Suspected LCL injury, thickening of common peroneal nerve

[Diane]

Hi Steve,

I scanned a male with a hyperextension knee injury, pain to lateral knee and anterolateral shin.

I think they may be a tear/injury to the distal LCL attachment. I think the biceps fem was ok.

The common peroneal nerve was also enlarged with an effusion. Is it common for the nerve to be injured during a hyperextension injury?

I was also wondering do LCL injuries require surgery or do they just scar up?

Thanks!

Diane

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[Stephen Bird]

Great case.

This is the best example of fluid around a peroneal nerve that I have seen.

This fluid does indeed indicate that there has been a poster-lateral knee joint capsule injury.

Your images of the LCL leave me uncertain as to the exact extent of the injury as there is always a lot of anisotropy where the LCL interdigitates and passes through the biceps femurs collagen adjacent to the fibula head.

The fluid around the CPD is generated by a defect on the poster-lateral knee joint capsule. There is a series of little ligaments that can tear here causing this fluid.

The ligaments in question include:
Fabellofibular ligament
Arcuate ligament
Popliteus fibular ligament

And others!!

There is some material published that we can see these structures with ultrasound, but in practice it isn not helpful.

These patients with posterolateral corner injuries need an MRI to sort out the extent of the injury.

The fluid around the CPN and the general collagen derangement around the distal LCL both indicate that there is a tear of some of these structures which make up the posterolateral corner of the knee joint capsule.

MRI next !

Great case,

Steve

[Diane]

Fab thanks as always Steve.

I attached a pic comparing the asymptomatic side to the injured knee. I was suspecting the LCL b/c on the unaffected side, it was nice and taut but wavy on the injured leg. Pic was taken with pt prone and both legs fully extended.

What are your thoughts? 🙂

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[Stephen Bird]

Yep,

I agree it is a posterolateral corner injury and the LCL is damaged.

For there to be all of that fluid around the CPN there has to be a tear in the joint capsule in that area.

Impossible to untangle with ultrasound alone.

But perfectly diagnostic of a posterolateral corner injury and off for an MRI to see what else has busted!

Great pics,

Steve.

[Diane]

Thanks!
The patient is due for a MRI soon so ill be back to post the results!

[Author]

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