An investigation of the contribution of the extraosseous tissues to the diaphyseal fracture callus using a rabbit tibial fracture model and in situ immunocytochemical localisation of osteocalcin

Development of a novel atrophic non-union model in rabbits: A preliminary study

Background and aim

The currently available atrophic non-union models rely on wide segmental excision of bone diaphysis to impede the process of healing but lack resemblance to the clinical scenario. The present study focused on developing an in vivo model of atrophic non-union fracture in rabbit radius that can replicate the clinical scenario.

Materials and methods

The atrophic non-union fracture model was developed by creating a 10 mm segmental bone defect in the radial diaphysis of five adult New Zealand White rabbits. The periosteum (2 mm) of the cut bone ends was cauterized using electrocautery to induce atrophy. Atrophic non-union was confirmed using radiographic and histologic evaluations on 30th postoperative day.

Results

The radiographic signs of healing were completely absent in all the rabbits on 30th postoperative day, indicating inert bone ends. Histological findings further confirmed the presence of inert bone ends, indicating the development of atrophic non-union.

Conclusion

The combination of the segmental bone defect, electrocautery induced thermal damage of bone end periosteum, and delayed treatment can induce the development of atrophic non-union fracture model in rabbits that can replicate the clinical scenario.

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In vivo model of atrophic non-union fracture in rabbit radius was developed that can replicate the clinical scenario.

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Radiographic and histological findings confirmed the presence of inert bone ends.

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Combination of segmental bone defect, electrocautery induced thermal damage, and delayed treatment can induce atrophic non-union fracture.

Effects of radiation and surgery on healing of femoral fractures in a rat model

Management of soft tissue sarcoma involves multimodality treatment, including surgery and radiotherapy. Pathologic fracture of the femur after such treatment in the thigh is one serious, late complication and nonunion rates of 80-90% are reported. We hypothesize that the combination of radiotherapy and periosteal stripping (during tumor resection) leads to greater impairment of the fracture repair process than either intervention alone. Female Wistar retired breeder rats were randomized into four treatment groups (control, radiotherapy, surgery, and combination of radiotherapy and surgery) and three end-points (21, 28, and 35 days post-fracture). Designated animals first underwent radiotherapy, followed by surgical stripping of the periosteum 3 weeks later and femoral fracture with fixation after another 3 weeks. Animals were sacrificed and fractures examined using microCT and histomorphometry. Simple transverse or short oblique femoral fractures were produced. By 35 days, control animals formed unions, periosteum-stripped animals formed hypertrophic non-unions and irradiated animals formed atrophic non-unions. Histomorphometry revealed an absence of chondroid and osteoid production in animals undergoing radiotherapy. The relative contribution of periosteal stripping to occurrence of non-union was statistically insignificant. Radiation prior to fracture reliably resulted in atrophic non-union in our model. The contribution of periosteal stripping was negligible.

Influence of cyclic bending loading on in vivo skeletal tissue regeneration from periosteal origin

INTRODUCTION

Periosteum osteogenic and chondrogenic properties stimulate the proliferation then differentiation of mesenchymal precursor cells originating from its deeper layers and from neighboring host tissues. The local mechanical environment plays a role in regulating this differentiation of cells into lineages involved in the skeletal regeneration process.

HYPOTHESIS

The aim of this experimental animal study is to explore the influence of cyclic high amplitude bending-loading on skeletal tissue regeneration. The hypothesis is that this mechanical loading modality can orient the skeletogenesis process towards the development of anatomical and histological articular structures.

MATERIAL AND METHODS

A vascularised periosteal flap was transferred in close proximity to each knee joint line in 17 rabbits. On one side, the tibiofemoral joint space was bridged and loading occurred when the animal bent its knee during spontaneous locomotion. On the other side, the flap was placed 12 mm distal to the joint line producing no loading during bending. Tissue regeneration was chronologically analyzed on histologic samples taken from the 4th day to the 6th month.

RESULTS

The structure and mechanical behavior of regenerating tissue evolved over time. As a result of the cyclic bending-loading regimen, cartilage tissue was maintained in specific areas of the regenerating tissue. When loading was discontinued, final osteogenic and fibrogenic differentiation occurred in the neoformed cartilage. Fissures developed in the cartilage aggregates resulting in pseudo-gaps suggesting similar processes to embryonic articular development. Ongoing mesenchymal stem cells stimulation was identified in the host tissues contiguous to the periosteal transfer.

DISCUSSION

These results suggest that the pseudarthrosis concept should be reconsidered within the context of motion induced articular histogenesis.

The periosteum: what is it, where is it, and what mimics it in its absence?

Nearly every bone in the body is invested in periosteum. The periosteum is in some ways poorly understood and has been a subject of controversy and debate. This tissue has a major role in bone growth and bone repair and has an impact on the blood supply of bone as well as skeletal muscle. Despite the importance of the periosteum is has received little attention in the literature in recent years.

