Post-traumatic osteoarthritis (PTOA) develops secondary to a joint injury and accounts for 12 % of all osteoarthritis. These injuries, often of the lower extremity joints, occur due to trauma or accidents related to athletic or military activities. They primarily affect younger individuals although PTOA can occur across the spectrum of age. Pain and functional disability caused by PTOA confer a heavy economic toll on patients, in addition to detrimentally affecting their quality of life. Both high energy injuries that cause articular surface fracture with or without subchondral bone disruption and low-energy injuries involving joint dislocations or ligamentous injury cause PTOA, albeit through different mechanisms. Regardless, chondrocyte death, mitochondrial dysfunction, reactive oxygen species production, subchondral bone remodeling, inflammation and cytokine release in the cartilage and synovium play integral roles in the pathogenesis of PTOA. Evolving surgical methods are focused on stabilizing articular surface and joint structure congruity. However, to date there are no disease modifying medical therapies against PTOA. Increased recent understanding of the pathogenesis of the subchondral bone and synovial inflammation as well as that of chondrocyte mitochondrial dysfunction and apoptosis have led to the investigation of new therapeutics targeting these mechanisms to prevent or delay PTOA. This review discusses new advances in our understanding of cellular mechanisms underlying PTOA, and therapeutic approaches that are potentially effective in reducing the self-propagating cycle of subchondral bone alterations, inflammation, and cartilage degradation. Within this context, we focus therapeutic options involving anti-inflammatory and anti-apoptotic candidates that could prevent PTOA.

Nonunion describes bone fractures that fail to heal, resulting in the fracture callus failing to fully ossify or, in atrophic cases, not forming altogether. Fracture healing is regulated, in part, by the balance of proinflammatory and anti‐inflammatory processes occurring within the bone marrow and surface cell populations. We sought to further understand the role of osteoimmunology (i.e., study of the close relationship between the immune system and bone) by examining immune cell gene expression via single‐cell RNA sequencing of intramedullary canal tissue obtained from human patients with femoral nonunions. Intramedullary canal tissue samples obtained by reaming were collected at the time of surgical repair for femur fracture nonunion (n = 5) or from native bone controls when harvesting autologous bone graft (n = 4). Cells within the samples were isolated and analyzed using the Chromium Single‐Cell System (10x Genomics Inc.) and Illumina sequencers. Twenty‐three distinct cell clusters were identified, with higher cell proportions in the nonunion samples for monocytes and CD14 + dendritic cells (DCs), and lower proportions of T cells, myelocytes, and promyelocytes in nonunion samples. Gene expression differences were identified in each of the cell clusters from cell types associated with osteoimmunology, including CD14 + DC, monocytes, T cells, promyelocytes, and myelocytes. These results provide human‐derived gene profiles that can further our understanding of pathways that may be a cause or a consequence of nonunion, providing the clinical rationale to focus on specific components of osteoimmunology. Clinical significance: The novel single‐cell approach may lead to clinically relevant diagnostic biomarkers during earlier stages of nonunion development and/or investigation into therapeutic options.

Background: Prompt administration of antibiotics is a critical component of open fracture treatment. Traditional antibiotic recommendations have been a first-generation cephalosporin for Gustilo Type-I and Type-II open fractures, with the addition of an aminoglycoside for Type-III fractures and penicillin for soil contamination. However, concerns over changing bacterial patterns and the side effects of aminoglycosides have led to interest in other regimens. The purpose of the present study was to describe the adherence to current prophylactic antibiotic guidelines. Methods: We evaluated the antibiotic-prescribing practices of 24 centers in the U.S. and Canada that were participating in 2 randomized controlled trials of skin-preparation solutions for open fractures. A total of 1,234 patients were evaluated. Results: All patients received antibiotics on the day of admission. The most commonly prescribed antibiotic regimen was cefazolin monotherapy (53.6%). Among patients with Type-I and Type-II fractures, there was 61.1% compliance with cefazolin monotherapy. In contrast, only 17.2% of patients with Type-III fractures received the recommended cefazolin and aminoglycoside therapy, with an additional 6.7% receiving piperacillin/tazobactam. Conclusions: There is moderate adherence to the traditional antibiotic treatment guidelines for Gustilo Type-I and Type-II fractures and low adherence for Type-III fractures. Given the divergence between current practice patterns and prior recommendations, high-quality studies are needed to determine the most appropriate prophylactic protocol.

