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VMO stands for Vastus Medialis Oblique (sometimes called obliquus). This is part of the Vastus Medialis muscle which is one of the four Quadriceps muscles of the thigh.
The fibres of VMO have a more oblique alignment than the other fibres of Vastus Medialis (hence the name!). It arises from the tendon of Adductor Magnus and converges to join the other Quadriceps muscles inserting via the patella tendon, to the tibial tuberosity at the top of the tibia (shin bone). The picture on the right shows the relative position of VMO, just above and to the inside of the knee cap.
VMO is an active and dynamic stabiliser of the patella. In healthy, pain free individuals the fibres of VMO are active throughout the range of movement. In patients with Patello-Femoral Knee Pain (Chondromalacia Patella) the fibres contract in phases, inconsistently and fatigue easily.
The specific role of VMO is to stabilise the patella within the patella groove and to control of the 'tracking' of the patella when the knee is bent and straightened. Mis-firing and weaknesses in the VMO cause mal-tracking of the patella and subsequent damage to surrounding structures and aching pain.
First you must ensure that VMO is contracting properly. Long-term injuries such as Patello-femoral knee pain are a result of VMO malfunction, however some acute injuries cause the inhibition of VMO (e.g. Anterior Cruciate Ligament rupture, Patella dislocation & Meniscal tears).
To check the contraction of VMO:
If the muscle does not contract, continue to practice whilst pressing down gently on the muscle and concentrating on contracting the fibres underneath your fingers.
If the muscle does contract, you can continue with strengthening exercises:
Holding the Contraction: