Posttraumatic arthritis is one of the most frequent causes of disability following joint trauma. The objective of this study was to develop a model of a closed articular fracture in the mouse knee joint to quantify the temporal sequence of joint degeneration in a model of posttraumatic arthritis. Closed intraarticular fractures were created in the tibial plateau of adult mice (C57BL/6) using a computer-controlled materials testing system and a custom-built indenter tip. Tibial plateau fractures were classified and imaged over time using high-resolution digital radiography. Animals were sacrificed at 2, 4, 8, and 50 weeks following fracture, and the experimental and contralateral control limbs were harvested for histology and micro-computed tomography (microCT) analysis. By radiographic analysis, tibial plateau fractures closely resembled clinical fractures. More complex and comminuted fractures correlated to significantly higher fracture energies. Histologic analysis demonstrated progressive joint degeneration as measured by a modified Mankin scale, with fibrillation and loss of proteoglycan in the articular cartilage. Subchondral bone thickening was also observed in experimental joints. The induction of a closed intraarticular fracture of the mouse tibial plateau generated a reproducible and clinically relevant joint injury that progressed to osteoarthritis-like changes by histologic and microCT evaluations. The ability to induce joint degeneration without an osteotomy or open arthrotomy provides a valuable new model for studying the natural sequelae of posttraumatic arthritis. Notably, the use of a murine model will facilitate the use of genetically modified animals for the investigation of specific genes implicated in the pathology of posttraumatic arthritis. ß

OBJECTIVE Post-traumatic arthritis is a frequent cause of disability and occurs most commonly and predictably after articular fracture. The objective of this investigation was to examine the effect of fracture severity on acute joint pathology in a novel murine model of intra-articular fracture. DESIGN Low and high energy articular fractures (n=25 per group) of the tibial plateau were created in adult male C57BL/6 mice. The acute effect of articular fracture severity on synovial inflammation, bone morphology, liberated fracture area, cartilage pathology, chondrocyte viability, and systemic cytokines and biomarkers levels was assessed at 0, 1, 3, 5, and 7 days post-fracture. RESULTS Increasing intra-articular fracture severity was associated with greater acute pathology in the synovium and bone compared to control limbs, including increased global synovitis and reduced periarticular bone density and thickness. Applied fracture energy was significantly correlated with degree of liberated cortical bone surface area, indicating greater comminution. Serum concentrations of hyaluronic acid (HA) were significantly increased one day post-fracture. While articular fracture significantly reduced chondrocyte viability, there was no relationship between fracture severity and chondrocyte viability, cartilage degeneration, or systemic levels of cytokines and biomarkers. CONCLUSIONS This study demonstrates that articular fracture is associated with a loss of chondrocyte viability and increased levels of systemic biomarkers, and that increased intra-articular fracture severity is associated with increased acute joint pathology in a variety of joint tissues, including synovial inflammation, cortical comminution, and bone morphology. Further characterization of the early events following articular fracture could aid in the treatment of post-traumatic arthritis.

IntroductionPost-traumatic arthritis (PTA) is a progressive, degenerative response to joint injury, such as articular fracture. The pro-inflammatory cytokines, interleukin 1(IL-1) and tumor necrosis factor alpha (TNF-α), are acutely elevated following joint injury and remain elevated for prolonged periods post-injury. To investigate the role of local and systemic inflammation in the development of post-traumatic arthritis, we targeted both the initial acute local inflammatory response and a prolonged 4 week systemic inflammatory response by inhibiting IL-1 or TNF-α following articular fracture in the mouse knee.MethodsAnti-cytokine agents, IL-1 receptor antagonist (IL-1Ra) or soluble TNF receptor II (sTNFRII), were administered either locally via an acute intra-articular injection or systemically for a prolonged 4 week period following articular fracture of the knee in C57BL/6 mice. The severity of arthritis was then assessed at 8 weeks post-injury in joint tissues via histology and micro computed tomography, and systemic and local biomarkers were assessed in serum and synovial fluid.ResultsIntra-articular inhibition of IL-1 significantly reduced cartilage degeneration, synovial inflammation, and did not alter bone morphology following articular fracture. However, systemic inhibition of IL-1, and local or systemic inhibition of TNF provided no benefit or conversely led to increased arthritic changes in the joint tissues.ConclusionThese results show that intra-articular IL-1, rather than TNF-α, plays a critical role in the acute inflammatory phase of joint injury and can be inhibited locally to reduce post-traumatic arthritis following a closed articular fracture. Targeted local inhibition of IL-1 following joint injury may represent a novel treatment option for PTA.

