Recombinant species-specific growth hormone increases hard callus formation in distraction osteogenesis.

The effect of growth hormone (GH) on secondary fracture healing and callus formation has been demonstrated in several previously investigated animal models. The aim of this study was to investigate and quantify the effects of GH on bone regenerates in a distraction osteogenesis model. In 20 mature female Yucatan micropigs, the tibia and fibula were osteotomized, stabilized with an external fixator, and distracted at 2 mm/day for 10 days after a 4 day latency period. The regenerates were allowed to consolidate for 10 days. Micropigs in the study group (ten animals) received a daily injection of 100 microg per kilogram body weight of recombinant porcine growth hormone (r-pGH). Micropigs in the control group (ten animals) received sodium chloride as placebo. After killing on day 25, a quantitative histomorphometrical analysis of the formed callus and the adjacent cortical bone was performed and the results of polychrome in vivo labeling were assessed. The regenerates of the r-pGH-treated animals showed a significantly larger callus area but no change in callus structure. We found islands of cartilage tissue in the regenerates of both groups; the calli from the control group exhibited a higher fraction of cartilage compared with the r-pGH group, but this was not significant. Quantification of the fluorescent in vivo labeling revealed that the distraction gap in GH-treated group showed significant ossification even during distraction. These results demonstrate that growth hormone can accelerate the maturation of the regenerate in distraction osteogenesis without changing the callus microstructure. This may prove to be a useful clinical tool for shortening the healing time in limb lengthening and bone segment transport.     

Homologous growth hormone accelerates bone healing--a biomechanical and histological study

The purpose of this study was to prove whether homologous growth hormone has a beneficial effect in the early phase of bone healing. Therefore the left tibias of 24 Yucatan micropigs were osteotomized and stabilized by plate fixation. The treatment group (12 animals) received 100 microg of recombinant porcine growth hormone (rpGH)/kg body w/day sc, whereas the control pigs (12 animals) received 1 ml sodium chloride as placebo. After a healing period of 4 weeks the animals were sacrificed and destructive torsional testing was performed. For histological evaluation 6 microm serial slices of the tibiae were stained with von Kossa. The total area of callus formation (CA) and the mineralized bone area (BA) were quantified by image analysis. The fraction of mineralized bone tissue within the callus area, the bone density (BD), was calculated as follows: BD = (BA/CA) x 100. Torsional failure load was 91% higher and torsional stiffness 61% higher in the treatment group than in the control group (P < 0.05). The histomorphometric measurements revealed an advance for the CA (GH: 127.6 +/- 38.9 mm(2); placebo: 75.9 +/- 50.7 mm(2); P < 0.005) as well as for the BA (GH: 89.3 +/- 25.8 mm(2); placebo: 55.9 +/- 38.5 mm(2); P < 0.001) for the GH-treated animals in comparison to the control animals. The BD was similar in both groups (GH: 70.6 +/- 8.4%; placebo: 74.0 +/- 6.24%; P = 0.28). These data indicate that administration of homologous GH stimulates callus formation and ossification in the early phase of bone healing, which consequently results in an increased mechanical strength and stiffness.     

No effect of growth hormone on bone graft incorporation: Titanium chamber study in the normal rat

A recent series of publications reported greatly improved mechanical properties and increased callus size during the late stages of fracture healing in normal (not hypophysectomized) rats after twice daily injections of growth hormone (GH). We tested whether GH could enhance the incorporation of bone allografts in a new experimental model where we have demonstrated an increase in bone allograft incorporation by local application of basic fibroblast growth factor (bFGF)- Cylinders of defatted allogeneic cancellous bone were placed as grafts in titanium Bone Conduction Chambers in the tibiae of female rats. Only one end of this chamber is open for tissue ingrowth. This permits us to measure the distance into the graft that new bone penetrates after entering the chamber. We injected 10 rats with 1.5 IU per rat of subcutaneous human recombinant GH twice daily for 6 weeks and another 10 rats with similar doses of sterile normal saline. GH caused a constant increase in the rate of weight gain and in the serum concentration of Insulin-like Growth Factor 1 (IGF 1). Tibiae became longer and the ash weight of the second tail vertebra was increased. We also noted an increased joint cartilage thickness. There was no difference in the amount of new bone that had penetrated and replaced parts of the graft in GH-treated or control rats and this was also the case with TcMDP activity of bone samples from both groups. New bone forms in the grafts by membranous (metaplastic) ossification. It appears that the effects of excessive GH stimulation on endochondral and membranous ossification in this model are markedly different.     

