 Young man injury to the thumb I'm gonna scroll and ask you to decide a what's the injury and be how severe is the injury I'm gonna stop right in the mid-coronal plane, and I'm gonna draw Let's draw I'm gonna use my MR picture. It's a template. I have a proximal phalanx. I Have a metacarpal And then I have collaterals I'm gonna change the color for my collaterals. I've got a radial collateral, which I see right here There's some signal in the radial collateral, especially on gradient echo imaging And that's okay in people that use their thumb a lot or older individuals as long as it could it's a continuous curvilinear structure I'm sure you've already noticed that the contiguous curvilinear structure is disrupted on the owner side But in the normal state we want to see something that looks a bit like this With about two millimeters of coverage on either side of the joint Okay, let's take our our lines away and look at the signs of an unstable ulnar collateral ligament tear first sign the metacarpal is falling off the face of the earth towards Your right or in other words the metacarpal looks like it's drifting eastward That's an indicator of instability Next sign obvious sign RCL No discernible clear-cut UCL just a ghost The next sign if we look at the adductor epineurosis, and I'm gonna draw There's the adductor epineurosis And we look at the stump of the UCL, which I see on my T1 weighted image right there and my fast-spin echo fat suppression image right there They look like they're crossing each other For normally the adductor epineurosis would be in this orientation the UCL would be in this orientation So the orientation has changed I call this the crisscross sign Another sign of UCL tear or rupture would be the yo-yo on a string sign. I Think that's probably best seen on this gradient echo image Here is the string of the yo-yo right here I'm gonna use my pen to show it Here's the string of the yo-yo, and there's the yo-yo right there The yo-yo on a string sign better seen on this thin section gradient echo image Another sign that I use Is called the fold over sign in other words it looks like the UCL has folded backwards on itself That's not easily appreciated here There's a glob of gray signal intensity tissue here, but on the gradient echo. Oh, there's the fold over It's going backwards This structure. I'm going to draw again You see I get my pen to work here we go this structure which normally should be going this way is going this way the fold over sign Another sign that I use quite readily is what I call the lollipop sign It looks like the stick of a lollipop is pointing straight out Let me draw again straight out from the metacarpal There's the base or stick of my lollipop or the base of my ice cream cone Then as I scroll more dorsally That area of interest here's we're going palmarly now towards the Sessamoids just to get oriented There are two sessamoids now. Let's scroll dorsally just so you get your bearings we go dorsally and there is our structure our UCL right there sticking out medially and It should not be present perpendicular to the axis of the proximal phalanx in the metacarpal it's sticking straight out Towards the adductors We are on the most dorsal aspect of the thumb So an exaggerated appearance of our lollipop sign in the dorsum of the thumb Finally, let's pull down our axial projections Take me a second to do this, but just trying to be as efficient as possible with your time Let's blow them up. We have a short axis t1 and a short axis gradient echo and We should see curvilinear radial collateral ligaments on both sides We do have a curvilinear. Sorry. We should see curvilinear collateral ligaments on both sides We do have a radial collateral ligament But only a ghost of our own or collateral ligament and where is it? It's pointing Dorsal and medial. I call this the dorsal medial lollipop sign Short axis view here it is right there There should be no structure there Pointed along the edge of the metacarpal that is a total clincher for the diagnosis of a Stener lesion So you've got lollipop sign dorsal medial lollipop sign yo-yo on a string sign Fold over sign Empty ulnar collateral ligament Fossa sign just to name a few as Indicators of the high-grade UCL or grade four stener type form of ulnar collateral ligament tear and by the way This injury has been so violent that we have affected other structures like the adjacent interosseous muscles and the adjacent abductor muscles as an aside there are four dorsal interossei and three palmar interossei Although the interosseous next to the thumb is not really an interosseous It is formed by the abductor policies. That's why there's only three along the palmar side and four along the dorsal side that is An example of a stener lesion with all the signs wrapped in a neat package