The local and systemic effects of immune function on fracture healing

The immune system plays an integral role in the regulation of cellular processes responsible for fracture healing. Local and systemic influences on fracture healing correlate in many ways with fracture-related outcomes, including soft tissue healing quality and fracture union rates. Impaired soft tissue healing, restricted perfusion of a fracture site, and infection also in turn affect the immune response to fracture injury. Modern techniques used to investigate the relationship between immune system function and fracture healing include precision medicine, using vast quantities of data to interpret broad patterns of inflammatory response. Early data from the PRECISE trial have demonstrated distinct patterns of inflammatory response in polytrauma patients, which thereby directly and indirectly regulate the fracture healing response. The clearly demonstrated linkage between immune function and fracture healing suggests that modulation of immune function has significant potential as a therapeutic target that can be used to enhance fracture healing.

Preclinical models of orthopaedic trauma: Orthopaedic Research Society (ORS) and Orthopaedic Trauma Association (OTA) symposium 2022

Orthopaedic trauma remains a leading cause of patient morbidity, mortality, and global health care burden. Although significant advances have been made in the diagnosis, treatment, and rehabilitation of these injuries, complications such as malunion, nonunion, infection, disuse muscle atrophy and osteopenia, and incomplete return to baseline function still occur. The significant inherent clinical variability in fracture care such as differing patient demographics, injury patterns, and treatment protocols make standardized and replicable study, especially of cellular and molecular based mechanisms, nearly impossible. Hence, the scientists dedicated to improving therapy and treatments for patients with orthopaedic trauma rely on preclinical models. Preclinical models have proven to be invaluable in understanding the timing between implant insertion and bacterial inoculation on the bioburden of infection. Posttraumatic arthritis (PTOA) can take years to develop clinically, but with a porcine pilon fracture model, posttraumatic arthritis can be reliably induced, so different surgical and therapeutic strategies can be tested in prevention. Conversely, the racehorse presents a well-accepted model of naturally occurring PTOA. With preclinical polytrauma models focusing on chest injury, abdominal injury, multiple fractures, and/or head injury, one can study how various injury patterns affect fracture healing can be systemically studied. Finally, these preclinical models serve as a translational bridge to for clinical application in human patients. With selection of the right preclinical model, studies can build a platform to decrease the risk of emerging technologies and provide foundational support for therapeutic clinical trials. In summary, orthopaedic trauma preclinical models allow scientists to simplify a complex clinical challenge, to understand the basic pathways starting with lower vertebrate models. Then, R&D efforts progress to higher vertebrate models to build in more complexity for translation of findings to the clinical practice.

Intravenous Cefazolin Achieves Sustained High Interstitial Concentrations in Open Lower Extremity Fractures

BACKGROUND

Infection remains a serious clinical concern in patients with open fractures, despite timely antibiotic administration and surgical debridement. Soft tissue and periosteal stripping may alter local tissue homeostasis and antibiotic pharmacokinetics in the injured limb. The tissue (interstitial) concentration of intravenously administered antibiotics at an open fracture site has not been characterized using direct sampling techniques.

QUESTION/PURPOSE

We performed this study to evaluate the concentration and pharmacokinetics of intravenously delivered cefazolin at an open fracture site after surgical debridement.

METHODS

Twelve patients with an open fracture distal to the knee who presented at a regional Level I trauma center were approached for enrollment in this nonrandomized, observational study. Of the 12 patients, eight adults (one female, seven male) with a median age of 32 years (range 23 to 51 years) were enrolled and underwent successful sample collection for analysis. Three patients had incomplete datasets because of equipment malfunction and one elected not to participate. Seven patients had open tibia fractures, and one patient had an open fibula fracture associated with a closed tibia fracture. There were six Gustilo-Anderson Type II injuries and two Type IIIA injuries. Empiric antibiotics were administered in the prehospital setting or in the emergency department according to institutional protocol. When patients were taken to the operating room, a 2-g intravenous dose of cefazolin was administered. After surgical debridement, fracture stabilization, and wound closure, a microdialysis catheter was placed transdermally into the injury zone (within 5 cm of the fracture site) and a second catheter was placed in the contralateral uninjured (control) limb. Additional doses of cefazolin were administered every 8 hours postoperatively. Baseline and periodic interstitial fluid and whole blood (plasma) samples were collected in the operating room and at prespecified times for 24 hours postoperatively. Free cefazolin in the interstitial fluid and plasma samples were analyzed by ultra-high-performance liquid chromatography using C 18 column separation with quadrupole time-of-flight mass spectrometry detection. Data from the second postoperative dose of cefazolin were used to characterize pharmacokinetic parameters through a noncompartmental analysis using time-concentration curves of free cefazolin and assuming first-order elimination. For pharmacodynamic analyses, the modal cefazolin minimum inhibitory concentration (MIC) of Staphylococcus aureus (1 µg/mL) was used.

RESULTS

With the samples available, no difference was observed in the median free cefazolin exposure over 24 hours ( f area under the curve [AUC] 0→24hrs ) between injured limbs (352 μg∙hr/mL [IQR 284 to 594 μg∙hr/mL]) and uninjured limbs (341 μg∙hr/mL [IQR 263 to 438 μg∙hr/mL]; p = 0.64). The median time to achieve the maximum concentration of free cefazolin ( f T max ) for injured limbs was delayed (2.7 hours [IQR 2.2 to 3.1 hours]) compared with control limbs (1.7 hours [IQR 1.2 to 2.0 hours]; p = 0.046). The time to the maximum concentration for plasma was not different from that of control limbs (p = 0.08). The time the cefazolin concentration was above the modal S. aureus MIC (T > MIC) in the injured and control limbs over 24 hours was 100% (IQR 100% to 100%) and 100% (IQR 97% to 100%), respectively.

CONCLUSION

These preliminary findings suggest that current prophylactic cefazolin dosing regimens result in successful antibiotic delivery to the traumatized limb in moderately severe open fractures. Although cefazolin delivery to open-fracture wound beds was delayed compared with healthy tissues, the cefazolin concentration was sustained above the European Union Committee Antimicrobial Susceptibility Testing modal MIC for S. aureus , demonstrating a high likelihood of a prophylactic antimicrobial environment at an open fracture site with this empiric antimicrobial regimen. Importantly, patients in this analysis had Gustilo-Anderson Types II and IIIA injuries. Further research with a larger patient cohort is needed to determine whether antibiotic delivery to traumatized soft tissues in patients with higher-grade open fractures (Gustilo-Anderson Types IIIB and IIIC) demonstrates similar pharmacokinetic characteristics.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Systematic review of intraoperative corticosteroid injections and the risk of infection in arthroscopic surgery

Background

Despite the fact that preoperative corticosteroid injections within three to six months of surgery increase the risk of postoperative infection, there is a growing trend of using corticosteroid injections intraoperatively as an effort to decrease postoperative pain and opiate use. Our aim with this review was to answer the question "Do intraoperative corticosteroid injections increase the risk of infections in arthroscopic surgery?"

Methods

A systematic search of MEDLINE, Cochrane, and PMC databases was conducted adhering to PRISMA 2020 guidelines after registration with PROSPERO (ID: CRD42023459138). We included studies comparing infection rates in patients who received intraoperative corticosteroid injections (IOCSI) to those who received no injection. The MINORS risk of bias tool was used to assess the quality of included studies.

Results

305 individual records were screened and a total of 8 studies met the criteria for inclusion in the study, containing data from over 700,000 patient records. All 7 retrospective studies showed an increase in infection rates and the single small randomized controlled trial had no infections in either the control or intervention group. The combined weighted odds ratio of infection rates in comparable studies was 2.23 95% CI (1.66-3.11).

Conclusions

Current data shows that IOCSIs more than double the risk of postoperative infection during arthroscopic surgery. Surgeons should consider and weigh the impact of infection to the minor clinical benefit corticosteroid injections add over other multimodal injections. We expect similar increases in infection rates in other surgeries where IOCSIs are used due to the inherent immunosuppressive mechanisms of corticosteroids.

Mobility Solutions After a Lower Extremity Fracture and Applicability to Battlefield and Wilderness Medicine

The potential for delayed evacuation of injured Service members from austere environments highlights the need to develop solutions that can stabilize a wound and enable mobility during these prolonged casualty care (PCC) scenarios. Lower extremity fractures have traditionally been treated by immobilization (splinting) followed by air evacuation - a paradigm not practical in PCC scenarios. In the civilian sector, treatment of extremity injuries sustained during remote recreational activities have similar challenges, particularly when adverse weather or terrain precludes early ground or air rescue. This review examines currently available fracture treatment solutions to include splinting, orthotic devices, and biological interventions and evaluates their feasibility: 1) for prolonged use in austere environments and 2) to enable patient mobilization. This review returned three common types of splints to include: a simple box splint, pneumatic splints, and traction splints. None of these splinting techniques allowed for ambulation. However, fixed facility-based orthotic interventions that include weight-bearing features may be combined with common splinting techniques to improve mobility. Biologically-focused technologies to stabilize a long bone fracture are still in their infancy. Integrating design features across these technologies could generate advanced treatments which would enable mobility, thus maximizing survivability until patient evacuation is feasible.

Fracture healing in a polytrauma rat model is influenced by mtDNA:cGAS complex mediated pro-inflammation

PURPOSE

The mitochondrial DNA (mtDNA) activated cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) signaling pathway is a key player in mediating immune responses in autoimmune disorders and cancer. However, its role in severe trauma associated fracture healing is unknown. This study investigated if the cGAS-STING signaling pathway contributes to delayed bone healing in polytrauma (PT) fractures.

