The Value of 3T MRI Scan
The importance of 3T MRI in diagnosis of knee injuries
Mr Ian McDermott
Consultant Knee Surgeon
As a specialist knee surgeon seeing large number of patients with knee injuries, I get a lot of people coming to see me for 2nd (or 3rd, or even umpteenth!) opinions, having already had an MRI scan and having already seen a consultant elsewhere. Often they have been told that their MRI scan was normal, that it showed ‘nothing’, or they were told that their scan showed just a bit of ‘wear and tear’ or some early arthritis – and they were simply advised to try physiotherapy and to just rest their knee.
If a patient has been told that there’s nothing wrong with their knee but if they can feel that actually there is something wrong, then more often than not, the patient is normally right!
MRI has been quoted in the literature as being only about 76% accurate for medial meniscal tears, 75% accurate for lateral meniscal tears1 and about 86% accurate for diagnosing ACL tears2. Therefore, for even the most common knee injuries MRI can miss up to ¼ of all potential actual pathologies! A clinician’s differential diagnosis, however, is based on a carefully taken history, a detailed clinical examination and a review of any potential imaging, all backed up with years of training and experience – which gives professional judgement. The value of a good clinician’s ‘gut feeling’ cannot be underestimated, as this comes from ‘deep knowledge’.
Whenever I see a patient whose symptoms and/or clinical signs are suggestive of significant knee pathology but who have already had an apparently ‘normal’ MRI scan, the first thing I want to do is to review the actual scan images myself. At the same time I also ask straight away what kind of scanner was used. Even scanners of the same strength can vary enormously in terms of quality. If the scan images are suboptimal then immediately I will recommend a repeat scan. More often than not, patients’ scans tend to have been performed on 1.5T scanners. I now have a very low threshold for advising someone with an apparently ‘normal’ 1.5T scan (even a seemingly decent quality one) but who have actually got ongoing knee symptoms, to simply have a repeat MRI scan – but on a high quality 3T scanner.
3T scanners give far higher resolution images with significantly better picture quality than a 1.5T scan – and this should now be considered the gold standard for most knee imaging. I’ve lost track now of the number of times that pathology has shown up quite clearly on a 3T scan in a knee where a previous 1.5T scan was reportedly ‘normal’.
The following recent real-life example is typical of the kind of case that I see on a regular basis that exemplifies the exact problems described above….
Gary is a 52-year-old Trader who presented with a 6-month history of right knee pain. Gary’s pain came on after a run, although there was no history of any specific actual trauma at all. Gary was complaining of ongoing pain around the medial side of his knee with slight swelling in the joint, and his symptoms were preventing him from being able to exercise properly.
Gary had been to see a Consultant elsewhere and he had been sent for an MRI scan. He was told that the scan showed nothing wrong except for a bit of wear and tear, and he was told that he was simply developing early arthritis in his knee. He was referred for physiotherapy.
Gary had some physio treatments but unfortunately his symptoms persisted, and he therefore came to see me for a second opinion.
When I saw Gary he was localizing his symptoms quite specifically to his medial joint line. McMurray’s test for meniscal tears (which has moderate specificity but fairly low sensitivity) was negative, but Thessaly’s functional test for meniscal tears (which has a lot higher sensitivity) was positive3. The rest of the knee seemed to be fine.
I reviewed Gary’s previous MRI scan images with him from CD. The scan had been performed on a 1.5T scanner and the image quality appeared reasonable enough. There was just slight increased signal in the tissue of the posterior horn of the medial meniscus, but this looked like just minor degeneration only, and not like an actual tear. The rest of the knee looked fine. Here the blue arrows are pointing to the apparently normal medial meniscus.
I sent Gary for a repeat MRI scan, but this time on a 3T scanner. This scan then confirmed very clearly that he did actually have a definite tear in the posterior horn of his medial meniscus. These images are shown below with the blue arrow pointing to the tears.
Gary felt that his ongoing knee symptoms were bad enough to justify getting something done, and he therefore decided to go ahead with an arthroscopy of his knee. The arthroscopy showed that there was quite a severe radial flap tear in the posterior horn of the medial meniscus (Figure on the left). This was not suitable for a meniscal repair, and therefore the torn tissue was simply trimmed with a partial meniscectomy. The meniscus after a partial meniscectomy is seen on the right (the procedure is to remove the torn tissue and to smooth off and stabilise the remaining meniscal tissue).
Gary is now just 4 weeks post-op, and already his pain has gone and he is back to exercising regularly in the gym, with walking and cycling, and he is continuing to make excellent progress.
MRI scans are an essential part of the assessment of any kind of serious knee problem. Not only does MRI help confirm a suspected diagnosis, but it also rules out any potential weird/rare/’nasty’ pathology in the joint. MRI is also an important tool in helping to plan what might actually need to be done inside a knee surgically, in terms of what equipment and what procedures might be required. Indeed, my personal opinion is that it is negligent to perform a knee arthroscopy without first obtaining an MRI scan.
MRI is not, however, the be all and end all, and it is certainly not perfect or infallible. MRI has a small false positive rate but quite a significant false negative rate. The professional clinical opinion of an experienced clinician is invaluable, and should not be underestimated. Therefore, if you ‘feel’ that something’s not quite right then you should trust your feelings and, for the benefit of your patient, you should take things further.
3T MRI gives superior picture quality to a 1.5T scan, and in any cases where there is any degree of confusion or concern then you should have a very low threshold for referring a patient for a 3T scan of their knee.
The final word should, rightly, come from the patient, and Gary’s specific comments on this issue are:
“I’m extremely glad that I did go to see Mr McDermott about my knee problems. It’s really worrying that things are being missed and that people are being given poor advice based on low quality imaging from second rate technology, when better quality imaging is actually available. I know my body, and I knew that there was something not right with my knee, despite what my previous doctor was telling me. Thankfully my knee has now been sorted properly and I’m now well on the road to recovery. I just wish that I’d had a 3T scan of my knee first time round, which would have saved me months of unnecessary pain and hassle, and I’m glad that my surgeon listened to me and believed me, and that he trusted his professional instincts rather than simply believing my previous scan results.”
1. Hardy et al. Sports Health 2012; 4(3): 222
2. Giannoudis et al. Journal of Trauma Management & Outcomes 2008; 2: 4
3. Karachalios et al. Journal of Bone and Joint Surgery (Am) 2005; 87(5): 955
Mr Ian McDermott
Consultant Orthopaedic Surgeon (Knee Specialist), London Sports Orthopaedics
Honorary Professor Associate, Brunel University School of Sport & Education