Long-term effects of saw osteotomy versus random fracturing on bone healing and remodeling in a sheep tibia model

Aging Influences Fracture Healing on the Cellular Level and Alters Systemic RANKL and OPG Concentrations in a Murine Model

Clinical complications frequently follow polytrauma and bleeding fractures, increasing the risk of delayed fracture healing and nonunions, especially in aged patients. Therefore, this study examines age's impact on fracture repair with and without severe bleeding in mice. Young (17-26 weeks) and aged (64-72 weeks) male C57BL/6J mice (n = 72 in total, n = 6 per group) are allocated into 3 groups: the fracture group (Fx) undergoes femur osteotomy stabilized via external fixator, the combined trauma group (THFx) additionally receives pressure-controlled trauma hemorrhage (TH) and Sham animals are implanted with catheter and fixator without blood loss or osteotomy. Femoral bones are evaluated histologically 24 h and 3 weeks post-trauma, while RANKL/OPG and β-CTx are measured systemically via ELISA after 3 weeks. Aging results in less mineralized bone and fewer osteoclasts within the fracture of aged mice in contrast to young groups after three weeks. Systemically, aged animals exhibit increased RANKL and OPG levels after fracture compared to their young counterparts. The RANKL/OPG ratio rises in aged Fx animals compared to young mice, with a similar trend in THFx groups. In conclusion, age has an effect during the later course of fracture healing on the cellular and systemic levels.

Visualization of bone formation in sheep's middle ear by using fluorochrome sequential labelling (FSL)

One factor for the lacking integration of the middle ear stapes footplate prosthesis or the missing healing of stapes footplate fractures could be the known osteogenic inactivity. In contrast, it was recently demonstrated that titanium prostheses with an applied collagen matrix and immobilised growth factors stimulate osteoblastic activation and differentiation on the stapes footplate. Regarding those findings, the aim of this study was to evaluate the potential of bone regeneration including bone remodeling in the middle ear. Ten one-year-old female merino sheep underwent a middle ear surgery without implantation of middle ear prostheses or any other component for activating bone formation. Post-operatively, four fluorochromes (tetracycline, alizarin complexion, calcein green and xylenol orange) were administered by subcutaneous injection at different time points after surgery (1 day: tetracycline, 7 days: alizarin, 14 days: calcein, 28 days: xylenol). After 12 weeks, the temporal bones including the lateral skull base were extracted and histologically analyzed. Fluorescence microscopy analysis of the entire stapes with the oval niche, but in particular stapes footplate and the Crura stapedis revealed evidence of new bone formation. Calcein was detected in all and xylenol in 60% of the animals. In contrast, tetracycline and alizarin could only be verified in two animals. The authors were able to demonstrate the osseoregenerative potential of the middle ear, in particular of the stapes footplate, using fluorescence sequence labelling.

Validation of a novel large animal intra-articular tibial plafond fracture model

BACKGROUND

Large animal fracture models that allow for anatomic fracture fixation are currently lacking. It was hypothesized that a compressed air impaction system can generate a reproducible tibial plafond fracture and be adjustable to create fractures consistent with high and low energy fractures seen in humans.

METHODS

Pilot testing of the impaction system was done by impacting polyurethane foam blocks at varying compressed air pressures. A guillotine impaction test was performed on the same foam blocks to create an energy conversion. A total of 12 porcine hindlimb hindlimbs were subjected to low-energy (42.2 J) and high-energy (73.9 J) impact to create tibial plafond fractures.

FINDINGS

Guillotine impaction test demonstrated strong correlations between potential energy and foam block impaction depth (R² = 0.99). Compressed air impaction system test strongly correlated with foam block impaction depth (R² = 0.99). All six porcine hindlimbs in the low-energy group developed simple coronal split tibial plafond fractures. All six porcine hindlimbs in the high-energy group developed complex, multi-fragmentary tibial plafond fractures.

INTERPRETATION

This porcine fracture model created tibial plafond fracture patterns with similar fracture morphology as human patients without violation of the soft tissue structures or adjacent joints. This model would allow for anatomic fixation, the study of post-traumatic osteoarthritis, or the delivery of locally targeted therapeutics to the ankle joint.

Fracture Healing Research-Shift towards In Vitro Modeling?

