the main findings is that, of this group, 95% of the MRIs were not considered helpful. It is essential to know how many actual patients make up that 95%, but this information isn’t given. We don’t even know how many of the radiographs showed over 50% joint space, or whether there were any instances where the MRI and radiograph results differed.
We know 22 patients had an MRI showing over 50% joint space loss, and we know 17 had MRI and weight-bearing radiographs. The authors seem to be operating under the idea that these two groups completely overlap, but they don’t provide the data to actually support it. It isn’t even explained what criteria was used to determine that those 62 MRI scans didn’t contribute to treatment recommendations.
What This Means
The study throws out numbers and percentages but doesn’t mention the ones that would actually be capable of supporting the conclusion. X-rays can be a screening tool for knee pain among middle-aged patients, but there isn’t any support for the idea that it is the best screening tool or even one able to show which patients an MRI can’t help. The authors seem to be making some claims without proof and, if they actually have the data, it would really help if they bothered to include it.
Muyibat, A., et. al., “The Use of MRI in Evaluating Knee Pain in Patients Aged 40 Years and Older,” Journal of the American Academy of Orthopaedic Surgeons, 2016; 10.5435/JAAOS-D-15-00681.