Function: Vastus medialis has been widely reported to be responsible for extending the leg the last 10%, however this commonly held claim has no basis, indeed there is a reasonable body of evidence to the contrary. The vasti instead 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. 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. Often medical and other allied health practitioners suggest improving the strength and/or activation of this muscle as a strategy in the treatment of Patello-femoral Pain Syndrome – sometimes called runner’s knee. The biomechanical cause of patellofemoral pain syndrome is unknown and may have more to do with weakness of extensors of the hip (ie gluteus maximus), which causes subsequent unusual internal rotation of the femur. Lunges are an exercise sometimes used to target this muscle. Relations: The Vastus medialis and Vastus intermedius appear to be inseparably united, but when the Rectus femoris has been reflected a narrow interval will be observed extending upward from the medial border of the patella between the two muscles, and the separation may be continued as far as the lower part of the intertrochanteric line, where, however, the two muscles are frequently | 
