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Case Review: 56 Year Old Male – Classifying Carpal Instability Part 2

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The MRAP coronal projection, with a gradient

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echo on the left, a T1 in the middle, and a

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PD spur on the right, affords you the ability

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to spot and grade various instabilities.

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Let's start with SLAC wrist,

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scapholunate advanced collapse.

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There are three grades of SLAC wrist.

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First grade, involvement of the radial styloid, or

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free margin, radial margin, of the scaphoid fossa only.

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That would be grade one.

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This fossa is abnormal.

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It's undulated, it's irregular,

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it's deformed, it's fractured.

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Grade 2 would involve the whole surface of the radius.

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The lunate fossa and surface is

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involved, so it ascends to grade 2.

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Grade 3.

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There is involvement of the distal pole of the

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lunate, where the capitate comes in contact with it.

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Oh, it's abnormal right there.

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We have met and ascended to the criteria for grade 3.

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That's SLAC wrist.

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Ulnar translocation.

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Taleisnik described two types of ulnar

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translocation where the lunate and triquetrum

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go east, marching on Philadelphia and

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New York while the radius stays at home.

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Type 1.

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In such cases, the radial collateral

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ligament, depicted by my arrow, is intact.

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The other type, or type 2, is when all three

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bones march on Philadelphia and New York.

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That is not happening.

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The next type of instability is

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dissociative instability, or diastasis,

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or failure of the scapholunate interval.

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Usually when this occurs, at least the dorsal and

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often all three components, dorsal, membranous, and

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volar components of the SL ligament have failed.

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The strongest stabilizer is the dorsal.

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As soon as you see that, your next move is to

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go to the region of the radioscaphocapitate

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ligament, which is here, and the ligament that's

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a little more proximal to it, which is laying

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down right there, right there, known as the

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radiolunotriquetral or long radiolunate ligament.

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That one is torn.

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In fact, although not shown clearly in this case,

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the radioscaphocapitate ligament is torn, but

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this is the location of it, and that is not the

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purpose of me showing these coronals right now.

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Just to tell you what maneuvers to perform.

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Yes, there is first CMC arthrosis,

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but that is a story for another day.

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So we have hit three, and now we'll

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conclude with the fourth type of

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instability, lunotriquetral instability.

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This often has to be inferred.

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As the ligament, the lunotriquetral

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ligament, is often very small.

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So if you don't see it, you can use the indirect

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signs of instability, such as advanced arthrosis.

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Patient has mild arthrosis.

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Fluid in the joint space.

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Patient does not have fluid in the joint space.

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Widening of more than 3 millimeters.

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Does not ascend to the criteria of

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widening more than 3 millimeters.

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Therefore, by secondary signs,

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the lunotriquetral ligament

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is deemed intact.

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We can usually see it directly, however.

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That concludes our four basic instabilities

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we can see, assess, and grade, including

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slack wrist, ulnar translocation, scapholunate

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failure, lunotriquetral failure.

Report

Faculty

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

Tags

Trauma

Non-infectious Inflammatory

Musculoskeletal (MSK)

MRI

Hand & Wrist

Acquired/Developmental

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