This article is from the Keeshonden Breed FAQ, by firstname.lastname@example.org (Kimberly J. Eashoo).
"Slipped stifles" simply means that slipping of the kneecap on the
rear legs. This condition, whether hereditary or caused by trauma, can
be identified by a veterinarian during an examination. Patellar
subluxation is correctable by surgery but because it is hereditary
(unless caused by injury) it is not recommended that dogs with this
condition be bred.