Truth be told, this is more aptly called “pope’s curse” because of the confusion it causes and heated discussions it generates. I spent the majority of a day sorting this all out (probably not the most efficient use of my time). From all the forums, books, and websites I’ve read on the subject I am sure I found the source of the confusion for at least the majority of people.
The best way to approach the issue is by first understanding two important concepts: 1) The lumbricals and what they do. 2) Is the patient being asked to extend their fingers or make a fist?
The last point in particular might clear up a lot of confusion. We’ll see why later. First lets start with the Lumbricals. What you need to know is that the Lumbricals are responsible for flexing the MCP and extending the PIP and DIP joints. The Median nerve controls the lumbricals for digits 2 and 3. The ulnar nerve controls the lumbricals for digits 4 and 5. Here’s is how a hand would look with all lumbricals working (flexing the MCP joints and extending the PIP and DIPs):
A nice way to remember this is that L umbricals make an “L” shape. Therefore if the lumbricals don’t work then we have the opposite: extended MCP and flexed PIP and DIP. Here are two images (one my hand, the other I got from google images):
Consider this more of a dramatization since I don’t actually have Klumpke’s palsy.
Note: MCPs extended, PIP/DIPs flexed. Klumpke’s palsy has also been called “total claw hand”, because as a commenter wonderfully pointed out there are injuries to both the median AND ulnar nerves.
Ok, so how does all relate to the Pope’s Blessing sign? It really all comes down to which lumbricals aren’t working. Let’s look at a distal ulnar nerve lesion. In this scenario the ulnar lumbricals don’t work, meaning the 4th and 5th fingers have extended MCP and flexed PIP/DIP (remember non-functioning lumbricals). As a result the 4th and 5th fingers appear partially flexed. Now here’s the key: If you ask the patient to extend their fingers you accentuate the discrepancy between fingers. We end up with extended 1st, 2nd, and 3rd digits while the 4th and 5th digits remain partially flexed giving us the classic pope’s blessing sign.
The confusion, I found out, was when in the past the Pope’s blessing sign was considered a distal median nerve lesion. Let’s consider why this was the case and why it might also appear to be a pope’s blessing sign (and why I call it the crooked Pope’s blessing).
With a distal median nerve lesion we are knocking out the lumbricals of digits 2 and 3. Remember what we said about non-functioning lumbricals? We end up with extended MCP and flexed PIP and DIP. If, as before, we ask the patient to extend their fingers we end up with the classic claw hand of a median nerve injury (see below). But, this looks nothing like a pope’s blessing you might ask. That’s because we asked the patient to extend their fingers. Here’s the key, please read carefully: If we asked the patient to “make a fist” instead, we end up with fully flexed 4th and 5th digits with the dysfunctional partially flexed 2nd and 3rd digits. If you do this with your own hand right now…you can see that the 2nd/3rd digits are elevated above the 4th and 5th and might appear as a pope’s blessing, albeit crooked due to the flexed 2nd and 3rd digits, hence the “crooked” pope’s sign.
Here is a chart I made that breaks all of this down in a clear format. I suggest you play with the different variations to see where the differences lie.
To recap, remember it really is about which lumbricals are working and which aren’t. As for the confusion regarding the pope’s blessing sign I hope that cleared things. The 2010 version of First Aid also has the same descriptions as above. The only problem I found was that it wasn’t clear whether the patient was being asked to flex their fingers or to extend them. Even so, I am still human and if you feel that something above is incorrect or unclear please leave a comment below and I will do my best to bring more clarity to the issue.
I hope this helped!