MR Imaging of the Proximal Rectus Femoris Musculotendinous Unit
Section snippets
Normal anatomy
The rectus femoris is the most superficial and anterior of all the quadriceps muscles. It functions to extend the knee, generate hip flexion torque, and stabilize the pelvis upon the weight-bearing femur. The muscle has two heads of origin: the direct or straight head, which arises from the anterior inferior iliac spine (AIIS), and the indirect or reflected head, which arises from the superior acetabular ridge (Fig. 1). The two heads form the conjoined tendon slightly below their origin. The
MR anatomy
The tendinous origins of the rectus femoris muscle are easily identified on axial, sagittal, and coronal MR images as low signal intensity structures that originate from the iliac bone (Fig. 3, Fig. 4, Fig. 5). The axial images are optimal for following the course of the deep and superficial components of the tendon (see Fig. 3). The most superior axial images at the AIIS level demonstrate the origin of the direct head. Slightly more distally, the more posterior origin of the indirect head from
Apophyseal avulsion injuries
Avulsion injury of the proximal rectus femoris is secondary to an uncoordinated powerful eccentric muscular contraction and is the third most common type of avulsion injury at the pelvis, surpassed only by hamstring and sartorius muscle injuries. In adults, the avulsion usually occurs at the tendon's attachment to the AIIS, whereas in adolescents, the avulsion is more likely to occur at the junction of the AIIS apophysis with the bone. Avulsion of the direct head at the AIIS is more frequent
Musculotendinous junction injuries
Musculotendinous injuries or strains are common in the hip and pelvis and are related to excessive stretching during contraction [3]. The rectus femoris is the most commonly injured muscle of the quadriceps muscles because of its long fusiform shape, its tendency for eccentric muscle contraction, its high percentage of type II fibers, and its extension across two joints. Common predisposing factors for injury are a history of a previous tear, poor muscle conditioning, inadequate warm-up
Muscle contusion and laceration
Because of its superficial location, the rectus femoris is susceptible to muscle contusions secondary to a nonpenetrating direct trauma [17], [18]. Patients usually present with pain, swelling, and ecchymosis. At MR imaging, the muscle is swollen, and interstitial edema and hemorrhage without disruption are noted (Fig. 14). A common delayed complication of muscle contusion is myositis ossificans [19]. Muscle laceration is usually caused by penetrating trauma. MR imaging depicts a complete
Summary
MR imaging is a useful modality for diagnosing and grading proximal rectus femoris injuries. MR imaging is also valuable in predicting the length of recovery and rehabilitation time of musculotendinous strains and in presurgical planning when resection of a chronic hematoma, deep scar tissue, or a pseudocyst is contemplated.
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