Effects of Growth Hormone and Low Dose Estrogen on Bone Growth and Turnover in Long Bones of Hypophysectomized Rats

Pituitary hormones are recognized as critical to longitudinal growth, but their role in the radial growth of bone and in maintaining cancellous bone balance are less clear. This investigation examines the histomorphometric effects of hypophysectomy (Hx) and ovariectomy (OVX) and the subsequent replacement of growth hormone (GH) and estrogen (E), in order to determine the effects and possible interactions between these two hormones on cortical and cancellous bone growth and turnover. The replacement of estrogen is of interest since Hx results in both pituitary and gonadal hormone insufficiencies, with the latter being caused by the Hx-associated reduction in follicle stimulating hormone (FSH). All hypophysectomized animals received daily supplements of hydrocortisone (500 μg/kg) and l-thyroxine (10 μg/kg), whereas intact animals received daily saline injections. One week following surgery, hypophysectomized animals received either daily injections of low-dose 17 β-estradiol (4.8 μg/kg s.c.), 3 X/d recombinant human GH (2 U/kg s.c.), both, or saline for a period of two weeks. Flurochromes were administered at weekly intervals to label bone matrix undergoing mineralization. Whereas Hx resulted in reductions in body weight, uterine weight, and tibial length, OVX significantly increased body weight and tibial length, while reducing uterine weight. The combination of OVX and Hx resulted in values similar to Hx alone. Treatment with GH normalized body weight and bone length, while not affecting uterine weight in hypophysectomized animals. Estrogen increased uterine weight, while not impacting longitudinal bone growth and reduced body weight. Hypophysectomy diminished tibial cortical bone area through reductions in both mineral appositional rate (MAR) and bone formation rate (BFR). While E had no effect, GH increased both MAR and BFR, though not to sham-operated (control) levels. Hypophysectomy reduced proximal tibial trabecular number and cancellous bone area, and increased trabecular separation. Both GH and E reduced cancellous osteopenia, although employing different mechanisms. GH reduced the decrease in trabecular thickness, whereas E reduced the decrease in trabecular number and the increase in trabecular separation. Hypophysectomy reduced both Tb.MAR and Tb.BFR while treatment with GH enhanced them. This investigation has shown that Hx and GH have a dramatic impact on selected static and dynamic indices of rat cortical and cancellous histomorphometry. Furthermore, the mechanisms of action of GH and E differ, and suggest that some of the skeletal changes associated with Hx are caused by deficiencies in estrogen as well as deficiencies in growth hormone. Received: 2 December 1996 / Accepted: 24 March 1997     

Staphylococcus aureus peptidoglycan impairs fracture healing: an experimental study in rats.

Staphylococcus aureus is the common organism causing musculoskeletal infections. Staphylococcus aureus peptidoglycan (SaPG) has been identified to increase the acute inflammatory response to wounding, increase reparative granulation tissue, and improve healing. The healing of bone fractures is a balanced process of granulation tissue that is calcified to obtain increasing stability. By increasing reparative collagen accumulation, however, SaPG may induce a shift towards immature fibrous callus production. Therefore, it was our hypothesis that SaPG would impair bone healing after fracture. In three groups, each of nine rats, a mid-diaphyseal osteotomy/fracture of the femoral bone was performed and then nailed. In one group of animals, SaPG was applied locally at the fracture site, and in another group SaPG was applied intraperitoneally (systemically). Control littermate received saline. The animals were sacrificed after 6 weeks, and the mechanical characteristics of the healing osteotomies were evaluated. We found that application of SaPG locally induced a hypertrophic and immature callus as evaluated by callus production, by bone mineral content and density, and by bending moment and rigidity. In the rats given SaPG intraperitoneally, bone healing went uneventful compared to the control rats. Collectively, these data show that SaPG induces an alteration in the normal bone healing response towards a less calcified callus production.     

