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Board Review Imaging

MRI Evaluation of Forefoot Pathology

Michael Troiano, DPM

Michael Troiano, DPM gives an overview of how MRIs work and how they can be beneficial to a patient with podiatric pathology. Dr Troiano reviews common forefoot injuries and abnormal MRI findings associated with each one.

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Goals and Objectives
  1. Understand how an MRI works
  2. Identify which structures of the foot can be seen on what view of an MRI
  3. Identify forefoot pathology on MRI
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  • CPME (Credits: 0.5)

    PRESENT eLearning Systems, LLC is approved by the Council on Podiatric Medical Education as a provider of continuing education in podiatric medicine.

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    Release Date: 03/16/2018 Expiration Date: 12/31/2018

  • Author
  • Michael Troiano, DPM

    Center for Foot and Ankle Disorders
    University of Pennsylvania - Penn Wound Care
    Adjunct Clinical Professor, TUSPM
    Philadelphia, PA

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    Michael Troiano Dr. Michael Troiano has disclosed that he has a financial relationship with HealthPoint

  • Lecture Transcript
  • Male Speaker: It gives me great, great pleasure to introduce my friend Michael Troiano. He is a 2004 graduate of Temple. He completed his residency at Graduate Hospital at Philly. Currently he’s in private practice at the Center for Foot and Ankle Disorders at Philly. He’s also an adjunct professor at Temple. His expertise is board certified reconstructive and ankle surgeon, and holds teaching faculty positions at a number of facilities. So without further ado, here’s my good friend Michael Troiano.

    Dr. Michael Troiano: Alright. Thank you for staying. I figured as this is one of the last lectures that we would have this weekend, I’ll kind of keep it light, fun, and airy. MRI reading is something that I teach at the college. I’ll never forget 2007, 2008, when I was hired to teach a class. Put together this huge PowerPoint with all these crazy pathology and all the students kind of looked at me like ten heads. As I’ve had the opportunity to kind of lecture around the country, I’ve seen a myriad of ability with MRI reading with people who are kind of experts to people who really shy away from ordering them because they’re uncomfortable. Maybe they were trained after MRIs became popular or what have you. Just never have the understanding to think three dimensionally. So we’re going to kind of take a short step away from the anatomy and the MRI and then get into some of the more common methodology and we’ll keep it light and airy. No normal. We as the podiatric surgeon cannot necessarily identify every single abnormal that we find. What we can do is we can identify abnormal scenarios. So if we know the normal, we can say that just kind of looks askew or what have you. We can make a phone call and see what’s going on. MRI should help you confirm the diagnosis. There’s no substitute for comprehensive physical examination. Why that’s important is so many times we’ll see somebody with an ankle sprain or what have you and we’ll say MRI says you’re okay. Then we say well, is he or she a malinger? What’s going on? Did this happen at work? Are they faking it? But physical examination is always king. Read your own MRIs. If you look at the litigious nature that is medicine, a lot of hospitals are now hiring musculoskeletal MRI. It should be radiologist. But a large portion of them don’t have them. Most hospital, most radiologists are going to focus on the big things that are going to get them sued like the aneurisms, the brain tumors, what have you. They don’t really care about the ATFL or the CFL. You are the expert. What that basically means is we have to identify the pathology that exists. If the physical examination is not corroborated by the MRI, let’s call that particular reading radiologist or get a second opinion. Let’s document. Take the extra step. Because chances are no one sees many foot and ankle as we do across the United States. So if you have a hunch or you have pathology or you think the radiologist miss something, they probably did. Recap. An MRI is basically a big magnet. The magnet turns on and off. When it turns on and off, there’s the pulse electrical magnetic field that passes through and excites hydrogen atoms and protons. That’s the kind of kiss principle to an MRI. Because of the magnetic field, it aviates or makes unnecessary the ability for two different types of people. Number one, those with pace makers, and number two those with implantable metals. Whether they be surgical, pre 1980, or shrapnel. From time to time you’ll see men and women who are metal laborers with little pieces of fracas in their eyes. You’ll have the World War 2 or Vietnam vet with shrapnel in his or her body. Then of course pacemakers are rampant now. With that said, as MRIs are getting more and more popular, pacemakers, metal, are getting more and more MRIable as well. So that’s not necessarily 100% true but the fast and hard rule is no metal, no pacemakers. There are some contraindications that are relative. Obesity, the table weight is usually about 350 pounds. Those are over 350 pounds. Go to your local veterinary school which may make them lose weight just going there. Pregnancy is not a contraindication because there is no ionizing radiation. Then of course claustrophobia is a relative contraindication. However, with that said, yes sir. Yup, that’s where I’m going [Laughs]. So claustrophobia is a relative contraindication as well. However most of our patients only go in from the hips downward. There are certain metallic-based tattoos which are coming into question now as to whether or not they cause an issue.

