Piano key test (Sachar)
For: TFCC / distal radio-ulnar joint
An injury to the triangular fibrocartilage complex, or to the distal radio-ulnar joint it stabilises (the joint between the lower ends of the two forearm bones), on the little-finger side of the wrist.
A weak test on its ownCaution: One small master's thesis (23 participants); only 7 had no TFCC injury, so the 100% specificity is fragile, and the thesis itself found a positive barely raises the probability.
What the numbers mean
- Positive result: no false positives were seen in the study, so no likelihood ratio can be calculated. How far to trust that depends on how many people without the condition were studied; see the caution above.
- Negative result: barely informative: a negative result changes little.
Source
Tuhi R. Diagnostic Accuracy in the Clinical Examination for Identifying a Triangular Fibrocartilage Complex Injury. MPhil thesis, Auckland University of Technology. 2023. Thesis (AUT repository) · single study
Figures as they will appear in Rule It In, Rule It Out (Trokos, forthcoming). If a newer or better study changes them, this page changes with the book. Figures last updated from the book on 2 October 2026.
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