Case Author(s): Dennis Hsueh, M.D. and Keith Fischer, M.D. , 03/06/04 . Rating: #D2, #Q4

Diagnosis: Pelvic avulsion fracture

Brief history:

15-year-old teenager who approximately three months ago felt a sharp left hip pain while playing "hacky-sack" or foot-bag. He continues to have left-sided hip pain.

Images:

Static 2 hour post injection anterior and posterior images

View main image(bs) in a separate image viewer

View second image(xr). AP view of the pelvis

View third image(xr). Frog-leg view of the pelvis

Full history/Diagnosis is available below

Diagnosis: Pelvic avulsion fracture

Full history:

15-year-old otherwise healthy teenager, who approximately three months ago, felt sharp left hip pain while playing hacky-sack or foot-bag. He continues to have left-sided hip pain.

Radiopharmaceutical:

Tc-99m MDP i.v.

Findings:

Bone scintigraphy: Limited delayed scintigrams of the pelvis and hips demonstrate abnormally increased uptake in the left anterior superior and inferior iliac spines. Both hips are normal.

AP and Frog-leg pelvis: A calcific density, that projects lateral to the left iliac crest, likely represents an avulsion of the left anterior superior and inferior iliac spines. Incidentally noted is a round calcific density projecting superior to the left iliac crest that may present a button on the patient or an enterolith. The hips are normal.

Discussion:

Plain radiographs and bone scintigraphy findings are consistent with healing avulsion fractures of the anterior superior and inferior iliac spines.

Avulsion fractures are common in the skeletally immature. Avulsion fractures result when abnormal stress is applied resulting in disruption at the weakest link - the apophyseal plate.

Anterior superior iliac spine avulsion fractures result from abnormal stress to the origin of the sartorius muscle. This occurs when the hip is extended and the knee flexed such as in jumping sports including basketball or volleyball. Anterior inferior iliac spine avulsion fracture results from abnormal stress to the origin of the rectus femoris muscle. This occurs with contraction of the rectus femoris muscle from vigorous kicking, such as in soccer.

Playing hacky sack requires a combination of jumping and kicking of a soft bean bag. Thus, it is not an unusual cause for these types of avulsion fractures.

Additional common sites of stress fracture in the pelvis include the lesser trochanter (insertion of the iliopsoas muscle) and the ischial tuberosity (origin of the hamstrings).

Normally about 80% of bone scintigraphy examinatinos demonstrate increased uptake at the site of fracture by 24 hours; about 95%, by 72 hours. In elderly or debiliated patients, increased uptake may not be demonstrated for several days. Gradual decline in activity occurs with time. About 65% of exams normalize by 1 year; 90%, by 2 years. The minimum time for normalization of activity is 6 months. Persistent activity can occur if healing has not resulted in anatomic alignment resulting in abnormal biomechanical stress and remodeling.

For companion case, see case bs076

REFERENCES: Browning KH. “Hip and Pelvis Injuries in Runners." The Physician and Sportsmedicine. Vol 29. 2001. Downloaded 1/31/04 from http://www.physsportsmed.com/issues/2001/01_01/browning.htm

Williams, SC (2001) Nuclear Medicine Online Reference Text. Bone Imaging: Trauma. Retrieved March 8, 2004, from Aunt Minnie Web Site: http://www.auntminnie.com/

Followup:

The patient did well with conservative management including 4-6 weeks of rest and ambulating with crutches.

Major teaching point(s):

See discussion

Differential Diagnosis List

The differential diagnosis of foci of increased Tc99m-MDP uptake would include trauma, infection, and tumor. In this patient, clinical history and plain radiographic findings support that the findings are post traumatic from an avulsion fracture.

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Skeletal System, Category:Effect of Trauma)

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Case number: bs137

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