Section: Canada Category: Imaging Radiology

MRI of the Ankle - Review of Normal Anatomy

Marlena Jbara, MD

Marlena Jbara, MD discusses normal ankle anatomy on MRI. Dr Jbara also develops a step-wise approach to help evaluate any MRI ankle study.

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Goals and Objectives
  1. Recognize normal ankle anatomy on MRI.
  2. Describe the best imaging strategy utilizing MRI to assess normal ankle anatomy.
  3. Compose a check list approach to evaluation of MRI ankle pathology
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  • Author
  • Marlena Jbara, MD

    Assistant Professor Radiology
    SIUH Northwell Health
    Staten Island, NY

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  • Lecture Transcript
  • TAPE STARTS – [00:00]

    Marlena Jbara: My name is Marlena Jbara and this is a review of MRI of the Ankle - A Review of Normal Anatomy. Disclosures. I, or a related party, have no financial relationship to disclose. Objectives. Recognize normal MRI anatomy of the ankle, understand best imaging strategy, utilizing MRI to assess ankle anatomy, develop a checklist approach to evaluation of normal MRI ankle anatomy.

    We begin our pattern search with MRI of the ankle looking at the lateral aspect of the ankle, noticing the talus and its articulations with the calcaneus. The talus also articulates not only with the calcaneus but with the navicular and a cuboid. We can see through the lateral side an opening between the talus and calcaneus to sinus tarsi. We can see the posterior calcaneal process with the insertion of the Achilles tendon and we can note the base of the fifth metatarsal seen in profile on the lateral view.

    Adding ligaments to our schema, we can see that the distal fibula is essentially taped on to its surrounding structures through a series of ligaments. Of course the all-important syndesmosis between the distal tibia and fibula, the anterior, superior, and inferior tibiofibular ligaments, and the posterior, superior and inferior tibiofibular ligaments. Moving distally, we can see the three structures that secure the distal fibula lateral malleolus to the talus, namely the anterior talofibular ligament, the calcaneal talofibular ligament and the posterior talofibular ligament.

    [02:06]

    We can see the peroneal tendons as they glide down the lateral aspect of the ankle, secured in place by the superior peroneal retinaculum. And again, by the inferior peroneal retinaculum where the fibers of the peroneus longus will dive lower than the peroneus brevis to avoid different friction syndromes. We can see a portion of the abductor digiti minimi has been cut off, and that is where it would attach on the plantar calcaneus. The ligaments within the sinus tarsi, the interosseous ligaments, and of course the ligaments securing the talus to the navicula, to dorsal talonavicular ligament.

    Adding to that schematic, we can now add the tendons and the extensor retinaculum here seen in the superior and inferior bifurcate versions of that ligament. We can see the superior and inferior peroneal retinaculum preventing the peroneal translation. We can see how much action is really on the base of the fifth metatarsal through the peroneus tertius, the peroneus brevis, and of course the abductor digiti minimi, a feature which adds a lot of confusion to why base of fifth metatarsal fractures don't always heal with conservative treatment.

    Looking on the medial side, we can see a very busy area through the tarsal tunnel, which includes the posterior tibial flexor digitorus and flexor hallucis longus tendons, as well as the posterior tibial nerve and artery as seen here. We can see the bursal sheets that line the tendons and provide areas of friction, offload within the body. We can see how the extensor tendons are retained by the superior and inferior extensor retinacula, flexible retinacula to allow motion of these tendons.

    [04:04]

    And now, we can begin our anatomy and search pattern, and we'll be looking at the sagittal imaging of the Achilles tendon, the sinus tarsi, the plantar fascia, and the bones of the ankle and foot. And essentially, we're going to look at all of the sagittal images, and then we're going to look at the remaining planes subsequently. So when we begin our tutorial, we're going to begin looking sagittally at these images and we can take a look. Moving in to the body, we begin to see the bony structures. There's fat suppression along the distal fibula and lateral aspect of the foot as seen here.

