Sunday Morning Cyclist with a Wrist Injury - Perilunate Dislocation

Dr David McCreary Emergency Physician

The Case

It’s a beautiful Sunday morning outside your ED and that can mean only one thing – the cyclists are out. Where there are cyclists, there are cyclists falling over. And where there are cyclists falling over, there are limb injuries.

Today we bring you a case from just such a Lycra-clad gentleman presenting with a painful and deformed right wrist.

Let’s get straight to it with a look at the X-ray, shall we?

What does the X-ray show?

There is fracture through the scaphoid waist with lateral dislocation of the scaphoid. A fleck of bone is noted posterior to the capitate. There is a volar tilt of the lunate with dorsal dislocation of the carpus relative to the lunate.

Impression: Findings are in keeping with a complex trans-scaphoid perilunate fracture-dislocation injury

Tell me more about perilunate dislocation, why does it matter?

Well my geeky education excitement for this case is that it is a great exam question, but also an injury that is commonly missed (though I admit that one is pretty obvious) on initial presentation so it’s important that we understand the injury pattern and mechanism.

Common, you say? How common?

Around 25% are reportedly missed on initial presentation - a stat I always find surprising but that’s what is frequently reported. I wonder whether this is due to more subtle presentations than that above, or due to “distal radius looks normal, must be a sprain” assessments, not remembering to look at the radius’ upstairs neighbours.

Around 10% of all wrist injuries - not my personal practice as I’m sure I’m not seeing 1 of these for every 10 wrists. Maybe I’m adding to the 25% - there’s a thought that will fester.

Mechanism

A fall onto a hyperextended wrist ± forearm supination

Classification

The Mayfield classification. Mayfield and pals did a cadaveric study where they loaded 32 wrists to failure in wrist extension, ulnar deviation and intercarpal supination and described the 4 distinct patterns that emerged from x-ray and dissection findings.

4 stages: progressing from I → IV in a clockwise fashion

1. Radioscaphocapitate ligament and scapholunate ligaments (a fracture through the scaphoid will do it) – that’s where you’ll get your Terry-Thomas sign

2. Disruption of the lunocapitate joint (a fracture through the capitate)

3. Lunotriquetral ligament (or fracture through triquetrum) – true perilunate dissociation

4. Radiolunate ligament (That’ll give you a lunate dislocation as all tethers are gone)

I find it easier to conceptualise and remember visually using this:

Adapted from (1)

Complications

• Median nerve injury / acute carpal tunnel syndrome

• Avascular necrosis of scaphoid and lunate (in treatment delay)

• Post traumatic osteoarthritis

What are we looking for on X-ray?

• On the AP it can be easily missed

• Look for disruption of Gilula’s lines:

Wouldn’t be an orthopaedic case if I didn’t use a picture courtesy of OrthoFlow - go get OrthoFlow…

Piece of pie sign - the abnormal triangular appearance of the lunate on a PA image of the wrist (can be a sign of either perilunate or lunate dislocation.

Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 9906

Spilt teacup sign - for lunate dislocation: abnormal volar displacement and tilt of the dislocated lunate on a lateral film.

Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 9906

Management

• Well clearly with all that hard to pronounce, deformed anatomy, these injuries are going to require operative fixation by our friendly neighbourhood bone doc

• In the meantime, however, they need urgent reduction to prevent median nerve injury, particularly if signs of acute carpal tunnel syndrome already present

• This is a video showing how to reduce - I really like their bedside finger traps for some pre-procedure traction. It also demonstrates how difficult it can be sometimes to agree on whether it’s peri or proper lunate

• Some practical advice for Lunate dislocations, however – unless there is acute carpal tunnel or you can’t get the patient rapidly to theatre for reduction under GA by orthopaedics, try to resist the temptation to reduce these in the ED. Lunate dislocations are are notoriously difficult to reduce non-operatively and have been known to cause injury to practitioners who have tried in the past – but ulnar collateral ligament injuries are a discussion for another blog. 👍

References

1. Kennedy SA, Allan CH. In Brief: Mayfield et al. Classification: Carpal Dislocations and Progressive Perilunar Instability. Clin Orthop Relat Res. 2012 Apr;470(4):1243–5.

2. Goodman AD, Harris AP, Gil JA, Park J, Raducha J, Got CJ. Evaluation, Management, and Outcomes of Lunate and Perilunate Dislocations. Orthopedics. 2019 Jan 1;42(1):e1–6.

3. OrthoFlow App – iOS & Android

Declarations/Shameless Plug:

Dave wrote the OrthoFlow App when he was a registrar along with a couple of Orthopaedic registrars (now consultants) and a GP (who drew the medical illustrations above). He has just finished writing the latest version for iOS which is available right now.

DAVE MCCREARY

Emergency Physician

Dave McCreary, MBChB MSc FRCEM Dave is an Emergency Physician who completed training between the UK and Australia and completed an MSc in Trauma Science with QMUL. His clinical interests include trauma, critical care, evidence based medicine and human factors. Dave is a regular contributor the RCEMLearning podcast and is a FOAMed editor for RCEMLearning. He dislikes coriander, decaff coffee and dermatology.