Objective. Posttraumatic arthritis is a frequent long-term complication of intraarticular fractures. A model of a closed intraarticular fracture in C57BL/6 mice that progresses to posttraumatic arthritis has been developed. The MRL/MpJ mouse has shown unique regenerative abilities in response to injury. The objective of this study was to determine if the MRL/MpJ mouse is protected from posttraumatic arthritis after intraarticular fractures.Methods. Intraarticular fractures were created in MRL/MpJ mice and C57BL/6 control mice (n ‫؍‬ 16 each). Limbs were analyzed for posttraumatic arthritis 4 and 8 weeks after fracture using microfocal computed tomography bone morphology, subchondral bone thickness evaluation, and histologic evaluation of cartilage degeneration. Serum cytokines and biomarkers were measured after the mice were killed.Results. Intraarticular fractures were successfully created in all 32 mice. In the experimental fractured limbs, C57BL/6 mice had a decrease in bone density, increased subchondral bone thickness, and increased cartilage degeneration compared with normal contralateral control limbs. In the MRL/MpJ mice, no differences in bone density, subchondral bone thickness, or histologic grading of cartilage degeneration were seen between fractured and contralateral control limbs. Cytokine analysis showed lower systemic levels of the proinflammatory cytokine interleukin-1␣ (IL-1␣) and higher levels of the antiinflammatory cytokines IL-4 and IL-10 in the MRL/MpJ mice.Conclusion. This study shows that the MRL/MpJ mouse is relatively protected from posttraumatic arthritis after intraarticular fracture. Further investigation into the mechanism involved in this response will hopefully provide new insight into the pathogenesis, prevention, and treatment of posttraumatic arthritis after intraarticular fracture.

Posttraumatic arthritis (PTA) is one of the most frequent causes of disability after trauma involving weight-bearing joints and is estimated to be responsible for approximately 10% of the 21 million Americans who have osteoarthritis. Despite a number of similarities in the pathology and end-stage disease of PTA with primary osteoarthritis, the mechanisms involved in the onset and progression of joint degeneration after articular fracture are poorly understood. The largest area of study regarding articular fractures and the development of arthritic changes has focused on the role of adequate surgical reduction of the articular surfaces. However, it is now apparent that a number of complex and interacting biomechanical, biochemical, and, possibly, genetic factors contribute to the development of osteoarthritic changes in the joint after joint trauma, ranging from the cell and molecular level to the joint and systemic level. In this paper, we discuss the potential roles of the initial impact and fracture as well as the subsequent alterations in joint loading, biomechanical and metabolic properties of the cartilage, local and systemic inflammatory cytokines, and viability of chondrocytes in the progression of PTA. An improved understanding of the mechanisms involved in the development of PTA will hopefully lead to the improvement of surgical and nonsurgical therapies for this disease.

