The vastus medialis muscle commonly is subdivided into two parts. This probably is due to the clinical significance of the vastus medialis oblique muscle as separate from the clinical significance of the vastus medialis longus and the large size of the vastus medialis oblique. The oblique portion of this muscle is the distal portion that has fibers that are more horizontal and therefore have more effect on preventing patellar displacement and less effect on producing knee extension. The resultant of the quadriceps femoris group produces an overall extensor pull on the knee and lateral pull on the patella. Excessive patellar lateral displacement is prevented by the bony projection of the lateral femoral condyle and the vastus medialis oblique muscle.

Guide the patient to sit. With the patient relaxed and with permission, place your fingers on the vastus medialis longus muscle belly in the mid-portion of the muscle on the medioanterior thigh. Guide the patient to extend the knee. With unclear muscle activity, increase the contraction of the vastus medialis oblique by asking the patient to straighten the knee while you provide a push on the leg (i.e. between the knee and the foot) in the direction of knee flexion. The vastus medialis oblique is activated because it is preventing the tendency for the patella to be pulled laterally due to the resultant lateral pull of the quadriceps femoris.