不同长度骨缺损模型中皮质骨内变化及作用

目的：本文应用非脱钙骨切片技术研究皮质骨在1mm和10mm骨缺损修复过程中的变化及其在骨修复中的作用。方法：新西兰大白兔30只，分成1、2、3、4、6周组，每组再分成1mm及10mm2组，每组3只，右侧分别为1、10mm骨缺损侧，左侧为对照。制作非脱钙骨切片，组织学观察骨缺损愈合过程中皮质骨结构变化。结果：组织学观察显示，两骨缺损模型修复过程的早期，皮质骨断端各表面均出现了骨融解现象，皮质骨陷窝内的骨细胞被溶解并释放出，与周围骨缺损修复组织联系紧密。4周后，在1mm骨缺损模型中，在外骨痂附近的皮质骨部位有许多的改建与再建的哈佛氏系统单位，皮质骨内的再建结构与外骨痂及连接骨痂内的再建结构紧密相连；而10mm模型中，皮质骨无明显变化。结论：伴随骨修复过程，骨缺损两端皮质骨发生特征性改变，在骨愈合再生期，可为骨修复过程提供促骨修复细胞及物质；而在骨愈合的改建期，也参与各种骨痂的改建过程。因此，皮质骨是骨修复过程的再生及重建过程中重要影响因素。     

Temporal and spatial expression of bone morphogenetic proteins in extracorporeal shock wave-promoted healing of segmental defect

Extracorporeal shock wave (ESW) is a noninvasive acoustic wave, which has recently been demonstrated to promote bone repair. The actual healing mechanism triggered by ESW has not yet been identified. Bone morphogenetic proteins (BMP) have been implicated as playing an important role in bone development and fracture healing. In this study, we aimed to examine the involvement of BMP-2, BMP-3, BMP-4, and BMP-7 expression in ESW promotion of fracture healing. Rats with a 5-mm segmental femoral defect were given ESW treatment using 500 impulses at 0.16 mJ/mm(2). Femurs and calluses were subjected to immunohistochemistry and RT-PCR assay 1, 2, 4, and 8 weeks after treatment. Histological observation demonstrated that fractured femurs received ESW treatment underwent intensive mesenchymal cell aggregation, hypertrophic chondrogenesis, and endochondral/intramembrane ossification, resulting in the healing of segmental defect. Aggregated mesenchymal cells at the defect, chondrocytes at the hypertrophic cartilage, and osteoblasts adjunct to newly formed woven bone showed intensive proliferating cell nuclear antigen expression. ESW treatment significantly promoted BMP-2, BMP-3, BMP-4, and BMP-7 mRNA expression of callus as determined by RT-PCR, and BMP immunoreactivity appeared throughout the bone regeneration period. Mesenchymal cells and immature chondrocytes showed intensive BMP-2, BMP-3, and BMP-4 immunoreactivity. BMP-7 expression was evident on osteoblasts located at endochondral ossification junction. Our findings suggest that BMP play an important role in signaling ESW-activated cell proliferation and bone regeneration of segmental defect.     

Smoking delays chondrogenesis in a mouse model of closed tibial fracture healing.

