Expression of angiogenic factors during distraction osteogenesis

Distraction osteogenesis is a unique and effective way to treat limb length inequality resulting from congenital and posttraumatic skeletal defects. However, despite its widespread clinical use, the cellular and molecular mechanisms by which this surgical treatment promotes new bone formation are not well understood. Previous studies in distraction osteogenesis have noted increased blood flow and vessel formation within the zone of distraction. These observations suggest that distraction osteogenesis may be driven in part by an angiogenic process. Using immunohistological analysis, the expression of two different angiogenic factors (VEGF and bFGF) was shown to localize at the leading edge of the distraction gap, where nascent osteogenesis was occurring. These cells were spatially adjacent to new vessels that were identified by staining for factor VIII. Microarray analysis detected maximal mRNA expression for a wide variety of angiogenic factors including angiopoietin 1 and 2, both Tie receptors, VEGF-A and -D, VEGFR2, and neuropilin 1. Expression of these factors was found to be maximal during the phase of active distraction. Expression of mRNA for extracellular matrix proteins and BMPs was also maximal during this period. A comparison between the patterns of gene expression in fracture healing and distraction osteogenesis revealed similarities; however, the expression of a number of genes showed selective expression in these two types of bone healing. These data suggest that bone formation during distraction osteogenesis is accompanied by the robust induction of factors associated with angiogenesis and support further investigations to elucidate the mechanisms by which angiogenic events promote bone repair and regeneration.     

Risk factors for and complications of distraction osteogenesis

Purpose

Distraction osteogenesis is commonly used for limb deformities and reconstruction of bone defects with satisfactory outcome for the patients. However, it is associated with a risk of complications. The present study aims to assess the incidence of complications and to identify the risk factors that may predict distraction osteogenesis-related complications.

Materials and methods

We retrospectively studied 63 patients (mean age 13.5 years; range 3–57 years) who had 74 distraction osteogenesis procedures from 2004 to 2009. A circular external fixator was used in 58 procedures, and a monolateral in 16 procedures. Fixator’s time, days of treatment, lengthening percentage, bone healing index, distraction regenerate length and index, risk factors and complications were evaluated. The mean follow-up was 5 years (range 2–7 years).

Results

Complications occurred in 57 of the 74 procedures (77 %); 70 % were major complications and 30 % were minor. Complications were more common in adults. Bone healing index, days of treatment and fixator’s time were univariate predictors of complications. Bone healing index and adult age were the only multivariate predictors of complications.

Conclusion

Adult age and bone healing index are the most important multivariate predictors of distraction osteogenesis-related complications. Routine follow-up after implant removal, selection of younger patients with minor risk factors and shorter fixator’s time are necessary to reduce the rate of distraction osteogenesis-related complications.     

Growth factor modulation of distraction osteogenesis in a segmental defect model

A model was established in 39 dogs to investigate the growth factor modulation of regenerate bone in distraction osteogenesis. A segment of the diaphysis of the radius was resected unilaterally. An osteotomy was made proximal to the segmental defect to create a transport segment. A monolateral external fixator was applied. After a latency period, the segment was transported across the defect. One week after the transport assembly contacted the distal pin clamp, an ipsilateral osteotomy of the proximal ulna was performed. In 20 dogs, transforming growth factor-beta was injected into the regenerate bone halfway through the transport period. Four dogs were sacrificed before docking, when the regenerate bone was still immature. In specimens harvested halfway through the transport period, evidence was found of intramembranous ossification during distraction. In specimens harvested after the transport assembly contacted the distal pin clamp, evidence was found that the mature regenerate formed by endochondral ossification. Therefore, a combined mechanism of ossification is proposed for this segmental defect model that includes mechanical stimulus for bone differentiation. The one-time administration of transforming growth factor-beta retarded the formation of a stable, united regenerate. It is concluded that transforming growth factor-beta caused an effect opposite to that which was desired.     

