Decisive differences in the bone repair processes of the metaphysis and diaphysis in young mice

Comparative Osteogenesis and Degradation Behavior of Magnesium Implant in Epiphysis and Diaphysis of the Long Bone in the Rat Model

Magnesium (Mg), as a biodegradable material, is a promising candidate for orthopedic surgery. Long-bone fractures usually occur in cancellous-bone-rich epiphysis at each end or the cortical-rich diaphysis in the center, with different bone healing processes. Little is known about the differences in results between the two regions when applying Mg implants. Therefore, this study aimed to compare the biodegradation and osteogenesis of Mg implants in a rat model's epiphysis and diaphysis of the long bone. Twelve male Sprague Dawley rats underwent Mg rod implantation in the distal femoral epiphyses and tibial diaphyses. Every three weeks for up to twelve weeks, degradation behavior, gas evolution, and new bone formation were measured by micro CT. Histomorphology was analyzed by Hematoxylin and Eosin, Villanueva bone staining, and TRAP staining for osteoclastogenesis evaluations. Micro-CT analysis showed statistically significant higher new bone formation in the epiphysis group than in the diaphysis group, which correlated with a lower gas volume. Histological analysis showed higher osseointegration of Mg implants in the epiphyseal region than in the diaphyseal region. The magnesium implant's osteoclastogenesis-inhibiting properties were shown in the surrounding areas in both the cortical bone of the diaphysis and the cancellous bone of the epiphysis. Our findings show the differences in the magnesium implant's osteogenesis and biodegradation in the epiphysis and the diaphysis. These dissimilarities indicate a better response of the epiphyseal region to the Mg implants, a promising biomaterial for orthopedic surgery applications.

What Did We Learn About Fracture Pain from Animal Models?

Progress in bone fracture repair research has been made possible due to the development of reproducible models of fracture in rodents with more clinically relevant fracture fixation, where there is considerably better assessment of the factors that affect fracture healing and/or novel therapeutics. However, chronic or persistent pain is one of the worst, longest-lasting and most difficult symptoms to manage after fracture repair, and an ongoing challenge remains for animal welfare as limited information exists regarding pain scoring and management in these rodent fracture models. This failure of adequate pre-clinical pain assessment following osteotomy in the rodent population may not only subject the animal to severe pain states but may also affect the outcome of the bone healing study. Animal models to study pain were also mainly developed in rodents, and there is increasing validation of fracture and pain models to quantitatively evaluate fracture pain and to study the factors that generate and maintain fracture pain and develop new therapies for treating fracture pain. This review aims to discuss the different animal models for fracture pain research and characterize what can be learned from using animal models of fracture regarding behavioral pain states and new molecular targets for future management of these behaviors.

Site-Specific Fracture Healing: Comparison between Diaphysis and Metaphysis in the Mouse Long Bone

The process of fracture healing varies depending upon internal and external factors, such as the fracture site, mode of injury, and mechanical environment. This review focuses on site-specific fracture healing, particularly diaphyseal and metaphyseal healing in mouse long bones. Diaphyseal fractures heal by forming the periosteal and medullary callus, whereas metaphyseal fractures heal by forming the medullary callus. Bone healing in ovariectomized mice is accompanied by a decrease in the medullary callus formation both in the diaphysis and metaphysis. Administration of estrogen after fracture significantly recovers the decrease in diaphyseal healing but fails to recover the metaphyseal healing. Thus, the two bones show different osteogenic potentials after fracture in ovariectomized mice. This difference may be attributed to the heterogeneity of the skeletal stem cells (SSCs)/osteoblast progenitors of the two bones. The Hox genes that specify the patterning of the mammalian skeleton during embryogenesis are upregulated during the diaphyseal healing. Hox genes positively regulate the differentiation of osteoblasts from SSCs in vitro. During bone grafting, the SSCs in the donor’s bone express Hox with adaptability in the heterologous bone. These novel functions of the Hox genes are discussed herein with reference to the site-specificity of fracture healing.

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.

Effect of ovariectomy induced osteoporosis on metaphysis and diaphysis repair process

The fracture repair process is known to be delayed in postmenopausal women, under estrogen-deficient status. Osteoporotic fracture mainly occurs in the metaphyseal region of the long bone; however, most studies on fracture healing have focused on the diaphyseal region. In this study, we compared the repair process between metaphysis and diaphysis of ovariectomized (OVX) and Sham mice, and analyzed the effects of short-term estrogen administration in OVX mice. Mice were divided into four experimental groups, including Sham, OVX, OVX + vehicle, and OVX + 17β-estradiol (E2). Bone apertures were formed in the tibial metaphysis and diaphysis. The samples were collected and examined by micro-computed tomography, and using histological, histochemical, and immunohistochemical analysis at different time points after the surgery. The cartilaginous callus was formed at the diaphysis site of both the groups, which was sequentially replaced by bone on the periosteum side. Medullary callus was formed in all the groups; however, the volume of the callus in OVX mice was significantly lesser (˜30%) than that in Sham mice. Furthermore, in the metaphysis, no differences were observed in the medullary callus and bone mineral density between the two groups from day 21 to 28. The diaphysis of OVX group was not completely repaired even by day 28. In both the sites of OVX mice, ALP activity and disappearance of Gr-1 positive cells were delayed compared to that of Sham. Estrogen administration improved medullary callus formation in the diaphysis, however not in the metaphysis. The effect of ovariectomy on the repair process in diaphysis was greater than that in metaphysis. Our findings clarify the differences between the metaphysis and diaphysis repair process using OVX mouse model and suggest that the estrogen sensitivities differ between the sites during the bone repair process.