Smoking delays the healing process and increases morbidity associated with many common musculoskeletal disorders, including long bone fracture. In the current study, a murine model of tibial fracture healing was used to test the hypothesis that smoking delays chondrogenesis after fracture. Mice were divided into two groups, a nonsmoking control group and a group exposed to cigarette smoke for 1 month prior to surgical tibial fracture. Mice were euthanized at 7, 14, and 28 days after surgery. The outcomes measured were immunohistochemical staining for type II collagen protein expression as a marker of cartilage matrix and proliferating cell nuclear antigen (PCNA) staining to measure proliferation at the site of injury. Toluidine blue staining and histomorphometry were used to quantify areas of cartilaginous and noncartilaginous fracture callus. Radiographs were analyzed for evidence of remodeling after injury. At day 7 after injury, mice exposed to cigarette smoke had a smaller fracture callus with less cartilage matrix compared to controls. Proliferation was present at high levels in both groups at this time point, but proliferating cells had a more immature morphology in the smoking group. At day 14, chondrogenesis was more active in smokers compared to controls, while a higher percentage of bone was present in the control animals. At day 28, X-ray analysis revealed a larger fracture callus remaining in the smoking animals. Together, these findings show that the chondrogenic phase of tibial fracture healing is delayed by smoking. This study represents, to our knowledge, the first analysis of molecular and cellular mechanisms of healing in a smoking mouse fracture model.     

Effects of low-dose, intermittent treatment with recombinant human parathyroid hormone (1-34) on chondrogenesis in a model of experimental fracture healing

Recent studies have demonstrated that intermittent administration of parathyroid hormone (PTH) enhances osteogenesis (hard callus formation) and increases mechanical strength in experimental fracture healing. Thus far, however, effects of PTH on chondrogenesis (soft callus formation) during fracture healing have not been fully elucidated. In the present study, we analyzed the underlying molecular mechanism by which exogenous PTH would affect chondrogenesis in a model of experimental fracture healing. Unilateral femoral fractures were produced in 2-month-old Sprague-Dawley rats. Daily subcutaneous injections of 10 microg/kg of recombinant human PTH(1-34) [rhPTH(1-34)] were administered over a 28-day period of fracture healing. Control animals were injected with vehicle solution (normal saline) alone. The results showed that, on day 14 after fracture, cartilage area in the PTH-treated group was significantly increased (1.4-fold) compared with the controls, but this increase was not observed at days 21 and 28. In the early stage of chondrogenesis (days 4-7), cell proliferation, expressed as the rate of proliferating cell nuclear antigen-positive cells, was increased in mesenchymal (chondroprogenitor) cells but not chondrocytes in the PTH-treated group compared with controls. In addition, gene expression of SOX-9 was up-regulated in the PTH-treated group on day 4 (1.4-fold), and this was accompanied by enhanced expression of pro-alpha1 (II) collagen (1.8-fold). After 14 days, there were no significant differences between groups in either cell proliferation or the expression levels of cartilage differentiation-related genes (SOX-9, pro-alpha1 (II) collagen, pro-alpha1 (X) collagen and osteopontin). These results suggest that intermittent treatment with low-dose rhPTH(1-34) induces a larger cartilaginous callus but does not delay chondrocyte differentiation during fracture healing.     

Local Anabolic Effects of Growth Hormone on Intact Bone and Healing Fractures in Rats

The local effects of rat growth hormone (rGH) injected at the surfaces of intact tibial diaphyses and healing tibial diaphysial fractures were investigated in 10-month-old female rats. Intact diaphysial bones: rats were injected daily for 14 days with vehicle, 2 µg rGH, or 20 µg rGH at the surface of the right tibial diaphysis. After 10 days of injection the animals were labeled with calcein. At the rGH-injected location, increased external diaphysial bone dimensions and increased calcein-labeled area were seen, and the responses to rGH were dose dependent. The new bone formed at the periosteal surface was woven bone. At the opposite left tibia, no systemic effect of rGH was found. rGH did not influence body weight changes during the treatment, or muscle mass or serum IGF-I at the end of the treatment. Healing diaphysial fractures: a closed fracture was made in the right tibial diaphysis, and stabilized by medullary nailing. The fractures were tested after 21 days and 98 days of healing. During the first 21 days of healing, all rats were injected daily with either vehicle or 20 µg rGH at the surface of the fracture line. In the 21-day healing rGH group, ultimate load, ultimate stiffness, external callus dimensions, and external callus volume of the fractures were increased. rGH did not affect body weight changes during this healing period or serum IGF-I at the end of the healing period. In the 98-day healing rGH group, ultimate load was still increased compared with the vehicle group, although a ninefold increase took place in the vehicle group between days 21 and 98 of healing. External callus dimensions of the fractures were increased in the rGH group, whereas body weight changes during the healing period were not affected.     

