Figure. Anteroposterior radiograph of the pelvis shows heterotopic ossification in the right hip.
A 76-year-old man presents with right hip “tightness” that has progressed over the past 4 months. He denies significant pain in the hip and his gait remains unchanged. He reports the right hip is a little tighter when getting out of the car and shifting in bed; he underwent total hip replacement a year ago. On physical examination of the right hip, the patient’s internal rotation measures 15°; abduction, 20°; and hip flexion, 95°. Anteroposterior radiograph of the pelvis shows heterotopic ossification in the right hip (Figure).
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Heterotopic ossification is the formation of bone in soft tissue and is most commonly seen after total hip arthroplasty. Heterotopic ossification starts to grow within 16 hours of surgery and progressively enlarges for up to 1 to 2 years postoperatively. Heterotopic ossification generally becomes visible on radiographs 3 to 4 weeks postoperatively.1-3
Hypertrophic osteoarthritis, Paget’s disease, ankylosing spondylitis, and diffuse idiopathic skeletal hyperostosis (DISH) are risk factors for heterotopic ossification formation.1 The amount of heterotopic ossification formation varies from small islands of bone in soft tissue progressing to bone spurs from the femur and pelvis to complete ankylosing of the hip.3
The amount of pain and loss of hip motion caused by heterotopic ossification can vary by the amount of ossification formed. In general, a significant loss of hip function is rare and many patients never notice that they have ossification.1 Patients at high risk of heterotopic ossification formation should be identified preoperatively and treated with nonsteroidal anti-inflammatory drugs (NSAIDs), most commonly indomethacin, and/or external beam radiation to prevent formation.1,2 Aspirin can also decrease the risk of heterotopic ossification formation and is commonly used for deep vein thrombosis prophylaxis postoperatively.
Once heterotopic ossification has formed and is visible on radiography, the only way to remove it is through surgical excision.2 The patient in this case is asymptomatic and his range of motion loss has not caused hip impairment so he should be treated with observation.1-3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.
1. Iorio R, Healy WL. Heterotopic ossification after hip and knee arthroplasty: risk factors, prevention, and treatment. J Am Acad Orthop Surg. 2002;10(6):409-416. doi:10.5435/00124635-200211000-00005
2. Cohn RM, Schwarzkopf R, Jaffe F. Heterotopic ossification after total hip arthroplasty. Am J Orthop. 2011;40(11):E232-235.
3. Kocic M, Lazovic M, Mitkovic M, Djokic B. Clinical significance of the heterotopic ossification after total hip arthroplasty. Orthopedics. 2010;33(1):16. doi:10.3928/01477447-20091124-13