    [5:06]

    Now again, you would think an implanted metal can travel. But skin really is not going to move. The worst thing you would see is kind of running of this tattoo. But at the least it can get painful. So it’s very, very important to counsel your patients prior to ordering the MRI on pacemaker, on implantable metals. I’ll tell you what. There’s been so many times that even preoperatively, especially young kids, people have Prince Alberts, people have their scrotums pierced, they have nipple rings. We have some crazy patients out in the world. So you really have to go through not necessarily a physical examination of those parts, but at least inquire as the piercings, tattoos, what have you. Then the MRI center will as well, but we have to catch them. Contrast dye. Everybody thinks that contrast dye should be used for every sort of osteomyelitis or abscess that exists. Not necessarily true. All contrast dye does, it kind of provides a backfield so you can see the images a little bit better, but not necessarily. If you’re going to order contrast dye, order creatinines because you can shut down someone’s kidneys. In fact, most MRI places will not allow you to order contrast dye without current creatinine. How does the MRI work? They basically excites hydrogen atoms and protons. So water in your body. There are two major images created, a T1 and a T2. The T1 is the anatomy image. The T2 is the pathology image. On a pathology image, what lights up bright or white is FITS, fluid, inflammation, tumor and synovitis. That’s the acronym. Fluid, inflammation, tumor, and synovitis, FITS. The T1, you will see bone image white, tendon image black, and muscle image grey. Again, that’s based on water and fluid. So dense structure like a tendon is black as night and something vascular like the bone is white. MRIs themselves are not three dimensional. What that means is we now have the advent of ordering the 3D CT scan where can take the CT scan and spin this foot and ankle around and look at it 3D. MRIs cannot. You have to be a spatially oriented person to be able to check the axial, the coronal, and the sagittal, and then put them in your mind as a 3D picture. Multiple slices to find pathology. We wouldn’t necessarily read one patient one page of a book and say I know what’s going on with that story. You can’t look at one slice of an MRI and know what’s going on with the patient. Of course multiple views. So if you think you have something going on with the peroneals, don’t just look at the sagittal. Look at the sagittal, the axial, the coronal, and all the images of that pathology which correspond. This is a more eloquent way of showing what image is white or dark on a T1 or T2. I’m not going to belabor the point. Got it? Okay. Alright. So the MRI image’s axial coronal and sagittal plates. Now the sagittal are very easy to understand because the sagittal look like a lateral view of a foot x-ray. It’s basically five millimeters slices from the outside or pinky toe, the fifth metatarsal moving medially. The axial and the coronal get a little bit more confusing. If you look historically, the axial or you’re taking a picture from the knee looking down at the bottom of the foot. So if we’re going to speak radiographically, it looks like a DP view or a AP of food x-ray. The coronal will look like an AP view of an ankle x-ray. It’s coming from the second toe and looking posteriorly at the ankle joint. Now, there are some modifications to that. Why is that? Because if we’re imaging a brain or a back or a belly, this person who’s laying on the table, we can make nice perpendicular orthogonal cuts where we can get 90 degree cuts. But why are we taking an MRI? Are we taking the MRI because the person has an osteochondral defect? Are we going to keep them dorsiflexed on the table for an hour? Is it because they have an ankle fracture? We’re going to keep them plantar flexed for an hour. So nine out of ten times that patient, as much as we try to standardize them, will lay in the position of comfort. A position of comfort for most people is plantar flexed, externally rotated, and a little supinated, okay? So we actually get a position to the MRI where they’re presenting to us the plantar medial aspect of their foot hiding from us the dorsolateral aspect of their foot. If all of us will lay on our tables in front of us right now, you would see that my MRI looks nothing like Cris’s, looks nothing like yours, looks nothing like yours in the back. Everybody has an own position of comfort. Some are more plantar flexed, some are more externally rotated.

