Feasibility Study of Experimental Protocol for the Time-Dependent Mechanical Response of Synthetic Tibia.

In this research, an experimental biomechanics construct was developed to reveal the mechanics of distal tibial fracture by submitting synthetic tibiae to cyclic loading, resulting in a combined stress state due to axial compression and bending loads. The synthetic tibia was fixed at the knee but allowed to rotate in the coronal and sagittal planes at the ankle. The first three loading regimes lasted for 4000 cycles/each, and the final until ultimate failure. After 12k±80 cycles, the observed failure patterns closely resembled distal tibial fractures. The collected data during cyclic loading were fitted into a phenomenological model to deduce the time-dependent response of the synthetic tibiae. Images were also collected and analyzed using digital image correlation to deduce the full-field state of strain. The latter revealed that longitudinal strain contours extended in the proximal-distal direction. The transverse strain contours exemplified a medial-to-lateral distribution, attributed to the combined contributions of the Poisson's effect and the flexural deformation from axial and bending components of the applied load, respectively. The experimental construct, full-field characterization, and data analysis approaches can be extended to elucidate the effect of different fixation devices on the overall mechanical behavior of the bone and validate computational models in future research.

Biomechanical comparison of composite and cadaveric humeri models in experiments on operated humeral shaft fractures.

A study was undertaken to determine how well contacting fracture fragments of composite bone replicated the behavior of fracture fragments in real bone. Ten composite and ten real humeral diaphyses were transected and reconstructed with limited-contact dynamic-compression plates. Two screws were placed on each side of the transection site and a calibrated electronic sensor sheet was placed between the imitated fracture fragments. After insertion of the distal screws, pressure measurements were made during insertion of the first proximal screw in compression mode, during insertion of the second screw in compression mode after loosening the first screw, and finally after retightening the first screw. The process was repeated after bending the plate. The contact area, the net compression force and the average compressive stress were computed and statistically compared. The composite bone and cadaveric bone differed in contact area and compressive stress but not in net compressive force. Plate bending did not produce a significant difference between composite and cadaveric bone. The results indicate that composite bone does not reproduce all the local fracture fragment conditions so that hardware testing in composite bone should proceed carefully. A gap between fracture fragments as is often used in comminuted fracture tests may remain as the most appropriate situation for fracture hardware testing.

Are methods to quantify osseous exposure in orthopedic surgery reliable?

BACKGROUND: Our study examined if there were any limitations when using various measurement techniques in the literature to quantify osseous exposure. Additionally, we also examined if surface contour had any influence on obtained measurements, which no previous study has attempted. MATERIALS AND METHODS: Three methods used to quantify osseous exposure area were identified, one in which involves manually applying mesh over exposure area. The other two use digital image capture software (ImageJ, Bethesda, MD). We simulated flat, convex, and mixed surface types using synthetic bone analogs. We assessed the degree of variability between mean values using an ANOVA or Kruskal-Wallis equality of populations rank test. Cronbach's alpha test of internal reliability was used to assess the internal reliability of measurement technique. RESULTS: ANOVA test for difference in measurement techniques on all three surface types was statistically significant (p < 0.05). Cronbach's alpha test of internal reliability for each technique on the convex surface did not obtain adequate significance (alpha >0.70). Only the mesh method obtained adequate alpha value for significance when applied to the flat and mixed surface types. DISCUSSION: Each of the three measurement techniques tested demonstrated poor internal reliability. We suggest taking care when comparing studies that use different quantification techniques when calculating osseous exposure for different surgical approaches. Future studies should explore alternative methods of osseous exposure quantification.

Consensus and Equipose in the Management of Military Trainee Femoral Neck Stress Fractures: A Survey of Military Surgeons.

