Hi, I’m back. Let’s dive back in:
Since Tuesday’s email covered patellar clunk syndrome, I thought now might be a good time to share my own clunk.
Thanks to my friend and colleague Dr. Brendon Mitchell (please tell him that I mentioned him by name), I saw one of our Hand attendings about this subacute wrist pain that I have developed.
Mechanism of injury? Researching too hard. (#researchyearflex) (Also, probably falling while bouldering a year ago, but never mind that.)
What I learned today
The “catch-up clunk” is a physical exam finding which indicates palmar mid-carpal instability. It’s also known as the mid-carpal shift test. Not to be confused with Watson's test, which is also sometimes described with a clunk, but indicates scaphoid instability.
Step 1: Steady the pronated forearm with one hand while applying palmar pressure with the opposite thumb on the base of the third metacarpal.
This maneuver accentuates the existing palmar subluxation of the distal row and disengages the normal intercarpal contact points.
Step 2: The examiner then moves the wrist from radial to ulnar deviation, and the test is positive if the patient experiences a painful clunk near full ulnar deviation.
When the clunk is felt and or heard, the distal row is snapping back into its physiologic position.
Well, almost. In some people, the contralateral wrist may also demonstrate a clunk if the ligaments are physiologically lax. I am one of those people.
This laxity is what allows the proximal row to sag into a volarly flexed (VISI) position in step 1. The affected ligaments are the volar arcuate, dorsal radiotriquetral, and/or periscaphoid (STT) ligaments.
Once the TH joint finally engages in step 2, “the physiologic joint reaction forces are reactivated and the proximal row is forcefully rotated from VISI into its physiologic extended (DISI) posture. It is this sudden, forceful rotation that causes the catch-up clunk of PMCI.”
Sources
Niacaris T, Ming BW, Lichtman DM. Midcarpal Instability: A Comprehensive Review and Update. Hand Clin. 2015 Aug;31(3):487-93. doi: 10.1016/j.hcl.2015.04.004. PMID: 26205710.