METHODS

For preliminary analyses, therapeutic dosage of RU.521 (cGAS inhibitor) (n = 2) was determined in C57BL/6 J mice by mass spectrometry, and IFNβ expression levels in serum and bronchioalveolar fluid (BALF) at 6 and 24 h (h) in RU.521/vehicle + mtDNA injected mice (n = 3/treatment and time point) was measured by ELISA. In the main study, plasma mtDNA was quantified by qPCR in a clinically relevant delayed fracture healing PT rat model with burn injury, blunt trauma, and a femoral fracture at 3 h post-trauma (hpt). Next, PT rats received either RU.521 (12 mg/kg in povidone; n = 8) or vehicle (povidone only; n = 5) immediately after injury and were followed up for 5 weeks post-trauma to assess bone regeneration by radiography and histology.

RESULTS

IFNβ levels were significantly decreased only at 24 h in BALF of RU.521 treated mice. At 3hpt mtDNA was significantly elevated in PT rats compared to rats without injury. When treated with RU.521, PT rats showed improvement in bone healing compared to vehicle control PT rats.

CONCLUSIONS

These data reveal that the cGAS-STING signaling pathway influences trauma-induced delayed bone healing. However, further evaluation of this pathway at the cellular and molecular levels to augment PT associated detrimental effects is needed.

Acute muscle mass loss was alleviated with HMGB1 neutralizing antibody treatment in severe burned rats

Burn injury is associated with muscle wasting, though the involved signaling mechanisms are not well understood. In this study, we aimed to examine the role of high mobility group box 1 (HMGB1) in signaling hyper-inflammation and consequent skeletal muscle impairment after burn. Sprague Dawley rats were randomly assigned into three groups: (1) sham burn, (2) burn, (3) burn/treatment. Animals in group 2 and group 3 received scald burn on 30% of total body surface area (TBSA) and immediately treated with chicken IgY and anti-HMGB1 antibody, respectively. Muscle tissues and other samples were collected at 3-days after burn. Body mass and wet/dry weights of the hind limb muscles (total and individually) were substantially decreased in burn rats. Acute burn provoked the mitochondrial stress and cell death and enhanced the protein ubiquitination and LC3A/B levels that are involved in protein degradation in muscle tissues. Further, an increase in muscle inflammatory infiltrate associated with increased differentiation, maturation and proinflammatory activation of bone marrow myeloid cells and αβ CD4+ T and γδ T lymphocytes was noted in in circulation and spleen of burn rats. Treatment with one dose of HMGB1 neutralizing antibody reduced the burn wound size and preserved the wet/dry weights of the hind limb muscles associated with a control in the markers of cell death and autophagy pathways in burn rats. Further, anti-HMGB1 antibody inhibited the myeloid and T cells inflammatory activation and subsequent dysregulated inflammatory infiltrate in the muscle tissues of burn rats. We conclude that neutralization of HMGB1-dependent proteolytic and inflammatory responses has potential beneficial effects in preventing the muscle loss after severe burn injury.

A Retrospective Analysis of Combat Injury Patterns and Prehospital Interventions Associated with the Development of Sepsis

BACKGROUND

Combat injury related wound infections are common. Untreated, these wound infections may progress to sepsis and septic shock leading to increased morbidity and mortality rates. Understanding infectious complications, patterns, progression, and correlated prehospital interventions are vital to understand the development of sepsis. We aim to analyze demographics, injury patterns, and interventions associated with sepsis in battlefield settings.

MATERIALS AND METHODS

This is a secondary analysis of previously published data from the Department of Defense Trauma Registry (DoDTR) from 2007 to 2020. We searched for casualties diagnosed with sepsis (excluding line-sepsis) throughout their initial hospitalization. Regression models were used to seek associations.

RESULTS

Our initial request yielded 28,950 encounters, of which 25,654 (88.6%) were adults that met inclusion, including 243 patients (0.9%) diagnosed with sepsis. Patients included US military (34%), non-North Atlantic Treaty Organization (NATO) military (33%) and humanitarian (30%) groups. Patients diagnosed with sepsis had a significantly lower survival rate than non-septic patients (78.1% vs. 95.7%, p < 0.001). There was no significant difference in administration of prehospital antibiotics between septic and the general populations (10.6% vs. 12.3%, p = 0.395). Prehospital intraosseous access (OR 1.56, 95% CI 1.27-1.91, p = 0.207) and packed red cell administration (1.63, 1.24-2.15, 0.029) were the interventions most associated with sepsis.

CONCLUSIONS

Sepsis occurred infrequently in the DoDTR when evacuation from battlefield is not delayed, but despite increased intervention frequency, developing sepsis demonstrates a significant drop in survival rates. Future research would benefit from the development of risk mitigation measures.

Placement of Antibiotic Powder in Open Fracture Wounds during the Emergency Room (POWDER): Design and Rationale for an Investigation of the Acute Application of Topical Antibiotic Powder in Open Fracture Wounds for Infection Prophylaxis

BACKGROUND

Open fractures are at high risk for complications both in the military and civilian setting. Treatments to prevent fractures are limited in the Role 1 (prehospital, battalion aid station) setting. The goal of this study is to assess the efficacy of topical vancomycin powder, administered within 24 hours of an open fracture injury, in the prevention of infection and infection-related complications.

METHODS

The POWDER study is a multicenter, prospective, randomized controlled clinical trial using a pragmatic open-label design. We will recruit 200 long bone open fracture patients from University Hospital at University of Texas Health at San Antonio (UTHSA) and the Brooke Army Medical Center (BAMC). We will screen and randomize patients in a 1:1 ratio to receive either usual care plus 2g topical vancomycin or usual care only. The primary objective of this study is to compare the proportion of infection and infection-related complications which occur in the 2 arms. An additional objective is to develop a risk-prediction model for open fracture wound complications.

CONCLUSIONS

The infection rates seen in open fractures remain alarmingly high in both combat and civilian settings. Several orthopedic surgery studies suggest vancomycin powder is effective in reducing surgical site infections when applied topically at the time of wound closure. We expect to see a reduction in infections in open fracture injuries treated acutely with vancomycin powder. This study may provide important information regarding the use of local vancomycin powder during the acute treatment of open fractures. If shown to be efficacious, vancomycin powder could provide a simple, time- and cost-effective infection prophylaxis strategy for these injuries.

Placement of Antibiotic Powder in Open Fracture Wounds during the Emergency Room (POWDER): Design and Rationale for an Investigation of the Acute Application of Topical Antibiotic Powder in Open Fracture Wounds for Infection Prophylaxis

BACKGROUND

Open fractures are at high risk for complications both in the military and civilian setting. Treatments to prevent fractures are limited in the Role 1 (prehospital, battalion aid station) setting. The goal of this study is to assess the efficacy of topical vancomycin powder, administered within 24 hours of an open fracture injury, in the prevention of infection and infection-related complications.

METHODS

The POWDER study is a multicenter, prospective, randomized controlled clinical trial using a pragmatic open-label design. We will recruit 200 long bone open fracture patients from University Hospital at University of Texas Health at San Antonio (UTHSA) and the Brooke Army Medical Center (BAMC). We will screen and randomize patients in a 1:1 ratio to receive either usual care plus 2g topical vancomycin or usual care only. The primary objective of this study is to compare the proportion of infection and infection-related complications which occur in the 2 arms. An additional objective is to develop a risk-prediction model for open fracture wound complications.

CONCLUSIONS

The infection rates seen in open fractures remain alarmingly high in both combat and civilian settings. Several orthopedic surgery studies suggest vancomycin powder is effective in reducing surgical site infections when applied topically at the time of wound closure. We expect to see a reduction in infections in open fracture injuries treated acutely with vancomycin powder. This study may provide important information regarding the use of local vancomycin powder during the acute treatment of open fractures. If shown to be efficacious, vancomycin powder could provide a simple, time- and cost-effective infection prophylaxis strategy for these injuries.

FK506 increases susceptibility to musculoskeletal infection in a rodent model

Background

Delayed fracture healing caused by soft tissue loss can be resolved by the administration of a Th1 immunosuppressant, such as FK506. Additionally, open fractures are at high risk for infection. We hypothesized that the inclusion of an immunosuppressant to a subject at risk for a musculoskeletal infection will increase the likelihood of infection.

Methods

A rat model of musculoskeletal infection was used. Sprague Dawley rats received a stabilized femur defect and were inoculated with 10⁴ CFU Staphylococcus aureus via a collagen matrix. Six hours after inoculation, the wounds were debrided of collagen and devitalized tissue and irrigated with sterile saline. The animals were randomized into two groups: carrier control and FK506, which were administered daily for 14 days and were euthanized and the tissues harvested to measure local bioburden.

Results

The dosing regimen of FK506 that restored bone healing increased the bioburden in the bone and on the fixation implant compared to the carrier control animals. As expected, the administration of FK506 decreased circulating white blood cells, lymphocytes, neutrophils, and monocytes. Additionally, the red blood cell count, hematocrit, and body weight were lower in those animals that received FK506 compared to carrier control.

Conclusions

FK506 administration decreased the systemic immune cell counts and increased the bacterial bioburden within a model of musculoskeletal infection. Collectively, these outcomes could be attributed to the overall T cell suppression by FK506 and the altered antimicrobial activity of innate cells, thereby allowing S. aureus to thrive and subsequently leading to infection of severe, musculoskeletal injuries. These observations reveal the crucial continued investigation for the clinical use of FK506, and other immunosuppressant compounds, in trauma patients who are at increased risk of developing infections.