BACKGROUND: Femoral neck stress fractures (FNSFs) are a unique injury pattern not commonly treated in the civilian trauma population; however, it is particularly high with military trainees engaged in basic combat training. To date, no study has surveyed a population of military orthopedic surgeons on treatment preferences for military service members (SMs) with FNSF. QUESTIONS: We aim to evaluate the extent of clinical equipoise that exists in the management of these injuries, hypothesizing that there would be consensus in the factors dictating surgical and non-surgical intervention for FNSF. PATIENTS AND METHODS: A 27-question survey was created and sent to U.S. military orthopedic surgeon members of the Society of Military Orthopaedic Surgeons. The survey was designed in order to gather the experience among surgeons in treating FNSF and identifying variables that play a role in the treatment algorithm for these patients. In addition, seven detailed, clinical vignettes were presented to further inquire on surgeon treatment preferences. Binomial distribution analysis was used to evaluate for common trends within the surgeon's treatment preferences. RESULTS: Seventy orthopedic surgeons completed the survey, the majority of whom were on active duty status in the U.S. Military (82.86%) and having under 5 years of experience (61.43%). Majority of surgeons elected for a multiple screw construct (92.86%), however the orientation of the multiple screws was dependent on whether the fracture was open or closed. Management for compression-sided FNSF involving ≥50% of the femoral neck width, tension-sided FNSF, and stress fractures demonstrating fracture line progression had consensus for operative management. Respondents agreed upon prophylactic fixation of the contralateral hip if the following factors were involved: Complete fracture (98.57%), compression-sided fracture line >75% (88.57%), compression-sided fracture line >50-75% with hip effusion (88.57%), contralateral tension-sided fracture (87.14%), and compression-sided fracture line >50-75% (84.29%). An FNSF < 50% on the contralateral femoral neck or a hip effusion was indeterminate in surgeons indicating need for prophylactic fixation. Majority of surgeons (77.1%) utilized restricted toe-touch weight-bearing for postoperative mobility restrictions. CONCLUSIONS: Consensus exists for surgical and non-surgical management of FNSF by U.S. military orthopedic surgeons, despite the preponderance of surgeons reporting a low annual volume of FNSF cases treated. However, there are certain aspects in the operative and non-operative management of FNSF that are unanimously adhered to. Specifically, our results demonstrate that there is no clear indication on the management of FNSF when an associated hip effusion is involved. Additionally, the indications for surgically treating contralateral FNSF are unclear. LEVEL OF EVIDENCE: IV.

A biomechanical comparison of superior ramus plating versus intramedullary screw fixation for unstable lateral compression pelvic ring injuries,,.

INTRODUCTION: Management of the anterior component of unstable lateral compression (LC) pelvic ring injuries remains controversial. Common internal fixation options include plating and superior pubic ramus screws. These constructs have been evaluated in anterior-posterior compression (APC) fracture patterns, but no study has compared the two for unstable LC patterns, which is the purpose of this study. METHODS: A rotationally unstable LC pelvic ring injury was modeled in 10 fresh frozen cadaver specimens by creating a complete sacral fracture, disruption of posterior ligaments, and ipsilateral superior and inferior rami osteotomies. All specimens were repaired posteriorly with two fully threaded 7 mm cannulated transiliac-transsacral screws through the S1 and S2 corridors. The superior ramus was repaired with either a 3.5 mm pelvic reconstruction plate (n = 5) or a bicortical 5.5 mm cannulated retrograde superior ramus screw (n = 5). Specimens were loaded axially in single leg support for 1000 cycles at 400 N followed by an additional 3 cycles at 800 N. Displacement and angulation of the superior and inferior rami osteotomies were measured with a three-dimensional (3D) motion tracker. The two fixation methods were then compared with Mann-Whitney U-Tests. RESULTS: Retrograde superior ramus screw fixation had lower average displacement and angulation than plate fixation in all categories, with the motion at the inferior ramus at 800 N of loading showing a statistically significant difference in angulation. CONCLUSION: Although management of the anterior ring in unstable LC injuries remains controversial, indications for fixation are becoming more defined over time. In this study, the 5.5 mm cannulated retrograde superior ramus screw significantly outperformed the 3.5 mm reconstruction plate in angulation of the inferior ramus fracture at 800 N. No other significance was found, however the ramus screw demonstrated lower average displacements and angulations in all categories for both the inferior and superior ramus fractures.

Controlling axonal regeneration with acellular nerve allograft limits neuroma formation in peripheral nerve transection: An experimental study in a swine model.