Objective To examine the relationship between inflammation and post-traumatic arthritis in a murine intra-articular fracture model. Methods Male C57BL/6 and MRL/MpJ “superhealer” mice received tibial plateau fractures using a previously established method. Mice were sacrificed at 0 (within 4 hours), 1, 3, 5, 7, 28 and 56 days after fracture. Synovial tissue samples were taken prior to fracture and at 0, 1, 3, 5 and 7 days to examine gene expression of pro-inflammatory cytokines using RT-PCR. Synovial fluid and serum samples were collected to measure cytokine concentrations using ELISA. Histologic analysis was used to evaluate whole joint synovitis and cartilage degradation, and immunohistochemistry to evaluate the distribution of interleukin-1 in the joint tissues from all time points. Results Compared to the C57BL/6 mice, the MRL/MpJ mice had lower intra-articular and systemic inflammation following joint injury, as evidenced by lower gene expression of TNF-α and IL-1β in synovial tissue, and lower protein levels of IL-1α and IL-1β in the synovial fluid, serum, and joint tissues. Furthermore, MRL/MpJ mice had lower gene expression of macrophage inflammatory proteins (MIPs) and macrophage derived chemokine (MDC/CCL22) in synovial tissue, and reduced acute and late-stage infiltration of synovial macrophages after joint injury. Conclusion C57BL/6 mice exhibited higher levels of inflammation than MRL/MpJ mice, which are protected from post-traumatic arthritis in this model. These data thus suggest an association between joint tissue inflammation and post-traumatic arthritis in mice.

Joint injury dramatically enhances the onset of osteoarthritis (OA) and is responsible for an estimated 12% of OA. Post-traumatic arthritis (PTA) is especially common after intraarticular fracture, and no disease-modifying therapies are currently available. We hypothesized that the delivery of mesenchymal stem cells (MSCs) would prevent PTA by altering the balance of inflammation and regeneration after fracture of the mouse knee. Additionally, we examined the hypothesis that MSCs from the MRL/MpJ (MRL) “superhealer” mouse strain would show increased multilineage and therapeutic potentials as compared to those from C57BL/6 (B6) mice, as MRL mice have shown exceptional in vivo regenerative abilities. A highly purified population of MSCs was prospectively isolated from bone marrow using cell surface markers (CD45−/TER119−/PDGFRα+/Sca-1+). B6 MSCs expanded greater than 100,000 fold in three weeks when cultured at 2% oxygen and displayed greater adipogenic, osteogenic, and chondrogenic differentiation as compared to MRL MSCs. Mice receiving only a control saline injection after fracture demonstrated PTA after 8 weeks, but the delivery of 10,000 B6 or MRL MSCs to the joint prevented the development of PTA. Cytokine levels in serum and synovial fluid were affected by treatment with stem cells, including elevated systemic interleukin-10 at several time points. The delivery of MSCs did not reduce the degree of synovial inflammation but did show increased bone volume during repair. This study provides evidence that intra-articular stem cell therapy can prevent the development of PTA after fracture and has implications for possible clinical interventions after joint injury before evidence of significant OA.

Objective Obesity and joint injury are both primary risk factors for osteoarthritis (OA) that involve potential alterations in the biomechanical and inflammatory environments of the joint. Post-traumatic arthritis (PTA) is a frequent long-term complication of intra-articular fractures. Obesity has been linked to primary OA and may potentially contribute to the development of PTA by a variety of mechanisms. The objectives of this study were to determine if diet-induced obesity influences the severity of PTA in mice and to examine interrelationships between joint degeneration and serum levels of inflammatory cytokines and adipokines in this response. Methods C57BL/6 mice were fed either normal chow (13% fat) or a high-fat diet (60% fat) starting at 4 weeks of age. At 16 weeks, half of each group received closed intra-articular fracture of the left knee. At 8 weeks post-fracture, knee osteoarthritis was assessed by cartilage and synovium histology in addition to bone morphology. Serum cytokine concentrations were determined with multiplex assay. Results Fractured knee joints of mice on a high-fat diet showed significantly increased osteoarthritic degeneration compared to non-fractured contralateral controls, while fractured knee joints of low-fat mice did not demonstrate significant differences from non-fractured contralateral controls. High-fat diet increased serum concentrations of interleukin-12p70, interleukin-6, and keratinocyte-derived chemokine, while decreasing adiponectin concentrations. Systemic levels of adiponectin were inversely correlated with synovial inflammation in control limbs. Conclusion Diet-induced obesity significantly increased the severity of osteoarthritis following intra-articular fracture. Obesity and joint injury together can alter systemic levels of inflammatory cytokines such as IL-12p70.