Scott C. Wagner

Heterotopic Ossification in High-energy Wartime Extremity Injuries: Prevalence and Risk Factors

BACKGROUNDnHeterotopic ossification in the extremities remains a common complication in the setting of high-energy wartime trauma, particularly in blast-injured amputees and in those in whom the definitive amputation was performed within the zone of injury. The purposes of this cohort study were to report the experience of one major military medical center with high-energy wartime extremity wounds, to define the prevalence of heterotopic ossification in these patients, and to explore the relationship between heterotopic ossification and other potential independent predictors.nnnMETHODSnWe retrospectively reviewed the records and radiographs of all combat-wounded patients admitted to this institution between March 1, 2003, and December 31, 2006. Patients with a minimum of two months of radiographic follow-up who underwent at least one orthopaedic procedure on an extremity constituted our study group; those who underwent at least one orthopaedic procedure but had not had heterotopic ossification develop constituted the control group. Variables recorded for each study subject included age and sex, location and mechanism of injury, method(s) of fracture fixation, number of débridement procedures, duration of negative pressure therapy, location of heterotopic ossification, presence and severity of traumatic brain injury, and Injury Severity Scores.nnnRESULTSnDuring the study period, 1213 war-wounded patients were admitted. Of those patients, 243 (157 in the heterotopic ossification group and eighty-six controls) met the inclusion criteria. The observed rate of heterotopic ossification was 64.6%. A significant relationship was detected between heterotopic ossification and the presence (p = 0.006) and severity (p = 0.003) of a traumatic brain injury. Risk factors for the development of heterotopic ossification were found to be an age of less than thirty years (p = 0.007, odds ratio = 3.0), an amputation (p = 0.048, odds ratio = 2.9), multiple extremity injuries (p = 0.002, odds ratio = 3.9), and an Injury Severity Score of >or=16 (p = 0.02, odds ratio = 2.2).nnnCONCLUSIONSnThe prevalence of heterotopic ossification in war-wounded patients is higher than that in civilian trauma. Although trends associated with local wound conditions were identified, the risk factors for the development of heterotopic ossification found in this study suggest that systemic causes predominate.

Measurement of Distal Ulnar Hounsfield Units Accurately Predicts Bone Mineral Density of the Forearm

Background: Hounsfield unit (HU) measurement obtained from computed tomography (CT) scans of the wrist is a potential new screening method for low bone mineral density (BMD). We hypothesized that HU measurements of the ulnar head obtained from CT scans would correlate with BMD assessed with dual x-ray absorptiometry (DXA) scans of the forearm. Methods: Patients with both upper-extremity CT and DXA scans performed at a single institution were included in the study. Hounsfield units were manually measured in the distal part of the ulna by 1 author blinded to the DXA results. Average values were then compared with forearm BMD values as determined with a DXA scan. Results: Seventy-seven CT scans of 74 patients were included. Average HU values were significantly lower in the osteoporotic and osteopenic groups in comparison with the normal BMD group. The upper limit of the 95% confidence interval for osteopenic patients was 145.9 HU. The average forearm T-score for patients with an HU value at or below the cutoff of 146 was significantly lower than the average T-score for those with an HU value of >146 HU (p < 0.0001). Sensitivity and negative predictive value for low BMD using this cutoff value were calculated to be 91% and 89%, respectively. Conclusions: Distal ulnar HU measurements accurately reflect the BMD of the forearm as diagnosed with a DXA scan. Our results suggest that distal ulnar HU measurements of ⩽146 HU are strongly associated with low BMD and that values above this cutoff accurately rule out low forearm BMD with a high degree of sensitivity and negative predictive value. Utilizing this technique may improve the capture of at-risk patients and streamline the screening process for osteoporosis. Level of Evidence: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Intrawound Antibiotic Powder Decreases Frequency of Deep Infection and Severity of Heterotopic Ossification in Combat Lower Extremity Amputations

Background Amputations sustained owing to combat-related blast injuries are at high risk for deep infection and development of heterotopic ossification, which can necessitate reoperation and place immense strain on the patient. Surgeons at our institution began use of intrawound antibiotic powder at the time of closure in an effort to decrease the rate of these surgical complications after initial and revision amputations, supported by compelling clinical evidence and animal models of blast injuries. Antibiotic powder may be useful in reducing the risk of these infections, but human studies on this topic thus far have been inconclusive. Purpose We sought to determine whether administration of intrawound antibiotic powder at the time of closure would (1) decrease the risk of subsequent deep infections of major lower-extremity combat-related amputations, and (2) limit formation and decrease severity of heterotopic ossification common in the combat-related traumatic residual limb. Methods Between 2009 and 2015, 252 major lower extremity initial and revision amputations were performed by a single surgeon. Revision cases were excluded if performed specifically to address deep infection, leaving 223 amputations (88.5%) for this retrospective analysis. We reviewed medical records to collect patient information, returns to the operating room for subsequent infection, and microbiologic culture results. We also reviewed radiographs taken at least 3 months after surgery to determine the presence and severity of heterotopic ossification using the Walter Reed classification system. We grouped cases according to whether limbs underwent initial or revision amputations, and whether the limbs had a history of a prior infection. Apart from the use of antibiotic powder and duration of followup, the groups did not differ in terms of age, mechanism of injury, or sex. We then calculated the absolute risk reduction for infection and heterotopic ossification and the number needed to treat to prevent an infection. Results Overall, administration of antibiotic powder resulted in a 13% absolute risk reduction of deep infection (14 of 82 [17%] versus 42 of 141 [30%]; p = 0.03; 95% CI, 0.20%-24.72%). In revision amputation surgery, the absolute risk reduction of infection with antibiotic powder use was 16% overall (eight of 58 versus 17 of 57; 95% CI, 1.21%-30.86%), and 25% for previously infected limbs (eight of 46 versus 14 of 33; 95% CI, 4.93%-45.14%). The number needed to treat to prevent one additional deep infection in amputation surgery is eight in initial amputations, seven in revision amputations, and four for revision amputation surgery on previously infected limbs. With the numbers available, we observed no reduction in the risk of heterotopic ossification with antibiotic powder use, but severity was decreased in the treatment group in terms of the number of residual limbs with moderate or severe heterotopic ossification (three of 12 versus 19 of 34; p = 0.03). Conclusions Our findings show that administration of intrawound antibiotic powder reduces deep infection in residual limbs of combat amputees, particularly in the setting of revision amputation surgery in apparently aseptic residual limbs at the time of the surgery. Furthermore, administration of antibiotic powder for amputations at time of initial closure decreases the severity of heterotopic ossification formation, providing a low-cost adjunct to decrease the risk of two complications common to amputation surgery. Level of Evidence Level III, therapeutic study