    The first structures we come upon laterally are going to be the peroneus longus and brevis, and we can see them tuck behind the lateral malleolus. These are low signal structures based on their low water content, and we're noticing how the peroneus brevis is in front of the peroneus longus here. Moving into that, we can see now the peroneus longus at the base of the cuboid tunnel. Moving more laterally, we begin to see that the sinus tarsi is opening up laterally into this large pyramidal-shaped area where you have this interosseous ligament. Notice your talus and your calcaneus, and even seeing a portion of the cuboid navicular articulation.

    Moving further in, we notice the interosseous ligaments and some of the extensor tendons coming down along the anterior ankle. Moving in further, again, we see this extensor tendon coming in, and we see more of the cartilage surface between the talus and navicula.

    [06:00]

    Further laterally, we begin to see how the sinus tarsi is becoming a smaller shaped pyramidal tunnel with the apex of a pyramid localized to the lateral aspect and the superior aspect of the medial side of the ankle. And moving in now, we can now start to see the Achilles tendon, the Achilles tendon and search on the posterior calcaneal tuberosity through a broad attachment.

    On this next image, we can see more of the Achilles tendon. We could see its peritenon and the regions of the retro tendon and retro calcaneal bursa as seen here. We can also see the root of the plantar fascia and we'll talk more about that in the coronal imaging. We're volume averaging some of the ligaments within the sinus tarsi on this image, and we're beginning to actually see some of the medial side, and we're beginning to see what's the sustentaculum talus, which I know that to be in the flexor hallucis longus tendon, which we'll go under that area. So we're beginning to volume average the posterior subtalar joint in this image.

    And now we can see more clearly that flexor hallucis longus tendon coming in. We can see some fibers of the Achilles tendon here and some of the plantar fascia as it inserts on the plantar calcaneus. Even more laterally, now you're seeing some of the medial flexor tendons coming in. We're seeing some of the sinus tarsi and the plantar fascia and of course the remaining bony structures. More laterally, noticing the structures within the tarsal tunnel, there's a good deal of vascularity and you're even seeing some of the volume averaging of the posterior tibial nerve.

    [07:58]

    Moving on to the axial plane as seen from above here with the distal tibia removed, notice all the cartilaginous surfaces in blue, the talus and the calcaneus forming both the medial and lateral columns of the hindfoot ankle.

    The axial images really represent our workhorse for evaluating tendon anatomy with three groups of tendons. Namely anteriorly, we have tibialis anterior, the extensor hallucis, the extensor digitorum and the peroneus tertius tendons. Medially, a busy area including the posterior tibial tendon, the flexor digitorum longus, and the posterior tibial artery nerve and vein between the flexor dig and the flexor hallucis longus tendons. Laterally, we have the peroneus longus and brevis, and of course posteriorly, we have the Achilles, the plantar that's inserting medially on the calcaneus, and your arrangement here around the tibia and fibula.

    In assessing the anatomy and search pattern to the axial imaging, we begin at the level of the distal tibia. And on this image, the first structures that we're going to encounter are those that we just spoke about. So anteriorly, you can see the larger tibialis anterior. When I'm considering how large it should be, I'm always looking in the posteromedial corner to the posterior tibial tendon, the flexor digitorum and flexor hallucis longus tendons. Between the flexor digitorum and the flexor hallucis longus tendon, we can see the posterior tibial nerve, artery and vein, and a variety of vessels in that compartment. Laterally, we have the peroneus brevis anterior to the peroneus longus, and the peroneus brevis often has its muscle belly at the distal fibula.

    [09:59]

    There may be accessories seen here called the peroneus quartus, very common variant. We can see the muscles and this is the beginning of the bony structures. And in this image, it's a T2-weighted image but the fat has not been suppressed at this superior aspect of the structure. We're seeing the Achilles tendon with its T-shaped configuration providing inherent strength.

    And moving down, we begin to notice these tendons as they course towards their respective areas in the ankle. And generally, we're going to follow one group at a time. So I'm just going to take us down on each image through the three sets of medial flexor tendons and a portion of the Achilles until we get to the ligamentous regions, and that would be the usual perusal of this image.

    So here again, we can see the tibialis anterior breaking away from the extensor to determine extensor hallucis longus tendons. We're noticing the posterior tibial flexor digitorum and flexor hallucis longus in between the structures of the tarsal tunnel, including the nerve here seen dorsally, notice of peroneus brevis and longus, and its relationship posterior to the fibula and of course the Achilles tendon. Further example, maintaining their constant relationships.

    And on this image, we begin to start to see a portion of the posterior tibia, fibular ligament, or the posterior syndesmosis as radiologists will call. We're seeing some of the vessels of the peroneal branches and even this would be the region of the peroneal nerve. And of course you can see a piece of the posterior tibial nerve here and now you can see more clearly the plantaris medially separate and apart from the Achilles tendon with its lower aspect of its muscle.

    [12:08]

    Now, you can begin to see some of the anterior syndesmosis coming in here where you see this sort of bulge of a ligament sort of bunched up on itself, and we're now out of the posterior syndesmosis. Here again, the constant structures of the extensor tendons, the medial flexors altogether being the PT, about the same size as the tibialis anterior and the peroneal tendons, peroneus brevis and longus.

    And on this axial image moving more inferiorly, we can see volume averaging of the ligaments of the anterior syndesmosis, the anterior superior and inferior tibia fibular ligaments. Again, we can see the extensor tendons, the tibialis anterior in the same relationship to the posterior tibial tendon being the same size and shape, generally speaking. We see the medial flexor tendons again with the tarsal tunnel between them containing all of the neurovascular structures of the medial hindfoot. Moving more posteriorly in the superficial posterior compartment, we can see the Achilles and its plantaris medially. Laterally again, we're seeing the peroneus brevis with its eyebrow-shaped tucked in front of the peroneus longus with a muscular component here at -- seen at the ankle. That would be considered low lying.

    Moving more inferiorly noticing the anterior and posterior syndesmosis, and again the three sets of tendons with the Achilles and the posterior compartment. And now with these levels, we can see the posterior tibial tendon as it abuts the posteromedial retromalleolar groove.

    [14:04]

    And we can learn things from the shape of the posterior groove in the presence of osteophytes or enthesophytes as to how much pressure is occurring along the tendon osseous interface, and maybe a clue for offloading if people who have over pronation biomechanics. We're noticing the -- again, these three sets of tendons, the medial flexors, the lateral flexors and the extensors here. We're seeing a bit of the volume averaging of what's called the intermalleolar ligament. And we're at the lower level of the syndesmosis here, we're volume averaging at the joint. We're going to begin to come in to the lateral, collateral ligament complex, so keep your eyes there.

    And on this image, we begin to see some of the structures coming in on the medial side namely the deep fibers of the deltoid ligament. So here again to orient ourselves, we have the posterior tibial, flexor digitorum and flexor hallucis longus tendons. And we have the deep posterior band of deltoid here. It's seen in volume average and we're going to see it much better when we take a coronal image straight through this region. We can also see a portion of what's called the tibiospring ligament. That's a portion of the superficial deltoid which is going to dive right in inferiorly to the superomedial band of spring ligament.

    Notice we have the posterior tibial nerve artery and vein here flunked between the flexor digitorum and flexor hallucis tendons. And laterally, we have the peroneus brevis and longus again, the brevis providing some kind of frictional relief from the peroneus longus, which is bulging into that region. We have a portion of what's called the superior peroneal retinaculum and that's a really interesting structure with a fibrous ridge and a retinacula band, preventing peroneus longus subluxation. We're beginning to see some of the tibialis anterior. It's inserting some volume average of the extensor hallucis, and of course of the extensor digitorum tendons.

