The Anatomy of the Vastus Medialis

The vastus medialis (vastus medialis oblique, or VMO) is a teardrop-shaped muscle that helps move the knee joint and stabilize the kneecap. It is one of the four quadriceps muscles in the front of your upper thigh.

Injury to the vastus medialis can cause knee pain and difficulty walking, running, or managing stairs.

This article discusses the anatomy and function of the vastus medialis, as well as conditions associated with it.

Anatomy

The vastus medialis originates from the intertrochanteric line on the inner part of your thigh bone (femur).

From there, it courses down the front and inner portion of the kneecap (patella) and joins the other quadriceps muscles (rectus femoris, vastus intermedius, and vastus lateralis). These muscles attach to the patella via the quadriceps tendon.

The vastus envelopes the patella and inserts the patellar tendon on the front of your shin bone (tibia).

The vastus medialis is innervated by the femoral nerve, which comes out from your lumbar spine at level two, three, and four. The femoral artery supplies blood to the vastus medialis.

Function of the Vastus Medialis

The vastus medialis works with the other quadriceps muscles to help you extend your knee joint. The muscle and its tendon go over the inner aspect of your knee, where it helps stabilize the kneecap.

Your patella is situated in a small groove on the end of your thigh bone. The groove allows your kneecap to track up and down when you bend and straighten your knee. As it tracks in the groove, the patella gets medial stability from the vastus medialis.

Conditions That Affect the Vastus Medialis

The function of your vastus medialis can be impaired by several conditions, which can result from surgery, trauma, or athletic injuries.

Injury to the muscle can cause weakness, change how your knee moves, or affect your ability to walk and run.

Patellofemoral Stress Syndrome (PFSS)

Patellofemoral stress syndrome occurs when your kneecap fails to track properly in the femoral groove. This results in pain around your kneecap and makes it hard to walk, jump, or run.

Since the vastus medialis is a major stabilizer of your kneecap, weakness here may be a cause of PFSS.

Femoral Nerve Injury

Your femoral nerve arises from your lower lumbar spine. An injury to it can cause paralysis (lack of movement) or paresis (partial lack of movement) of your quads and vastus medialis.

Conditions like arthritis, a herniated disc, or spinal tumors can also cause nerve injury here. The resulting weakness may make straightening your knee difficult or impossible. Your ability to walk, rise from a chair, or climb stairs, may be affected.

VMO Weakness After Surgery or Injury

If you have knee surgery, there will likely be swelling around your knee joint. The swelling can irritate the nerves that supply the muscles, including the vastus medialis, leading to weakness.

These symptoms usually improve as the swelling gets better and the injury heals.

Patellar Dislocation or Subluxation

If you have a patellar dislocation, your vastus medialis may become injured or torn. This injury can cause pain, muscle weakness, and difficulty walking or running.

Vastus Strain Due to Trauma

A sudden blow to your thigh can result in strain to the vastus medialis, causing pain, swelling, and muscle weakness.

Plica Syndrome

A plica is a small fold of tissue that surrounds part of your kneecap. If this tissue becomes pinched between your kneecap and femoral groove, it can be painful.

As a stabilizer of your kneecap, the vastus medialis helps keeps it in place and prevents the plica from getting pinched.

If you have knee pain or weakness, see your healthcare provider. They may refer you to a physical therapist who can help you recover.

Rehabilitation

An injury to your knee or vastus medialis muscle may limit your normal functional ability. Rehabilitation will depend on the type of injury and your individual needs.

For an acute injury to your vastus medialis, it's generally recommended that you allow some time for rest initially, then begin gentle movement as you heal.

Exercises that improve muscle flexibility and strength can help you fully regain mobility as well as prevent future problems.

Vastus Medialis Strain

If you tear or strain your vastus medialis, the first treatment is a period of rest. You may need a knee brace or compression sleeve to support your knee and control swelling as you recover.

After a week or so of rest, try starting gentle exercises such as heel slides, quad sets, and straight leg raises. Stretching for your quadricep will also gently elongate the muscle.

VMO Weakness From Femoral Nerve Injury

If your femoral nerve becomes pinched by arthritis or a bulging disc in your back, it can cause vastus medialis weakness and limit your ability to walk.

The first step in treatment is to get the pressure off your femoral nerve to restore normal nerve communication with the vastus medialis. Once the nerve is free, you can use strengthening exercises to regain normal knee function.

Patellofemora Stress Syndrome

Since the vastus medialis is a major knee stabilizer, weakness in the muscle can be a cause of PFSS.

Treatment of PFSS involves improving vastus strength with quad sets, straight leg raises, and patellar tracking exercises.

The position of your knee is controlled by your hip muscles (gluteus medius). Treating PFSS can also involve strengthening your hip muscles along with your vastus medialis.

Vastus Inhibition After Injury or Surgery

Swelling is common after a knee injury or surgery and can inhibit the function of your quad and vastus medialis.

Heat or ice may be used to reduce swelling. Exercises like heels slides and stationary bike riding may also be useful.

As part of your longterm recovery, you may work with a physical therapist to improve vastus medialis function.

Physical therapists sometimes use a special type of neuromuscular electrical stimulation (NMES) to encourage the vastus contract properly and help regain normal muscle function.