If You Do the Twist: MSK US of the Ankle - SD

Introduction

Hi, my name is Kenneth Lee.
I'm a musculoskeletal radiologist at the University of Wisconsin.
I'm going to talk to you about musculoskeletal ultrasound of the ankle.
The ankle is a really nice joint for ultrasound application.
The title of my talk is If You Do the Twist, Musculoskeletal Ultrasound of the Ankle.
My name is Kenneth Lee. I'm at the University of Wisconsin.
I have no financial or commercial relationships to disclose.

Objectives

The objectives of this talk is to briefly discuss the ultrasound versus MR evaluation of the ankle.
Review the normal anatomy of the ankle to help set the stage and to show that ultrasound's well suited to evaluate tendon and ligament injuries of the ankle.
Lastly, I will introduce ultrasound guided interventions involving the ankle.

Talk Outline

Just as a brief outline for our talk, we'll talk about ultrasound versus MRI evaluation as an evidence-based approach.
We'll touch on the normal anatomy and some common pathology, starting with the Achilles tendon, going to the medial and lateral ankle tendons and ligaments, and then finishing off with the plantar fascia and the tarsal tunnel.

Ultrasound versus MRI Evaluation

So first, ultrasound evaluation.
We like to think of it as an, it answers a specific question.
So if you have a tendon tear, like to rule that out with ultrasound, it's really good for superficial structures such as Achilles tendon ligaments, plantar fascia, and also some soft tissue lumps and bumps.
MR evaluation is different.
It's more of a generalized approach, for ankle pain, especially for fractures 'cause of its high soft tissue contrast, is also very good for looking at tendon and ligament injuries, but you could also look for bone marrow evaluation, the talar dome, any cartilage defects and loose bodies within the joint space.
Things that ultrasound cannot evaluate.
And then also for mass and tumor workup as rheumatologic diseases as well that affect the joint.

Accuracy of Ultrasound versus MR for Ankle Tendon Tears

So let's talk about the accuracy of ultrasound versus MR for ankle tendon tears.
The Achilles tendon under ultrasound is highly accurate.
Peroneal tendons as well as the PTT, which is a posterior tibial tendon.
And the ATFL, which is the anterior tibiofibular ligament is very good under ultrasound evaluation with a high accuracy well above 90%.

Normal Anatomy of the Ankle

So let's talk about the normal anatomy of the ankle.
This helps set the stage, of ultrasound evaluation and how to diagnose tendon injuries.
So first part is the medial side where you get the posterior tibial tendon that inserts on the navicular bone and then the flexor digitorum longus tendon.
And then lastly, the flexor hallucis longus tendon.
That courses underneath the sustentaculum tali.
We teach our residents a mnemonic Tom, Dick and Harry to remember the order of the medial ankle tendons.
So as I go around the ankle joint to the posterior aspect, you can appreciate the normal anatomy and the relative relationship of the tendon to each other and to the bone, which will become important when we look at the normal anatomy under ultrasound.
And the posterior part is the Achilles tendon, which is the largest tendon in our body and the most commonly injured.
And then a small plantaris tendon, which is the vestigial tendon that inserts on the medial side of the Achilles.
Let's go to the lateral side, which is made up of the peroneal tendons.
You have your peroneus brevis on your peroneus longus tendon.
That courses underneath the cuboid.
We'll see that under ultrasound as well nicely.
And then finally, the extensor compartment, which is made up of the anterior tibial tendon, the extensor hallucis longus tendon, and then the extensor digitorum longus.
A nice mnemonic here is instead of Tom, Dick and Harry is Tom Hates Dick.
So this is a basic anatomy of what we see.

Achilles Tendon

So let's start with the Achilles tendon.
We usually lay these patients prone with their ankle dangling over the bed, and you can see on this corresponding MR our Achilles tendon, this normal nice black structure.
So if you correspond that with ultrasound, you can see the uniform thickness and echo texture and size of the Achilles tendon.
We like to give our clinicians an extended field of view here where we can give, a larger picture of the relative relationship of the anatomy to each other.
You can see the nice Achilles tendon extending to the musculotendinous junction, the calcaneus of the bony acoustic landmark.
And then finally the posterior malleolus.
So the Achilles tendon, this is an axial image MR.
If I flip this 180 degrees to correspond to the prone position of the foot on the patient's bed.
This is what the Achilles looks like.
Nice oval structure is not rounded, uniform and echo texture and size.
This is a good look at what the normal Achilles tendon looks like.
We like to assess the Achilles tendon using dynamic, measures of dorsiflexion of the ankle joint.
You can look for tendon tears, the Achilles that becomes more conspicuous.
This is just an example of the normal excursion of an intact Achilles tendon.
Here's a look of a abnormal Achilles tendon, what we call Achilles tendinopathy.
You can see here we lose the normal uniform echo texture and size of the Achilles tendon.
It becomes thickened and heterogeneous and hypoechoic.
If you put power Doppler on, you can see increased flow of hyperemia that's suggestive of Achilles tendinopathy.
Here's an example of Achilles tendon tear.
You can see on this lateral projection X-ray, a soft tissue lump in the posterior aspect of the ankle.
This person got an MR.
You can see on the sagittal T1 weighted image a full thickness tear, complete tear of the mid substance of the Achilles tendon.
This is a corresponding ultrasound image here in the long axis, you can see the torn tendon ends and debris and hemorrhage within the full thickness defect.
You can also appreciate Kager's fat pad herniating into this complete tear on the short axis on one of the torn ends, you can see how you lose that normal oval appearance.
It becomes heterogeneously hypoechoic and thickened.
Here's an example of retrocalcaneal bursitis, and a cause of painful posterior heel pain in patients.
You can see the fluid collection behind the calcaneus and in front of the Achilles in the corresponding image where you lay the patient prone.
You can see this thickening of the bursa as well as fluid distending the retrocalcaneal bursa.
And on color flow you can see hyperemia.
Here's an example of retro Achilles bursitis.
So if you go a little bit more posterior, you can see fluid behind the Achilles tendon on MR.
It was equivocal, whether this be a fluid collection or a mass.
Nice thing about ultrasound is it can really differentiate well between a cystic structure versus a solid structure.
This is what it looked like on the axial fat sat image.
Here's the ultrasound of that same patient where we're laying them prone.
You can see the lump corresponding to the area.
In this case, this patient was an athlete who was wearing high heeled shoes or high heeled sneakers while training and had this rubbing up against the posterior heel causing this adventitial bursa, which is a benign entity that we call retro Achilles bursitis.

Medial Side of the Ankle

Alright, let's move on from the Achilles to the medial side of the ankle.
Remember the posterior tibial tendon is the largest and most medial tendon it inserts on the navicular bone.
Here you can see the nice normal structure under ultrasound, uniform and echo texture and size and thickness as it courses behind the medial malleolus and then goes to insert on a navicular bone.
This is a normal look of the posterior tibial tendon.
Next is the flexor digitorum longus tendon, which of course is right behind the posterior tibial tendon.
It's a smaller structure but nicely depicted under ultrasound.
You can see here as it courses by the talus.
This is a cine sweep of the relative relationship of the flexor digitorum longus to the calcaneus.
Here's a bony acoustic landmark here.
What I'd like you to appreciate as we scan a little bit more plantar, you'll see the bony acoustic landmark of the calcaneus come into view.
And then you can find the flexor hallucis longus.
So there you go. Flexor hallucis longus tendon right there.
Alright, so here's an example of abnormalities that we see along the medial ankle tendons versus posterior tibial tenosynovitis where you can see abnormal synovial hypertrophy around the normal posterior tibial tendon.
You can see here color flow surrounding the posterior tibial tendons suggestive of hyperemia.
This person with tenosynovitis. Here's an example of a longitudinal split tear the posterior tibial tendon.
You can see the arrow marker points to the abnormal posterior tibial tendon with this hypoechoic cleft that suggests of a yin yang sign.
It's difficult to see on the long axis view, but this is what a longitudinal split tear looks like and here's our surgical correlation for that.
Alright, so the medial ankle ligament that can be seen as a deltoid ligament.
It's a complex of these four ligamentous structures that we often separate into superficial and deep.
We can see this under ultrasound, however, we're not often asked to evaluate this, but I wanted to illustrate that.
You can see this, you can see on the ultrasound images to the left and the MR images to the right, the normal structure of the deltoid ligament.
If you evert the ankle, you can even bring out the deltoid ligament and see that in a more conspicuous nature.

Lateral Ankle

All right, let's move on to the lateral ankle here.
The two tendons that are of interest are the peroneus longus and the peroneus brevis tendons, they lie right adjacent to each other.
You can see here on the ultrasound image to the right, the peroneus longus tendon as it courses underneath the cuboid. The peroneus brevis goes on to insert on the base of the fifth metatarsal bone.
It's the smaller of the two and can be seen nicely, very superficial.
So here's an axial MR image showing the peroneus brevis and longus tendon.
If I rotate this image 90 degrees, this is this red box shows you the corresponding ultrasound image.
Here is the bony acoustic landmark of the most lateral aspect of the lateral malleolus.
And you can see the peroneus longus and brevis as it courses behind it.
The peroneus brevis tendon is the one that's closest to bone.
So brevis for bone lies closest to the posterior aspect of the lateral malleolus.
So here's an example of an axial T1 and T2 image of the ankle.
And you can see here under ultrasound marked hyperemia, some synovial thickening and the herniation of that peroneus longus into this split tear.
The peroneus brevis tendon.
So this is an example of a peroneus brevis longitudinal split tear. Ultrasound's also good for evaluating tendons.
Subluxation, or tear associated with metal is not hindered by metal hardware within the joint.
Here's an example of a person that had catching along this fibular plate and we were asked to evaluate the tendon.
You can see here the heads of the screws corresponding to the fibular plate.
You can see the nice tendon that's intact and with dynamic imaging moves nicely along without any catching or tendon tear.
Alright, the lateral ligaments of the ankle can be nicely seen under ultrasound here is the anterior tibiofibular ligament.
You can see here is nicely seen under ultrasound is smaller in echo texture and size than the normal tendon structure.
Here's a corresponding MR image here.
What's also nice is that with dynamic assessment with dorsiflexion, you can stretch the ligament to make sure it's intact.
This is an example of a normal tibiofibular ligament that's intact.
F corresponds to the fibula or the lateral malleolus, the tibia.
And then if you stretch, if you dorsiflex, you can stretch the ligament out to ensure that it's intact in a tear.
It would gap wide open.
Here's an example of a high ankle sprain of that ligament.
You can see here this ankle mortise view of the ankle widening of the medial clear space.
You can see here on this corresponding axial T2 fat sat image disruption of the anterior tibiofibular ligament.
And then here this hypoechoic defect corresponding to a tear within that ligament suggested of a high ankle sprain.
Here's another ligament that we like to evaluate under ultrasound a little bit more distally.
It's called the anterior talofibular ligament or the ATFL.
This is also nicely seen, similar echo texture and size to the anterior tibiofibular ligament.
Here's an example of a lateral ankle sprain in the ATFL.
You can see on this Netter diagram and an inversion injury of the ankle joint.
You can see the normal echo texture and size of the ATFL and this is the corresponding torn where you lose that echo texture pattern.
You see this large hypoechoic defect and disruption of the ATFL in this person with the lateral ankle sprain.
Here's an example of an old ATFL tear where you get marked thickening and heterogeneity of the ATFL and in the long axis.
You can see that very well as well as the bowing and convex outward appearance of the ligament.
You can see here on Doppler flow increased hyperemia in this area of patient's pain of a chronic ankle sprain.
Here's a calcaneofibular ligament.
This is a nice ligament three times stronger than the ATFL.
Here's an MR image coronal T1 image that rotated 90 degrees.
So it's correspond to the patient's positioning on the table with ultrasound imaging.
You can see here nicely the calcaneus as well as the calcaneofibular ligament.
And then the peroneus tendons that are nicely hammocked within this calcaneofibular ligament.
So with plantar flexion you can stress this ligament to make sure that it's intact.
As you can see here, nice normal intact ligament.
The peroneus tendon lifts up as you're stressing the intact calcaneofibular ligament in this case.

