The vastus medialis ( vastus internus or teardrop muscle) is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group.
The vastus medialis muscle originates from a continuous line of attachment on the femur, which begins on the front and middle side (anteromedially) on the intertrochanteric line of the femur. It continues down and back (posteroinferiorly) along the pectineal line and then descends along the inner (medial) lip of the linea aspera and onto the medial supracondylar line of the femur. The fibers converge onto the inner (medial) part of the quadriceps tendon and the inner (medial) border of the patella.
The obliquus genus muscle is the most distal segment of the vastus medialis muscle. Its specific training plays an important role in maintaining patella position and limiting injuries to the knee. With no clear delineation, it is simply the most distal group of fibers of the vastus medialis.
A division of the vastus medialis muscle into two groups of fibers has been hypothesized, a long and relatively inline group of fibres with the quadriceps ligament, the vastus medialis longus; and a shorter and more obliquely oriented with group of fibres, the vastus medialis obliquus. There is as yet insufficient evidence to conclusively confirm or deny this hypothesis.
Misfiring and fatiguing of the VMO causes mal-tracking of the patella and subsequent damage to surrounding structures creating increased force on the knees, often resulting in injuries such as patellofemoral pain syndrome, anterior cruciate ligament rupture, chondromalacia, and tendinitis. Through the use of electromyography, researchers can evaluate and record the electrical activity produced by the skeletal muscle of the VMO to analyze the biomechanics and detect any possible abnormalities, weakness, or fatigue. With an analysis of muscle activity of the VMO through the use of electromyography, proper rehabilitative plans and goals can be established to not only correct the already established abnormality, but even prevent such injuries if tested sooner. Preventing injuries is crucial as well as teaching proper training techniques to ensure there are no valgus collapse forces causing unplanned stress on other structures of the knee, causing asymmetry, and predisposing that individual for injury.
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