Preclinical evaluation of a commercially available biofilm disrupting wound lavage for musculoskeletal trauma

BACKGROUND

Treatment of open fractures remains a significant challenge in trauma care as these fractures are accompanied by extensive soft tissue damage, exposing the wound site to contaminants and increasing infection risk. Formation of biofilm, a capsule-like environment that acts as a barrier to treatment, is a primary mode by which infecting pathogens persist at the wound site. Therefore, a pressing need exists to identify irrigation methods that can disrupt biofilm and expose pathogens to treatment. This study aims to evaluate the antibiofilm wound lavage, Bactisure™, in comparison with saline for care of severe musculoskeletal wounds and elucidate potential effects on antibiotic treatment success.

METHODS

UAMS-1 Staphylococcus aureus biofilms were formed in vitro and treated with Bactisure™ wound lavage or sterile normal saline, alone, or in combination with sub-biofilm inhibitory levels of vancomycin. Characterization methods included quantification of biofilm biomass, quantification of viable biofilm bacteria, and biofilm matrix imaging. For in vivo assessment, a delayed treatment model of contaminated open fracture was used wherein a critical-sized defect was created in a rat femur and wound site inoculated with UAMS-1. Following a 6 h delay, wounds were debrided, irrigated with lavage of interest, and antibiotic treatments administered. Bacterial enumeration was performed on bone and hardware samples after two weeks.

RESULTS

An immediate reduction in biofilm biomass was observed in vitro following antibiofilm lavage treatment, with a subsequent 2- to 3- log reduction in viable bacteria achieved after 24 h. Furthermore, biofilms treated with antibiofilm lavage in combination with vancomycin exhibited a minor, but statistically significant, decrease in viable bacteria compared to irrigation alone. In vivo, a minor, not statistically significant, decrease in median bioburden was observed for the antibiofilm lavage compared to saline when used in combination with antibiotics. However, the percentage of bone and hardware samples with detectable bacteria was reduced from 50 to 38%.

CONCLUSIONS

These results suggest that the antibiofilm wound lavage, Bactisure™, may hold promise in mitigating infection in contaminated musculoskeletal wounds and warrants further investigation. Here, we proposed multiple mechanisms in vitro by which this antibiofilm lavage may help mitigate infection, and demonstrate this treatment slightly outperforms saline in controlling bioburden in vivo.

Spatial rhBMP2 delivery from hydroxyapatite scaffolds sustains bone regeneration in rabbit radius

Regenerating large bone defects requires a multi-faceted approach combining optimal scaffold designs with appropriate growth factor delivery. Supraphysiological doses of recombinant human bone morphogenetic protein 2(rhBMP2); typically used for the regeneration of large bone defects clinically in conjunction with an acellular collagen sponge (ACS), have resulted in many complications. In the current study, we develop a hydroxyapatite/collagen I (HA/Col) scaffold to improve the mechanical properties of the HA scaffolds while maintaining open connected porosity. Varying rhBMP2 dosages were then delivered from a collagenous periosteal membrane and paired with HA or HA/Col scaffolds to treat critical sized (15mm) diaphyseal radial defect in New Zealand white rabbits. The groups examined were ACS+76µg rhBMP2 (clinically used INFUSE dosage), HA+76µg rhBMP2, HA+15µg rhBMP2, HA/Col+15µg rhBMP2 and HA/Col+15µg rhBMP2+bone marrow derived stromal cells (bMSCs). After 8 weeks of implantation, all regenerated bones were evaluated using micro computed tomography, histology, histomorphometry and torsional testing. It was observed that the bone volume regenerated in the HA/Col + 15 µg rhBMP2 group was significantly higher than that in the groups with 76µg rhBMP2. The same scaffold and growth factor combination resulted in the highest bone mineral density of the regenerated bone, and the most bone apposition on the scaffold surface. Both the HA and HA/Col scaffolds paired with 15 µg rhBMP2 had sustained ingrowth of the mineralization front after 2 weeks compared to the groups with 76µg rhBMP2 which had far greater mineralization in the first 2 weeks after implantation. Complete bridging of the defect site and no significant differences in torsional strength, stiffness or angle at failure was observed across all groups. No benefit of additional bMSC seeding was observed on any of the quantified metrics, while bone-implant apposition was reduced in the cell seeded group. This study demonstrated that the controlled spatial delivery of rhBMP2 at the periosteum at significantly lower doses can be used as a strategy to improve bone regeneration around space maintaining scaffolds.

The intersection of fracture healing and infection: Orthopaedics research society workshop 2021

Infection is a common cause of impaired fracture healing. In the clinical setting, definitive fracture treatment and infection are often treated separately and sequentially, by different clinical specialties. The ability to treat infection while promoting fracture healing will greatly reduce the cost, number of procedures, and patient morbidity associated with infected fractures. In order to develop new therapies, scientists and engineers must understand the clinical need, current standards of care, pathologic effects of infection on fractures, available preclinical models, and novel technologies. One of the main causes of poor fracture healing is infection; unfortunately, bone regeneration and infection research are typically approached independently and viewed as two separate disciplines. Here, we aim to bring these two groups together in an educational workshop to promote research into the basic and translational science that will address the clinical challenge of delayed fracture healing due to infection. Statement of clinical significance: Infection and nonunion are each feared outcomes in fracture care, and infection is a significant driver of nonunion. The impact of nonunions on patie[Q2]nt well-being is substantial. Outcome data suggests a long bone nonunion is as impactful on health-related quality of life measures as a diagnosis of type 1 diabetes and fracture-related infection has been shown to significantly l[Q3]ower a patient's quality of life for over 4 years.  Although they frequently are associated with one another, the treatment approaches for infections and nonunions are not always complimentary and cannot be performed simultaneously without accepting tradeoffs. Furthermore, different clinical specialties are often required to address the problem, the orthopedic surgeon treating the fracture and an infectious disease specialist addressing the sources of infection. A sequential approach that optimizes treatment parameters requires more time, more surgeries, and thus confers increased morbidity to the patient. The ability to solve fracture healing and infection clearance simultaneously in a contaminated defect would benefit both the patient and the health care system.

Neutralization of HMGB1 improves fracture healing and γδ T lymphocyte counts at the fracture site in a polytrauma rat model

Purpose

Delayed fracture healing is a common consequence of polytrauma (PT) occurring in patients with multiple injuries. We believe that when early release of high mobility group box 1 (HMGB1) molecules from necrotic tissues exceed their normal levels in blood, they dysregulate immune responses associated with normal healing. This study investigates the detrimental effect of such dysregulate immune responses by targeting HMGB1 in a PT rat model with debilitating injuries. We hypothesized that neutralization of extracellular HMGB1 immediately post-trauma would ameliorate local immune dysregulation and improve fracture healing in a PT rat model.

Methods

PT rats received a single dose of either anti-rat HMGB1 polyclonal antibody (PT-Ab HMGB1) or IgY isotype (PT-IgY), were left untreated (PT-C), or had a single injury/osteotomy only (OST). Fracture healing was evaluated by micro-computed tomography (µCT) and histology at 5 weeks; and macrophages and T cell counts within the fracture site were determined with flow cytometry  at 1 week.

Results

Notably, bone regeneration within the fracture site in PT-Ab HMGB1 rats was improved with comparable connective tissue organization than PT-C rats. Further, only γδTCR⁺ T cells, but not macrophages and CD4⁺ and CD8⁺ T cells, were diminished at the fracture site in PT-C and PT-IgY rats. Interestingly, the PT-Ab HMGB1 rats had increased γδTCR⁺ T cells compared to PT-C and PT-IgY, suggesting their potential role in regulating fracture healing.

Conclusions

Therefore, the initial burst of systemic HMGB1 following trauma may have a role in regulating bone regeneration via the modulation of a subclass of T cells within the fracture site, suggesting it’s importance as a therapeutic target in PT to combat immune dysregulation and delayed fracture healing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00453-3.

Administration of particulate oxygen generators improves skeletal muscle contractile function after ischemia-reperfusion injury in the rat hindlimb

Extended tourniquet application, often associated with battlefield extremity trauma, can lead to severe ischemia-reperfusion (I/R) injury in skeletal muscle. Particulate oxygen generators (POGs) can be directly injected into tissue to supply oxygen to attenuate the effects of I/R injury in muscle. The goal of this study was to investigate the efficacy of a sodium percarbonate (SPO)-based POG formulation in reducing ischemic damage in a rat hindlimb during tourniquet application. Male Lewis rats were anesthetized and underwent tourniquet application for 3 h at a pressure of 300 mmHg. Shortly after tourniquet inflation, animals received intramuscular injections of either 0.2 mg/mL SPO with catalase (n = 6) or 2.0 mg/mL SPO with catalase (n = 6) directly into the tibialis anterior (TA) muscle. An additional Tourniquet-Only group (n = 12) received no intervention. Functional recovery was monitored by in vivo contractile testing of the hindlimb at 1, 2, and 4 wk after injury. By the 4 wk time point, the Low-Dose POG group continued to show improved functional recovery (85% of baseline) compared with the Tourniquet-Only (48%) and High-Dose POG (56%) groups. In short, the low-dose POG formulation appeared, at least in part, to mitigate the impact of ischemic tissue injury, thus improving contractile function after tourniquet application. Functional improvement correlated with maintenance of larger muscle fiber cross-sectional area and the presence of fewer fibers containing centrally located nuclei. As such, POGs represent a potentially attractive therapeutic solution for addressing I/R injuries associated with extremity trauma.NEW & NOTEWORTHY Skeletal muscle contraction was evaluated in the same animals at multiple time points up to 4 wk after injury, following administration of particulate oxygen generators (POGs) in a clinically relevant rat hindlimb model of tourniquet-induced ischemia. The observed POG-mediated improvement of muscle function over time confirms and extends previous studies to further document the potential clinical applications of POGs. Of particular significance in austere environments, this technology can be applied in the absence of an intact circulation.

