The vastus medialis (aka vastus internus), often called the 'teardrop' muscle, is a medially located muscle of the quadriceps.

The Vastus Medialis is one of four muscles which resides in the front of the thigh. The vasti appear to act largely in a co-ordinated manner throughout the control of knee extension. Much has been made of the ability of the Vastus Medialis to translate the patella medially, however since approximately 70% of the contractile fibres attach directly to the common extensor tendon (which then inserts centrally to the superior patella) the functional ability to achieve this goal may be overstated, and is likely dwarfed by the bony congruence of the patella in the trochlea notch. However, this does not apply to persons with trochlear aplasia or hypoplasia, which refer to an absence or extreme shallowness of the trochlear groove. Some authorities maintain there is a separate aspect to the Vastus Medialis muscle - the "Vastus Medialis Obliquus" or more commonly the "VMO" which is reported to have a more oblique or horizontal orientation to the bulk of the remainder of the muscle thereby disposing it to be better able to 'pull' the patella medially. Unfortunately careful inspection of many cadavers reveals that the fibres of the Vastus Medialis are largely parallel and there is no significant separate aspect of the contractile fibres fitting this description which would suggest it is time to lay this clinical myth to rest.