Determining the Mineral Apposition Rate of Heterotopic Ossification in Military Healthcare System Patients after Total Joint Replacement: A Case Series

Heterotopic ossification (HO) is frequently reported following total joint replacement (TJR) surgery. Symptomatic HO may limit the range of motion, cause pain, and require surgical excision. Deciding an appropriate time for ectopic bone excision is based on clinical judgment, and a more welldefined link between clinical predictors and histological analysis is needed to minimize recurrence. A case series was performed with military healthcare system patients undergoing TJR, who required removal of periarticular ectopic bone. Patients were prescribed oxytetracycline to assess the mineral apposition rate (MAR; ie, bone growth rate) of HO, and excised specimens were analyzed using scanning electron microscopy and light microscopy. Two males and one female were enrolled in this study, with height of 69.0 ± 7.8 inches, weight of 237.7 ± 28.3 pounds, and age of 61 ± 7 years at the time of HO removal. Ectopic bone occurred in two cases following total knee arthroplasty and one total hip arthroplasty. Data indicated that MAR levels were 1.7 times higher than that reported previously for nonpathological human bone (1.7 ± 0.7 μm/day; range: 1.3-2.6 μm/day), and microscopic imaging confirmed that the osseous tissues were still actively remodeling at the time of surgical intervention. Further characterization is needed to optimize HO excision timing and to better understand this pathological bone disorder.