Fractures are one of the most frequently occurring traumatic events worldwide. Approximately 10% of fractures lead to bone healing disorders, resulting in strain for affected patients and enormous costs for society. In order to shed light into underlying mechanisms of bone regeneration (habitual or disturbed), and to develop new therapeutic strategies, various in vivo, ex vivo and in vitro models can be applied. Undeniably, in vivo models include the systemic and biological situation. However, transferability towards the human patient along with ethical concerns regarding in vivo models have to be considered. Fostered by enormous technical improvements, such as bioreactors, on-a-chip-technologies and bone tissue engineering, sophisticated in vitro models are of rising interest. These models offer the possibility to use human cells from individual donors, complex cell systems and 3D models, therefore bridging the transferability gap, providing a platform for the introduction of personalized precision medicine and finally sparing animals. Facing diverse processes during fracture healing and thus various scientific opportunities, the reliability of results oftentimes depends on the choice of an appropriate model. Hence, we here focus on categorizing available models with respect to the requirements of the scientific approach.

Severe Hemorrhagic Shock Leads to a Delayed Fracture Healing and Decreased Bone Callus Strength in a Mouse Model

BACKGROUND

Multiple trauma is frequently associated with hemorrhagic shock and fractures of the extremities. Clinically, the rate of impaired fracture healing (delayed healing and nonunion) seems to be increased in patients with multiple injuries compared with patients with isolated fractures. As the underlying pathogenesis remains poorly understood, we aimed to analyze the biomechanical properties during fracture healing in a murine model.

QUESTIONS

The aim of this study was to determine whether fracture healing after severe hemorrhagic shock results in (1) delayed bridging as determined by macroscopic and radiographic assessment, (2) altered conditions of callus components as determined by µCT, and (3) decreased maximum bending moment measured by a three-point-bending test compared with ordinary fracture healing.

METHODS

Male C57BL/6NCrl mice were randomly assigned to five groups and four different times (five to 10 mice per group and time). Only the right femur from each mouse was used for analysis: the trauma hemorrhage (TH) group received a pressure-controlled hemorrhagic shock via catheter; the osteotomy (Fx) group underwent osteotomy and implantation of an external fixator on the right femur; the combined trauma (THFx) group received hemorrhagic shock and an external fixator with osteotomy; the sham group underwent implantation of a catheter and external fixator but had no blood loss or osteotomy, and the control group underwent no interventions. After 2, 3, 4, or 6 weeks, five to 10 animals of each group were sacrificed. Bones were analyzed macroscopically and via radiographs, µCT, and three-point-bending test. Statistical significance was set at a probability less than 0.05. Comparisons were performed using the Mann-Whitney U or the Kruskal-Wallis test.

RESULTS

In the Fx group, the osteotomy gap was stable and bridged after 2 weeks in contrast to some bones in the THFx group where stable bridging did not occur. No difference was observed between the groups. µCT analysis showed reduced density of bone including callus (THFx: 1.17 g/cm³; interquartile range [IQR], 0.04 g/cm³; Fx: 1.22 g/cm³; IQR, 0.04 g/cm³; p = 0.002; difference of medians [DM], -0.048; 95% CI, -0.073 to -0.029) and increased share of callus per volume of bone mass (%) after 2 weeks in the THFx group compared with the Fx group (THFx: 44.16%; IQR, 8.66%; Fx: 36.73%; IQR, 4.39%; p = 0.015; DM, 7.634; 95% CI, 2.018-10.577). The three-point-bending test established a decreased maximum bending moment in the THFx group compared with the Fx group 2 weeks after surgery (THFx: 7.10 Nmm; IQR, 11.25 Nmm; Fx: 11.25 Nmm; IQR, 5.70 Nmm; p = 0.026; DM, -5.043; 95% CI, -10.867 to -0.74). No differences were observed between the THFx and Fx groups after more than 2 weeks.

CONCLUSION

In this in vivo mouse fracture model, we conclude that hemorrhagic shock retards fracture healing during the early phase of the facture healing process.

CLINICAL RELEVANCE

A severe hemorrhagic shock in patients could result in initial delayed fracture healing and needs special attention. We plan to conduct a prospective, observational clinical research study to analyze if delayed fracture healing occurs in patients after severe blood loss.

Repetitive reduction lead to significant elevated IL-6 and decreased IL-10 levels in femoral osteotomies: A quantitative analysis of a robot-assisted reduction process in a rat model

INTRODUCTION

The field of robot-assisted fracture reduction has been developed by several research groups over more than one decade by now, with the main goals of increasing the fracture reduction accuracy. However, the influence of different reduction paths to patients' physiology is not fully known yet. The aim of our study was to compare the impacts of a robot-assisted direct reduction path versus an artificially prolonged reduction path by measuring the cytokine responses in an in vivo rat model.

