微型外固定器制作大鼠股骨萎缩型骨不连模型的实验研究

目的 探讨以自行研究设计的微型外固定器建立股骨萎缩型骨不连动物模型。方法 以自行研究设计的外固定器为固定装置,选取24 只健康雄性Lewis大鼠,随机分为2组：骨不连组和对照组,每组12只。于大鼠右侧股骨截骨,在2个断端之间留1 mm间隙,于股骨前外侧面近端放置一对自攻螺纹钉,同样方法,在远端放置另一对自攻螺纹钉。其中骨不连组去除骨髓和破坏骨膜,对照组不进行此操作。术后2、4、8周影像学观察股骨对位情况、外固定器的位置及截骨区的愈合情况。术后8周取材行组织学检查和生物力学检测。结果 术后8周时X线片示：对照组骨断端已愈合,髓腔再通;骨不连组骨断端处无连续性骨痂通过,骨断端清晰可见。组织学检查显示：对照组有大量新骨形成,骨断端与正常骨无差异;骨不连组截骨区无骨性连接,截骨端未愈合。8 周时生物力学检测显示：对照组的扭转刚度平均为(2.64±0.40)N·mm/deg,骨不连组为(0.21±0.20)N·mm/deg,差异有统计学意义（t=16.168,P=0.000）。结论 本实验研究为组织工程及细胞生物技术治疗萎缩型骨不连的研究提供了一种可靠的动物模型。     

Assessment of bone union/nonunion in an experimental model using microcomputed technology

BACKGROUND: High-resolution microcomputed tomography (microCT) is one of the most recent technical developments to visualize and quantify primarily cancellous bone. Regarding bone formation, microCT is becoming increasingly important, although its reliability has not yet been evaluated. Our study had two goals: to develop a reproducible nonunion model and to determine the efficacy of microCT for the assessment of bone healing in this model. METHODS: The designed fracture model in the rat simulates secondary fracture healing. After plate fixation to the femur, diaphysis transverse middiaphyseal osteotomy was performed with a reciprocating saw, resulting in a 0.38-mm gap with a defect of bone and periosteum corresponding to the thickness of the blade. Proximally and distally to this gap, the periosteum was preserved. Thus, three separate zones were defined: proximal femur diaphysis with periosteum, gap, and distal femur diaphysis with periosteum. In the nonunion group (NM group), a model of impaired bone healing (nonunion), silicone foil was wrapped around the femur diaphysis to block any influence from surrounding tissue. Coverage of the bone repair site by thigh muscles was designed for a model of bone union (M group). Four weeks postoperatively, callus formation was determined by conventional anterior-posterior and lateral plain radiographs. Ten weeks later, a second x-ray series was done as the clinical standard evaluation method. Afterward, specimens were harvested for microCT examination (two-dimensional and three-dimensional [3D]). Biomechanical testing was carried out to determine fracture healing. RESULTS: Our model is highly reproducible and results in bone nonunion in five out of six cases (83.3%). In determining fracture site, plain radiographs the least reliable method in comparison to the biomechanical testing which is the most accurate reference method. In contrast, microCT (the 3D reconstruction) showed significant correlation (r = 1) to the results assessed by biomechanical testing, whereas microCT was correct in 100%. We found bone healing in five out of six animals in the M group verified by microCT (in accordance to biomechanical data). In the M group, significantly enhanced bone formation (50%) (p = 0.008) was observed within the osteotomy site (i.e. within the gap), but there was no difference in periosteal bone formation between the groups proximally and distally to the gap. Interestingly, we did not find statistically significant differences in mineralization. CONCLUSION: We conclude that microCT with 3D reconstruction is the optimal method diagnostic tool in fracture healing, especially in nonunion. Furthermore, direct coverage of the fracture site by muscle flaps results in a mineralized enhanced bone formation within the osteotomy site (i.e. within the gap). Skeletal muscle coverage hypothetically might have osteogenic augmentation potential, thus being able to prevent pseudoarthrosis.     

Nonunion using a canine model

The investigation involved a search for a model of atrophic nonunion. Fifty-two mature, adult, mongrel dogs were used to study the repair after creating a 0.5-cm bone defect in the mid-diaphysis of the radius. In addition, a 2-cm wide strip of periosteum was circumferentially resected from each osteotomy extremity. No immobilization was used thereafter. The reparative process was assessed by X-rays, histology, vascular injection, and scintigraphy. The dogs we distributed into three groups according to the time of follow-up (1, 3, and 6 months). Two kinds of repair were recognized after 3 months and were well-established after 6 months: disturbed healing with much callus (54%) and disturbed healing with absent or scanty callus (46%). In the first instance, the periosteum had regenerated and produced the external callus. The bone ends were capped with fibrocartilage; the vascularization around the defect was increased and displayed a well-defined vascular picture. In the healing pattern with absent external callus (atrophic nonunion), the bone defect was enlarged and filled with fibrous tissue, but there was no deficient vascularization in and around the osteotomy. Radioactivity counting showed an increased uptake around the osteotomy site in both types of repair, which persisted over time but was higher in the 1-month group. It was concluded that the present model yields a consistent pattern of a disturbed reparative process that mimics human cases of atrophic or hypertrophic nonunion. The differences between the two kinds of repair seemed to be related to the periosteal capacity of regeneration.     

