Reaching up to the knees. / Submerged to the knees. / (figuratively, by extension) Deeply involved in something, or preoccupied with something.

(slang) A casual outdoor sexual encounter (commonly with a prostitute), usually in an alleyway or against a wall, with the man standing and the woman's knees raised.

The medical condition genu valgum

(baseball, slang) A curveball (or occasionally a knuckleball) that fools the hitter, causing his or her knees to buckle (i.e. bend).

plural of knee baby

Breeches reaching down to or just below the knee.

plural of knee pit

(informal) poplit (shallow depression located at the back of the knee joint)

Any of various overuse injuries involving pain around the kneecap.

(informal) The shallow depression located at the back of the knee joint.