    [16:04]

    On these images here, we begin to see some of the region of the anterior talofibular ligament and the posterior talofibular ligament. We can see we're starting to come out of the deep deltoid and we can still see the posterior tibial, flexor digitorum, and flexor hallucis longus tendon again with the tarsal tunnel between, and the structures of the tarsal tunnel lying between them. Again, the Achilles and the plantaris here and the posterior superficial compartment.

    It's in this image, we really get a nice view of what the anterior talofibular ligament looks like, and of course the posterior talofibular ligament here. You're beginning to see some portions of the spring ligament, the superomedial band of spring ligament. Here's your posterior tibial flexor digitorum and flexor hallucis longus tendon with the tarsal tunnel all seen here. Seeing some of the Achilles, again with its normal low signal tendons, these small areas of increased intensity maybe related to degeneration and normal tendon morphology as we age.

    Moving more axially a few anatomic features that can be seen here besides the posterior tibial, flexor digitorum and flexor hallucis longus, is that we can see that the flexor hallucis longus tendon actually lives between two calicles of what's called the posterior talar process. So the lateral calicle of the posterior process performs one of the bony constraints of the flexor hallucis longus and there's a tendon. There's a ligament that crosses over this and the FHL can glide in this what's called this tenoosseous tunnel.

    [17:59]

    And patients who have os trigonum would have an unfused lateral calicle here and that may cause problems for the tendon, and that tenosynovitis can be created. And the type of tenosynovitis might be cellular and sticky, causing gliding problems of the FHL, something called stenosing tenosynovitis. In this example here, we can see some of the fibers of the posterior talofibular ligament and a few of the inferior fibers of the anterior talofibular ligament. You're seeing some of the superomedial band of the spring ligament, again the Achilles and the plantaris.

    And on this axial image, what we can really see is the posterior tibial tendon coming to approach the middle navicula and the superomedial band of the spring ligament here. Of course the flexor digitorum -- I'm sorry, the flexor hallucis longus tendons here, and we then know this structure to be what will be the sustentaculum talus of the calcaneus as it goes underneath it on the next images. Here, we can see the brevis in front of the longus. We've past the lateral malleolus and we're coming into a structure here which will be the calcaneofibular ligament between the coming down from the calcaneus and deep to the peroneal tendons. You're seeing the talus and navicular articulation here and its relationship.

    And another cool thing you see here is actually the sinus tarsi and you can understand the medial pyramidal shape where the point of the triangle, the apex of the triangle is medial and the base is wide as laterally. Further seeing on this axial image, some of the features of the superomedial band of spring ligament, there will be bands that are underneath the talar head essentially forming a sling and those are the other two bands of the spring ligament, namely the medial, lateral and plantar oblique components.

    [20:02]

    Again, you can see the peroneal tendons here. This is going to be appears of the calcaneofibular ligament as it's deep and it's attaching to the calcaneus. And you can see that here as it attaches to the calcaneus. And on this image, we get the sense of the peroneus brevis in front of the longus. There's a coming out of the inferior peroneal retinaculum. The brevis is going to go down to the base of the fifth metatarsal where the longus is going to curve under and attach to the base of the first metatarsal.

    More looking at the peroneal tendon as they're decussating at this point coming in to some of the bones of the midfoot, seeing the Achilles as its insertion with some trace retrocalcaneal bursitis. And of course continuing more inferiorly, we're seeing some of the lower structures of the tarsal tunnel, the nerve artery and vein as they get to an area called the porta pedis. The flexor digitorum and flexor hallucis longus tendons will cross at this level soon called Henry's knot, and that will be an area of -- that can also collect tenosynovitis.

    And of course, the tendons coursing more inferiorly, the peroneus brevis seen here laterally, the peroneus longus hugging the calcaneus and about to go through a cuboid tunnel. We're seeing the crossing fibers of flexor digitorum and flexor hallucis longus here as we passed Henry's knot. And further passing of Henry's knot and the peroneus longus going under the calcaneus towards the cuboid tunnel.