Effects of ultrasound, radial extracorporeal shock waves, and electrical stimulation on rat bone defect healing

Fractures associated with osteoporosis are a major public health concern. Current treatments for fractures are limited to surgery or fixation, leading to long-term bedrest, which is linked to increased mortality. Alternatively, utilization of physical agents has been suggested as a promising therapeutic approach for fractures. Here, we examined the effects of ultrasound, radial extracorporeal shock waves, and electrical stimulation on normal or osteoporotic fracture healing. Femoral bone defects were created in normal or ovariectomized rats. Rats were divided into four groups: untreated, and treated with ultrasound, shock waves, or electrical stimulation after surgery. Samples were collected at 2 or 4 weeks after surgery, and the healing process was evaluated with micro-CT, histological, and immunohistochemical analyses. Ultrasound at intensities of 0.5 and 1.0 W/cm² , but not 0.05 W/cm² , accelerated new bone formation. Shock wave exposure also increased newly formed bone, but formed abnormal periosteal callus around the defect site. Conversely, electrical stimulation did not affect the healing process. Ultrasound exposure increased osteoblast activity and cell proliferation and decreased sclerostin-positive osteocytes. We demonstrated that higher-intensity ultrasound and radial extracorporeal shock waves accelerate fracture healing, but shock wave treatment may increase the risk of periosteal callus formation.

Trabecular architecture during the healing process of a tibial diaphysis defect

The adaptation of trabecular bone microstructure to mechanical loads has been intensively investigated. However, loading-unrelated aspects of trabecular architecture remain unclear. We used synchrotron radiation-based X-ray microtomography to study the 3D microarchitecture of newly formed trabecular tissue in a defect produced in the cortical region of the rat tibia diaphysis, in the absence (7, 14, and 21 days) or the presence (21 days) of carbonated hydroxyapatite/alginate (cHA) microspheres. This work provides the first evidence that the woven bone trabecular network, formed during the healing process, displays a well-organized 3D microarchitecture consisting of nodes with 3 (3-N), 4 (4-N) and 5 (5-N) connecting trabeculae, with a mean relative abundance of (3-N)/(4-N)/(5-N) = 66/24/7, for the analyzed periods. The measured inter-trabecular angles (ITA) distribution presented a Gaussian profile, with mean value at 115° for 3-N nodes, and 105° for 4-N nodes, close to the angles of idealized 3D regular structures (120° and 109.5°, respectively). Changes in the dispersion of ITA distribution suggested that a highly symmetric trabecular fabric organized under tensegrity principles is formed early during the bone healing process. Post-implantation, cHA disaggregated into multiple fragments (~20-400 μm), stimulating osteoconduction and bone growth toward the interior of the medullary cavity. The presence of biomaterials in bone defects affected the trabecular dimensions; however, it did not interfere with the formation of geometrical motifs with topological parameters similar to those found in the sham-defects. STATEMENT OF SIGNIFICANCE: The trabecular bone microstructure enables the tissue to meet the necessary mechanical and functional demands. However, the process of trabecular microarchitecture formation during healing, in the absence or presence of a bone graft, is not yet well understood. This work demonstrated that, from the beginning of its formation in cortical bone defects, the woven-bone trabecular network is spatially organized according to the principle of tensegrity. This microarchitecture is comprised of highly symmetric geometric motifs and is an intrinsic characteristic of trabecular growth, regardless of hierarchical scale or mechanical stimulation. The addition of a biodegradable nanostructured calcium phosphate graft did not disrupt trabecular microarchitecture; however, graft biodegradation should be controlled to optimize the reproduction of intrinsic trabecular motifs throughout the defect.

Wnt-modified materials mediate asymmetric stem cell division to direct human osteogenic tissue formation for bone repair

The maintenance of human skeletal stem cells (hSSCs) and their progeny in bone defects is a major challenge. Here, we report on a transplantable bandage containing a three-dimensional Wnt-induced osteogenic tissue model (WIOTM). This bandage facilitates the long-term viability of hSSCs (8 weeks) and their progeny, and enables bone repair in an in vivo mouse model of critical-sized calvarial defects. The newly forming bone is structurally comparable to mature cortical bone and consists of human and murine cells. Furthermore, we show that the mechanism of WIOTM formation is governed by Wnt-mediated asymmetric cell division of hSSCs. Covalently immobilizing Wnts onto synthetic materials can polarize single dividing hSSCs, orient the spindle and simultaneously generate a Wnt-proximal hSSC and a differentiation-prone Wnt-distal cell. Our results provide insight into the regulation of human osteogenesis and represent a promising approach to deliver human osteogenic constructs that can survive in vivo and contribute to bone repair.