Orthopaedic Implant Coatings: Recent Approaches and Clinical Translation

Despite improved surgical techniques and prophylactic procedures, orthopaedic implant-associated infections remain high with complications that can lead to devastating outcomes for the patient. Implant coatings and associated surface modification techniques represent a promising means to prevent infections. Various approaches have emerged to address the challenges associated with implant infections, such as antibacterial resistance, biofilm prevention, and appropriate efficacy kinetics. Methods including antibiotic and antimicrobial peptide surface tethering, use of osteo-conductive and -inductive materials, and altering hydrophobicity and hydrophilicity of the implant surface, have all demonstrated efficacy toward diminished infection risk. Though many of these techniques have shown great potential in in vitro and in vivo studies, clinical translation remains limited with very few commercially available implant coatings globally. This review summarizes recent advancements in orthopaedic implant coatings, pre-clinical studies, and clinical translation, as well as potential future marketed products. (Journal of Surgical Orthopaedic Advances 31(3):169-176, 2022).

Bone infection: a clinical priority for clinicians, scientists and educators

Bone infection has received increasing attention in recent years as one of the main outstanding clinical problems in orthopaedic-trauma surgery that has not been successfully addressed. In fact, infection may develop across a spectrum of patient types regardless of the level of perioperative management, including antibiotic prophylaxis. Some of the main unknown factors that may be involved, and the main targets for future intervention, include more accurate and less invasive diagnostic options, more thorough and accurate debridement protocols, and more potent and targeted antimicrobials. The underlying biology dominates the clinical management of bone infections, with features such as biofilm formation, osteolysis and vascularisation being particularly influential. Based on the persistence of this problem, an improved understanding of the basic biology is deemed necessary to enable innovation in the field. Furthermore, from the clinical side, better evidence, documentation and outreach will be required to translate these innovations to the patient. This review presents the findings and progress of the AO Trauma Clinical Priority Program on the topic of bone infection.

Administration of a selective retinoic acid receptor-γ agonist improves neuromuscular strength in a rodent model of volumetric muscle loss

PURPOSE

Volumetric muscle loss is a uniquely challenging pathology that results in irrecoverable functional deficits. Furthermore, a breakthrough drug or bioactive factor has yet to be established that adequately improves repair of these severe skeletal muscle injuries. This study sought to assess the ability of an orally administered selective retinoic acid receptor-γ agonist, palovarotene, to improve recovery of neuromuscular strength in a rat model of volumetric muscle loss.

METHODS

An irrecoverable, full thickness defect was created in the tibialis anterior muscle of Lewis rats and animals were survived for 4 weeks. Functional recovery of the tibialis anterior muscle was assessed in vivo via neural stimulation and determination of peak isometric torque. Histological staining was performed to qualitatively assess fibrous scarring of the defect site.

RESULTS

Treatment with the selective retinoic acid receptor-γ agonist, palovarotene, resulted in a 38% improvement of peak isometric torque in volumetric muscle loss affected limbs after 4 weeks of healing compared to untreated controls. Additionally, preliminary histological assessment suggests that oral administration of palovarotene reduced fibrous scarring at the defect site.

CONCLUSIONS

These results highlight the potential role of selective retinoic acid receptor-γ agonists in the design of regenerative medicine platforms to maximize skeletal muscle healing. Additional studies are needed to further elucidate cellular responses, optimize therapeutic delivery, and characterize synergistic potential with adjunct therapies.

Effects of nanocrystalline hydroxyapatite concentration and skeletal site on bone and cartilage formation in rats

Most fractures heal by a combination of endochondral and intramembranous ossification dependent upon strain and vascularity at the fracture site. Many biomaterials-based bone regeneration strategies rely on the use of calcium phosphates such as nano-crystalline hydroxyapatite (nHA) to create bone-like scaffolds. In this study, nHA was dispersed in reactive polymers to form composite scaffolds that were evaluated both in vitro and in vivo. Matrix assays, immunofluorescent staining, and Western blots demonstrated that nHA influenced mineralization and subsequent osteogenesis in a dose-dependent manner in vitro. Furthermore, nHA dispersed in polymeric composites promoted osteogenesis by a similar mechanism as particulated nHA. Scaffolds were implanted into a 2-mm defect in the femoral diaphysis or metaphysis of Sprague-Dawley rats to evaluate new bone formation at 4 and 8 weeks. Two formulations were tested: a poly(thioketal urethane) scaffold without nHA (PTKUR) and a PTKUR scaffold augmented with 22 wt% nHA (22nHA). The scaffolds supported new bone formation in both anatomic sites. In the metaphysis, augmentation of scaffolds with nHA promoted an intramembranous healing response. Within the diaphysis, nHA inhibited endochondral ossification. Immunohistochemistry was performed on cryo-sections of the bone/scaffold interface in which CD146, CD31, Endomucin, CD68, and Myeloperoxidase were evaluated. No significant differences in the infiltrating cell populations were observed. These findings suggest that nHA dispersed in polymeric composites induces osteogenic differentiation of adherent endogenous cells, which has skeletal site-specific effects on fracture healing. STATEMENT OF SIGNIFICANCE: Understanding the mechanism by which synthetic scaffolds promote new bone formation in preclinical models is crucial for bone regeneration applications in the clinic where complex fracture cases are seen. In this study, we found that dispersion of nHA in polymeric scaffolds promoted in vitro osteogenesis in a dose-dependent manner through activation of the PiT1 receptor and subsequent downstream Erk1/2 signaling. While augmentation of polymeric scaffolds with nHA enhanced intramembranous ossification in metaphyseal defects, it inhibited endochondral ossification in diaphyseal defects. Thus, our findings provide new insights into designing synthetic bone grafts that complement the skeletal site-specific fracture healing response.

Settable Polymeric Autograft Extenders in a Rabbit Radius Model of Bone Formation

Autograft (AG) is the gold standard for bone grafts, but limited quantities and patient morbidity are associated with its use. AG extenders have been proposed to minimize the volume of AG while maintaining the osteoinductive properties of the implant. In this study, poly(ester urethane) (PEUR) and poly(thioketal urethane) (PTKUR) AG extenders were implanted in a 20-mm rabbit radius defect model to evaluate new bone formation and graft remodeling. Outcomes including µCT and histomorphometry were measured at 12 weeks and compared to an AG (no polymer) control. AG control examples exhibited new bone formation, but inconsistent healing was observed. The implanted AG control was resorbed by 12 weeks, while AG extenders maintained implanted AG throughout the study. Bone growth from the defect interfaces was observed in both AG extenders, but residual polymer inhibited cellular infiltration and subsequent bone formation within the center of the implant. PEUR-AG extenders degraded more rapidly than PTKUR-AG extenders. These observations demonstrated that AG extenders supported new bone formation and that polymer composition did not have an effect on overall bone formation. Furthermore, the results indicated that early cellular infiltration is necessary for harnessing the osteoinductive capabilities of AG.

Systemic T Cell Exhaustion Dynamics Is Linked to Early High Mobility Group Box Protein 1 (HMGB1) Driven Hyper-Inflammation in a Polytrauma Rat Model

We previously reported an early surge in high mobility group box protein 1 (HMGB1) levels in a polytrauma (PT) rat model. This study investigates the association of HMGB1 levels in mediating PT associated dysregulated immune responses and its influence on the cellular levels of receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4). Using the same PT rat model treated with anti-HMGB1 polyclonal antibody, we evaluated changes in circulating inflammatory cytokines, monocytes/macrophages and T cells dynamics and cell surface expression of RAGE and TLR4 at 1, 3, and 7 days post-trauma (dpt) in blood and spleen. Notably, PT rats demonstrating T helper (Th)1 and Th2 cells type early hyper-inflammatory responses also exhibited increased monocyte/macrophage counts and diminished T cell counts in blood and spleen. In blood, expression of RAGE and TLR4 receptors was elevated on CD68+ monocyte/macrophages and severely diminished on CD4+ and CD8+ T cells. Neutralization of HMGB1 significantly decreased CD68+ monocyte/macrophage counts and increased CD4+ and CD8+ T cells, but not γδ+TCR T cells in circulation. Most importantly, RAGE and TLR4 expressions were restored on CD4+ and CD8+ T cells in treated PT rats. Overall, findings suggest that in PT, the HMGB1 surge is responsible for the onset of T cell exhaustion and dysfunction, leading to diminished RAGE and TLR4 surface expression, thereby possibly hindering the proper functioning of T cells.

