VMO stands for vastus medialis oblique and is part of the vastus medialis quadriceps muscle at the front of the thigh. Here we explain why strengthening this muscle is so important for knee rehabilitation.
The position of the vastus medialis oblique is just above and to the inside of the knee cap. The fibres of VMO have a more oblique alignment than the other fibres of vastus medialis. It arises from the tendon of adductor magnus muscle 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.
Why is VMO important?
VMO is important in keeping the kneecap tracking correctly. It is an active and dynamic stabiliser of the patella. In healthy, pain free individuals the fibers of the VMO are active throughout the range of movement. In patients with patellofemoral knee pain or 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 Patellofemoral knee pain are often caused by VMO malfunction, however some acute injuries also cause the inhibition of VMO for example anterior cruciate ligament rupture, patella dislocation & meniscal tears.
To check the contraction of VMO sit with your legs out in front and a rolled up towel under the injured knee which should be slightly bent. Put your fingers over the area of VMO muscle on the inside of the thigh and contract the muscle. The knee should push down into the towel and the leg straighten so that the foot lifts off the couch. You should feel a strong contraction under your fingers.
If the muscle does not contract, continue to practice whilst pressing down gently on the muscle and concentrating on contracting the fibers underneath your fingers. If the muscle does contract, continue with strengthening exercises.
Isometric quadriceps contraction
Sitting on a chair palpate or feel the VMO muscle. Start to slowly straighten the knee and ensure the VMO contracts. Maintain the contraction throughout the movement as you fully straighten the knee and bend it again. Repeat this twice daily until you can maintain a strong constant contraction 10 times in a row
Once you can hold the contraction as above, start to integrate this into functional movements such as heel drops and lunges. Heel drops are performed by standing on a step and dropping the heel forwards off the step to slightly bend the knee. Don't go too far, just enough to feel the vastus medialis oblique contracting. It is important to keep the knee in a straight line and control the hips. Many therapists will advocate taping the patella whilst doing this exercise to ensure correct tracking.
Play Heel drop exercise video.
For the lunge, with a split stance initially place one or two fingers on the VMO of the front leg. Perform a lunge by bending the front knee and dropping the back knee towards the floor. Maintain VMO contraction throughout the lunge. Initially perform as many as you can while maintaining a strong constant contraction and gradually increase the number up to 20.
Repeat this process in step-up exercises too, although you may not always be able to reach to feel the muscle contract. Try performing a squat against a wall by sliding your back down the wall until your knees are at a right angle. Your shins should remain vertical.
Play Lunge exercise video.
Place a large ball such as a football in between your knees and squeeze it. This activates the adductor muscles and because VMO arises from the tendon of adductor magnus, also stimulates VMO to contract. Hold for 3 seconds and repeat 10 times, gradually increasing to 5 second holds and 20 repetitions.