Soft Tissue Lumps and Bumps

Soft tissue lumps and bumps are nicely seen with and evaluated with ultrasound.
This is a patient that had an anterior lump right in front of their ankle.
It's a sagittal T1 image with a marker at its site that you can see marked thickening.
Of this fusiform structure on the axial PD image, you can see thickening of this area.
Under ultrasound we saw an abnormality of the anterior tibialis tendon markedly thickened and then an anechoic meniscus at the level of the ankle joint here, suggestive of a complete tear.
We like to give extended field of views for a better relationship to the tear to the ankle joint so that our clinical providers can see this.
Well. You can see our tibia, the talus that demarcate the ankle joint and the tear, which is at the level of the ankle joint.
Here's another example of a common soft tissue lump we're asked to evaluate called a dorsal ganglion cyst was a benign degenerative cyst.
An X-ray shows degenerative change at the naviculocuneiform joint corresponding ultrasound image shows this fluid-filled anechoic structure projecting from the naviculocuneiform joint suggestive of a ganglion cyst, which is a benign lesion.

Plantar Fascia

Alright, plantar fascia.
Another common indication for ultrasound that we're asked to evaluate in our clinic.
You can see the plantar fascia nicely in both the long axis and the short axis.
Even though we call it the fascia, it is likely a tendinous aponeurosis that we can see nicely, causes the most common cause for inferior heel pain.
You can see here a thickening of the plantar fascia on this extended field of view as it normalizes to the normal thickness.
An abnormal thickened plantar fascia is five millimeters in thickness or greater, and that's measured from this yellow arrow down to the bony acoustic landmark of the calcaneus.
Here's an example of PRP for the plantar fascia.
PRP stands for platelet rich plasma.
Here we are asked to inject a concentrated platelets filled with growth factors to help with the healing process.
In patients with tendinopathy, you can see here from the left to right plantar fascia abnormal thickening on the left side to about 6.4 millimeters compared to the 4.3 millimeters on the normal asymptomatic right.
Our needle approach is usually long axis from the heel pad into the plantar fascia as we're needling the plantar fascia.
We're depositing platelet rich plasma within this plantar fascia to promote healing.
Our protocol is sterile preparation.
We do a tibial nerve block to help with the pain.
You can see here the tibial nerve that courses with the neurovascular bundle.
We do skin numbing at the heel pad.
We'll do dry needling in three locations and we inject three milliliters of PRP.
The preparation here as show you a centrifuge where we use a patient's own blood, approximately 30 ccs and it gets spun down this closed system to about three milliliters and it's the three milliliter of platelet plasma that is used to inject into this abnormally thickened plantar fascia.
Here's an example of MRI evidence of healing.
You can see here on the sagittal T2 weighted fat sat image and normally thickened plantar fascia, there's quite a bit of peritendinous edema and bone marrow edema at the calcaneus.
Approximately three months later, a follow-up MR shows resolution of that peritendinous edema.
The thickening remains but maybe less apparent and there's still edema within the calcaneus and this person that had plantar fasciopathy but now with pain relief three months post PRP injection.

Tarsal Tunnel

Alright, lastly, the tarsal tunnel anatomy is a fibro-osseous canal that we're asked to evaluate on the medial side of the ankle.
The roof is made up of the flexor retinaculum, which is a thin fascial layer that you can see on this Netter diagram on the right.
The floor is the medial aspect of the talus, also made up of the sustentaculum tali and the medial wall the calcaneus and the contents include the neurovascular bundle as well as the three tendons of Tom, Dick and Harry that I mentioned.
Here's an example of the tarsal tunnel.
You can see the nice posterior tibial nerve as it runs along the vessels is a hyperechoic structure.
We like to call a fascicular pattern versus the fibrillar pattern of a normal tendon.
We like to evaluate this both in the short axis and the long axis and what's important because of the fibro-osseous tunnel.
If there's any space occupying masses, it may cause pain and numbness down into the foot.
Here's an example of a ganglion, which again is that benign lesion that can occur anywhere.
But in this case, in the tarsal tunnel, you can see on the sagittal T2 image this multiloculated benign ganglion cyst adjacent to the posterior tibial tendon and nerve corresponding ultrasound image showing that cystic benign lesion adjacent to the nerve causing pinching and paresthesia.
In this patient, sometimes we're asked to aspirate this and inject with steroids to cause pain relief in this benign lesion.

Summary

So in summary, ultrasound is well suited for evaluating the soft tissue structures of the ankle.
It is also useful for guiding injections and aspirations involving the ankle.
Thank you very much.