Homologous growth hormone accelerates healing of segmental bone defects

The effect of homologous recombinant porcine growth hormone (r-pGH) on secondary fracture healing was investigated in a diaphyseal defect of the tibia in Yucatan micropigs. A 1 cm defect of the tibia was created surgically and stabilized with an AO 3.5 mm DCP plate. The treatment group (12 animals) received 100 microg of r-pGH per kilogram of body weight subcutaneously once per day, whereas the control pigs (12 animals) received 1 mL of sodium chloride as placebo. For evaluation of the GH-axis, serum levels of insulin-like growth factor-I (IGF-I) were sampled every fourth day. The animals were killed 6 weeks after surgery. Quantitative computed tomography (qCT) was performed to determine bone mineral density (BMD) and bone mineral content (BMC) of the defect zone. The torsional stiffness and the torsional failure load were measured by destructive torsional testing of the defect and contralateral tibiae. qCT measurements revealed a significant increase in the BMC of the defect zone in the treatment group compared with controls (GH BMC = 2833 +/- 679 mg, placebo BMC = 2215 +/- 636 mg; p < 0.05), whereas the BMD values were similar in both groups (GH BMD = 668 +/- 60 mg/mm(2), placebo BMD = 629 +/- 52 mg/mm(2), p = 0.12). Torsional failure load was 70% higher and torsional stiffness 83% higher in the treatment group than in the control group (p < 0.05). The mean serum level of IGF-I in the treatment group increased to 382% of the preoperative basal level and decreased to 69% in the control group, and this difference was highly significant (p < 0.001). Our data indicate that daily administration of recombinant GH leads to an increase of serum IGF-I levels and stimulates secondary fracture healing, resulting in increased mechanical strength and stiffness of the callus.     

Low-intensity ultrasound enhances maturation of callus after segmental transport

The purpose of this study was to determine whether low-intensity ultrasound can be used to enhance callus maturation. Fifteen-millimeter bone defects at the metatarsal bones of sheep were treated with a segmental bone transport for 16 days. The callus formations in the bone defects were allowed to mature for 63 days before the animals were sacrificed. Eighteen sheep were operated on and divided into two groups. One group was treated with low-intensity ultrasound for 20 minutes per day, whereas the other group served as an untreated control group. Biomechanical tests after removal of the metatarsals showed significantly higher axial compression stiffness and significantly higher indentation stiffness of callus tissue in the healing zone in the group treated with ultrasound. Also, histologic analysis of the cortical defect zone showed significantly more callus formation and more active zones of endochondral ossification in the group treated with ultrasound. Stimulation of callus maturation by ultrasound is possible, similar to stimulation of fresh fracture healing, and may be used to shorten clinical treatment times.     

