title: Comparison of development of heterotopic ossification in injured US and UK Armed Services personnel with combat-related amputations: preliminary findings and hypotheses regarding causality.
abstract: BACKGROUND
  Recent reports have documented the rate of heterotopic ossification (HO) formation in the residual limbs of combat-related amputees from the US Armed Forces injured in Operations Iraqi and Enduring Freedom. Final amputation level within the zone of injury and blast as the mechanism of injury were identified as possible risk factors for the occurrence and grade of HO. There has been no previous description of HO in combat-related amputees from the UK service personnel. The purpose of this study was to examine potential differences in the prevalence of HO between UK and US Allied Forces, with particular attention to these risk factors, patient exposures, and any treatment differences between these two groups.
  
  
  METHODS
  We reviewed the medical records and radiographs of 35 combat-related amputations from the UK and contrasted them with 213 previously reported amputations in US military personnel. We evaluated prevalence and severity of residual limb HO, Injury Severity Score (ISS), the mechanism and zone of injury, type and level of amputation, number of debridements, method of wound irrigation, presence of severe head injury and/or burns injury, use of topical negative pressure therapy and pulse lavage, number of days until wound closure, type of closure, and subsequent infections. All patients had a minimum of 2-month posthospital discharge radiographic follow-up. Comparisons were made using Fisher's exact, one-way analysis of variance, and chi2 analyses.
  
  
  RESULTS
  There was no significant difference in either the overall prevalence of HO or the prevalence of moderate to severe HO in the two populations. Twenty of 35 (57.1%) limbs in the UK amputations developed HO compared with 134 of 213 (63%) in the US amputations (p > 0.05). The UK amputations had 12 cases (34.3%) of moderate to severe HO compared with 72 cases (33.8%) in the US amputations (p > 0.05). However, there was a significant difference in the number of UK amputations 0 of 20 (0%) versus the number of US amputations 25 of 134 (12%; p = 0.04), which required excision of symptomatic lesions. There was a significant association in the development of HO in UK personnel with the use of topical negative pressure treatment (p = 0.05) and increasing ISS scores (p = 0.04) and in the development of moderate to severe HO with increasing ISS (p = 0.006) and severe HI (p = 0.04). Unlike in the previous report, no significant association was found in UK personnel between any of the remaining hypothesized risk factors and either the presence or grade of HO.
  
  
  CONCLUSIONS
  Although no difference was identified in the overall prevalence of HO, there are inconsistencies in the possible underlying causes of HO between the two cohorts. Further research is required in an ongoing effort to determine a causal relationship between treatment and subsequent HO formation.
authors.affiliation: Regenerative Medicine, US Army Institute of Surgical Research, Fort Sam Houston, Texas 78234, USA. kate.brown2@amedd.army.mil
authors.forename: Kate V
authors.initials: KV
authors.lastname: Brown
authors.forename: Shresth
authors.initials: S
authors.lastname: Dharm-Datta
authors.forename: B Kyle
authors.initials: BK
authors.lastname: Potter
authors.forename: John
authors.initials: J
authors.lastname: Etherington
authors.forename: Alan
authors.initials: A
authors.lastname: Mistlin
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Hsu
authors.forename: Jon C
authors.initials: JC
authors.lastname: Clasper
mesh_terms: D000293:Adolescent; D000328:Adult; D000671:Amputation, Surgical / Q000009:adverse effects*; D000672:Amputation Stumps / Q000000981:diagnostic imaging*; D000673:Amputation, Traumatic / Q000150:complications* / Q000000981:diagnostic imaging; D000674:Amputees; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D008889:Military Personnel; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D015995:Prevalence; D011859:Radiography; D012189:Retrospective Studies; D013997:Time Factors; D006113:United Kingdom / Q000453:epidemiology; D014481:United States / Q000453:epidemiology; D014857:Warfare; D055815:Young Adult