BACKGROUND: Symptomatic neuromata are a common indication for revision surgery following amputation. Previously described treatments, including traction neurectomy, nerve transposition, targeted muscle re-innervation, and nerve capping, have provided inconsistent results or are technically challenging. Prior research using acellular nerve allografts (ANA) has shown controlled termination of axonal regrowth in long grafts. The purpose of this study was to determine the ability of a long ANA to prevent neuroma formation following transection of a peripheral nerve in a swine model. MATERIALS AND METHODS: Twenty-two adult female Yucatan miniature swine (Sus scrofa; 4-6 months, 15-25 kg) were assigned to control (ulnar nerve transection only, n = 10), treatment (ulnar transection and coaptation of 50 mm ANA, n = 10), or donor (n = 2) groups. Nerves harvested from donor group animals were treated to create the ANA. After 20 weeks, the transected nerves including any neuroma or graft were harvested. Both qualitative (nerve architecture, axonal sprouting) and quantitative histologic analyses (myelinated axon number, cross sectional area of nerve tissue) were performed. RESULTS: Qualitative histologic analysis of control specimens revealed robust axon growth into dense scar tissue. In contrast, the treatment group revealed dwindling axons in the terminal tissue, consistent with attenuated neuroma formation. Quantitative analysis revealed a significantly decreased number of myelinated axons in the treatment group (1232 ± 540) compared to the control group (44,380 ± 7204) (p < .0001). Cross sectional area of nerve tissue was significantly smaller in treatment group (2.83 ± 1.53 mm2 ) compared to the control group (9.14 ± 1.19 mm2 ) (p = .0012). CONCLUSIONS: Aberrant axonal growth is controlled to termination with coaptation of a 50 mm ANA in a swine model of nerve injury. These early results suggest further investigation of this technique to prevent and/or treat neuroma formation.

Does operative treatment of geriatric pelvic ring injuries lead to a high risk of one-year mortality?

INTRODUCTION: Non-operative management of pelvic ring injuries in the elderly is associated with a high risk of one-year mortality. The majority of these injuries are the result of a low-energy mechanism, however, due to the multiple medical comorbidities in this patient population the injuries are associated with a high degree of morbidity. The purpose of this study was to determine the one-year mortality risk after operative treatment of pelvic ring injuries in a geriatric patient population and the effect of patient and injury characteristics on the risk of mortality. PATIENTS AND METHODS: We performed a retrospective review of patients over the age of 70 who underwent operative fixation of a pelvic ring injury at two Level 1 trauma centers between January 2016 and June 2019. Medical records were reviewed for patient and injury characteristics including: Charlson Comorbidity Index (CCI), American Society of Anesthesiologists (ASA) physical status score or Injury Severity Score (ISS), hospital and intensive care unit (ICU) length of stay (LOS). The primary outcome of interest was the one-year mortality risk following operative treatment. Secondary outcomes included the effect of patient and injury characteristics on the one-year mortality risk and the hospital LOS. RESULTS: Ninety patients were included with an average age of 79.8  ±  6.5 years. The overall mortality was 8.9% (n = 8) and was significantly associated with the CCI. There was no significant effect related to the ASA physical status score or ISS. The average hospital LOS was 9.2 ± 7.3 days and was associated with the CCI, ASA physical status score, and ISS. DISCUSSION: Non-operative management of pelvic ring injuries in geriatric patients is associated with a high risk of one-year mortality. Our findings suggest operative treatment of these fractures is associated with an acceptable risk of one-year mortality that falls below the commonly reported range for non-operatively managed injuries. Furthermore, the risk of mortality was significantly associated with the patient's pre-injury state as determined by the CCI.

Does Provisional Minifragment Fixation Prevent Compression With Dynamic Compression Plating? A Biomechanical Analysis.