Fracture after distraction osteogenesis

We reviewed 173 patients undergoing distraction osteogenesis to determine the incidence, location and timing of fractures occurring as a complication of the procedure. There were 17 fractures in 180 lengthened segments giving an overall rate of fracture of 9.4%. Unexpectedly, the pattern and location of the fractures were very variable; six were within the regenerate itself, six at the junction between the regenerate and the original bone and five at distant sites in the limb. Of those occurring in the regenerate, five were noted to be associated with compression and partial collapse of the regenerate. In three patients collapse and deformity developed gradually in the distracted segment over the six months after removal of the frame. The method of treatment of these fractures should be chosen to take into account multiple factors, which are additional and often different from those to be considered during management of acute traumatic injuries. Internal fixation appears to be most appropriate for displaced fractures, although in small children, or in those in whom there has been, or is, infection of the screw tracks, a new period of treatment using external fixation may be needed. Fixation by intramedullary nailing was associated with a risk of infection, even if screw tracks were assessed as healthy at the time of insertion of the nail. Internal fixation with the use of plates is safe for displaced, unstable fractures in children.     

Rat model of distraction osteogenesis

Prior studies of distraction osteogenesis in dog and rabbit models have shown predominantly intramembranous bone formation. Other models of fracture healing normally display mixtures of both endochondral and intramembranous bone formation. We have established a rat model of tibial lengthening that reliably reproduces the pattern of zonal osteogenesis previously observed in dog and rabbit models. A distraction rate of 0.25 mm twice a day with a 0-day latency period produced intramembranous bone with zones of progressive mineralization from collagen. With this protocol, rats bridged the distraction gap with a 25% increase in the tibial bone length. After 20 days of distraction and 50 days of consolidation, the three-point bending stiffness, as a percentage of the contralateral control, reached a level equivalent to that measured in the canine model for a 15% lengthening (28-day distraction and 84-day consolidation). Radiodensitometric analysis of the regenerate bones measured 97% of the unaffected contralateral tibial densities, and mineral analyses demonstrated that calcium and phosphorus levels in the regenerate bone reached 78% of contralateral tibial levels by day 70. We concluded that a rat model of distraction ostegenesis will be useful for a wide range of studies involving rapid intramembranous bone formation.     

Limb salvage using distraction osteogenesis

Distraction osteogenesis is a novel technique for the biological restoration of segmental bone defects. Definitive treatment of musculoskeletal tumors often requires large bony resections that can leave patients with significant osseous defects. Limb salvage using distraction osteogenesis is an attractive reconstructive alternative that may, in fact, offer advantages over other conventional techniques. We present our initial experience with the use of distraction osteogenesis in limb salvage.     

External fixation for distraction osteogenesis

Distraction osteogenesis methods are indicated in cases of deformity when alternative surgery is not able to produce adequate anatomic restoration and functionality of the foot and ankle. Recent advances in deformity evaluation and techniques of correction may encourage a greater number of surgeons to incorporate distraction osteogenesis into their treatment of complex foot and ankle problems.     

Systemic regulation of distraction osteogenesis: a cascade of biochemical factors.

This study investigates the systemic biochemical regulation of fracture healing in distraction osteogenesis compared with rigid osteotomy in a prospective in vivo study in humans. To further clarify the influence of mechanical strain on the regulation of bone formation, bone growth factors (insulin-like growth factor [IGF] I, IGF binding protein [IGFBP] 3, transforming growth factor [TGF] beta1, and basic FGF [bFGF]), bone matrix degrading enzymes (matrix-metalloproteinases [MMPs] 1, 2, and 3), human growth hormone (hGH), and bone formation markers (ALP, bone-specific ALP [BAP], and osteocalcin [OC]) have been analyzed in serum samples from 10 patients in each group pre- and postoperatively. In the distraction group, a significant postoperative increase in MMP-1, bFGF, ALP, and BAP could be observed during the lengthening and the consolidation period when compared with the baseline levels. Osteotomy fracture healing without the traction stimulus failed to induce a corresponding increase in these factors. In addition, comparison of both groups revealed a significantly higher increase in TGF-beta1, IGF-I, IGFBP-3, and hGH in the lengthening group during the distraction period, indicating key regulatory functions in mechanotransduction. The time courses of changes in MMP-1, bone growth factors (TGF-beta1 and bFGF), and hGH, respectively, correlated significantly during the lengthening phase, indicating common regulatory pathways for these factors in distraction osteogenesis. Significant correlation between the osteoblastic marker BAP, TGF-beta1, and bFGF suggests strain-activated osteoblastic cells as a major source of systemically increased bone growth factors during callus distraction. The systemic increase in bFGF and MMP-1 might reflect an increased local stimulation of angiogenesis during distraction osteogenesis.     