    [10:01]

    So use the reading radiologist, the podiatric surgeon have to take a look at this and account for patient variability. So again we have the coronals looking from the second toe moving posteriorly, the axials from the knee to the bottom of the foot, and sagittals looking from lateral to medium. Alright. So to go through some of the normal pathology. I always say start with what you know. Someone will come into your house, you’d say go down the road, take a left in McDonalds or right to the gas station. We’re looking for landmarks. I always use the peroneals as landmarks because they’re easy to find. So what we have tagged in the picture of the peroneals. Moving from lateral to medial, we see the peroneals. The peroneus longus obviously traversing. Getting ready to traverse underneath the cuboid. Next slice more medially. We’re starting to see the calcaneal cuboid joint. That picture on the left, up left hand corner, is what’s called the scout film. S-C-O-U-T, scout. So that if you lose your dimension, you can look up at that picture and that red line corresponds to the slice for what you’re concerned, okay? In fact if you’re using the computer and you’re using the mouse, that red line will slide back and forth. As we continue to move more medially, we begin to see the plantar fascia. Plantar fascia lateral and then central bands. As we continue to move even more medially, we’ll start to see the medial flexors. In this case the flexor hallucis longus. Flexor hallucis longus runs very intimately with the os trigonum area or the posterior process of the talus. As we continue to move even more medially, we’ll start to see the medial flexors, abductor. Then of course what you could see in the picture on the right is the posterior tibial tendon getting ready to insert on to the navicular tuberosity. Coronal moving from distal to proximal. We see the great toe, second toe, third toe, fourth toe, no fifth toe. This is not an arthoplasty performed by Harold Schoenhaus. It’s just the fifth toe doesn’t exist yet because we haven’t gone proximal enough. In the next slice we start to see the sesamoids and sesamoid apparatus underneath the first metatarsal which we’re going to get into a little bit more depth. Now you can see that fifth toe distal phalanx. Moving more proximally, we start to see the base of the fifth toe with the midshaft first metatarsal level. If we can just spend one second on the picture on the right, concentrate on that fifth area. All of a sudden that bone is grey. The reason why that bone is grey is because it’s an avascular area. That avascular area is not pathology in this patient but it’s the cartilage cap. It’s the joint. So because there’s not much water to a joint, there’s not much cartilage water, it images darkly. As we move more proximally, we begin to see the metatarsal cuneiform joint again with the grey area, number one metatarsal cuneiform joint. We can see the Lisfranc’s ligament, which really is an intraosseous ligament, isn’t it? We look in anatomy books and we think wow, that’s dorsal, that’s plantar. It’s not. It’s an interosseous ligament. You can see it very nicely there on the coronal. As we move more proximally, we begin to see the head of the tail and navicular joint on the right. Even more proximally we see the medial malleolus. This is why I say if we can take a minute here, this is why I say it looks like an AP view of an ankle x-ray. Because one could imagine and the picture on the right two medial malleolar screws there. Why don’t you see the fibula there? Because anatomically the fibula lays 15 degrees on average posterior to the medial malleolus. So it would make sense if that medial malleolus is anterior to the posterior fibula. We see the sustentaculum tali. Nice picture of that with the FHL underneath. When we continue to move more posteriorly, we finally see the fibula. Now obviously we’re going to burn out the medial malleolus soon and that’s the picture on the right. We’re all fibula. No medial malleolus. But again, it looks like an AP view of an ankle x-ray. Now, an AP view of an ankle x-ray will have all the metarsals and toes superimposed upon one another but we can take slices and isolate each joint and each bone. If we continue to move more posteriorly, we begin to see the Achilles. Alright. Axial, slices from the knee to the bottom of the foot. We’re not going to get into some of this pathology. But again, just taking pictures down. I want to show the tibiofibular ligament, the AITFL, and the PITFL, making up the sindesmosis. Then moving even more distally we begin to see the arrow, the black arrow there which is the answer anterior talofibular ligament. Then peroneus brevis, isolated anteriorly, and peroneus longus behind it. In the left side, we can see Tom Dick and very nervous Harry. Anteriorly, we see tibialis anterior with flexor hallucis longus at the muscle belly level and then flexor digitorum longus which is lateral to that.

    [15:07]