OBJECTIVES: To compare the compressive force generated by a 3.5-mm compression plate with and without provisional fixation using a 2.0-mm minifragment plate. METHODS: Fourth generation composite large humeral sawbones underwent transection and were divided into 2 groups. The first group underwent fixation with a 3.5-mm compression plate; the second group underwent provisional fixation with a 2.0-mm plate followed by definitive fixation using a 3.5-mm plate. Using a load cell, the compressive force generated was measured after insertion of each of 2 eccentrical placed screws and the total compression recorded. RESULTS: There was no difference in the force generated after each successive compression screw (P = 0.59 and 0.58, respectively). Likewise, there was no significant difference in the total compression generated when the preload was accounted for (P = 0.93). CONCLUSION: Provisional minifragment fixation does not have any adverse effect on the forces generated during compression plating. These findings suggest that provisional minifragment plates do not need to be removed before definitive fixation.

Can preoperative radiographs predict hardware complication or fracture displacement after operative treatment of pelvic ring injuries?

INTRODUCTION: Operative fixation of pelvic ring injuries is associated with a high risk of hardware failure and loss of reduction. The purpose of this study was to determine whether preoperative radiographs can predict failure after operative treatment of pelvic ring injuries and if the method of fixation effects their risk. PATIENTS AND METHODS: We conducted a retrospective cohort study of 143 patients with pelvic ring injuries treated with operative fixation at a level 1 trauma center. Preoperative radiographs were examined for the presence of the following characteristics: bilateral rami fractures, segmental or comminuted rami fractures, contralateral anterior and posterior injuries, complete sacral fracture, and displaced inferior ramus fractures. The method of fixation was classified based on the presence of anterior, posterior, or combined anterior and posterior fixation as well as whether or not posterior fixation was performed at a single or multiple sacral levels. Post-operative radiographs were examined for hardware failure or loss of reduction. RESULTS: Twenty-one patients (14.7%) demonstrated either hardware complication or fracture displacement within 6 months of surgery. Male sex was associated with a decreased risk of hardware complication (OR 0.11 [0.014, 0.86]; p=0.03). Posterior pelvic ring fixation at multiple sacral levels was associated with a decreased risk of fracture displacement (OR 0.21 [0.056, 0.83]; p=0.02). We were unable to demonstrate a significant association between preoperative radiographic characteristics and risk of hardware failure or fracture displacement. CONCLUSION: Our study demonstrates that both gender and the method of posterior fixation are associated with hardware failure or displacement.

Repeated Noise Exposure Does Not Reach Hazardous Levels During Total Joint Arthroplasty.

INTRODUCTION: Noise exposure is an occupational health concern for certain professions, especially military servicemembers and those using power tools on a regular basis. The purpose of this study was to quantify noise exposure during total hip arthroplasty (THA) and total knee arthroplasty (TKA) cases compared to the recommended standard for occupational noise exposure. MATERIALS AND METHODS: A sound level meter was used to record cumulative and peak noise exposure levels in 10 primary THA and 10 primary TKA surgeries, as well as 10 arthroscopy cases as controls. Measurements at the distance of the surgeon were taken in all cases. In TKA cases, measurements were taken at 3 feet and 8 feet from the surgeon, to simulate the position of the anesthetist and circulating nurse, respectively. RESULTS: Time-weighted average was significantly higher in THA (64.7 ± 5.2 dB) and TKA (64.5 ± 6.8 dB) as compared to arthroscopic cases (51.1 ± 7.5 dB, P < 0.001) and higher at the distance of the surgeon (64.5 ± 6.8 dB) compared to the anesthetist (52.9 ± 3.8 dB) and the circulating nurse (54.8 ± 11.2 dB, P = 0.006). However, time-weighted average was below the recommended exposure level of 85 dB for all arthroplasty cases. Peak levels did not differ significantly between surgery type or staff role, and no values above the ceiling limit of 140 dB were recorded. Surgeon's daily noise dose percentage per case was 1.78% for THA and 2.04% for TKA. CONCLUSION: Noise exposure in THA and TKA was higher than arthroscopic cases but did not exceed occupational standards. A daily dose percentage of approximately 2% per case indicates that repeated noise exposure likely does not reach hazardous levels in modern arthroplasty practice.

Does Intramedullary Nail Fixation of the Tibia Pose the Same Risk of Pulmonary Complications as Intramedullary Nail Fixation of the Femur? A Propensity Score-Matched Analysis.