Prosthetic devices shaped as tubular chambers for the treatment of large diaphyseal defects by guided bone regeneration

Guided tissue regeneration is based on the hypothesis that the different tissues have unequal abilities to penetrate a wounded area during the healing process. The use of a device acting as a chamber allows the growth of a particular tissue and prevents the ingrowth of other tissues which impair the healing process. At the same time the chamber protects and maintains in situ the intrinsic growth factors so that they may perform their specific activity. Guided tissue regeneration currently plays a well-recognized role mostly in dentistry and peripheral nerve surgery but interesting perspectives have also opened up in orthopedics. Considering the possibility of using guided bone regeneration in the repair of diaphyseal bone defects, this updated survey highlights some critical points and pathways related to the state-of-the-art of this promising procedure, focusing particularly on the properties of the material to make the tubular chamber, the use of osteopromotive factors and the most appropriate animal model to be used for the experimental evaluation.

Cellular and molecular characterization of a murine non-union model

PURPOSE

We have developed a method to study the molecular and cellular events underlying delayed skeletal repair in a model that utilizes distraction osteogenesis.

METHODS

The clinical states of delayed union and non-union were reproduced in this murine model by altering distraction parameters such as the inclusion and exclusion of a latency phase and variations in the rate and rhythm of distraction. Radiographic, cellular, and molecular analyses were performed on the distraction tissues.

RESULTS

Eliminating the latency period delayed bony union, but did not appreciably alter the extent of platelet endothelial cell adhesion marker (PECAM) immunostaining. Following elimination of a latency phase and a threefold increase in the rate of distraction, there was a further delay in bone regeneration and a higher rate of non-union (60%). Instead of bone, the distraction gap was comprised of adipose or fibrous tissue. Once again, despite the rigorous distraction protocol, we detected equivalent PECAM staining within the distraction gap. In a minority of cases, cartilage and osseous tissues occupied the distraction gap likely by a prolonged process of endochondral ossification.

CONCLUSIONS

Here, we have altered the mechanical environment in such a way to reproducibly create delays in skeletal regeneration. These delays in skeletal tissue regeneration appear to develop even in the presence of endothelial cells, which suggests that mechanisms other than a disruption to the vascular network can account for some cases of non-union.

Experimental Study on the Effect of Mechanical Stimulation on the Early Stage of Fracture Healing

In an attempt to ascertain the effects of mechanical stimulation on callus in the early stage of bone fracture healing, a tibial fracture was induced in rats and mechanical stimulation applied to the fractures. The callus was then measured quantitatively, while the fractures were analyzed both radiographically and histologically. Following the induction of a closed transverse fracture in the tibia, external anchors were applied and the rats raised by suspending the fractured leg. The rats were divided into two main groups: a Stimulation Group (S Group) and a Control Group (C Group) without the application of any mechanical stimulation. The S Group was further divided into the following three subgroups: an axial compression group (Sc Group) receiving stimulation in the positive direction; an axial distraction group (Sd Group) receiving stimulation in the negative direction; and an axial dynamization group (Sdy Group) receiving stimulation in both directions alternately. For mechanical stimulation, 1.4-N sine waves were applied continuously for 30 minutes a day, three times a week, starting 2 days after fracture-inducing surgery. At 3, 7, and 14 days after surgery, transverse sections of each fractured bone sample were prepared. At 14 days after surgery, each transverse section was divided into two peripheral and central regions to permit calculation of the area ratio of callus. Radiographically, no marked differences were observed among the groups; histologically, differences were seen 7 days after surgery, suggesting that mechanical stimulation facilitated bone healing soon after surgery. At 14 days after surgery, the amount of callus for the C Group was less than that for all three stimulation groups. In the C Group, the amount of callus in the peripheral region was greater than in the central region, and in the Sc Group, the results were the same: callus in the peripheral region was greater than in the central region. In the Sd Group, callus was greater in the central region than in peripheral regions. In the Sdy Group, favorable callus was observed in both the central and peripheral regions. These findings suggest that axial compression facilitates callus primarily in the peripheral region, while axial distraction facilitates callus primarily in the central region. When axial compression and distraction were alternated (dynamization), callus was significantly facilitated in both the central and peripheral regions. Of the three axial stimulation techniques, dynamization was the most effective in facilitating callus in the early stage of bone fracture healing.

Does adult fracture repair recapitulate embryonic skeletal formation?