The effect of PTH(1‐34) on fracture healing during different loading conditions

Parathyroid hormone (PTH) and PTH(1‐34) have been shown to promote bone healing in several animal studies. It is known that the mechanical environment is important in fracture healing. Furthermore, PTH and mechanical loading has been suggested to have synergistic effects on intact bone. The aim of the present study was to investigate whether the effect of PTH(1‐34) on fracture healing in rats was influenced by reduced mechanical loading. For this purpose, we used female, 25‐week‐old ovariectomized rats. Animals were subjected to closed midshaft fracture of the right tibia 10 weeks after ovariectomy. Five days before fracture, half of the animals received Botulinum Toxin A injections in the muscles of the fractured leg to induce muscle paralysis (unloaded group), whereas the other half received saline injections (control group). For the following 8 weeks, half of the animals in each group received injections of hPTH(1‐34) (20 µg/kg/day) and the other half received vehicle treatment. Fracture healing was assessed by radiology, dual‐energy X‐ray absorptiometry (DXA), histology, and bone strength analysis. We found that unloading reduced callus area significantly, whereas no effects of PTH(1‐34) on callus area were seen in neither normally nor unloaded animals. PTH(1‐34) increased callus bone mineral density (BMD) and bone mineral content (BMC) significantly, whereas unloading decreased callus BMD and BMC significantly. PTH(1‐34) treatment increased bone volume of the callus in both unloaded and control animals. PTH(1‐34) treatment increased ultimate force of the fracture by 63% in both control and unloaded animals and no interaction of the two interventions could be detected. PTH(1‐34) was able to stimulate bone formation in normally loaded as well as unloaded intact bone. In conclusion, the study confirms the stimulatory effect of PTH(1‐34) on fracture healing, and our data suggest that PTH(1‐34) is able to promote fracture healing, as well as intact bone formation during conditions of reduced mechanical loading. © 2013 American Society for Bone and Mineral Research.     

异体软骨痂移植的初步结果

目的 通过观察异体软骨痂移植后的生物学过程判断其作为植骨材料的可行性。方法 将1只SD大鼠的双侧股骨干造成闭合骨折,1周时切开获取软骨痂,－196℃冻存2周后移植于5只SD大鼠的左侧胫骨干部分缺损区（此骨缺损模型的成骨活动只表现为膜内化骨的方式）,右侧植入异体松质骨作为对照组。将取材标本制成不脱钙切片,经亮绿和藏红T染色。结果 术后1周取材1例,缺损区实验侧和对照侧均未见有软骨组织和骨组织形成。术后2周处死其余4只大鼠,实验侧（3／4）可见有软骨组织和骨组织形成。骨组织内已有髓腔形成,骨组织周围是软骨组织,与宿主骨之间有纤维组织相隔。结论 异体软骨痂移植后未被吸收,可经软骨内化骨的方式产生骨组织,为软骨痂作为植骨材料的进一步研究和开发提供了初步依据。     

The bone inductive capacity of various bone transplanting materials used for treatment of experimental bone defects.

The bone defect repairing capacities of autogenous cancellous bone (ACB), decalcified bone (DB), autodigested "low-antigenic" bone matrix (LBM) and preserved bone (PB) were tested in experimental defects in rabbit scapulae. The healing of the defects was most effective with ACB transplants as judged by roentgenologic and microscopic studies. The DB and LBM transplants caused states of healing comparable to each other, and the PB transplants showed the least satisfactory results in this experiment. The ACB, DB and LBM transplants caused bone induction, which resulted in the formation of new bone, subsequent resorption of the transplanted material and rapid reshaping of the callus. The PB transplants caused no bone induction; only some growth of callus on the edges of the defect was observed and pieces of the transplanted material were seen as late as 10 weeks after the operation as dead particles encapsulated by fibrous tissue. The infiltrations of inflammatory cells around the PB transplants indicated a considerable host versus graft reaction whereas this reaction was less with the other materials tested.     

An injectable composite material containing bone morphogenetic protein‐2 shortens the period of distraction osteogenesis in vivo

To investigate new methods that can decrease the duration of bone transport (BT) distraction osteogenesis, we injected composite materials containing recombinant human bone morphogenetic protein‐2 (BMP‐2) and induced the generation of a callus bridge by rapid segmental transport (4 mm/day) in a rabbit bone defect model. The composite materials consisted of BMP‐2 (0, 30, or 100 µg), β‐tricalcium phosphate powder (βTCP, 100 mg/animal; particle size, <100 µm), and polyethylene glycol (PEG; 40 mg/animal). A paste of equivalent composition was percutaneously injected at the lengthening and the docking sites after surgery and after BT, respectively. The radiographic, mechanical, and histological examinations 12 weeks post‐operative revealed that the generation of bridging callus in the presence and in the absence of BMP‐2 was significantly different. The callus mass in the bone defect region was adequately and consistently developed in the presence of 100 µg of BMP (administered for 6 weeks), and the bones were consolidated in 12 weeks. Such an adequate callus formation was not observed in the control animals without BMP‐2 treatment. The result of this experimental study suggests the potential application of BMP‐2 in accelerating callus formation and in enabling rapid bone transporting, thereby shortening the treatment period for the repair of diaphyseal bone defects by distraction osteogenesis. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:452–456, 2011     