Adjuvant antibiotic-loaded bone cement: Concerns with current use and research to make it work

Antibiotic-loaded bone cement (ALBC) is broadly used to treat orthopaedic infections based on the rationale that high-dose local delivery is essential to eradicate biofilm-associated bacteria. However, ALBC formulations are empirically based on drug susceptibility from routine laboratory testing, which is known to have limited clinical relevance for biofilms. There are also dosing concerns with nonstandardized, surgeon-directed, hand-mixed formulations, which have unknown release kinetics. On the basis of our knowledge of in vivo biofilms, pathogen virulence, safety issues with nonstandardized ALBC formulations, and questions about the cost-effectiveness of ALBC, there is a need to evaluate the evidence for this clinical practice. To this end, thought leaders in the field of musculoskeletal infection (MSKI) met on 1 August 2019 to review and debate published and anecdotal information, which highlighted four major concerns about current ALBC use: (a) substantial lack of level 1 evidence to demonstrate efficacy; (b) ALBC formulations become subtherapeutic following early release, which risks induction of antibiotic resistance, and exacerbated infection from microbial colonization of the carrier; (c) the absence of standardized formulation protocols, and Food and Drug Administration-approved high-dose ALBC products to use following resection in MSKI treatment; and (d) absence of a validated assay to determine the minimum biofilm eradication concentration to predict ALBC efficacy against patient specific micro-organisms. Here, we describe these concerns in detail, and propose areas in need of research.

Negative pressure wound therapy does not diminish efficacy of topical antibiotic powder in a preclinical contaminated wound model

AIMS

High-energy injuries can result in multiple complications, the most prevalent being infection. Vancomycin powder has been used with increasing frequency in orthopaedic trauma given its success in reducing infection following spine surgery. Additionally, large, traumatic injuries require wound coverage and management by dressings such as negative pressure wound therapy (NPWT). NPWT has been shown to decrease the ability of antibiotic cement beads to reduce infection, but its effect on antibiotic powder is not known. The goal of this study was to determine if NPWT reduces the efficacy of topically applied antibiotic powder.

METHODS

Complex musculoskeletal wounds were created in goats and inoculated with a strain of Staphylococcus aureus modified to emit light. Six hours after contaminating the wounds, imaging, irrigation, and debridement and treatment application were performed. Animals received either vancomycin powder with a wound pouch dressing or vancomycin powder with NPWT.

RESULTS

There were no differences in eradication of bacteria when vancomycin powder was used in combination with NPWT (4.5% of baseline) compared to vancomycin powder with a wound pouch dressing (1.7% of baseline) (p = 0.986), even though approximately 50% of the vancomycin was recovered in the NPWT exudate canister.

CONCLUSION

The antimicrobial efficacy of the vancomycin powder was not diminished by the application of NPWT. These topical and locally applied therapies are potentially effective tools that can provide quick, simple treatments to prevent infection while providing coverage. By reducing the occurrence of infection, the recovery is shortened, leading to an overall improvement in quality of life. Cite this article: Bone Joint Res 2021;10(2):149-155.

Localized mandibular infection affects remote in vivo bioreactor bone generation

Mandibular reconstruction requires functional and aesthetic repair and is further complicated by contamination from oral and skin flora. Antibiotic-releasing porous space maintainers have been developed for the local release of vancomycin and to promote soft tissue attachment. In this study, mandibular defects in six sheep were inoculated with 106 colony forming units of Staphylococcus aureus; three sheep were implanted with unloaded porous space maintainers and three sheep were implanted with vancomycin-loaded space maintainers within the defect site. During the same surgery, 3D-printed in vivo bioreactors containing autograft or xenograft were implanted adjacent to rib periosteum. After 9 weeks, animals were euthanized, and tissues were analyzed. Antibiotic-loaded space maintainers were able to prevent dehiscence of soft tissue overlying the space maintainer, reduce local inflammatory cells, eliminate the persistence of pathogens, and prevent the increase in mandibular size compared to unloaded space maintainers in this sheep model. Animals with an untreated mandibular infection formed bony tissues with greater density and maturity within the distal bioreactors. Additionally, tissues grown in autograft-filled bioreactors had higher compressive moduli and higher maximum screw pull-out forces than xenograft-filled bioreactors. In summary, we demonstrated that antibiotic-releasing space maintainers are an innovative approach to preserve a robust soft tissue pocket while clearing infection, and that local infections can increase local and remote bone growth.

Time Course of Immune Response and Immunomodulation During Normal and Delayed Healing of Musculoskeletal Wounds

Single trauma injuries or isolated fractures are often manageable and generally heal without complications. In contrast, high-energy trauma results in multi/poly-trauma injury patterns presenting imbalanced pro- and anti- inflammatory responses often leading to immune dysfunction. These injuries often exhibit delayed healing, leading to fibrosis of injury sites and delayed healing of fractures depending on the intensity of the compounding traumas. Immune dysfunction is accompanied by a temporal shift in the innate and adaptive immune cells distribution, triggered by the overwhelming release of an arsenal of inflammatory mediators such as complements, cytokines and damage associated molecular patterns (DAMPs) from necrotic cells. Recent studies have implicated this dysregulated inflammation in the poor prognosis of polytraumatic injuries, however, interventions focusing on immunomodulating inflammatory cellular composition and activation, if administered incorrectly, can result in immune suppression and unintended outcomes. Immunomodulation therapy is promising but should be conducted with consideration for the spatial and temporal distribution of the immune cells during impaired healing. This review describes the current state of knowledge in the spatiotemporal distribution patterns of immune cells at various stages during musculoskeletal wound healing, with a focus on recent advances in the field of Osteoimmunology, a study of the interface between the immune and skeletal systems, in long bone fractures. The goals of this review are to (1) discuss wound and fracture healing processes of normal and delayed healing in skeletal muscles and long bones; (2) provide a balanced perspective on temporal distributions of immune cells and skeletal cells during healing; and (3) highlight recent therapeutic interventions used to improve fracture healing. This review is intended to promote an understanding of the importance of inflammation during normal and delayed wound and fracture healing. Knowledge gained will be instrumental in developing novel immunomodulatory approaches for impaired healing.

Single dose of anti-high mobility group box 1 protein (HMGB-1) neutralizing antibody ameliorates dysregulated inflammation and restores fracture healing in a polytrauma rat (Rattus norvegicus) model

Polytrauma (PT) is associated with dysregulated inflammation (DI) and complicated/delayed fracture healing. We recently reported delayed fracture healing and increased circulating levels of HMGB-1 in a rat model of PT compared to osteotomy (OST). Since HMGB-1 binds to and activates TLR2, TLR4 and RAGE surface receptors to induce pro-inflammation, we investigated this protein’s role in delayed healing. We hypothesized that neutralization of cell-free HMGB-1 immediately after PT would resolve DI and restore fracture healing in PT. Anti-HMGB-1 polyclonal antibody (2mg/kg) was administered via IP injection following PT (PT-Ab) and bone/tissue volume (BV/TV) of fractures was evaluated by micro-CT imaging at 5 weeks post PT. As hypothesized, by neutralizing HMGB-1, fracture healing was improved with significantly higher BV/TV ratio in PT-Ab compared to PT rats. Changes to circulating CD68+ CD86+ (M1) and CD68+CD163+ (M2) monocyte/macrophage populations, as well as alterations to CD4+ and CD8+ T cells and their RAGE and TLR4 surface expression, were assessed on 1 and 3 days post-injury (d). While circulating M1 and M2 populations are scarce in naïve rats, these populations elevated post trauma. M1 was significantly higher in PT than in OST and PT-Ab at 1d but not at 3d. M2 was significantly high in only OST at 1d. In contrast to OST, we observed decreased RAGE and TLR4 expression on circulating T cells at 1d in PT and PT-Ab and at 3d in PT but not in OST and PT-Ab. Our observations suggest that elevated levels of HMGB-1 following severe trauma initiate immune dysregulation causing delayed fracture repair and the data presented herein indicates that HMGB-1 may be a therapeutic target to restore normal immune response and normal fracture healing in PT.

Characterization of the local and systemic temporal changes to the lipid mediator and cytokine cascades following osteotomy and polytrauma

Polytrauma (PT) inducesglobal changes to inflammatory signaling, contributing to delayed fracturehealing. In a rat model of PT encompassing burn, blunt trauma, and osteotomy, we characterized the local and systemic temporal changes to the lipid mediator(LM) cascade, circulating white blood cells (WBCs), and local levels of growthfactors (GF)s and cytokines. Male rats received either a non-critical 3mmfemoral osteotomy (OST) or PT trauma procedures and were survived for 6, 24,48, 72, 96, 168, or 240hrs and blood, plasma, and fractured femurs werecollected. Whole femurs were homogenized to extract LMs, protein, and RNA, while blood and plasma were used for WBC and LM analysis, respectively. At the fracture site, prostaglandin (PG) E2 was significantly higher in OST at 24 and 72hrs, levels of PGF2α were higher in OST at 24hrs, while resolvin (Rv) D1 was higher in PTat 6hrs post injury. There were no differences in the expression ofcyclooxygenase-2 (COX-2), or lipoxygenase-5 (LOX-5) and LOX-15. In plasma, there were no significant differences in PG levels at any time. Plasma RvE1 was elevated in PT immediately following injury while maresin 1 (MaR1) was significantly lower in PT at 168hrs. Total WBCs and lymphocytes (103cells/uL) were lower in PT overall and significantly so at 72 and 96hrs, respectively. Additionally, the percent of neutrophils in PT was significantlyelevated and percent lymphocytes was decreased at 48 and 168hrs compared toOST. Protein analysis of the fracture site found early elevation of cytokines(IL-1β, IL-13, IL-6) and GFs in PT at 48 and 72hrs. These results indicate thatchanges to circulating LM and WBCs may provide predictive measures of non-unionand therapeutic targets to improve fracture healing.

