Avulsion fracture of anterior inferior iliac spine

Clinical History

History of injury during soccer a few days before

Imaging Findings

The patient presented with a history of injury during soccer a few days before. He experienced a sudden severe pain in his left hip during the game with localized tenderness in the region. Physical examination revealed focal pain by palpation and disability to walk.
Radiographic assessment with standard anteroposterior view of the pelvis showed an avulsed bony fragment in the region of the anterior inferior iliac spine.
MRI was performed. Axial and coronal T1-weighted (TR/TE: 400/25) and STIR (TR/TE: 5200/25) images were obtained. Axial T1-weighted image showed avulsion of the anterior inferior iliac spine with findings of muscle strain in the associated muscles. STIR images showed edema in the region.

Discussion

Avulsion injuries, which are becoming more common, frequently occur in adolescents or young adults participating in athletics as result of sudden, forceful or unbalanced contraction of the attached musculotendinous unit. These fractures are usually related to the time of appearance of ossification of the apophyses and their fusion to the corresponding pelvic tuberosities. The four bony structures in the hip region prone to the avulsion injury are (1) the anterior superior iliac spine, (2) the anterior inferior iliac spine, (3) the ischial tuberosity and (4) iliac crest.
Avulsion fracture of the anterior inferior iliac spine occurs as a result of over pull of the straight head of the rectus. Radiographs confirm the diagnosis, suggested by physical examination, patient’s age and biomechanical analysis of the accident. It is important to evaluate the contra-lateral side as well as the injured side in these injuries, because they occur through secondary center of ossification and because what appears to be a fracture may simply be an anatomic variant.
Axial T2-weighted or STIR images are usually necessary to identify areas of edema or hemorrhage associated with these fractures. Avulsed bone appears dark on either gradient –echo or STIR images and may be indistinguishable from adjacent soft tissues.
The healing phase of an avulsion fracture with abundant reactive ossification in the soft tissues may clinically and radiographically be mistaken for neoplasia. In such cases, a Tru-Cut needle biopsy may be needed in order to reveal the reactive nature of the process.
A high index of suspicion is necessary to diagnose this relatively rare injury. A few days of bed rest for pain relief, followed by protected weight-bearing until comfort is achieved, is adequate. Surgery has a role in cases of significant displacement of the fragment or of formation exostosis needing excision.

Differential Diagnosis List

Final Diagnosis

Avulsion fracture of anterior inferior iliac spine

URL:	https://www.eurorad.org/case/1274
DOI:	10.1594/EURORAD/CASE.1274
ISSN:	1563-4086