Quadriceps Strain

The quadriceps femoris muscle is located in the front of the thigh and is made up of four muscles: (1) rectus femoris, (2) vastus medialis, (3) vastus lateralis, and (4) vastus intermedius. The rectus femoris is in the middle of the thigh and covers the other quadriceps muscles. The vastus muscles are all deep to the rectus femoris and lie next to each other. The vastus medialis is the most medial, the vastus lateralis is the most lateral, and the vastus intermedius is in between the lateralis and medialis.

The rectus femoris originates from the ilium and therefore crosses both the hip and knee joint, whereas the vastus muscles originate from the femur and cross only the knee joint. All four of these muscles attach to the patella via the quadriceps tendon.

The quadriceps muscles are used to extend the knee as well as decelerate knee flexion when the heel strikes the ground. Because the rectus femoris muscle crosses the hip joint as well as the knee joint, it also functions as a hip flexor. These muscles are active during running, jumping, and walking. These muscles are composed predominantly of Type II fibers, which make them well suited for forceful rapid activities; however, they tire more easily than muscles composed of mainly Type I fibers, which are better suited for sustained activities.

Quadriceps muscle strains are actually small tears in the muscle. Muscle strains usually occur when an eccentric contraction occurs. An eccentric contraction occurs when the force generated by the muscle cannot overcome the resistance placed on the muscle. This causes the muscle fibers to lengthen as they contract (Figure 1). This type of contraction is used as a method of decelerating a body part or an object.

The musculotendinous junction is the location within the muscle where the strain most often occurs. Muscles that cross two joints in the body, such as the rectus femoris, are more susceptible to strain.

Quadriceps strains most often occur in individuals who are older and skeletally mature—that is, their physes, or growth plates, have closed. Younger, skeletally immature patients tend not to have quadriceps strains; oftentimes if a muscular strain is sustained, it is a low-grade strain. Instead of muscle strains, younger athletes are more susceptible to avulsion fractures. An avulsion fracture of the anterior-superior iliac spine can be caused by a forceful contraction of the quadriceps muscle in a child or adolescent who still has an open apophysis.

Figure 1 Quadriceps Muscles Strain

Notes: A quadriceps strain is among the most common injuries in sports. The quadriceps muscle most commonly injured is the rectus femoris, because, unlike the other three quadriceps muscles, it crosses two joints, the hip and the knee.