Today we are going to talk about a study published in Foot and Ankle International in 1998. The research study was led my Dr. Matthew Rocket (a well-respected Foot & Ankle Surgeon) in Houston Texas.
This was a great study comparing the effectiveness of MRI and diagnostic ultrasound when trying to decide whether or not there is an actual tear in a tendon around the foot and ankle.
What the researchers did was diagnostic ultrasound and ankle MRI on patients that were suspected of tendon tears. Once they were actually in surgery they were able to look at the tendon and see whether or not there was really a tear, or not.
What they found was that MRI sensitivity for tendon tears around the foot and ankle was only 23.4%.
Ultrasound sensitivity for tendon tears around the foot and ankle was 100%. When you look at all the factors MRI was about 65% accurate and ultrasound was about 94% accurate.
So how can that be?
We often think that MRI gives us a complete and total picture of what’s happening in the foot or ankle. After all, if you’ve ever looked at your own MRI and seen that you have about 100 images or so you really think that you’re looking at every single thing from every single angle. But you simply are not.
What you’re really seeing is slices of the foot and ankle from three different directions to produce a whole bunch of different pictures. All of those pictures are taken with the foot in one particular position, without any movement at all.
One of the advantages of diagnostic ultrasound is that we can actually stress, strain, stretch and pull tissues to see whether or not anything changes when the foot, toes and tendons are put in a different position.
Sometimes when you have a tear in the tendon, it has been chronic because you are runner who’s been running on it. After some time, the water content goes down and it becomes much less visible on MRI.
But when we look at it with ultrasound and actually stretch the tendon, that tendon tear can become more obvious.
False Negatives Happen!
Don’t get over-sold on MRI.
Rockett MS, Waitches G, Sudakoff G, Brage M. Use of ultrasonography versus magnetic resonance imaging for tendon abnormalities around the ankle. Foot Ankle Int. 1998 Sep;19(9):604-12. doi: 10.1177/107110079801900907. PMID: 9763166.