|Origin||Anterior and lateral surface of the femur & lateral intermuscular septum|
|Insertion||Quadriceps tendon, which inserts into the patellar ligament, which inserts onto the tibial tuberosity|
|Action||Extends the knee|
|Nerve||Femoral nerve (L2, L3, L4)|
Location & Overview
The vastus intermedius muscle is one of the four quadricep muscles, along with the vastus lateralis, vastus medialis, and rectus femoris. The vastus intermedius is located deep to the rectus femoris, between the vastus medialis and vastus lateralis. It is almost hidden by the other muscles and cannot be palpated . Some studies have also reported a fusion of the vastus intermedius and vastus lateralis muscles  . In extreme cases of this fusion, the two muscle present as an almost complete fusion .
Pathologies involving the vastus intermedius muscle are less commonly reported compared to other quadricep muscles, likely due to its deep location. However, strains and contusions can still occur, typically as a result of overuse or direct trauma . Weakness of the vastus intermedius muscle may contribute to instability of the knee joint and increased risk of injury .
Strengthening exercises targeting the vastus intermedius muscle are essential for maintaining knee joint stability and overall lower limb function. Exercises that engage the vastus intermedius include squats, lunges, leg presses, and leg extensions  . Incorporating these exercises into a well-rounded training program can help prevent injuries and enhance athletic performance.
Origin & Insertion
The vastus intermedius originates on the anterior and lateral surface of the shaft of the femur . The femur, also known as the thigh bone, is the longest and strongest bone in the human body. The anterior surface refers to the front side of the femur, while the lateral surface refers to the outer side of the bone. The vastus intermedius also originates from the lateral intermuscular septum, a deep fascia fold separating the anterior and posterior compartments of the thigh . The vastus intermedius then inserts into the quadriceps tendon, a strong band of fibrous tissue that connects the muscle to the patella (or kneecap)  . Most of the vastus intermedius’ tendon fibers insert at the base of the patella .
The quadriceps tendon serves as a common insertion point for all four quadricep muscles, including the vastus intermedius. This shared tendon allows the muscles to work together to extend the knee joint. By connecting to the quadriceps tendon, the vastus intermedius helps with the overall function and stability of the knee joint, alongside the other quadricep muscles .
The quadriceps tendon connects to the patellar tendon, which in turn inserts onto the tibial tuberosity. The tibial tuberosity is a bony prominence on the upper part of the tibia (shin bone), located just below the knee joint .
The vastus intermedius, along with the other quadricep muscles (vastus lateralis, vastus medialis, and rectus femoris), plays an important role in extending the knee joint . Knee extension is essential for various daily activities, such as walking, running, climbing stairs, and standing up from a seated position. During these activities, the vastus intermedius contracts and works synergistically with the other quadricep muscles to straighten the leg at the knee joint .
In addition to knee extension, the vastus intermedius is also involved with maintaining knee stability . As one of the deeper quadricep muscles, the vastus intermedius provides support to the patella and helps distribute force across the knee joint. This supportive role is useful for maintaining proper knee alignment and preventing excessive stress on the joint during activities that require dynamic knee movements, such as sports and exercise . Moreover, the vastus intermedius contributes to the eccentric control of the knee during activities such as descending stairs and landing from a jump. Eccentric control refers to the ability of a muscle to generate force while lengthening, which acts like a brake to slow down joint movement .
The vastus intermedius muscle receives its innervation from the femoral nerve, which is derived from the lumbar spinal nerve roots L2, L3, and L4 . The femoral nerve is a large nerve that originates from the lumbar plexus in the lower back, passes through the pelvis, and descends into the thigh. It is the primary nerve which innervates the quadriceps muscle group, including the vastus intermedius, vastus lateralis, vastus medialis, and rectus femoris muscles .
Proper function of the femoral nerve is vital for the coordinated movements and stability of the knee. Damage or injury to the femoral nerve can result in muscle weakness or even paralysis, affecting the ability to extend the knee and potentially leading to difficulty when walking or maintaining balance 
Blood is supplied to the vastus intermedius via the femoral artery .
Want some flashcards to help you remember this information? Then click the link below:
Vastus Intermedius Flashcards
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