CASE 50

By: Dr. Subramaniyan Ramanathan MD and Dr. Mahmoud Alheidous.

HISTORY: 16-year-old male professional football player presents with right hip pain.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

AP pelvic radiograph appears unremarkable. Closer look at the oblique view shows subtle bone fragment close to right anterior inferior iliac spine (AIIS). MRI of pelvis demonstrates the apophyseal avulsion in the right AIIS at the attachment of straight head of rectus femoris with fluid cleft indicating complete tear. Associated mild degree of marrow edema noted. Rectus femoris tendon as such is intact.

DIAGNOSIS:

Anterior inferior iliac spine avulsion injury.

PEARLS AND DISCUSSION:

The rectus femoris muscle has two tendinous origins, 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 and the posterolateral aspect of the hip joint capsule. The rectus femoris is the most commonly injured muscle of the quadriceps muscle group. The straight or direct head of the rectus femoris muscle originates from the AIIS and forceful extension at the hip joint can lead to an avulsion injury at this point. Most often seen in adolescents as in any other pelvic avulsion injuries with male predilection and associated with sports which involves kicking.

Patients complain of localized pain and swelling and limited range of motion. Avulsed bony fragment may not be obvious on radiograph and an oblique view has better diagnostic value than AP, radiograph of the pelvis. Comparison radiographs of the contralateral hip may aid in distinction between an open apophysis and an avulsion fracture. MRI of pelvic is diagnostic and may be useful for identifying minimally displaced or non-displaced avulsions, purely tendinous avulsions and avulsions or apophysitis that occur prior to apophyseal ossification. MRI may miss a small bone fragment but, if the injury is acute, it will show edema at the apophysis, often extending along the tendon origin. Most patients heal with conservative management, but recovery may take up to 4 months.

FURTHER READING:

1. Stevens MA, El-khoury GY, Kathol MH et-al. Imaging features of avulsion injuries. Radiographics. 19 (3): 655-72.

2. Resnick JM, Carrasco CH, Edeiken, Yasko AW, Ro JY, Ayala AG. Avulsion fracture of the anterior inferior iliac spine with abundant reactive ossification in the soft tissue. Skeletal Radiol 1996;25:580-584

3. Ouellette H, Thomas BJ, Nelson E, Torriani M. MR imaging of rectus femoris origin injuries. Skeletal Radiol 2006;35:665-672.dysplasia.