    [22:00]

    And of course the peroneus brevis is almost attached to the peroneus longus going under the foot. We're seeing some volume averaging of the intrinsic muscles of the foot. This is the flexor digitorum brevis and a few more slices along the inter aspect of the foot and the long access plane again.

    Moving on in our anatomy and search pattern to coronal imaging or transaxial imaging of the foot really, and what we can really see in this area are going to be the ligaments, the deltoid, the spring, and the calcaneofibular ligament being the highlighted features in this area. We're going to look at the bones of the talar dome, the tarsal tunnel, of course more the sinus tarsi and the plantar fascia. And we begin our coronal search pattern from the posterior aspect coming anteriorly. The first images we're going see are going to include the Achilles tendon and long access is not a super useful way to look at the Achilles, but we can see it, and you can see the Achilles tendon coming down to insert. And more of the same, the Achilles is inserting, seeing the posterior calcaneus with some of the muscular fibers.

    And again, we can see on the lateral aspect of the ankle now, the peroneus longus and brevis coming into view, and we can see the peroneus longus and brevis behind the lateral malleolus coming out inferiorly.

    [24:00]

    And of course we can see more of the posterior talofibular ligament, more of the posterior syndesmosis, and the peroneus longus under the peroneus brevis as they decussate, and move towards their respective attachments, the peroneus brevis going to the base of the fifth metatarsal, and the peroneus longus coming across to the base of the first metatarsal.

    Moving more anteriorly, we begin to see some of the fibers of the anterior talofibular ligament here and some of the fibers of the anterior syndesmosis. Of course, the peroneus longus and brevis seen again. But what we can really see here is really the talar dome and the relationship of the subtalar joints. We can see the low signal or higher signal cartilage layer opposed to the cortical bone, which is a low black signal line. We're beginning to see that the peroneus longus is going deep and the peroneus brevis is still up high. We see a little bit of the anterior syndesmosis here and a small portion of the anterior talofibular ligament. But the real power of this image is really in seeing the coronal views of the talus and calcaneus so we don't miss any osteochondral injuries.

    Moving more immediately, of course we can see the deltoid ligament. The deep fibers often have his bowtie appearance and we're coming into the great structures of the plantar aspect of the foot. We have come through the tarsal tunnel, whether it's posterior tibial nerve artery and vein, and of course the posterior tibialis, flexor digitorum, and flexor hallucis under the sustentaculum talus. We can appreciate the muscles of the foot, namely the deepest being the quadratus plante, and of course the abductor hallucis, the abductor digiti minimi and the flexor digitorum brevis.

    [26:02]

    Notice the vascular structures moving towards the region of the porta pedis. And of course more fibers of the deep deltoid, the three medial flexor tendons under the flexor hallucis longus. We can see again the sustentaculum talus. We're noticing the brevis is going to attach and the longus is going along the cuboid tunnel.

    Anatomy and search pattern of the plantar muscles. This is just a nice slide to show the abductor hallucis, the flexor digitorum brevis, abductor digiti minimi and quadratus plante musculature, all seen best coronally. A nicer look at the tibiospring component of the spring -- deep -- I'm sorry, superficial deltoid complex, and the three medial flexor tendons coming down through the tarsal tunnel. More of the three flexor tendons coming down through the tarsal tunnel. We're seeing a bit of the volume averaging of the talocalcaneal ligaments of sinus tarsi as seen here laterally where the base is wider, the apex being the smaller medial portion.

    And now, we're going to see some of the extensor tendons coming down the tibialis anterior, extensor hallucis and extensor digitorum tendons. We can volume average the muscles of the foot as well. We'll see that in a later slide. Again, more of the same - -the tendons coming down to their insertions.

    [28:08]

    In summary, we've reviewed normal MRI anatomy of the ankle. We've developed an imaging strategy utilizing MRI to assess ankle anatomy and we've reviewed a checklist approach to evaluation of normal MRI ankle anatomy. Thank you for your time and attention.

    TAPE ENDS [28:39]