OBJECTIVES: To compare duration of mechanical ventilation and pulmonary outcomes in patients treated with intramedullary nail (IMN) fixation of the tibia versus the femur. DESIGN: Retrospective cohort study. SETTING: Level I trauma center. PATIENTS: One thousand thirty patients were categorized based on treatment: those treated with IMN of the tibia (n = 515) and those treated with IMN of the femur (n = 515). INTERVENTION: IMN fixation of tibial and femoral fractures. OUTCOME MEASUREMENTS: The primary outcome was duration of mechanical ventilation. Secondary outcomes included length of intensive care unit (ICU) stay and risk of tracheostomy, pulmonary embolism (PE), acute respiratory distress syndrome (ARDS), and mortality. RESULTS: In an unadjusted analysis, femoral fractures were associated with increase in ventilator days (mean difference, 1.4; P < 0.001), ICU days (mean difference, 1.8; P < 0.001), and odds of tracheostomy (odds ratio, 1.7; P < 0.01). No difference was shown in likelihood of PE, ARDS, or mortality (P > 0.2). Propensity score-matched estimates showed no differences in any measured outcomes (P > 0.40). In patients with Injury Severity Scores >17, we found no difference in length of ventilator or ICU days or likelihood of tracheostomy, PE, ARDS, or mortality in the unadjusted (P > 0.2) or propensity score-matched estimates (P > 0.3). CONCLUSIONS: These findings suggest that IMN fixation of the tibia is associated with duration of mechanical ventilation and risk of poor pulmonary outcomes similar to those of femoral nailing, after adjustment for baseline characteristics. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Incidence and Characteristics of Humeral Shaft Fractures After Subpectoral Biceps Tenodesis.

BACKGROUND: Biceps tenodesis is a procedure that can address biceps and labral pathology. While there is an increased risk of humeral fracture after biceps tenodesis, it has been described only in case reports. PURPOSE: To identify the incidence, demographics, and characteristics of humeral shaft fractures after biceps tenodesis. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: The US Military Health System Data Repository was searched for patients with a Current Procedural Terminology code for biceps tenodesis between January 2013 and December 2016. The cohort of identified patients was then searched for those assigned a code for humeral fracture per the International Classification of Diseases, 9th Revision and 10th Revision. The electronic health records and radiographs of patients who were diagnosed with a humeral fracture were then evaluated to confirm that the fracture was related to the biceps tenodesis. Records were then reviewed for patient demographics, radiographs, operative reports, and clinical notes. RESULTS: A total of 15,085 biceps tenodeses were performed between January 2013 and December 2016. There were 11 postoperative and 1 intraoperative humeral fractures. The incidence of fracture was <0.1%. All fractures were extra-articular spiral fractures that propagated through the tenodesis site. Eight patients were treated with functional bracing, 3 with open reduction and internal fixation, and 1 with a soft tissue biceps tenodesis revision. Of 8 patients successfully treated nonoperatively, 6 regained full range of shoulder motion. Only 2 of the 4 patients who required operative treatment regained full range of shoulder motion. CONCLUSION: Humeral shaft fracture after biceps tenodesis is a rare complication that occurs in 7.9 out of 10,000 cases. Fractures occurred after various methods of fixation, including suture anchor, cortical button, and interference screw. Most patients were initially treated nonoperatively, and those who healed usually achieved full range of motion; however, those who required operative intervention often had restricted range of motion on final follow-up. Future studies should determine risk factors for fracture after biceps tenodesis.

Effect of NSAIDs on Bone Healing Rates: A Meta-analysis.

INTRODUCTION: NSAIDs inhibit osteogenesis and may result in delayed union or nonunion. The purpose of this meta-analysis was to determine whether their use leads to delayed union or nonunion. METHODS: We systematically reviewed the literature reporting the effect of NSAIDs on bone healing. We included studies of pediatric and adult patients NSAID exposure and healing bone. The outcomes of interest were delayed union, nonunion, or pseudarthrosis with at least six months of follow-up. A maximum likelihood random-effects model was used to conduct meta-analysis and meta-regression. RESULTS: NSAID exposure increased delayed union or nonunion (odds ratio [OR], 2.07; confidence interval [CI], 1.19 to 3.61). No effect was noted in pediatrics (OR, 0.58; CI, 0.27 to 1.21) or low dose/short duration of exposure (OR, 1.68; CI, 0.63 to 4.46). CONCLUSION: Analysis of the literature indicates a negative effect of NSAIDs on bone healing. In pediatric patients, NSAIDs did not have a significant effect. The effect may be dose or time dependent because low-dose/short-duration exposure did not affect union rates.

