A 17-year-old teenage boy presented with acute right-sided pelvic pain after an intense workout for his school track and field team. Pelvic radiographs were obtained (Figure 1).
The most likely diagnosis from the history, presentation and pelvic radiograph image is:
a) pelvic osteosarcoma
b) avulsion injury at sartorius muscle origin at anterior inferior iliac spine
c) post-traumatic myositis ossificans
d) avulsion injury at sartorius muscle origin at anterior superior iliac spine
e) avulsion injury at rectus femoris muscle origin at anterior inferior iliac spine
The most likely diagnosis is: e) avulsion injury at rectus femoris muscle origin at anterior inferior iliac spine
The radiograph reveals a 2 cm avulsed fragment of bone at the site of the anterior inferior iliac spine (AIIS), which is the origin site for the rectus femoris muscle. The fragment reveals smooth well-corticated lateral margins and ill-defined medial margins, where the fragment was torn away from the underlying parent bone.
Pelvic avulsion injuries occur in young athletes, with immature skeletons, when excessive muscular forces exceed the tensile strength of the apophyseal attachment to the central skeleton at the muscle origin. During running, jumping, lunging and kicking, major forces are distributed through hip flexors and hamstrings resulting in the most frequent avulsion injuries occurring at the origin of these tendons. Avulsion injury of the ischial apophysis by the hamstrings is common in runners, dancers and gymnasts, with pain typically referred to the buttock region. Avulsion injuries of the anterosuperior (sartorius origin) and anteroinferior (rectus femoris origin) iliac spines are most commonly seen in the sprinting phase of running, hurdling and in kicking sports such as soccer and rugby.
Accurate imaging and diagnosis of athletes with sports injuries is essential. Consequences of missing a diagnosis could be devastating and possibly end an athlete’s career. A conventional AP radiograph of the pelvis is the imaging modality of choice for patients suspected of having a pelvic avulsion injury, as the diagnosis can often be ascertained without further imaging. However, apophyseal avulsions may be radiographically occult (unable to be seen) if the apophysis is not yet ossified or only minimally so. Occasionally, the underlying bony pelvis may obscure a displaced ossified apophysis in an older athlete. In these cases, the radiographic findings can be negligible or absent despite the fact that an avulsion has indeed occurred. Both MRI and ultrasound can be very helpful in making the diagnosis in these cases. Sonography is advantageous because of its faster examination time and decreased cost, and is sensitive although not specific. MRI will reveal underlying bone marrow edema, inflammatory reaction and hemorrhage in the proximal musculotendinous structure, although the actual bone fragment may be missed if it’s too small (or in too young an athlete) to contain fatty marrow within.
Recovery from an anterior pelvic avulsion injury (sartorius and rectus femoris) typically takes 5-6 weeks compared with hamstring avulsion injury, which may take twice as long. Avulsions, if diagnosed early, usually heal with conservative treatment and modification of activities (albeit rather difficult in most active young athletes). Surgical repair is considered if the avulsed apophysis or bony fragment is displaced more than 2 cm from the underlying parent bone. Hamstring avulsions are also more prone to complications, because of potential involvement of the adjacent sciatic nerve by direct compression from the avulsed fragment or by abundant callous formation during the healing process. An accurate assessment of the neurologic status of the involved extremity is vital both immediately following the injury and during the healing process, to avoid unnecessary complications.
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