Morphology of bony callus growth in healing of a sheep tibial osteotomy

Long bone fractures typically heal via formation of an external callus, which helps stabilise the bone fragments. Callus composition and morphology influence the mechanical environment, which in turn regulates the progression of healing. Therefore characterising callus development over time is crucial in understanding this mechanobiological regulation. Although bony callus is often assumed to grow towards the fracture from either side, this is not consistent with observations from large animal studies and clinical cases. Therefore, we sought to quantify the morphology of bony callus over time in a large animal model.Sheep tibiae were x-rayed weekly over eight weeks following an osteotomy (n=5), with fixation allowing up to 10% axial displacement under normal weight-bearing. After scaling radiographs by known landmarks and normalising greyscales, bony callus boundaries were defined by manual segmentation. The lateral callus area and coordinates of its centroid were calculated from each image.The external callus initially formed adjacent to the osteotomy site. Over the first four weeks, callus growth from its outer surfaces was characterised by its centre of area moving outwards and away from the osteotomy, on both proximal and distal fragments. Subsequent weeks showed consolidation and resorption from the outer surface of the callus.Our approach allowed bony callus development to be tracked in individuals throughout healing. Contrary to the view that periosteal bone formation originates distant from the fracture, our data showed bony callus adjacent to the defect from early stages, followed by approximately concentric growth. This discrepancy highlights the need for data specific to experimental conditions, and particularly early stages of healing, for evaluating theoretical models of mechanical regulation.     

Effect of osteoporosis medications on fracture healing

Antiosteoporotic medications are often used to concurrently treat a patient’s fragility fractures and underlying osteoporosis. This review evaluates the existing literature from animal and clinical models to determine these drugs’ effects on fracture healing. The data suggest that these medications may enhance bone healing, yet more thorough prospective studies are warranted. Pharmacologic agents that influence bone remodeling are an essential component of osteoporosis management. Because many patients are first diagnosed with osteoporosis when presenting with a fragility fracture, it is critical to understand how osteoporotic medications influence fracture healing. Vitamin D and its analogs are essential for the mineralization of the callus and may also play a role in callus formation and remodeling that enhances biomechanical strength. In animal models, antiresorptive medications, including bisphosphonates, denosumab, calcitonin, estrogen, and raloxifene, do not impede endochondral fracture healing but may delay repair due to impaired remodeling. Although bisphosphonates and denosumab delay callus remodeling, they increase callus volume and result in unaltered biomechanical properties. Calcitonin increases cartilage formation and callus maturation, resulting in improved biomechanical properties. Parathyroid hormone, an anabolic agent, has demonstrated promise in animal models, resulting in accelerated healing with increased callus volume and density, more rapid remodeling to mature bone, and improved biomechanical properties. Clinical data with parathyroid hormone have demonstrated enhanced healing in distal radius and pelvic fractures as well as postoperatively following spine surgery. Strontium ranelate, which may have both antiresorptive and anabolic properties, affects fracture healing differently in normal and osteoporotic bone. While there is no effect in normal bone, in osteoporotic bone, strontium ranelate increases callus bone formation, maturity, and mineralization; forms greater and denser trabeculae; and improves biomechanical properties. Further clinical studies with these medications are needed to fully understand their effects on fracture healing in order to simultaneously treat fragility fractures and underlying osteoporosis.     