Background: Biofilms protect bacteria from the host immune system and many antibiotics, making the treatment of orthopaedic infections difficult. Halicin, a recently discovered antibiotic, has potent activity against nonorthopaedic infections in mice and the planktonic, free-living forms of many bacterial species, including Staphylococcus aureus, a common cause of orthopaedic infections. Importantly, halicin did not induce resistance in vitro and was effective against drug-resistant bacteria and proliferating and quiescent bacteria. Quiescence is an important cause of antibiotic tolerance in biofilms. However, whether halicin acts on biofilms has not been tested. Questions/purposes: (1) Does halicin reduce the viability of S. aureus in less mature and more mature biofilms as it does in planktonic cultures? (2) How do the relative effects of halicin on S. aureus biofilms and planktonic cultures compare with those of conventional antibiotics (tobramycin, cefazolin, vancomycin, or rifampicin) that are commonly used in clinical orthopaedic infections? Methods: To measure minimal biofilm eradication concentrations (MBECs) with less mature 3-day and more mature 7-day biofilms, we used 96-well peg plates that provided high throughput and excellent reproducibility. After S. aureus-Xen36 biofilm formation, planktonic bacteria were removed from the cultures, and the biofilms were exposed to various concentrations of halicin, tobramycin, cefazolin, vancomycin, or rifampicin for 20 hours. Biofilm viability was determined by measuring resazurin reduction or by counting colony-forming units after sonication. To determine effects of halicin and the conventional antibiotics on biofilm viability, we defined MBEC₇₅ as the lowest concentration that decreased viability by 75% or more. To determine effects on bacterial viability in planktonic cultures, minimum inhibitory concentrations (MICs) were determined with the broth dilution method. Each result was measured in four to 10 independent experiments. Results: We found no differences between halicin’s effectiveness against planktonic S. aureus and 3-day biofilms (MIC and MBEC₇₅ for 3-day biofilms was 25 μM [interquartile range 25 to 25 and 25 to 25, respectively]; p > 0.99). Halicin was eightfold less effective against more mature 7-day biofilms (MBEC₇₅ = 200 μM [100 to 200]; p < 0.001). Similarly, tobramycin was equally effective against planktonic culture and 3-day biofilms (MIC and MBEC₇₅ for 3-day biofilms was 20 μM [20 to 20 and 10 to 20, respectively]; p > 0.99). Tobramycin’s MBEC₇₅ against more mature 7-day biofilms was 320 μM (320 to 480), which is 16-fold greater than its planktonic MIC (p = 0.03). In contrast, the MBEC₇₅ for cefazolin, vancomycin, and rifampicin against more mature 7-day biofilms were more than 1000-fold (> 1000; p < 0.001), 500-fold (500 to 875; p < 0.001), and 3125-fold (3125 to 5469; p = 0.004) greater than their planktonic MICs, respectively, consistent with those antibiotics’ relative inactivity against biofilms. Conclusion: Halicin was as effective against S. aureus in less mature 3-day biofilms as those in planktonic cultures, but eightfold higher concentrations were needed for more mature 7-day biofilms. Tobramycin, an antibiotic whose effectiveness depends on biofilm maturity, was also as effective against S. aureus in less mature 3-day biofilms as those in planktonic cultures, but 16-fold higher concentrations were needed for more mature 7-day biofilms. In contrast, cefazolin, vancomycin, and rifampicin were substantially less active against both less and more mature biofilms than against planktonic cultures. Clinical Relevance: Halicin is a promising antibiotic that may be effective against S. aureus osteomyelitis and infections on orthopaedic implants. Future studies should assess the translational value of halicin by testing its effects in animal models of orthopaedic infections; on the biofilms of other bacterial species, including multidrug-resistant bacteria; and in combination therapy with conventional antibiotics.

Fracture non-union is a significant orthopaedic problem affecting a substantial number of patients yearly. Treatment of nonunions is devastating to patients and costly to the healthcare system. Unfortunately, the diagnosis of non-union is typically made in a reactionary fashion by an orthopaedic surgeon based on clinical assessment and radiographic features several months into treatment. For this reason, investigators have been trying to develop prediction algorithms; however, these have relied on population-based approaches and lack the predictive capability necessary to make individual treatment decisions. There is also a growing body of literature focussed on identifying blood biomarkers that are associated with non-union. This review describes the research that has been done in this area. Further studies of patient-centered, precision medicine approaches will likely improve fracture non-union diagnostic/prognostic capabilities.

Bony union is a primary predictor of outcome after surgical fixation of long bone fractures. Murine models offer many advantages in assessing bony healing due to their low costs and small size. However, current fracture recovery investigations in mice frequently rely on animal sacrifice and costly analyses. The modified Radiographic Union Score for Tibia fractures (mRUST) scoring system is a validated metric for evaluating bony healing in humans utilizing plain radiographs, which are relatively inexpensive and do not require animal sacrifice. However, its use has not been well established in murine models. The aim of this study was to characterize the longitudinal course of mRUST and compare mRUST to other conventional murine fracture analyses. 158 mice underwent surgically created midshaft femur fractures. Mice were evaluated after fracture creation and at 7, 10, 14, 17, 21, 24, 28, 35, and 42 days post-injury. mRUST scoring of plain radiographs was performed by three orthopaedic surgeons in a randomized, blinded fashion. Interrater correlations were calculated. Micro-computed tomography (μCT) was analyzed for tissue mineral density (TMD), total callus volume (TV), bone volume (BV), trabecular thickness, trabecular number, and trabecular separation. Histomorphometry measures of total callus area, cartilage area, fibrous tissue area, and bone area were performed in a blinded fashion. Ultimate torque, stiffness, toughness, and twist to failure were calculated from torque-twist curves. A sigmoidal log-logistic curve fit was generated for mRUST scores over time which shows mRUST scores of 4 to 6 at 7 days post-injury that improve to plateaus of 14 to 16 by 24 days post-injury. mRUST interrater correlations at each timepoint ranged from 0.51 to 0.86, indicating substantial agreement. mRUST scores correlated well with biomechanical, histomorphometry, and μCT parameters, such as ultimate torque (r=0.46, p<0.0001), manual stiffness (r=0.51, p<0.0001), bone percentage based on histomorphometry (r=0.86, p<0.0001), cartilage percentage (r=-0.87, p<0.0001), tissue mineral density (r=0.83, p<0.0001), BV/TV based on μCT (r=0.65, p<0.0001), and trabecular thickness (r=0.78, p<0.0001), among others. These data demonstrate that mRUST is reliable, trends temporally, and correlates to standard measures of murine fracture healing. Compared to other measures, mRUST is more cost-effective and non-terminal. The mRUST log-logistic curve could be used to characterize differences in fracture healing trajectory between experimental groups, enabling high-throughput analysis.