Presentation
7.5 months following motor vehicle accident. Severe decreased right hip range of motion associated with pain.
Patient Data
Frontal view of the pelvis and right hip demonstrates prior open-reduction and internal fixation (ORIF) of the left iliac bone and bilateral sacroiliac joints. Chronic fractures of the left superior and inferior pubic rami are present.
Lateral to the right hip joint, there is abnormal bone in the soft tissues paralleling the long axis of the femoral neck. This was not present at time of initial trauma and represents post-traumatic heterotopic ossification.
Given chronic pain and limited range of motion, the patient underwent a triple-phase bone scan as part of an orthopedic surgical evaluation.
The flow phase was normal, with no asymmetry or increased flow to the region of the right hip.
The blood pool phase was mildly positive, showing radiotracer accumulation lateral to the right hip, corresponding with the heterotopic ossification.
On delayed phase images, there is moderately intense radiotracer uptake in the same location, mimicking the shape of the heterotopic ossification seen on radiographs. There is also uptake in the region of the left iliac bone and sacroiliac joint, seen best on the posterior view of the pelvis, corresponding with prior fractures and open-reduction and internal fixation (ORIF).
Given the 2-phase positive nature of the findings, a follow-up exam in 3 months was recommended to reassess.
Case Discussion
Heterotopic ossification (HO) occurs after a variety of insults such as direct trauma, arthroplasty, spinal cord injury, or traumatic brain injury. It is the formation of metaplastic bone in the extra skeletal soft tissues, most commonly muscle. The hip, as in this patient, is most frequently afflicted and pain and/or decreased range of motion are the most typical complaints. Definitive treatment is surgical resection but should be delayed until the heterotopic ossification has reached maturity to reduce surgical risks and post operative recurrence. A three-phase bone scan can be used to assess the maturity. If the HO shows no increased uptake compared to normal osseous structures, then it is mature, and surgery can be performed. If increased radiotracer uptake is present, particularly on the blood flow and/or pool phases, the HO is likely still immature. Then subsequent serial scans may be obtained every 2-3 months to assess for a decrease in uptake followed by steady state for another 2-3 month, indicating maturation.
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