高能量骨折延期手术促进骨愈合的实验研究

目的研究延期手术刺激旺盛的外骨痂生长在高能量骨折中的作用,探索提升骨折愈合能力的新途径。方法取成年狗20只,随机分为ABCD四组,各组均行股骨中段线锯截骨,电凝破坏周围骨膜,制造1 cm缺损,8孔钢板固定。A组截骨14 d后行内固定,B组即时内固定,C组即时内固定,但不用电凝破坏骨膜,D组14 d后行内固定,但固定时切除骨端周围已形成的肉芽。结果狗股骨破坏骨膜制造骨缺损后,早期手术固定组无外骨痂生长,几乎无内骨痂生长,引发了萎缩性骨不连;在同样破坏骨膜制造骨缺损的情况下延期手术固定组产生了旺盛的骨痂生长,产生了稳定固定下的骨痂愈合。结论高能量骨折早期手术固定抑制外骨痂生长,容易造成骨痂生长不良的低质量愈合现象。延期手术固定可以刺激良好的外骨痂生长,改善骨折愈合能力,预防骨不连的发生。     

Development of an atrophic nonunion model and comparison to a closed healing fracture in rat femur.

Although most fractures heal, some fail to heal and become nonunions. Many animal models have been developed to study problems of fracture healing. The majority of nonunion models have involved segmental bone defects, but this may not adequately represent the biologic condition in which nonunions clinically develop. The objective of the present study is to develop a nonunion model that better simulates the clinical situation in which there is soft tissue damage including periosteal disruption and to compare this model to a standard closed fracture model utilizing identical fracture stabilization, providing a similar mechanical environment. A total of 96 three month old Long Evans rats were utilized. A 1.25 mm diameter K-wire was inserted into the femur in a retrograde fashion, and a mid-diaphyseal closed transverse fracture was created using a standard three-point bending device. To create a nonunion, 48 of the rats received additional surgery to the fractured femur. The fracture site was exposed and 2 mm of the periosteum was cauterized on each side of the fracture. Fracture healing was evaluated with serial radiographs every two weeks. Animals were maintained for intervals of two, four, six or eight weeks after surgery. Specimens from each time interval were subjected to biomechanical and histological evaluation. None of the cauterized fractures healed throughout the eight weeks experimental duration. The radiographical appearance of nonunion models was atrophic. This investigation showed pronounced differences between the experimental nonunions and standard closed fractures both histologically and biomechanically. In conclusion, we have developed a reproducible atrophic nonunion model in the rat femur that simulates the clinical condition in which there is periosteal disruption but no bone defect.     

Prevention of atrophic nonunion development by recombinant human bone morphogenetic protein-7.

Severe periosteal and soft tissue disruption at the time of fracture may result in the formation of an atrophic nonunion. We have developed a reproducible atrophic nonunion in an animal model. The purpose of this study was to evaluate whether the immediate application of recombinant human BMP-7 to the fracture site could rescue the healing process in this nonunion model. A total of 56 three month old Fisher 344 rats were utilized. A 1.25 mm diameter K-wire was inserted into the femur in a retrograde fashion, and a mid-diaphyseal closed transverse fracture was created using a standard three point bending device. To create a nonunion, the fracture site was exposed and 2 mm of the periosteum was cauterized on each side of the fracture. The fracture site was immediately treated with either the application of rhBMP-7 50 microg in 25 microl of rat tail tendon collagen buffer (BMP-7 group), or with 25 microl of rat tail tendon collagen buffer only (Control group). Fracture healing was evaluated with serial radiographs every two weeks for an eight weeks period. Specimens at four and eight weeks were subjected to biomechanical and histological evaluation. None of the Control group healed throughout the eight weeks experimental duration. At four weeks 63% of the BMP-7 group had healed, and all had healed by six weeks. This investigation showed pronounced differences between the BMP-7 group and the Control group both histologically and biomechanically. In conclusion, we have demonstrated that the immediate application of BMP-7 may rescue the fracture healing process and prevent the development of nonunion following severe periosteal disruption.     