Revisiting the "race for the surface" in a pre-clinical model of implant infection

Orthopaedic implant use increases infection risk. Implant infection risk can be explained by the "race for the surface" concept, where there is competition between host-cell integration and bacterial colonisation. Although generally accepted, the temporal dynamics have not been elucidated in vivo. Using a bilateral intramedullary rat model, Staphylococcus aureus was injected into the tail vein either immediately after or 1, 3 and 7 d following implant placement. This allowed assessment of the temporal interplay between bacterial colonisation and host-cell adhesion by uncoupling implant placement and bacterial challenge. 2 weeks following inoculation, animals were anaesthetised, euthanised and implants and tissues harvested for bacterial enumeration. To assess host participation in implant protection, additional animals were not inoculated but euthanised at 1, 3 or 7 d and the host cells adhered to the implant were evaluated by flow cytometry and microscopy. As time between implant placement and bacterial challenge increased, infection rate and bioburden decreased. All implants had measurable bioburden when challenged at day 1, but only two implants had recoverable bacteria when inoculated 7 d after implant placement. This protection against infection corresponded to a shift in host cell population surrounding the implant. Initially, cells present were primarily non-differentiated stem cells, such as bone marrow mesenchymal stem cells, or immature haematopoietic cells. At day 7, there was a mature monocyte/macrophage population. The present study illustrated a direct relationship between host immune cell attachment and decrease in bacterial colonisation, providing guidance for antimicrobial release devices to protect orthopaedic implants against bacterial colonisation.

Pharmacological Mitigation of Fibrosis in a Porcine Model of Volumetric Muscle Loss Injury

Volumetric muscle loss (VML) resulting from extremity trauma presents functional deficits and fibrosis, ultimately manifesting disability. The extensive fibrotic accumulation is expected to interfere with neural, trophic, vascular, and mechanical connectivity of any possible regenerative medicine approaches. Our objective was to quantify the muscle properties and stiffness following injury and investigate if the fibrotic deposition could be mitigated using an antifibrotic agent; we hypothesized that antifibrotic treatment would prevent the overwhelming fibrotic response. Yorkshire Cross pigs (n = 10) were randomized to sham or a nontreated ∼20% VML injury. Immediately following surgery, injured animals were further randomized to nintedanib (Ofev; 300 mg/day) or no treatment for 30 days. Longitudinal analysis of muscle function via peroneal nerve stimulation, compartment volume, and quantitative muscle stiffness using shearwave elastography were conducted. Terminally comprehensive histopathologic, biochemical, and genetic investigations were conducted on the skeletal muscle and fibrosis. Through 4 weeks post-VML, nontreated muscles presented a significant deficit (23%) in maximal torque compared to the sham operated (p < 0.01). The stiffness in the VML defect area increased significantly (7-fold) in the VML-nontreated leg than the VML antifibrotic-treated legs by 4 weeks postinjury, which was coupled with the nontreated muscle having ∼40% more hydroxyproline per mg of tissue than those receiving antifibrotic treatment (p = 0.01). This work indicates that VML injury progressively induces fibrosis and muscle stiffness. Antifibrotic treatment can mitigate the pathologic development of fibrosis. Future work should evaluate optimal timing and duration of treatments combined with regenerative medicine approaches in efforts to improve function. Impact statement This work primarily evaluated the effect of a clinically available antifibrotic therapy (nintedanib) on the development of fibrosis after volumetric muscle loss (VML) injury in a large animal model. As a primary outcome measure of fibrosis, skeletal muscle stiffness was repeatedly measured in vivo and noninvasively using a quantitative ultrasound device with shearwave elastography capability. The most salient finding of the study is that the antifibrotic nintedanib significantly reduced the development of VML injury-induced fibrous tissue deposition and stiffness.

Nanocrystalline hydroxyapatite-poly(thioketal urethane) nanocomposites stimulate a combined intramembranous and endochondral ossification response in rabbits

Resorbable bone cements are replaced by bone osteoclastic resorption and osteoblastic new bone formation near the periphery. However, the ideal bone cement would be replaced by new bone through processes similar to fracture repair, which occurs through a variable combination of endochondral and intramembranous ossification. In this study, nanocrystalline hydroxyapatite (nHA)-poly(thioketal urethane) (PTKUR) cements were implanted in femoral defects in New Zealand White rabbits to evaluate ossification at 4, 12, and 18 months. Four formulations were tested: an injectable, flowable cement and three moldable putties with varying ratios of calcium phosphate to sucrose granules. New bone formation and resorption of the cement by osteoclasts occurred near the periphery. Stevenel's Blue and Safranin O staining revealed infiltration of chondrocytes into the cements and ossification of the cartilaginous intermediate. These findings suggest that nHA-PTKUR cements support combined intramembranous and endochondral ossification, resulting in enhanced osseointegration of the cement that could potentially improve patient outcomes.

Duration of extremity tourniquet application profoundly impacts soft-tissue antibiotic exposure in a rat model of ischemia-reperfusion injury

INTRODUCTION

Extremity tourniquet (TNK) application is an effective means of achieving compressible hemorrhage control in the emergency prehospital and clinical trauma setting. Modern United States military medical doctrine recommends TNK use to prevent lethal hemorrhage from extremity injury, followed by systemic prophylactic antibiotics to prevent wound infection. Because tissue pharmacokinetics of prophylactic antimicrobials during and after TNK-induced limb ischemia are largely unknown, this study was conducted to empirically determine the relationship between TNK application time and soft tissue antibiotic exposure in order to guide medical personnel in the management of extremity trauma.

MATERIALS AND METHODS

Hind limbs of anesthetized male Sprague Dawley rats were exsanguinated, and ischemia maintained by a pneumatic cuff placed at the level of the mid femur on one limb; the non-ischemic contralateral limb served as comparison tissue. Systemic prophylactic antibiotics (cefazolin, moxifloxacin, or ertapenem) were administered intravenously before or after TNK release following 2 or 4 h of ischemia with subsequent re-dosing every 12 h for 3 days. Free antibiotic in the interstitial fluid (ISF) of the tibialis anterior muscle of both hind limbs was recovered via microdialysis during ischemia and over three periods during reperfusion: immediately following TNK release, at 24 h post TNK release, and at 72 h post TNK release. Plasma and ISF free drug concentrations were determined by high-performance liquid chromatography.

RESULTS

Tourniquet application prevented delivery of prophylactic antibiotics into distal soft tissue for the duration of ischemia, and caused a profound reduction in skeletal muscle drug exposure for up to 72 h following TNK release. A progressive decline in tissue antibiotic exposure during reperfusion was observed as TNK times increased from 2 h to 4 h. The timing and severity of reduced drug distribution in post-ischemic skeletal muscle varied substantially among the three antibiotic classes evaluated.

CONCLUSIONS

Prolonged tourniquet application can significantly reduce distribution of prophylactic antibiotics into soft tissue during and after ischemia, potentially impairing prophylaxis of extremity wound infection. Our findings support the examination of alternative approaches to wound infection prophylaxis under conditions of delayed casualty evacuation when occlusive hemorrhage control measures are utilized.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.

Mechanisms by which hydrogen sulfide attenuates muscle function following ischemia-reperfusion injury: effects on Akt signaling, mitochondrial function, and apoptosis

Ischemia–reperfusion injury is caused by a period of ischemia followed by massive blood flow into a tissue that had experienced restricted blood flow. The severity of the injury is dependent on the time the tissue was restricted from blood flow, becoming more severe after longer ischemia times. This can lead to many complications such as tissue necrosis, cellular apoptosis, inflammation, metabolic and mitochondrial dysfunction, and even organ failure. One of the emerging therapies to combat ischemic reperfusion injury complications is hydrogen sulfide, which is a gasotransmitter that diffuses across cell membranes to exert effects on various signaling pathways regulating cell survival such as Akt, mitochondrial activity, and apoptosis. Although commonly thought of as a toxic gas, low concentrations of hydrogen sulfide have been shown to be beneficial in promoting tissue survival post-ischemia, and modulate a wide variety of cellular responses. This review will detail the mechanisms of hydrogen sulfide in affecting the Akt signaling pathway, mitochondrial function, and apoptosis, particularly in regards to ischemic reperfusion injury in muscle tissue. It will conclude with potential clinical applications of hydrogen sulfide, combinations with other therapies, and perspectives for future studies.

Poly(Thioketal Urethane) Autograft Extenders in an Intertransverse Process Model of Bone Formation

IMPACT STATEMENT

The development of autograft extenders is a significant clinical need in bone tissue engineering. We report new settable poly(thioketal urethane)-based autograft extenders that have bone-like mechanical properties and handling properties comparable to calcium phosphate bone cements. These settable autograft extenders remodeled to form new bone in a biologically stringent intertransverse process model of bone formation that does not heal when treated with calcium phosphate bone void fillers or cements alone. This is the first study to report settable autograft extenders with bone-like strength and handling properties comparable to ceramic bone cements, which have the potential to improve treatment of bone fractures and other orthopedic conditions.

