The "dimple sign" is a transverse groove in the skin at the medial joint line caused by invagination of a portion of the medial capsule. Presence of this sign suggests a posterolateral knee dislocation that cannot be manually reduced.
Reprinted by permission from: Springer: Indian Journal of Orthopaedics. Saini R, Mootha AK, Goni VG, Dhillon MS. Neglected irreducible posterolateral knee dislocation. Indian J Orthop 2010; 44:468. Copyright © 2010.
https://www.springer.com/journal/43465.