Fourth brachymetatarsia treated with distraction osteogenesis

BACKGROUND: This study investigated metatarsal lengthening by distraction osteogenesis for fourth brachymetatarsia in 22 metatarsals (16 patients). METHODS: From May 1997 to May 2000, lengthening was performed with a monoexternal fixator, and distraction was started at a rate of 0.5 mm per day after a latency period of approximately 7-10 days. RESULTS: The average gain in length was 16.5 mm (range, 13-21 mm), equivalent to an increase of 39% (range, 28-51%), and the average healing index was 72.9 days/cm (range, 51.7-95.7 days/cm). The American Orthopaedic Foot and Ankle Society (AOFAS) average score for lesser toe was 86.3 (range, 47-100). The most common residual complication was subluxation of metatarsophalangeal (MTP) joint in five cases, with partial or total stiffness of the MTP joint. These complications happened in the group of metatarsals excessively lengthened more than 40% and made the AOFAS score poorer. The other complications were three cases of angular deformity in the lengthened bone, and two cases of pin-tract infection. CONCLUSION: Although distraction osteogenesis is an effective method to address fourth brachymetatarsia, stiffness or subluxation of the MTP joint was not uncommon. To avoid complications that can happen as a result of excessive lengthening, careful preoperative radiographic measurement to calculate the optimal amount of lengthening may help us to avoid overlengthening and the complications that accompany it.     

Treatment of brachymetatarsia by distraction osteogenesis

Metatarsal lengthening by distraction osteogenesis was performed on 17 brachymetatarsia patients with 39 metatarsal bones. To lengthen the first metatarsal in an attempt to prevent development of varus deformity of the hindfoot after lengthening, horizontal lengthening in the anterior direction was performed rather than lengthening through the anatomical axis. In addition, care was taken to ensure that the fourth metatarsal bone screw did not interpose with the fifth extensor tendon during the fourth metatarsal lengthening. Lengthening was successful except in 1 case with mean lengthening of 19.5 mm (48.8%) for the first metatarsal and 17.1 mm (36.2%) for the fourth metatarsal. Because of joint stiffness, plantar capsulotomy was performed on 7 cases, 6 of which had been previously operated on bilaterally. Varus deformity of the hindfoot after the first metatarsal lengthening and entrapment of the fifth extensor tendon after the fourth metatarsal lengthening was not detected in any case.     

First ray reconstruction with distraction osteogenesis

Disarticulation of the thumb at the metacarpophalangeal joint level is not beneficial either aesthetically or functionally without additional surgery because it requires a bulky and an unacceptable prosthesis to be made for this amputation level. In this study, the authors have presented our experience of 12 metacarpal distractions in thumb amputated patients. Twelve male patients who had thumb amputation due to gunshot wounds were included in the study. Before the operation, aesthetic hand prostheses were made for 5 of the 12 patients. Callus distraction was performed with the use of a mini Ilizarov type external fixator in 7 cases and uniplanar dynamic mini external fixator in 5 cases too. External fixators were removed after the completion of the radiographic consolidation. Five patients whose prosthesis had been made before the operation wore their prosthesis for an average 6.8 months (5 - 14) due to poor appearance and poor construction. Union of the lengthened segment was observed in all cases. Average lengthening was 28.9 mm (range from 25 - 37). Average healing time was 2.1 months (range from 1.8 - 2.5). Average healing index was 0.73 month/cm (range from 0.65 - 0.88). Pin tract infection was seen in 7 cases (58.3%). Volar angulation developed after removing the external fixator in 1 case. Webplasty was performed in all cases. Patients were evaluated by means of Disability of the Arm, Shoulder and Hand (DASH) score and pick-up test. It was concluded that the metacarpus lengthening by callus distraction technique may be a functionally and cosmetically effective reconstruction method for traumatic thumb amputations. It is believed that the possibility for a functionally and aesthetically acceptable fabrication of a thumb prosthesis, by providing a suction suspension with distraction and/or webplasty procedures.     