Bone formation is a continuous process that begins during fetal development and persists throughout life as a remodeling process. In the event of injury, bones heal by generating new bone rather than scar tissue; thus, it can accurately be described as a regenerative process. To elucidate the extent to which fetal skeletal development and skeletal regeneration are similar, we performed a series of detailed expression analyses using a number of genes that regulate key stages of endochondral ossification. They included genes in the indian hedgehog (ihh) and core binding factor 1 (cbfa1) pathways, and genes associated with extracellular matrix remodeling and vascular invasion including vascular endothelial growth factor (VEGF) and matrix metalloproteinase 13 (mmp13). Our analyses suggested that even at the earliest stages of mesenchymal cell condensation, chondrocyte (ihh, cbfa1 and collagen type II-positive) and perichondrial (gli1 and osteocalcin-positive) cell populations were already specified. As chondrocytes matured, they continued to express cbfa1 and ihh whereas cbfa1, osteocalcin and gli1 persisted in presumptive periosteal cells. Later, VEGF and mmp13 transcripts were abundant in chondrocytes as they underwent hypertrophy and terminal differentiation. Based on these expression patterns and available genetic data, we propose a model where Ihh and Cbfa1, together with Gli1 and Osteocalcin participate in establishing reciprocal signal site of injury. The persistence of cbfa1 and ihh, and their targets osteocalcin and gli1, in the callus suggests comparable processes of chondrocyte maturation and specification of a neo-perichondrium occur following injury. VEGF and mmp13 are expressed during the later stages of healing, coincident with the onset of vascularization of the callus and subsequent ossification. Taken together, these data suggest the genetic mechanisms regulating fetal skeletogenesis also regulate adult skeletal regeneration, and point to important regulators of angiogenesis and ossification in bone regeneration.

The early stages of the repair of adult human diaphyseal fractures

Periosteum was obtained within 10 days of injury from the site of 17 adult tibial diaphyseal fractures during internal fixation. Osteogenic cells, non-osteogenic cells and vascular elements were identified in situ using a variety of techniques. In all cases, the periosteum was thickened with randomly distributed plaques of cartilage and bone. Cells covering newly formed bone trabeculae expressed osteocalcin. Lectin-binding revealed high vascularity. Few mast cells were observed. Macrophages and acid phosphatase positive cells, some multinucleate, were observed in abundance. These findings suggest that the repair of the adult human diaphyseal fracture is similar to that of experimental fractures in rapidity of onset, high vascularity and in bone and cartilage formation. They differ in the fact that chondrogenesis and osteogenesis appear to be simultaneous in human fractures but sequential in experimental fractures. The paucity of mast cells suggests that they probably play no significant role in the repair of the human fractures.

The development of the growth plate after birth: a study by osteocalcin immunocytochemistry

The post natal development of the growth plate was studied in the rabbit lower limb using an immunocytochemical technique which localized osteocalcin in situ. At birth, there is poor columnar organization of the physis and bone is not produced. Instead the predominant activity is cartilage remodelling. The columnar architecture develops later when endochondral ossification is also observed.

Osteocalcin expression in the groove of Ranvier of the rabbit growth plate

The biology of the growth plates of rabbits of different ages was studied using an immunocytochemical technique which localized osteocalcin. Immunoreactivity was observed in the cells of the groove of Ranvier. Other findings suggest that the groove is a separate structure from the cartilaginous physis and is the terminal end of the diaphysis/periosteum complex.

Connective tissue parameters in experimental nonunion

A previously developed experimental model for producing nonunions in rats was used to study the biochemical changes of connective tissue parameters in impaired fracture repair. The model is based on rotational instability between the fracture fragments. A mid-diaphyseal femoral osteotomy was performed on 30 male rats and fixed with a loose-fitting intramedullary nail. The rats were killed 1, 2, 3, 7, 9, and 12 weeks postoperatively, and the development of nonunions was verified with radiographs. The calluses were dissected free and set for biochemical analysis. The contents of nitrogen, hydroxyproline, calcium, and phosphorous, as well as the RNA/DNA ratio, were determined. It appeared that in the impaired fracture repair there is an extended matrix production phase continuing until 7 weeks postoperatively. Simultaneously, the number of callus cells increased, indicating an extended expression of the mitotic signals for callus cells. The net synthesis of collagen matrix seemed to be sufficient, but the mineral binding capacity of the newly synthetised collagen was impaired. Later, the cessation of chondrogenic and osteogenic activity could be observed with the formation of nonmineralized fibrous tissue between the fracture fragments.

Localisation of bone-forming cells during fracture healing by osteocalcin immunocytochemistry: an experimental study of the rabbit tibia

An immunocytochemical method was used to localise osteocalcin-producing cells during fracture healing in a rabbit model. In preliminary studies, tibial growth plates from young rabbits were used as a source of new bone formation, in order to determine the optimal tissue preparatory techniques. In the present study, a tibial shaft fracture was created in adult rabbits to study closed fracture healing. An indirect peroxidase method was used to stain paraffin-embedded tissue sections for osteocalcin. Osteocalcin-producing cells were positively identified at the periosteal and endosteal surfaces near the fracture site. Osteocalcin staining was not demonstrated in the surrounding soft tissues. At the interface between newly formed bone trabeculae and the cartilage layer within the callus, chondrocytic cells consistently showed localisation of osteocalcin. Within cartilaginous areas of the callus, some chondrocytes showed positive staining for osteocalcin. These cells were often seen in the proximity of blood vessels. The findings suggest that during fracture healing, under certain conditions, chondrocytes are capable of producing osteocalcin and thus could be considered capable of possible transformation into osteoblasts.