MATERIALS AND METHODS

Thirty-six male CD(©) rats were assigned into three groups with an external fixator and osteotomy on the left femur. Seven days later, the robot was attached and one group was reduced in a single attempt, while the other group underwent 10 attempts by the robot. The third group was the control group without reduction. Before, and as well as 6, 24 and 48h after the reduction process blood samples were collected. IL-1, IL-6, IL-10, IL-17, and MCP-1 concentrations where analysed via ELISA or cytometric bead assay. Muscle biopsies in the osteotomy area were collected 48h after the reduction process for histological analyses. Statistical significance was set at p≤0.05.

RESULTS

Analysis of the cytokines showed that the pro-inflammatory cytokine IL-6 of the Ten-Attempts reduction group significantly increased 6h after reduction compared to the control group. IL-6 further showed markedly elevated levels 6h after surgery in the Ten-Attempts reduction group compared to the Single-Attempt reduction group. On the anti-inflammatory side, IL-10 showed a significant decrease in the Ten-Attempts reduction group 6h after reduction compared to the Single-Attempt reduction and control group. Muscle biopsies showed a significant increase of pathological changes in both reduction groups and an increase in the severity of bleedings of the Ten-Attempts reduction group compared to the Single-Attempt reduction and control group.

CONCLUSION

A direct and gentle reduction procedure as feasible by the aid of a robot is preferable over a prolonged reduction in terms of cytokine response and tissue changes.

A Novel Shape Memory Plate Osteosynthesis for Noninvasive Modulation of Fixation Stiffness in a Rabbit Tibia Osteotomy Model

Nickel-titanium shape memory alloy (NiTi-SMA) implants might allow modulating fracture healing, changing their stiffness through alteration of both elastic modulus and cross-sectional shape by employing the shape memory effect (SME). Hypotheses: a novel NiTi-SMA plate stabilizes tibia osteotomies in rabbits. After noninvasive electromagnetic induction heating the alloy exhibits the SME and the plate changes towards higher stiffness (inverse dynamization) resulting in increased fixation stiffness and equal or better bony healing. In 14 rabbits, 1.0 mm tibia osteotomies were fixed with our experimental plate. Animals were randomised for control or induction heating at three weeks postoperatively. Repetitive X-ray imaging and in vivo measurements of bending stiffness were performed. After sacrifice at 8 weeks, macroscopic evaluation, µCT, and post mortem bending tests of the tibiae were carried out. One death and one early implant dislocation occurred. Following electromagnetic induction heating, radiographic and macroscopic changes of the implant proved successful SME activation. All osteotomies healed. In the treatment group, bending stiffness increased over time. Differences between groups were not significant. In conclusion, we demonstrated successful healing of rabbit tibia osteotomies using our novel NiTi-SMA plate. We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating. Thus, future orthopaedic implants could be modified without additional surgery.

Non-osteotomy and osteotomy large animal fracture models in orthopedic trauma research

Large animal fracture models are important in the field of orthopedic trauma research. New implants are tested in animals before being implanted into humans. Large animals like sheep or swine often are more properly to simulate conditions in humans, e.g. biomechanical demands, compared to rodents. Cited articles mainly analyze shock or fracture healing. Both osteotomy and non-osteotomy fracture models have been used in the past. However, comparative studies are rare and clear recommendation when to use which model are missing. This review will summarize large animal fracture models putting special emphasis on non-osteotomy fracture models.

Use of clinical assessment tools in the evaluation of fracture healing

Fracture healing is an optimized biological process yet the ability to determine when a fracture is healed, or to measure the healing response can present a clinical challenge. This review will focus on the evidence for the implementation of imaging modalities as tools to assist in evaluating fracture union. This is particularly important for common fractures that have a propensity to have delayed union or non-union, where a diagnosis of non-union would alter the treatment. We also present methods, such as biochemical markers and clinical scores that are in development or have the potential to aid in the diagnosis of non-union. Ultimately, clinical exam combined with the available modalities can help the clinician judge the progression of healing with some confidence. There is still a need for continued development of new modalities and tests to improve accuracy of the diagnosis of non-union, as well as predict which fractures are at risk for non-union.