MRI ANKLE: HOW TO IDENTIFY FLEXOR RETINACULUM TEARS AND STRIPPING

This is really a sort of a pattern of what happens to ligaments and retinacula with acute trauma. But the thing is that what we need to, the extra bit here is that you have a ligament tear, say a deltoid tear, deltoid ligament tear. And again, most people just, most reports will just say, this is a high-grade tear of the deltoid.

But you need to look around, you need to see what else is there. So, one of the other things that tears with the deltoid is the flexor retinaculum. So, let’s look at that. So here we’ve got a high-grade tear of the deep fibers of the deltoid and also the superficial. So, we could stop there. mean, the clinician is probably going to be happy enough. But we need to look at what other structures are there and the other structure, the deep fiber is a deltoid attached to the medial malleolus here. The other structure that attaches to the medial malleolus is this. This is a section, a dissection section, and this is the flexor retinaculum. And the flexor retinaculum, mostly we know it because it encloses the tarsal tunnel. But when you have trauma, particularly to the deltoid ligament, this can be torn and it’s important to be able to identify that. So, what does the normal flexor retinaculum look like? Again, these patterns of normal, all retinacula are pretty well the same, whether you’re talking about the flexor retinaculum, the extensor retinaculum, any retinaculum anywhere. They’re generally low signal, and they’re well defined, and they’re relatively thin. So, this is what we see here. This is the Flexor retinaculum on the coronal scan. This is it on the axial scan. And, if we look at it on these coronal images, you can see, this is this black line that is going up and attaching to the medial malleolus. Now the deep fibers of the deltoid which are here, let me go there, which are here, they also attach in this region. So, which is why if you tear that deltoid you will also, not you will, but it has a good chance if it’s a severe tear there’s a good chance that you will tear the flexor retinaculum as well.

This other structure here is the superficial one, the superficial fibrous, the deltoid. So generally, what happens is that you’ll get a high-grade tear here and this sort of just extends out. So, the superficial will be torn and also the flexor retinaculum. And on the axial scans, what does it look like? Well, you can see it. This is it here, or part of it is here. And as we scroll up, what you see is that it starts to approximate that medial malleolus. And together with the deep fibers of deltoid, they attach almost together. There’s no real gap between them. But if you’re looking for retinaculum, the best way to look for is on the coronal images.

So then what do we look for? So, the first thing is that they’re not isolated tears. You’re not going to get someone coming in with an ankle sprain or trauma to the ankle and the flexor retinaculum is the only thing that’s torn. Generally, what happens that you see it with a tear of the deltoid. So, you should have a fairly high-grade tear of the deltoid and then there’s also an involvement of the flexor retinaculum. And what we see is the same. So again, this pattern thing. Tendon injury, sorry, ligament injury or retinacular injury, they all become hyper intense, and they become ill-defined and they become thickened. There are only three things they do. So, this is why I like MSK. It’s pretty simple because I really like simple things. And the simplicity of this is that whenever you have trauma to a ligament or through a retinaculum, the most common pattern you’re going to see is that they will become hyper intense, they will thicken, and they will become ill-defined. So, if you look at this lower portion of the retinaculum here, it’s nice and black, it’s low signal and it’s well defined. As you come up towards the attachment, it becomes ill-defined, hyper intense and thickened, which is what virtually every retinaculum or ligament will do.

What do we look for? So, we look for two things. The first thing you’re going to see is actually the deltoid tear. Second bit is to look for the ligament. There are two things that can happen to it. One is, sorry, let me go back. One is what we’ve just discussed is a tear. So, you see hyper intensity, but there’s no stripping. But the flexor retinaculum can also get stripped off. So, if you look at the retinaculum here, it comes up and then there’s a gap between it and bone. So, this is the retinaculum that’s been stripped. So instead of tearing, it’s basically just pulled periosteum off. So again, same pattern that we saw in the first section, just at a different spot. But the pathology is the same, the mechanism is the same. It’s just the, instead of the retinaculum failing or the ligament failing, the periosteum fails, and the periosteum gets lifted off. And then you see two lines. If I go back here, single black line. Now we’ve got two black lines. This is a flexor retinaculum tear plus periosteal stripping and there’s some bone marrow edema as well. So, the bone marrow edema is the thing that can draw your attention to it. But I think what you do is that when you’re reporting this, if you see a deltoid ligament tear, the next bit you need to go and look at is the flexor retinaculum, which is just next door to it. It’s easy.

What does that look like? So, let’s look at this. So, we’re going from, I think, distal to proximal. So, here’s the flexor retinaculum. This part is normal. It’s nice and black. But as we start coming up, it becomes ill-defined. Not terribly thickened there, but it’s hyper intense. And again, there. And then the other thing we see is that there are two black lines. It’s been stripped off the bone. And then in between, this will be hemorrhage and edema.

And this person also has edema, bone marrow edema as well. This is the pretty high-grade tear of the deep fibers of the deltoid. So, there’s no normal fibers there at all. So really generally you need a decent amount of tearing of the deltoid to see this. And on the axial scans, you can see it, but it’s not that great. So, here’s the flexor retinaculum. As we come up, this is it here torn. But it’s very hard. I find it hard conceptually to actually see easier to see this, if You see it on the on these coronal scans. So, for that, for the flexor retinaculum, look at the coronal scans. OK, key points for this are, when you have a deltoid ligament tear, look next door, look at the flexor retinaculum and look at it on the coronal images. What you’re looking for is ill-definition of the retinaculum, hyper intensity, you’ll get thickening as well and quite often, if there is periosteal stripping, there’s injury to bone, will get bone marrow edema as well.