Clarke's sign (patellar grind test)
For: Chondromalacia patellae at arthroscopy (knees without patellofemoral pain)
Softening or damage of the cartilage on the back of the kneecap, as seen at arthroscopy. In this study the knees did not have patellofemoral pain.
Treat with caution (see below)Caution: Studied in people without patellofemoral pain; the authors recommended dropping the test.
What the numbers mean
- Positive result: barely informative: a positive result changes little.
- Negative result: barely informative: a negative result changes little.
Source
Doberstein ST, Romeyn RL, Reineke DM. The diagnostic value of the Clarke sign in assessing chondromalacia patella. J Athl Train. 2008;43(2):190–196. Journal article (DOI) · 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.
Get the book for how to do and read each knee test with published figures, and which ones to trust for the ACL, meniscus and kneecap
This page gives the published figures. Rule It In, Rule It Out adds how to do this test, what counts as positive, how to read the result, and, where studied, whether combining it with other tests helps.
Coming in late 2026 as a PDF and a paperback. Join the list to hear when it's out
One study, one test, once a month
Rule It In is a free evidence letter for musculoskeletal clinicians: one recent study explained, one examination test with its real numbers. From Trokos, publisher of Rule It In, Rule It Out.