Topical rifampin powder for orthopedic trauma part I: Rifampin powder reduces recalcitrant infection in a delayed treatment musculoskeletal trauma model

Open fractures become infected despite meticulous debridement and care. Locally applied antibiotics, commonly embedded in polymethylmethacrylate, deliver high doses of drug directly to the fracture site. Direct application of antibiotic powder, which is being applied prophylactically in spine surgery, is a recent interest in the trauma sector, where bacterial biofilms are more prevalent. Traditional antibiotics, such as vancomycin, are poor performers against bacterial biofilms thus are ineffective in delayed treatment. Rifampin is an effective eradicator of Staphylococcal biofilms. Here, a rat model of musculoskeletal trauma was used to evaluate the utility of locally applied rifampin powder for reducing established orthopedic Staphylococcal infections in a delayed treatment scenario that previously indicated the limited use of local vancomycin. By applying rifampin powder directly to the contaminated segmental defect, the number of bacteria, as well as clinical indications of infection, were significantly reduced compared to vancomycin and daptomycin. Considering the Infectious Disease Society of America's recommendation to use rifampin in combination with another antibiotic to reduce the onset of rifampin resistance, rifampin powder was also applied in combination with vancomycin or daptomycin with insignificant changes in eradication performance. No indications of rifampin resistance were identified. Clinical Significance: The use of locally applied rifampin is a promising therapy for mature and tolerant musculoskeletal infections. Published 2018. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:3136-3141, 2018.

Topical rifampin powder for orthopaedic trauma part II: Topical rifampin allows for spontaneous bone healing in sterile and contaminated wounds

Infectious complications can reduce fracture healing rate. Broad spectrum antibiotics are commonly administered to prevent and treat musculoskeletal infections. Local antibiotics are applied to the wound site to increase therapeutic concentrations without increasing systemic toxicity, however, may hinder local tissue recovery. Rifampin has been shown to eradicate mature Staphylococcal biofilms and its use proven for treating musculoskeletal infections. In this study, a spontaneously healing defect model in a rat was used to investigate the impact rifampin powder has on endogenous bone healing in both a sterile and contaminated wound. No significant differences were identified in bone volume fraction via microcomputed tomography, radiological scoring, or histology between an empty defect and animals that received vancomycin or rifampin powder in a sterile wound. When applied to a contaminated musculoskeletal wound, the rifampin powder had significantly greater bone formation compared to the control, as measured by microcomputed tomography, plain radiology, and histology. In addition, the animals treated with rifampin powder had reduced bacteria, reduced white blood cell count and reduced number of clinical indications of infection. Interestingly, while the vancomycin group still displayed signs of infection via quantitative microbiology, plain radiology, and histology, there was significant bone formation within the defect and reduction of systemic signs of infection. We demonstrated that the use of rifampin powder allows bone to heal in both a sterile and contaminated model of musculoskeletal infection. To our knowledge, this is the first time the direct impact of local antibiotics on bone healing has been investigated. Published 2018. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:3142-3150, 2018.

Settable polymer/ceramic composite bone grafts stabilize weight-bearing tibial plateau slot defects and integrate with host bone in an ovine model

Bone fractures at weight-bearing sites are challenging to treat due to the difficulty in maintaining articular congruency. An ideal biomaterial for fracture repair near articulating joints sets rapidly after implantation, stabilizes the fracture with minimal rigid implants, stimulates new bone formation, and remodels at a rate that maintains osseous integrity. Consequently, the design of biomaterials that mechanically stabilize fractures while remodeling to form new bone is an unmet challenge in bone tissue engineering. In this study, we investigated remodeling of resorbable bone cements in a stringent model of mechanically loaded tibial plateau defects in sheep. Nanocrystalline hydroxyapatite-poly(ester urethane) (nHA-PEUR) hybrid polymers were augmented with either ceramic granules (85% β-tricalcium phosphate/15% hydroxyapatite, CG) or a blend of CG and bioactive glass (BG) particles to form a settable bone cement. The initial compressive strength and fatigue properties of the cements were comparable to those of non-resorbable poly(methyl methacrylate) bone cement. In animals that tolerated the initial few weeks of early weight-bearing, CG/nHA-PEUR cements mechanically stabilized the tibial plateau defects and remodeled to form new bone at 16 weeks. In contrast, cements incorporating BG particles resorbed with fibrous tissue filling the defect. Furthermore, CG/nHA-PEUR cements remodeled significantly faster at the full weight-bearing tibial plateau site compared to the mechanically protected femoral condyle site in the same animal. These findings are the first to report a settable bone cement that remodels to form new bone while providing mechanical stability in a stringent large animal model of weight-bearing bone defects near an articulating joint.

Rapid degradation and non-selectivity of Dakin's solution prevents effectiveness in contaminated musculoskeletal wound models

BACKGROUND

Dakin's solution (buffered sodium hypochlorite) has been used as a topical adjunct for the treatment of invasive fungal infections in trauma patients. Prudent use of Dakin's solution (DS) for complex musculoskeletal wound management implies balancing antimicrobial efficacy and human tissue toxicity, but little empirical evidence exists to inform clinical practice. To identify potentially efficacious DS concentrations and application methods, we conducted two animal studies to evaluate the ability of DS to reduce bacterial burden in small and large animal models of contaminated musculoskeletal wounds.

METHODS

An established rat (Rattus norvegicus) contaminated femoral defect model was employed to evaluate the antimicrobial efficacy of DS as a topical adjunctive treatment for Staphylococcus aureus infection. A range of clinically-relevant DS concentrations (0.00025%-0.125%) were tested, both with and without periodic replenishment during treatment. Next, an established goat (Capra hircus) musculoskeletal wound model, consisting of a Pseudomonas aeruginosa contaminated proximal tibia cortical defect, muscle crush, and thermal injury, was utilized to evaluate the antimicrobial efficacy of dilute DS (0.0025% and 0.025%) as a surgical irrigant solution. In situ reactive chlorine concentrations were monitored throughout each treatment using an automated iodometric titration approach.

RESULTS

In a rat wound model, DS treatment did not significantly reduce S. aureus bioburden after 14 days as compared to saline control. Two treatment groups (0.01% single application and 0.025% multiple application) exhibited significantly higher bacterial burden than control. In a goat musculoskeletal wound model, neither 0.0025% nor 0.025% DS significantly altered P. aeruginosa bioburden immediately following treatment or at 48 h post-treatment. Overall, DS applied to exposed soft tissue exhibited rapid degradation, e.g., 0.125% DS degraded 32% after 5 s progressing to 86% degradation after 15 min following single application.

CONCLUSIONS

We did not observe evidence of a therapeutic benefit following Dakin's solution treatment for any tested concentration or application method in two contaminated musculoskeletal wound models. Despite confirmation of robust bactericidal activity in vitro, our findings suggest DS at current clinically-used concentrations does not kill tissue surface-attached bacteria, nor does it necessarily cause host tissue toxicity that exacerbates infection in the setting of complex musculoskeletal injury.

Infection Precedes Heterotopic Ossification in Combat Wounded

Heterotopic ossification is the formation of ossified bone in soft tissue, particularly after soft tissue trauma. Heterotopic ossification is known cause of pain, prosthetic/orthotic malfit, and reoperation following combat extremity injury. The purpose of this research was to examine injury and treatment characteristics that are associated with heterotopic ossification in a broader population of deployment-injured subjects. The Department of Defense Trauma Registry and Military Orthopaedic Trauma Registry was queried for a sample of deployment-injured subjects and the complication of heterotopic ossification. Heterotopic ossification was identified in 15% of subjects following 5% of all injuries. Symptoms attributed to the heterotopic bone were present in 40% of subjects with diagnosed with heterotopic ossification. Heterotopic ossification was not associated with injury severity or aggressiveness of open wound treatment. However, infection was the only positive predictor of heterotopic ossification resulting in two-times greater odds of heterotopic bone formation. This finding is consistent with prior research suggesting that heterotopic ossification requires persistent inflammation to be present in at-risk soft tissue. Among all wounds sustained during deployment injury, heterotopic may not be abundantly common; however, the risk may be further minimized by focused infection control.

Risk of Obtaining Routine Cultures During Presumed Aseptic Orthopaedic Procedures

Treating patients with antibiotics that are selected based on routine cultures obtained from presumed aseptic orthopaedic procedures may lead to an increased risk of antibiotic-related complications without reducing the rate of late deep infection. Routine cultures obtained from 60 of 169 procedures resulted in 23 (38.3%) positive and 37 (61.7%) negative results. Twenty-two patients (13.5%) developed late infections. Seven of 14 patients with positive cultures, who were treated with antibiotics, developed a late infection, while two of nine patients with routine cultures, who received no antibiotic treatment, developed a late infection. Six of 37 patients with negative cultures and seven of 109 patients with no cultures developed a late infection. In patients who developed late deep infection, the microorganism isolated on routine culture only corresponded to the microorganism causing late infection 55.5% of the time. Of all patients treated with antibiotics, seven (29%) experienced an antibiotic-related complication (p = .01). (Journal of Surgical Orthopaedic Advances 26(4):239-245, 2017).

Current therapies in treatment and prevention of fracture wound biofilms: why a multifaceted approach is essential for resolving persistent infections

Traumatic orthopedic injuries, particularly extremity wounds, are a significant cause of morbidity. Despite prophylactic antibiotic treatment and surgical intervention, persistent infectious complications can and do occur. Persistent bacterial infections are often caused by biofilms, communities of antibiotic tolerant bacteria encased within a matrix. The structural and metabolic differences in this mode of growth make treatment difficult. Herein, we describe both established and novel, experimental treatments targeted at various stages of wound healing that are specifically aimed at reducing and eliminating biofilm bacteria. Importantly, the highly tolerant nature of these bacterial communities suggests that most singular approaches could be circumvented and a multifaceted, combinatorial approach will be the most effective strategy for treating these complicated infections.

