The Piano Key Sign- Understanding Compression of the Ulna head
I often receive emails from patients with TFCC tears who report wrist splinting (normal wrist extension/cock-up) makes their wrist hurt more than without the splinting. The Piano Key Sign is a common test performed by physicians as a part of the clinical assessment of the wrist.
Simply described, imagine the ulna head as a piano key. The examiner would press on the ulna head and if painful, would indicate a positive Piano Key Sign. A stable wrist would cause the ulna head to spring back like a piano key without pain. You can read all about the test all over medical textbooks as an indicator of a TFCC tear or DRUJ (distal radial ulna joint) instability.
One would, using common sense, wonder why we would recommend a splint for the wrist that compresses the ulna head in any of the treatment plans for patients with suspected TFCC tears. The simple answer is: if you have a suspicion of a TFCC tear, do NOT compress the ulna head- ever.
Take a look at a standard over the counter wrist splint:
There certainly are times when you need the support of a wrist splint. There is value in this sort of splinting. The longer the splint goes up your forearm, the less rotation of the wrist you can perform. Since rotation strains the TFCC, limiting rotation is important. There are also cases where the Extensor Carpi Ulnaris (ECU) tendon is injured and, in these cases, you can help calm the ECU by limiting wrist flexion which stretches the ECU. There are also cases where the injury is to the scaphoid-lunate ligament as well as to the TFCC. In these cases, wrist extension should be limited.
If wrist flexion and extension are important to limit and the TFCC is also injured, consider taking the tension off the ulna by loosening the strap that pushes on it. Make sure there is NO compression to the ulnar head.
I studied this in my clinic by testing weight bearing tolerance in patients with TFCC tears. In the first group of cases, I taped the wrist circumferentially with 2-inch tape, compressing the ulna head. Then I tested their weight bearing tolerance. The outcome was clear in cases with complete TFCC tears; compression of the ulna decreases stability. This only happens in patients with moderate to severe tears of the TFCC. In the other group of patients, I put the WristWidget® on and tested weight bearing tolerance. In these cases, their weight bearing tolerance went UP with the ulna head free of compression.
These rules do not apply for normal wrists. Oftentimes, we see weightlifters and athletes in all professions taping their wrists. They do this because they feel support. If you take healthy wrists and tape them circumferentially with compression of the ulna, their weight bearing tolerance increases just a little. If you put the WristWidget® on, the weight bearing tolerance decreases just a little. This was an unexpected finding and counter-intuitive. The weight bearing tolerance of a normal wrist will decrease if you lose wrist extension. Since the WristWidget® limits the last 10 degrees of wrist extension, it causes the weight bearing to decrease a bit. The tape does not limit wrist extension as much and therefore causes a slight increase. Lots of athletes tape their wrists so that wrist extension is supported. This is a very beneficial taping technique to limit the load on the Scaphoid Lunate ligament but it has no influence on the TFCC in normal wrists.
So, next time you scream when someone pushes on your ulna head, you understand what is going on. When your cast or splint is causing you pain, try this test. Try changing that middle strap. Get the compression off the ulna. The next time the doctor does this test, you will know its name: The Piano Key Sign.