Saving the lower limb with GlassBONE™ - Successful surgical revision of pseudarthrosis after infected open proximal tibia fracture type IIIC with bioactive glass grafting - A case report

Background

The management of bone defect due to trauma or surgical debridement is a current problem in orthopedic trauma surgery, often complicated by infection and bone nonunion. The graft is one of the most challenging variables in surgical treatment. Bioactive Glass (BAG) as a biocompatible and osteogenic product is a promising bone substitute showing good results in maxillo-facial-, spine surgery and treatment of osteomyelitis. Surprisingly, there is very little data on BAG use in trauma surgery.

Case presentation

A 51-year-old male patient, involved in a motorcycle accident, suffered an open proximal tibia fracture, type IIIC, of the left leg. Patient was admitted in January of 2013 to a general orthopedic department for surgical treatment. After several surgical revisions due to infection, vascular damage, and bone nonunion, the patient was successfully treated with Masquelet therapy followed by GlassBONE™ grafting (GlassBONE™ 45S5; Norarker). The patient demonstrated excellent results over the course of a two-year follow-up.

Conclusions

In our experience, GlassBONE™ 45S5 has proven to be an effective bone substitute even in difficult grafting conditions, including multiple surgical revisions for bone nonunion and infection. In our case, at the end of 2 years and 3 months of follow-up, the patient reported no pain, and had no signs of infection. Bone union and full weight bearing was achieved.

This case report is oriented by the CARE guidelines for clinical case reports; the patient gave consent for publication.

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GlassBONE™ 45S5 has proven to be an effective bone substitute even in difficult grafting conditions.

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Bone nonunion was successfully treated with Masquelet therapy followed by GlassBONE™ grafting.

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Bone loss due to fracture or surgical debridement is a current problem in orthopedic trauma surgery.

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Bone fractures are the most widespread trauma in humans.

The effects of intraperitoneal metoprolol administration on healing of bone defects in rat tibia: a pilot study

OBJECTIVES

Metoprolol is a cardioselective competitive beta-1 adrenergic receptor antagonist with antihypertensive properties, devoid of intrinsic sympathomimetic activity. Various studies have suggested the effect of beta-blockers on bone remodeling. We aimed to investigate whether metoprolol affects bone remodeling by altering anti-inflammatory and pro-inflammatory cytokines.

MATERIALS AND METHODS

Surgical defects of 3 mm diameter were created in tibiae of 72 Sprague-Dawley rats. Rats were randomly assigned to a control group without metoprolol treatment (n = 36), and a test group treated with 0.1 mg/kg/day metoprolol (n = 36). Six rats from each group were sacrificed at days 0, 1, 3, 5, 7, and 14. The percentages of cells, which showed positive immunohistochemical staining for IL-1β, IL-6, IL-10, and RANKL, were assessed in the defect area. Differences in percentages of stained cells within each of the test and control groups over various time intervals were tested using one-way ANOVA test. A P value of < 0.05 was considered statistically significant.

RESULTS

No significant differences in IL-1β, IL-10, IL-6, and RANKL expressions were found between test and control groups at the same interval. Significant reduction was observed at different time intervals in the same group (P < 0.05).

CONCLUSION

Metoprolol did not reduce bone-active cytokine: IL-1β, IL-6, and RANKL. It also did not elevate IL-10 expression levels. Thus, it does not appear to decrease osteoclastogenesis.

CLINICAL RELEVANCE

Results from this animal model help us understand any effect of metoprolol on bone healing by potential contribution to different real-world clinical research.

Different effects of Wnt/β-catenin activation and parathyroid hormone on diaphyseal and metaphyseal in the early phase of femur bone healing of mice

Parathyroid hormone (PTH) and agents related to the manipulation of Wnt/β-catenin signalling are two promising anabolic anti-osteoporotic therapies that have been shown to promote the healing of bone fractures. Now, it is widely accepted that cortical bone and trabecular bone are two different compartments, and should be treated as separate compartments in pathological processes, such as fracture healing. It is currently unknown whether PTH and the activation of β-catenin signalling would demonstrate different effects on cortical bone and trabecular bone healing. In the current study, single 0.6-mm cortex holes were made in the femur metaphysis and diaphysis of mice, and then, PTH application and β-catenin activation were used to observe the promoting effect on bone healing. The effects of β-catenin and PTH signalling on fracture healing were observed by X-ray and CT at 3, 6, and 14 days after fracture, and the levels of β-catenin were detected by RT-PCR assay, and the number of specific antigen-positive cells of BRDU, OCN, RUNX2 was counted by immunohistochemical staining. While β-catenin activation and PTH were found to demonstrate similar effects on accelerating metaphyseal bone healing, activation of β-catenin showed a more striking effect than PTH on promoting diaphyseal bone healing. These findings might be helpful for selecting proper medication to accelerate fracture healing of different bone compartments.