Chlorhexidine-releasing implant coating on intramedullary nail reduces infection in a rat model

The use of internal intramedullary nails for long bone fracture fixation is a common practice among surgeons. Bacteria naturally attach to these devices, increasing the risk for wound infection, which can result in non- or malunion, additional surgical procedures and extended hospital stays. Intramedullary nail surface properties can be modified to reduce bacterial colonisation and potentially infectious complications. In the current study, a coating combining a non-fouling property with leaching chlorhexidine for orthopaedic implantation was tested. Coating stability and chlorhexidine release were evaluated in vitro. Using a rat model of intramedullary fixation and infection, the effect of the coating on microbial colonisation and fracture healing was evaluated in vivo by quantitative microbiology, micro-computed tomography, plain radiography, three-point bending and/or histology. Low dose systemic cefazolin was administered to increase the similarities to clinical practice, without overshadowing the effect of the anti-infective coating. When introduced into a contaminated wound, the non-fouling chlorhexidine-coated implant reduced the overall bacteria colonisation within the bone and on the implant, reduced the osteolysis and increased the radiographic union, confirming its potential for reducing complications in wounds at high risk of infection. However, when implanted into a sterile wound, non-union increased. Further studies are required to best optimise the anti-microbial effectiveness, while not sacrificing fracture union.

Local control of polymicrobial infections via a dual antibiotic delivery system

BACKGROUND

Contaminated traumatic open orthopedic wounds are frequently complicated by polymicrobial contamination and infection. In high-risk wounds, the standard of care comprises debridement and irrigation combined with antibiotics which can be applied directly or combined with systemic antibiotics. Recently, bioabsorbable chitosan sponges have been shown to be an effective single-agent delivery device for local antibiotics with and without negative pressure wound therapy (NPWT). Severely contaminated orthopedic wounds, however, are often complicated by polymicrobial infections, necessitating multiple antibiotic agents. As such, the purpose of this study was to determine if a chitosan sponge would provide a suitable delivery vehicle for multiple antibiotics for the treatment of a polymicrobial infection in a large animal polytraumatic extremity wound model.

METHODS

A complex polytraumatic extremity wound was created in 11 adult male Boer goats. Each wound was contaminated with a bioluminescent strain of S. aureus (1 ml of 10⁸ colony forming units/ml) and of P. aeruginosa (1 ml of 10⁸ CFU/ml) which are genetically engineered to allow quantification with a photon-counting camera. Six hours following initial wound creation and contamination, wounds were debrided and irrigated with low-pressure normal saline. The animals were randomized into one of two treatments: wet-to-dry dressings alone or a commercially available chitosan sponge loaded with 1 g vancomycin and 1.2 g of tobramycin. Each animal was then recovered and reimaged 48 h later for total bacteria content; tissue samples were taken from the wound bed to determine relative bacterial colonization.

RESULTS

All animals in the chitosan sponge group saw significant reductions in overall bacterial load of S. aureus and P. aeruginosa (p = 0.001). The bioluminescence was also significantly reduced compared to the wet-to-dry dressing group (p = 0.0001). Furthermore, whereas the antibiotic sponge group displayed near complete eradication of bacteria, the wounds treated with the wet-to-dry dressings alone displayed a significant 2-log increase in total bacteria at 48 h p = 0.0001). S. aureus was the predominant species found in the wounds, comprising 95 and 99% of all bacteria found in the chitosan sponge and wet-to-dry, respectively.

CONCLUSION

Dual antimicrobial therapy loaded in a chitosan sponge is an effective way to reduce polymicrobial infections traumatic extremity wound.

Military and Civilian Collaboration: The Power of Numbers

The purpose of this study was to compare the number and types of extremity injuries treated at civilian trauma centers (CIV CENs) versus military treatment facilities (MTFs) participating in the Major Extremity Trauma Research Consortium (METRC) and to investigate the potential benefits of a clinical research network that includes both civilian trauma centers and MTFs. Two analyses were performed. First, registry data collected on all surgically treated fractures at four core MTFs and 21 CIV CENs over one year were compared. Second, actual numbers and distribution of patients by type of injury enrolled in three METRC studies were compared. While MTFs demonstrated higher percentages of severe injuries including open fractures, traumatic amputations, vascular injuries, contamination, and injuries with bone, muscle, and skin loss when compared to CIV CENS, the CIV CENs treated a substantially higher number and, more importantly, enrolled patients in almost all categories. Comparison of service members to civilians was challenged by several differences between the two patient populations including mechanism of injury, the medical care environment, and confounding factors such as age, social setting and co-morbidities. Despite these limitations, in times without active military conflict, clinical trials will likely rely on civilian trauma centers for patient enrollment; only when numbers are pooled across a large number of centers can requisite sample sizes be met. These data demonstrate the benefits of maintaining a military-civilian partnership to address the major gaps in research defined by the Military.

Antibiotic-loaded bone graft for reduction of surgical site infection in spinal fusion

BACKGROUND CONTEXT

Infections remain a leading complication associated with spinal arthrodesis, regardless of the use of prophylactic antibiotics and improved surgical techniques, with incidence of infection as high as 8.2%. Infection prolongs antibiotic usage, increases hospital time, and inevitably inflates overall treatment costs. Local antibiotics, such as vancomycin, have been used in combination with fusion materials over the past decade to decrease infection risk. An ideal graft material would serve a dual role: encouraging vertebral fusion while reducing the incidence of infection.

PURPOSE

The objective of this study was to thoroughly evaluate the use of a vancomycin-loaded demineralized bone matrix (vDBM) for fusion capability while reducing the incidence of surgical site infection.

STUDY DESIGN

Antimicrobial efficacy and spinal fusion were evaluated using a preclinical rabbit model of posterolateral fusion.

MATERIALS AND METHODS

Vancomycin-loaded demineralized bone matrix was prepared and evaluated for in vitro release kinetics and bacterial inhibition. In vivo antibacterial efficacy and fusion capability were performed using a model of posterolateral fusion in a rabbit. First, 10 New Zealand white rabbits underwent a bilateral posterolateral fusion procedure, were inoculated with Staphylococcus aureus, and were treated with either demineralized bone matrix (DBM) or vDBM. Fourteen days after the procedure, the animals were anesthetized and euthanized, and the transverse process was harvested and enumerated for bacterial quantification. Concurrently, 21 New Zealand white rabbits underwent the same procedure and were euthanized 8 weeks after surgery and were evaluated for fusion by manual palpation and radiographic scoring. In addition, two groups of six animals received the DBM or vDBM material as described, but the graft was combined with equal volumes of milled harvest iliac crest bone graft (ICBG). Eight weeks after surgery, these animals were euthanized and also evaluated for fusion by manual palpation and radiographic scoring.

RESULTS

Vancomycin continued to be released from the vDBM over the course of 6 days while maintaining sufficient eluate concentrations to maintain a zone of inhibition similar or larger than a vancomycin control. In vivo, vDBM significantly reduced the amount of bacteria within the fusion site compared with DBM, with a 4-log decrease in bacterial bioburden. The use of vDBM, however,showed a decrease in the fusion rate compared with DBM when used in a sterile wound. In a S. aureus-contaminated wound, both the DBM and the vDBM showed decreased fusion rates.Considering DBM materials were most commonly used as autograft extenders, additional animals received either DBM plus ICBG in a sterile wound or vDBM plus ICBG in a contaminated wound. Both groups had similar fusion rates and similar fusion volumes after 8 weeks in vivo.

CONCLUSIONS

Whereas vDBM reduced the overall bioburden within a contaminated surgical site of posterolateral fusion, the addition of the vancomycin to the DBM reduced the fusion capability of the DBM graft. The addition of ICBG to vDBM restored the fusion capability of the graft while reducing the overall infection.

Tacrolimus as an adjunct to autologous minced muscle grafts for the repair of a volumetric muscle loss injury

BACKGROUND

Volumetric muscle loss (VML) following extremity orthopaedic trauma or surgery results in chronic functional deficits and disability. A current translational approach to address the devastating functional limitations due to VML injury is the use of an autologous minced muscle graft (~1 mm3 pieces of muscle tissue) replacement into the injured defect area, although limitations related to donor site morbidity are still unaddressed. This study was designed to explore adjunct pharmacological immunomodulation to enhance graft efficacy and promote muscle function following VML injury, and thereby reduce the amount of donor tissue required.

FINDINGS

Using a validated VML porcine injury model in which 20% of the muscle volume was surgically removed, this study examined muscle function over 3 months post-VML injury. In vivo isometric torque of the peroneus teritus (PT) muscle was not different before surgery among sham, non-repaired, non-repaired with tacrolimus, graft-repaired, and graft-repaired with tacrolimus VML groups. Bi-weekly torque analysis of the VML injured musculature presented a significant strength deficit of ~26% compared to pre-injury in the non-repaired, non-repaired with tacrolimus, and graft-repaired groups. Comparatively, the strength deficit in the graft-repair with systemic tacrolimus was marginally improved (~19%; p = 0.056). Both of the minced graft repaired groups presented a greater proportion of muscle tissue in full-thickness histology specimen.

CONCLUSIONS

We demonstrate that adjunctive use of tacrolimus with an ~50% minced muscle graft replacement resulted in modest improvements in muscle function 3 months after injury and repair, but the magnitude of improvement is not expected to elicit clinically meaningful functional improvements.