Posttraumatic Heterotopic Ossification Workup

Updated: Apr 23, 2019
  • Author: Auri Bruno-Petrina, MD, PhD; Chief Editor: Stephen Kishner, MD, MHA  more...
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Workup

Laboratory Studies

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  • Progressive loss of joint mobility and markers of increased osteoblastic activity, such as an elevated fractionated alkaline phosphatase level, warrant a comprehensive musculoskeletal examination with a 3-phase bone scan and radiographs to confirm the presence, distribution, and extent of heterotopic ossification (HO). [5, 6, 7]

  • The diagnosis of HO following brain injury typically is made by the clinical examination and by assessing for elevations in alkaline phosphatase. Early increases in alkaline phosphatase may be difficult to interpret, because the level rises with other causes, such as fractures or hepatotoxicity. The level of alkaline phosphatase has been reported to parallel the activity of ossification. It was found that when ossification stopped, the level returned to normal. Alkaline phosphatase fractionation studies reportedly can distinguish among different reasons for electrical levels.

  • Osteocalcin, another marker of osteoblastic activity, does not appear to be useful in the early detection of HO or in the assessment of its maturity. The erythrocyte sedimentation rate is too nonspecific to be of much help in the diagnosis of HO, but an elevated level associated with other clinical features suggests the need for further evaluation.

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Imaging Studies

Heterotopic ossification (HO) typically cannot be seen on plain radiographs until several weeks after clinical manifestations (including pain, swelling, erythema, restricted ROM) become evident.

Radiographs may not show abnormalities during the acute phase of erythema and swelling. Later radiographs (1-2 weeks after onset) often show only soft-tissue swelling. Radiographs show immature ossification and then the appearance of mature bone. HO may take 8-14 months to reach maturity. Plain radiographs may not show evidence of HO until 4-5 weeks after injury. On anteroposterior radiography, HO is usually located inferior and medial to the humeral head.

Because of the limitations of plain radiography, radionuclide bone scanning is the preferred diagnostic test for earlier detection. [8]

Excision may be undertaken to improve passive shoulder functions. Computed tomography (CT) scans of the shoulder (cross sections) and 3-dimensional reconstruction assist with preoperative planning. Radiographic assessment of joints with HO may be severely limited by difficulties in positioning the patient for the necessary view.

A retrospective study by Bachman et al indicated that CT scanning can be used prior to the excision of HO from the elbow to distinguish the paths of the radial and median nerves and to precisely determine the distance of these nerves from the ossification. In a study of 22 patients who had undergone removal of HO from the elbow, CT scan distinguished the radial nerve from the HO in 21 patients and the median nerve from the HO in 17 cases. The distance of HO from these nerves (3 mm and 9 mm from the radial and median nerves, respectively) was also determined. [9]

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Other Tests

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  • Many clinicians rely on triple-phase bone scanning technology for early detection of heterotopic ossification (HO). Triple-phase technetium-99m (99m Tc) bone scanning detects early increases in vascularity and is a reliable indicator in making a diagnosis. [5] The first and second phases of the triple-phase bone scan show increased uptake. Areas demonstrating increased blood flow and soft-tissue concentration of the tracer on early imaging (blood flow phase) correlate with sites of subsequent HO development. The optimal timing of the imaging for accurate assessment of the presence of ectopic bone has not been established, but 3 weeks or more following the injury should be sufficient for early detection.

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Procedures

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  • Various authors who have reviewed the association between the human leukocyte antigen (HLA) system and heterotopic ossification (HO) have suggested that a genetic predisposition to an associated systemic factor exists; thus, an antigenic marker should be available to mark susceptible patients. Others have found no evidence of any association between the HLA system and HO. An association between HLA-B 18 and patients with neurologic disorders, as well as with patients who develop HO, has been described. However, 75% of patients with HO lack this marker.

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Histologic Findings

Histologic examination demonstrates that tissue developed through heterotopic ossification (HO) is composed of true osseous tissue rather than of calcified soft tissue. Heterotopic bone is metabolically active and exhibits approximately triple the normal rate of bone formation and double the normal number of osteoclasts.

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