The vastus medialis (/ˈvæstəs ˌmɛdiˈeɪlᵻs/ or /ˈvæstəs ˌmɛdiˈælᵻs/) (vastus internus or teardrop muscle) is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group.