Osteopenia and impaired fracture healing in aged EP4 receptor knockout mice

The EP4 receptor, one of the subtypes of the prostaglandin E2 (PGE2) receptor, plays a critical role in the anabolic effects of PGE2 on bone. However, its role in the maintenance of bone mass in aged animals and its role in fracture healing is not well known. Our studies addressed these issues by characterizing the skeletal phenotype of aged, EP4 receptor knockout (KO) mice, and by comparing fracture healing in aged KO mice versus wild type (WT) mice. There was no significant difference in body weight and femoral length between KO and WT mice at 15 to 16 months of age. Lower bone mass was seen radiographically in both axial and long bones of KO mice relative to WT mice. Micro-CT images of the distal femurs showed thinner cortices, fewer trabeculae, and a deteriorated trabecular network in KO mice. Total bone content, trabecular content, and cortical content, as assessed by pQCT in the distal femur, were lower in KO mice than WT controls. Histomorphometric measurements showed that trabecular bone volume and bone formation rate were significantly decreased whereas osteoclast number on trabecular surface and eroded surface on endocortical surface were significantly increased in KO mice. These data indicated that deleting the EP4 receptor resulted in an imbalance in bone resorption over formation, leading to a negative bone balance. The lower bone formation rate in EP4 KO mice was primarily due to decreased mineralizing surface, suggesting that the defect in overall bone formation was mainly due to the defect in osteoblastogenesis. Fracture healing was examined in KO and WT mice subjected to a transverse femoral fracture. Callus formation was significantly delayed as evidenced both radiographically and histologically in the fractured femurs of KO mice compared with those of WT mice. KO mice had significant decreases in total callus area, cartilaginous callus area, and bony callus area 2 weeks after fracture. By 4 weeks, complete bony bridging was seen in WT mice but not in KO mice. These data demonstrate that the absence of the EP4 receptor decreases bone mass and impairs fracture healing in aged male mice. Our findings indicate that the EP4 receptor is a positive regulator in the maintenance of bone mass and fracture healing.     

Systemic application of growth hormone enhances the early healing phase of osteochondral defects--a preliminary study in micropigs

Healing of osteochondral defects following trauma remains a significant clinical problem, often leading to osteoarthritis. Growth hormone (GH) has been shown to accelerate formation of bone and cartilage tissue in the growth plates and in cell cultures. To investigate the influence of systemically administered recombinant porcine growth hormone (r-pGH) on the healing of osteochondral defects we performed a histomorphometrical analysis of full-thickness cartilage defects in the femoral condyle of micropigs. Forty-eight mature female Yucatan micropigs were divided into two groups, one receiving a daily injection of r-pGH (100 microg/kg), the other receiving sodium chloride as placebo. A circular 6-mm-diameter full-thickness defect of the cartilage was created, extending 1.5 mm into the subchondral bone. The animals were sacrificed after 4 (n = 24) and 6 (n = 24) weeks. The von-Kossa stain was used to visualise the calcified structures; cartilage and the fibrous tissue were marked with a combined Safranin-O/light-green stain. The defect filling and the percentage of bone, cartilage, and fibrous tissue into the defect were evaluated using an image analysis system. Furthermore, histological grading was performed using the modified Wakitani score. After 4 weeks no differences were observed between both groups. The defect filling after 6 weeks with newly formed bone was significantly higher in the r-pGH-treated group. The formation of cartilage and fibrous tissue showed a trend towards better healing in the GH-treated group; however, there was no significant difference. In the r-pGH-treated group, the percentage of total defect filling was significantly higher. The evaluation of the vascularity showed a significantly lower number of vessels in the GH-treated group after 6 weeks. Histomorphological grading revealed a significantly lower total Wakitani score in the GH-treated group, which represents a better healing result compared to the controls. The results of the present study suggest that circulating r-pGH or one of its mediators may accelerate osteochondral defect healing by stimulating the formation of osseous and chondral tissue. The analysis of the vascularity leads to the assumption of an advanced maturation of the osteochondral defects under the influence of GH.