Vascularity in a new model of atrophic nonunion

Our aim was to develop a clinically relevant model of atrophic nonunion in the rat to test the hypothesis that the vessel density of atrophic nonunion reaches that of normal healing bone, but at a later time-point. Atrophic nonunion is usually attributed to impaired blood supply and is poorly understood. We determined the number of blood vessels at the site of an osteotomy using immunolocalisation techniques in both normally healing bones and in atrophic nonunion. At one week after operation there were significantly fewer blood vessels in the nonunion group than in the healing group. By eight weeks, the number in the atrophic nonunion group had reached the same level as that in the healing group. Our findings suggest that the number of blood vessels in atrophic nonunion reaches the same level as that in healing bone, but at a later time-point. Diminished vascularity within the first three weeks, but not at a later time-point, may prevent fractures from uniting.     

Comparison of healing process in open osteotomy model and open fracture model: Delayed healing of osteotomies after intramedullary screw fixation

Murine osteotomy and fracture models have become the standard to study molecular mechanisms of bone healing. Because there is little information whether the healing of osteotomies differs from that of fractures, we herein studied in mice the healing of femur osteotomies compared to femur fractures. Twenty CD‐1 mice underwent a standardized open femur osteotomy. Another 20 mice received a standardized open femur fracture. Stabilization was performed by an intramedullary screw. Bone healing was studied by micro‐CT, biomechanical, histomorphometric and protein expression analyses. Osteotomies revealed a significantly lower biomechanical stiffness compared to fractures. Micro‐CT showed a reduced bone/tissue volume within the callus of the osteotomies. Histomorphometric analyses demonstrated also a significantly lower amount of osseous tissue in the callus of osteotomies (26% and 88% after 2 and 5 weeks) compared to fractures (50% and 100%). This was associated with a delayed remodeling. Western blot analyses demonstrated comparable BMP‐2 and BMP‐4 expression, but higher levels of collagen‐2, CYR61 and VEGF after osteotomy. Therefore, we conclude that open femur osteotomies in mice show a markedly delayed healing when stabilized less rigidly with an intramedullary screw. This should be considered when choosing a model for studying the mechanisms of bone healing in mice. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:971–978, 2015.     

Percutaneous autologous concentrated bone marrow grafting in the treatment for nonunion

The purpose of this study was to evaluate the clinical and radiographic treatment effects of percutaneous autologous concentrated bone marrow grafting in nonunion cases and to evaluate the effectiveness of this grafting procedure. We enrolled 17 cases those had atrophic changes due to continuous nonunion for over 9 months after injury and had undergone low-intensity pulsed ultrasound treatment for more than 3 months. The site of nonunion was the femur in 10 cases, the tibia in 5 cases, the humerus in 1 case, and the ulna in 1 case. They underwent percutaneous autologous concentrated bone marrow grafting and continued low-intensity pulsed ultrasound stimulation treatment after grafting. Patients were evaluated using the visual analogue scale for pain at immediately before the procedure, 3, 6, and 12 months after grafting. Plain radiographs of the affected site were taken and evaluated about the healing of the nonunion site at each clinical evaluation. As quantitative assessment, CT scans were undertaken before the procedure and 6 months after grafting. The visual analogue scale pain score was reduced consistently after grafting in all patients. About the healing at the nonunion site, 11 and 13 cases of bone union were observed at 6 and 12 months after grafting. The mean volume of callus formation based on CT images was 4,147 (262–27,392) mm³ total between grafting and 6 months. Percutaneous autologous concentrated bone marrow grafting is an effective procedure for the treatment of patients with nonunion.     

Recombinant human vascular endothelial growth factor enhances bone healing in an experimental nonunion model

The re-establishment of vascularity is an early event in fracture healing; upregulation of angiogenesis may therefore promote the formation of bone. We have investigated the capacity of vascular endothelial growth factor (VEGF) to stimulate the formation of bone in an experimental atrophic nonunion model.Three groups of eight rabbits underwent a standard nonunion operation. This was followed by interfragmentary deposition of 100 microg VEGF, carrier alone or autograft. After seven weeks, torsional failure tests and callus size confirmed that VEGF-treated osteotomies had united whereas the carrier-treated osteotomies failed to unite. The biomechanical properties of the groups treated with VEGF and autograft were identical. There was no difference in bone blood flow. We considered that VEGF stimulated the formation of competent bone in an environment deprived of its normal vascularisation and osteoprogenitor cell supply. It could be used to enhance the healing of fractures predisposed to nonunion.     