Palovarotene inhibits connective tissue progenitor cell proliferation in a rat model of combat-related heterotopic ossification.

Heterotopic ossification (HO) develops in the extremities of wounded service members and is common in the setting of high-energy penetrating injuries and blast-related amputations. No safe and effective prophylaxis modality has been identified for this patient population. Palovarotene has been shown to reduce bone formation in traumatic and genetic models of HO. The purpose of this study was to determine the effects of Palovarotene on inflammation, progenitor cell proliferation, and gene expression following a blast-related amputation in a rodent model (n = 72 animals), as well as the ability of Raman spectroscopy to detect early HO before radiographic changes are present. Treatment with Palovarotene was found to dampen the systemic inflammatory response including the cytokines IL-6 (p = 0.01), TNF-α (p = 0.001), and IFN-γ (p = 0.03) as well as the local inflammatory response via a 76% reduction in the cellular infiltration at post-operative day (POD)-7 (p = 0.03). Palovarotene decreased osteogenic connective tissue progenitor (CTP-O) colonies by as much as 98% both in vitro (p = 0.04) and in vivo (p = 0.01). Palovarotene treated animals exhibited significantly decreased expression of osteo- and chondrogenic genes by POD-7, including BMP4 (p = 0.02). Finally, Raman spectroscopy was able to detect differences between the two groups by POD-1 (p < 0.001). These results indicate that Palovarotene inhibits traumatic HO formation through multiple inter-related mechanisms including anti-inflammatory, anti-proliferative, and gene expression modulation. Further, that Raman spectroscopy is able to detect markers of early HO formation before it becomes radiographically evident, which could facilitate earlier diagnosis and treatment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1135-1144, 2018.

The traumatic bone: trauma-induced heterotopic ossification.

Heterotopic ossification (HO) is a common occurrence after multiple forms of extensive trauma. These include arthroplasties, traumatic brain and spinal cord injuries, extensive burns in the civilian setting, and combat-related extremity injuries in the battlefield. Irrespective of the form of trauma, heterotopic bone is typically endochondral in structure and is laid down via a cartilaginous matrix. Once formed, the heterotopic bone typically needs to be excised surgically, which may result in wound healing complications, in addition to a risk of recurrence. Refinements of existing diagnostic modalities, like micro- and nano-CT are being adapted toward early intervention. Trauma-induced HO is a consequence of aberrant wound healing, systemic and local immune system activation, infections, extensive vascularization, and innervation. This intricate molecular crosstalk culminates in activation of stem cells that initiate heterotopic endochondral ossification. Development of animal models recapitulating the unique traumatic injuries has greatly facilitated the mechanistic understanding of trauma-induced HO. These same models also serve as powerful tools to test the efficacy of small molecules which specifically target the molecular pathways underlying ectopic ossification. This review summarizes the recent advances in the molecular understanding, diagnostic and treatment modalities in the field of trauma-induced HO.

Early local delivery of vancomycin suppresses ectopic bone formation in a rat model of trauma-induced heterotopic ossification.