    As we continue to move more plantarly, we see the midfoot area. As we continue to move even more plantarly, we can almost image the whole dorsal plantar x-ray view of a foot. Except for again, nobody like a textbook or a cadaver MRI would look like this because everyone’s laying in the position of comfort. So if I ever get an opportunity to speak about rear foot pathology with MRI, we can address some of that. Maybe that’s a next year thing. But for now, we’re going to get into some forefoot pathology. These are not conditions that you don’t necessarily know. These are conditions that you may not see on MRI a lot. That’s the purpose of this lecture. So please don’t think I’m insulting your knowledge base. But first and foremost, turf toe. Turf toe is tearing of the joint capsule along the metatarsal head. Most commonly caused by hyperextension. This is people in car accidents, people playing sports. Obviously conservative therapy, orthotics and offloading first MPJ range of motion. Turf toe is important because it can lead to later arthritis. Hallux limitus need joint resurfacing, fusion, what have you. Of course plain films or x-rays may not show separation of the semamoid. So these people have pain submetatarsal phalangeal joint which is intractable and very, very painful because of how tight this joint is. If we look at normal, the first picture is the thin midline FHL. You can see that plantar plate with the long red arrow which is intact. You should have a little recess at the proximal phalanx of fluid that is normal on the T2 or stir. They should get a little bit more thick at the sesamoid apparatus. That is a normal first MPJ in the sagittal view. Coronally, we can see the intermetatarsal ligament which is depicted with the I, and then of course the medial lateral sesamoids and the flexor hallucis longus tendon under that. The arrows which are flanking the sesamoids are the suspensory ligaments. Of course the abductor and adductor on the picture in the right. God bless you. Abnormal MPJ. We begin to see gapping proximally at the 1st metatarsal phalangeal joint sesamoid junction. We begin to see more fluid and we see discontinuity of those prior image structures. On the coronal, we can see a discontinuity of the suspensory ligament. We can also identify the sesamoid apparatuses as torn. You don’t have to take pictures if you want. I’ll see you after this and I’ll give you the full PowerPoint if you don’t have it already. But you’re welcome to take pictures if you want. Don’t confuse with a fractured sesamoid. So many times someone will come and lecture and then your next 30 patients have turf toe. Fractured sesamoids still exist. They have bone marrow edema or deep bone contusion properties which is swelling of that sesamoid. Predislocation syndrome. First described in podiatry by the late and great Gerard Yu. Often times mistaken for a neuroma. Lachman’s test which is taking that second metatarsal, pushing it against the first and dorsally or plantarly displacing it. Renders pain right where the x and the y exist in between them realistically. Obviously you want to splint this toe down clinically. Surgically you can actually repair the capsule. But on MRI, the normal you can see a nice confluent and consistent plantar plate. Medial and lateral collateral ligament should be intact on the coronal and the axial views. But when there’s discontinuous plantar plate, you begin to see gapping, the toe tilting one way or another. Usually medially. Of course fluid building up in the plantar plate. Here’s another picture with bone marrow edema and fluid in the plantar plate. Neuroma. Obviously we’re not going to belabor what a neuroma is. But this is what a neuroma looks like on an MRI. It is dense neural tissue. You can see in the picture labeled A. It’s inner space, usually it herniates a bit plantarly, not dorsally which is interesting because when we do our molder sign, it’s actually plantarly displacing into the dorsal tissues. On the stir, we’re not necessarily going to see a lot of fluid. You can see the picture on the bottom right hand corner under where it says neuroma. There’s a lot of fluid there but the neuroma is actually submetatarsal three and four.

    [20:03]

    That’s just fluid due to inflammation there. You could see a nicer picture on the left. Very quickly, if you look outside of the confines of the picture on the left, the neuroma picture right here, that’s a vitamin E capsule. So just like when we’re taking x-rays we’d say, where does it hurt, and we put a little metal dot there. That’s where the x-ray person will x-ray. We know where the pathology is. We use a vitamin E capsule or the tech does, so that the reading radiologist knows where the pain exist. LisFranc’s ligament. Here’s normal LisFranc’s ligament depicted by the red. We’ve seen that already. On the axial we see it on the right on the red. It’s discontinuous here on the left and the right picture. So you see a fair amount of fluid gapping and discontinuous LisFranc’s ligament. Also MRI can be of use. But just because you don’t have a positive MRI doesn’t mean that you have a LisFranc’s injury. You want to do a weight bearing CT scan. Stress fracture, indicated by bone marrow edema which you can see here on the right, which is white swelling bone marrow edema. Incidentally you see an osteomyelitis, deep bone contusion stress fracture. Here again you can see it in the picture in the middle on the stir or T2. MRI findings, bone marrow edema are nonspecific. Plantar fibromatosis or plantar fibroma. We can see our vitamin E capsule. Directly under the skin is the plantar fibroma. It is dense and dark on a T2 which you can see here consistent with the plantar fascia. Ganglions are obviously very fluid filled and transilluminate on an MRI like they do in physical examination. They’re white fluid filled, associated with joints tendons. Here’s another. Then avascular necrosis. Let me just spend one second. Here is a follow up to Dr. Marie’s talk. MRI with fibrous necrosis will show this double line sign. So on the T1, you see hypointense which is dark, and the T2 is mixed hypointense and hyperintense. That’s a classic sign there. You can see the cartilage cap which dark. Behind it this hyperintense. Gases osteomyelitis, again, often times have a positive history. In other words, obviously you’re suspecting an infection or what have you. But not always. Someone’s very immunospressed. Gas bubbles on an MRI one can see pretty easily. Also advantage of CT scan to follow up for the gas. That is my spiel. Thank you very much.