Relationship Between Volumetric Measurements of Heterotopic Ossification in Wounded Service Members and Clinically Available Screening Tools

In Brief Heterotopic ossification (HO) often causes symptoms requiring surgical resection and may delay rehabilitation regimens for wounded service members. Clinical screening tools for assessing HO have included serum alkaline phosphatase (AP), nuclear scintigraphic activity, and patient pain scores. However, no studies to date have investigated the relationship of these clinical predictors with HO incidence and volume. Ten servicemen with transfemoral amputations were included in this retrospective study. Volumetric measurements of HO were calculated using thresholding software, and computed tomography scans were performed 12.6 ± 6.8 months after injury. Subject AP levels, white blood cell (WBC) counts, and pain scores were assessed to determine if these factors were predictors of ectopic bone volumes. The mean volume of HO was 44.73 ± 39.35 cm3. Statistical analysis demonstrated that the volume of HO and serum AP levels were significantly correlated (p = 0.002). However, average pain scores were not a significant predictor of HO volume (p = 0.212). Infections developed in 9 of the 10 subjects, and WBC counts and HO volumes were significantly correlated (p = 0.028). The magnitude of serum AP levels and WBC counts may be effective factors for predicting the expected volume of ectopic bone in combat-injured service members with transfemoral amputations. Although ectopic bone formation has been previously categorized using bone scans and serum AP levels, no quantitative measurement method has existed for assessing heterotopic ossification (HO) volume. Data from this study indicated that serum AP levels and white blood cells (WBC) were significant predictors of HO volumes. However, patient pain scores were not a valid predictor. In the future, the magnitude of serum AP levels and WBC counts may better predict the expected volume of trauma-related HO, but require large-scale studies with adequate power in order to confirm the findings of this small patient series.