Heterotopic ossification (HO) is a debilitating sequela of high-energy injuries. It frequently requires surgical excision once symptomatic and there is no practical prophylaxis for combat-injured patients. In this study, we examined the effect of local vancomycin powder on HO formation in a small animal model of blast-related, post-traumatic HO. Male Sprague-Dawley rats were subjected to a polytraumatic extremity injury and amputation with or without methicillin-resistant Staphylococcus aureus infection. Animals were randomized to receive a single local application of vancomycin (20 mg/kg) at the time of injury (POD-0, n = 34) or on postoperative day-3 (POD-3, n = 11). Quantitative volumetric measurement of ectopic bone was calculated at 12-weeks post-injury by micro-CT. Bone marrow and muscle tissues were also collected to determine the bacterial burden. Blood for serum cytokine analysis was collected at baseline and post-injury. Vancomycin treatment on POD-0 suppressed HO formation by 86% and prevented bone marrow and soft tissue infections. We concurrently observed a marked reduction histologically in nonviable tissue, chronic inflammatory cell infiltrates, bone infection, fibrous tissue, and areas of bone necrosis within this same cohort. Delayed treatment was significantly less efficacious. Neither treatment had a marked effect on the production of pro-inflammatory cytokines. Our study demonstrates that local vancomycin treatment at the time of injury significantly reduces HO formation in both the presence and absence of infection, with decreased efficacy if not given early. These findings further support the concept that the therapeutic window for prophylaxis is narrow, highlighting the need to develop early treatment strategies for clinical management. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2397-2406, 2017.

Heterotopic Ossification following Tissue Transfer for Combat-Casualty Complex Periarticular Injuries.

BACKGROUND: Although mechanisms underlying heterotopic ossification remain unknown, certain risk factors can influence heterotopic bone formation. The purpose of this study was to determine whether flaps used in periarticular reconstruction had any effect on heterotopic ossification formation. METHODS: A retrospective review of periarticular injuries requiring flap coverage from 2003 through 2014 was performed. Flap types, Injury Severity Scores, functional outcomes, and complications were reviewed. Radiology findings were assessed to determine heterotopic ossification rates and grades. RESULTS: Three hundred eighty-nine flaps were performed for traumatic extremity coverage over the 13-year study period. Sixty-nine of these flaps were used for periarticular coverage. The rate of periarticular heterotopic ossification was 47 percent for fasciocutaneous versus 54 percent for muscle-based flap coverage (p = 0.88). There were no significant differences in Injury Severity Score (p = 0.44) or overall heterotopic ossification formation (p = 0.97) between groups; however, the grade of heterotopic ossification within muscle-based flap cohort was significantly higher (1.70 for muscle versus 1.06 for the fasciocutaneous cohort; p = 0.002). CONCLUSIONS: Combat-related trauma is associated with high rates of heterotopic ossification, with an overall formation rate exceeding 85 percent for our patients requiring periarticular flap coverage. Although no difference in the rate of heterotopic ossification formation was found between fasciocutaneous and muscle flap coverages, a significantly increased severity of heterotopic ossification was seen in periarticular muscle-based flaps. These findings suggest that flap composition might not affect the rate of heterotopic ossification formation but may have an effect on ectopic bone formation severity.

The effect of bacterial infection on the biomechanical properties of biological mesh in a rat model.

BACKGROUND: The use of biologic mesh to repair abdominal wall defects in contaminated surgical fields is becoming the standard of practice. However, failure rates and infections of these materials persist clinically. The purpose of this study was to determine the mechanical properties of biologic mesh in response to a bacterial encounter. METHODS: A rat model of Staphylococcus aureus colonization and infection of subcutaneously implanted biologic mesh was used. Samples of biologic meshes (acellular human dermis (ADM) and porcine small intestine submucosa (SIS)) were inoculated with various concentrations of methicillin-resistant Staphylococcus aureus [10(5), 10(9) colony-forming units] or saline (control) prior to wound closure (n = 6 per group). After 10 or 20 days, meshes were explanted, and cultured for bacteria. Histological changes and bacterial recovery together with biomechanical properties were assessed. Data were compared using a 1-way ANOVA or a Mann-Whitney test, with p<0.05. RESULTS: The overall rate of staphylococcal mesh colonization was 81% and was comparable in the ADM and SIS groups. Initially (day 0) both biologic meshes had similar biomechanical properties. However after implantation, the SIS control material was significantly weaker than ADM at 20 days (p = 0.03), but their corresponding modulus of elasticity were similar at this time point (p>0.05). After inoculation with MRSA, a time, dose and material dependent decrease in the ultimate tensile strength and modulus of elasticity of SIS and ADM were noted compared to control values. CONCLUSION: The biomechanical properties of biologic mesh significantly decline after colonization with MRSA. Surgeons selecting a repair material should be aware of its biomechanical fate relative to other biologic materials when placed in a contaminated environment.