Piano Key Sign
The Piano-Key Sign Test is a test carried out for the clinical assessment of wrist instability. It is used as an indicator for distal radio-ulnar joint instability and tears of the triangular fibrocartilage complex of the wrist.
In the Piano-key Sign Test, the wrist is supported in pronation by the examiner. The hand is stabilized in the neutral position from the ulnar side and force is applied to the head of ulnar.
The test is positive if the ulnar head goes back to its anatomic position after the removal of the force applied to the ulnar head. This bears resemblance with when a piano key springs up after the force from a finger is removed from the key, hence, the name "piano-key" sign. This instability and pain are judged relative to the contralateral wrist. 
No instability or movement observed on removal of pressure on the ulnar head.
The Piano-key Sign Test has a specificity of 0.96 and a sensitivity of 0.59. 
- Vezeridis PS, Yoshioka H, Han R, Blazar P. Ulnar-sided wrist pain. Part I: anatomy and physical examination. Skeletal radiology. 2010 Aug;39(8):733-45.
- American Society for Surgery of the Hand. The hand: examination and diagnosis. Churchill Livingstone; 1990.
- Duke Orthopaedics: Wheeless’ Textbook of Orthopaedics Website. Avaliable at: https://www.wheelessonline.com/muscles-tendons/tfcc-examination/. Accessed February 10, 2021.
- Lindau T, Adlercreutz C, Aspenberg P. Peripheral tears of the triangular fibrocartilage complex cause distal radioulnar joint instability after distal radial fractures. The Journal of hand surgery. 2000 May 1;25(3):464-8.