延伸骨痂的骨化模式

在世界上曾经风迷一时的Ilizarov外固定方法因其较为安定的成绩,现在在骨科领域里已经成为规定的术式。然而在另一方面,人们对张压力效应和牵引性组织形成原理的理解程度,还有就其原理是否已被科学性地阐明都存有疑义。在此,根据多年来的动物实验结果以及文献的检索,就有关延伸骨痂的骨化模式的问题加以探讨。     

A murine model of distraction osteogenesis

Distraction osteogenesis is both a valuable clinical technique and a useful tool for investigating the basic mechanisms involved in bone tissue regeneration. Here we describe the development of a murine model of this procedure that can be used in transgenic animals to investigate the role of specific genes in tissue regeneration. Ring fixators were applied to the lower leg of 12 normal adult male mice. An osteotomy was made in the diaphysis of the tibia, and 7 days after the operation the bone fragments were distracted by 0.25 mm twice a day for 10 days. Specimens were examined immediately at the end of distraction and after 14-70 days of consolidation. At the end of distraction, the distraction gap was filled with fibroblast-like cells arranged longitudinally. After 14 days of consolidation, there was radiographical evidence of bone formation in the distraction gap and, after 28 days of consolidation, the bone fragments were fused with regenerated bone. By 70 days of consolidation, the regenerated bone had been almost completely remodeled and the intramedullary canal reestablished. This study is the first to report consolidation of the distraction gap with regenerated bone in a murine model of distraction.     

Angiogenesis during mandibular distraction osteogenesis.

Recruitment of a blood supply is critical for successful bone induction and fracture healing. Despite the clinical success of distraction osteogenesis (DO), an analysis of angiogenesis during membranous bone DO has not been performed. The purpose of this study was to evaluate the temporal and spatial pattern of angiogenesis during mandibular DO. The right hemimandible of adult male rats was osteotomized, and a customized distraction device was applied. Following a 3-day latency period, distraction was begun at a rate of 0.25 mm twice daily for 6 days (3.0 mm total; 12% increase in mandibular length). Three animals each were sacrificed on days 2, 4, and 6 of distraction (D1, D2, and D3 respectively), or after 1, 2, or 4 weeks of consolidation (C1, C2, and C3 respectively). Two experienced pathologists reviewed the regenerate histology, and angiogenesis was assessed by counting the number of blood vessels per intermediate-power field (IPF). Statistical analysis was performed using analysis of variance, with p < or = 0.05 considered significant. Results demonstrate that mandibular DO was associated with an intense vascular response during the early stages of distraction (D1). On average, 31.5+/-7.9 vessels were noted in each IPF examined during this time point. The number of blood vessels in the distraction regenerate decreased significantly during the later distraction time points, with approximately 14.0+/-2.0 and 14.7+/-3.5 blood vessels per IPF in sections obtained after days 4 and 6 of distraction (D2, D3) respectively. However, blood vessels at these time points took on a more mature histological pattern. During the consolidation period, the number of blood vessels noted in the regenerate decreased with 8.0+/-2.6, 9.3+/-2.1, and 4.0+/-2.0 vessels per IPF in sections obtained after 1, 2, or 4 weeks of consolidation (C1, C2, C3) respectively (p < 0.05 compared with vessel counts during the earliest distraction time point). This study demonstrates for the first time that an intense vascular response associated with mandibular DO occurs primarily during the early stages of distraction. The authors hypothesize that as distraction continues, newly formed vessels likely undergo consolidation, thus forming more mature vessels capable of withstanding distraction forces. Future studies will assess the effects of therapeutic interventions designed to increase angiogenesis during DO on bony regenerate formation.     

Management of nonunion with distraction osteogenesis

Nonunions of long bone fractures represent a clinical entity that is commonly perpetuated by a high velocity injury. There are both bony and soft tissue factors responsible for the nonunion. This paper is focused on the reported clinical and radiographic outcomes whenever treatment protocols pertaining to distraction osteogenesis are implemented.