Free body after ankle inversion injury but not reported by CT

[Xue Heng]

Hi, Steve. Happy new year!
Here is a case I encountered recently. This patient was a 32-year-old male with ankle inversion injury 2-3 weeks ago, and was prepared to have the operation.
In addition to the thickened and hypoechoic ATFL, CFL, and deltoid ligament, I saw 3 echogenic free bodies around the ankle joint. One is below the distal fibula, one is superficial to the talus, and one is superficial to the calcaneus (inside CFL).
Although the 3 free body could also be observed by CT, the report only describe the one below the distal fibula, and the surgeon only deal with the one below the distal fibula.
Are the other two free bodies clinically insignificant? Or they are anatomical variant?
Thank you for your every reply, Steve!
Fig.1 Thickened ATFL and free body superficial to the talus.
Fig.2 Free body below the distal fibula.
Fig.3 Thickened CFL and free body superfical to the calcaneus.
Fig.4 Free fluid of ankle joint.

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[Stephen Bird]

Hi Xue,

Nice images,

I agree with the CT report in some respects.

The fragment just dial to the distal fibula is a small piece of fibula that has been either tugged off as the joint capsule was torn or chipped off as part of a collision event. Either way it makes a small bony fragment in the antero-lateral gutter which can be cleaned up during the surgery to prevent future impingement issues. Looking at your CFL image makes me think it is a small bony avulsion that has come off the fibula origin of the CFL. These are often just left in situ as surgery for these injuries are rare in Australia and conservative management with physio is much more common. We see them all the time on plain radiograph series in patients who have had prior inversion injury (which is really common)

The echogenic material at the distal end of the ATFL is not really a free body, but rather it is a little piece of talus which has been avulsed as the ATFL was torn from the talus. As a minimum it is a piece of calcified fibrocartilage from the enthesis of the ATFL, if it is visible on CT it more likely represents a small bony avulsion. Either way it is connected to the ATFL and if left there will bond back to the talus as the ATFL (joint capsule) fibroses. Many ATFL tears result in these small avulsions and they are not surgically removed. I suspect if you surgically remove them you leave the remaining ATFL a little short to bridge the anatomical gap.
With your ATFL image the fibula end of the transducer is perfect, but the talar end ia a little too proximal. If you look at the image you can se hyaline cartilage on the talus so you are not lined up on the location that small fragment came from. If you rotate the distal (talar) of the transducer slightly towards the plantar aspect of the foot you will line it up with the correct attachment point of the talus and you will likely see the defect in the talus where it was tugged from.
A good key is to know the transducer needs to be parallel to the sole of the foot for this location to be correct.

The echogenoic area at the end of the CFL is exactly the same (a piece of calcified fibrocartilage from the enthesis or if it is visible on CT it more likely represents a small bony avulsion). The same principles apply.

Remember the anatomy of the enthesis which is constructed in this order:

Collagen
Unossified fibrocartilage
Calcified fibrocartilage
Cortical bone

All ligaments have an enthesis attachment to the skeleton and when you tear the ligament from the bone it must fail at one of these layers.

If it fails at the collagen layer there is no avulsion at all
If it fails at the unossified fibrocartilage you will not see an echogenic focus on the retracted end
If it fails at the calcified fibrocartilage you will see an echogenic focus on the retracted end which I often refer to as peri-osteal stripping
If it fails at the cortical bone you will see a larger calcified echogenic focus on the retracted end which is also visible as a bony density on CT (this is what you have seen)

So in summary your patient has an ATFL avulsion from the talar end and a CFL avulsion from both ends.

I bet it was swollen and bruised !

I am going to make a short tutorial on the pathways of failure which are possible with ankle trauma.
They tend to follow fairly defined patterns and the one you have observed is where the tibia and fibula try to disassociate themselves from the hind foot.

Steve

[Xue Heng]

Thank you Steve, for your very patient and detailed answer.
I learn a lot from your website and forum. Thank you!
I’m looking forward your new tutorial.

• This reply was modified 2 years ago by Xue Heng.

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