‘蹲膝盖’ (cūn xī gài) is a colloquial, informal verb meaning ‘to sprain the knee’ — specifically, to injure the knee joint by twisting, overextending, or landing awkwardly while squatting, kneeling, or changing direction quickly. Though it literally combines 蹲 (to squat), 膝 (knee), and 盖 (a cover or cap — here used as a colloquial suffix for body parts like 膝盖 ‘kneecap’), the phrase functions as a single action verb, not a literal description of squatting on the kneecap.

This expression is commonly used in everyday spoken Chinese, especially when recounting sports injuries, slips on stairs, or falls during physical activity. It carries a sense of sudden, unintended injury and often implies mild-to-moderate pain and temporary mobility limitation. It is not used in formal medical contexts — doctors would say ‘膝关节扭伤’ (xī guān jié niǔ shāng) instead. The term is regionally widespread but most frequent in northern and central dialect-influenced Mandarin.