Photo by toksuede
Football (or soccer) is a venerable game that existed for several hundred years. The original balls were made out of animal bladders, which were cleaned, inflated, and kicked around. Not surprisingly, injuries related to the kicking motion have also existed for hundreds of years. The kicking motion can place a high degree of stress on muscles and tendons that originate in the pelvis, such as the rectus femoris muscle.
The rectus femoris muscle has two distinct origins. The direct (straight) head arises from the anterior–inferior iliac spine (AIIS), while the indirect (reflected) head originates from the superior acetabular ridge and hip capsule. The indirect (reflected) head is the primary head. The two heads unite, and form the rectus femoris muscle, shown in red below:
A frontal view of the pelvis depicts the origin of the direct head (red) from the AIIS, and the origin of the indirect head (blue) from the superior acetabular ridge:
Remember that the indirect head in inferior (both words begin with "i"). An oblique view of the pelvis better depicts the relationship of the two origins to the acetabulum:
The two heads of the rectus femoris tendon are well depicted on the following oblique axial image, which depicts the origin of the direct head (red) from the AIIS, and the origin of the indirect head (blue) from the superior acetabular ridge:
In the following case, a 14 year old boy experienced sharp pain while kicking a soccer ball. A coronal STIR image shows an avulsion of the direct head of the rectus femoris (red arrow) from the AIIS:
Axial images show the avulsed bone fragment (red arrow) and the attached tendon, as well as the intact indirect head (yellow arrow) of the rectus femoris:
Consecutive sagittal images show the avulsed bone fragment (red arrow), direct arm of the rectus femoris (green arrow) and indirect arm of the rectus femoris (yellow arrow):
Rectus femoris tears typically affect the direct head, but one can also involvement of the indirect head, alone or in concert with direct head tears. With direct head tears, one often sees a flake of bone on conventional radiographs, corresponding to an avulsion fragment. MRI can help confirm the diagnosis.
Avulsion of the anterior superior iliac spine can simulate this injury if the fragment is retracted inferior to the level of the anterior inferior iliac spine (Stevens et al. Radiographics 19:655-672, 1999). Rectus femoris tears can lead to a soft tissue mass, and a chronic rectus femoris tear can mimic a tumor (Temple et al, AJSM 26:544-548, 1998).
Injuries of the rectus femoris typically respond well to conservative therapy. Avulsions of both the anterior superior and anterior inferior iliac spines tend to be less symptomatic and disabling than avulsions of the ischial tuberosity, and recovery typically occurs over a few weeks (Combs JA, Physician Sports Med 22:41-49, 1994). Fortunately, rectus femoris tears usually respond well to conservative therapy, and heal over several weeks.
Vic David MD