Osteogenic ability of free periosteal autografts in tibial fractures with severe soft tissue damage: an experimental study

OBJECTIVE: The present study was undertaken to assess whether free nonvascularized autologous periosteum transplants enhance bone healing in a rabbit fracture model designed to resemble a tibial fracture with severe soft tissue damage. DESIGN: Transplantation of free autologous periosteal grafts on the anteromedial site of the tibia (experimental group) was compared with nontransplantation on the contralateral tibia (control group). We produced a standardized transverse osteotomy of both tibial diaphyses in white male adult New Zealand rabbits. The endomedullary cavity was reamed and nailed, and then a one-centimeter segment of periosteum was excised from either side of the osteotomy. To prevent periosteal and extraosseous ingrowth at the osteotomy site, a silastic sheet was wrapped around two-thirds of the circumference of the tibia. In the first group, on the silastic-free bone window, we then spanned the osteotomy with a free, nonvascularized, longitudinally oriented autologous periosteum and sewed it to the adjacent periosteum both proximally and distally. In the second group, the periosteum was placed transversely, leaving a gap between it and the adjacent periosteum proximally and distally. Revascularization of the graft was determined with the colored microsphere technique. MAIN OUTCOME MEASUREMENTS: Histomorphometric analysis of the periosteal callus was done on a transparent grid superimposed on enlarged photographs of the histologic sections. RESULTS: Free, nonvascularized, longitudinally placed autologous periosteum in contact with intact periosteum produced significantly more periosteal callus than was seen in the control group, in which no periosteal graft was used. However, when transversely placed periosteal grafts were set in the silastic-free bone window and there was no contact with surrounding remnants of intact periosteum, no significant difference in callus production was noted when compared with the control. Revascularization of these grafts was seen within one week after transplantation. Bone healing occurred mainly through endochondral ossification. CONCLUSION: Our data suggest that orthotopically placed autologous nonvascularized periosteum retains its osteogenic potential in a poorly vascularized environment such as a tibial fracture with severe soft tissue damage. The effect is enhanced if the graft is in contact with intact periosteum. Histologically, callus formation after periosteal grafting resembles endochondral and intramembranous ossification.     

基因修饰的组织工程骨联合带血管蒂骨膜移植修复长段骨缺损的研究

目的评价骨形态发生蛋白2（bone morphogenetic protein2,BMP-2）基因修饰的组织工程骨联合带血管蒂骨膜移植修复长段骨缺损的效果。方法分离培养兔骨髓基质干细胞,经BMP-2基因转染后复合异种骨支架体外构建基因修饰的组织工程骨（gene modified tissue engineering bone,GMB）。建立兔双侧桡骨缺损（长2.5cm）模型,采用5种方法修复。A组：GMB＋带血管蒂骨膜移植;B组：GMB＋血管束植入;C组：GMB＋游离骨膜移植;D组：GMB;E组：单纯支架。于术后第4、8、12周行X线、组织学、生物力学测定和微血管墨汁灌注等观察血管形成及成骨情况。结果①A组血运建立快,第8周时即可修复骨缺损,其修复机制包括膜内成骨和软骨成骨两种机制;②B组血管束发出分支向移植骨内长入,但中心区成骨缓慢,第12周时骨缺损得到完全修复;③C组第4周时游离骨膜成活并发出微小血管,第8周时形成薄层外骨痂,第12周时骨缺损基本修复;④D组在BMP-2基因诱导下成骨速度和质量优于E组,可在第12周时使骨缺损部分修复,但中心区呈＂空心＂现象;而E组第12周时形成骨不连,缺损区内被纤维组织填充。结论带血管蒂骨膜与BMP-2基因修饰的组织工程骨联合移植,既提供了血运又提供了骨膜成骨细胞,同时具有良好的骨生成、骨诱导和骨引导作用,是治疗节段性骨缺损较为理想的方法。     

可控性应力与微动对骨折愈合影响的组织学研究

目的 探讨骨折端在不同轴向应力作用下,不同骨折愈合时期所需轴向应力的适宜力值. 方法 32只青山羊均行股骨干中段横行截骨制作骨折模型,按骨折端施加实验动物自身体质量的0倍(对照组)、1/6(A组)、1/3(B组)、1/2(C组)应力分为4组,每组8只.术后4、8周分批处死,每次每组处死4只,行大体观察和组织学观察,测量骨折端骨外膜骨痂面积. 结果 对照组有1只动物骨折端发生成角畸形,实验A、B、C组分别有1、2、4只动物骨折端发生成角畸形.术后4周,对照组、A、B、C组骨折端骨外膜骨痂面积平均值分别为(1.15±0.34)、(1.86±0.28)、(2.18±0.36)、(1.99±0.33)cm~2,A、B、C组分别与对照组比较,骨折端骨痂生成多,骨外膜骨痂面积差异有统计学意义(P<0.05).术后8周,沿轴向排列骨外膜骨痂中骨性骨痂多、致密,皮质骨松化明显;对照组、A、B、C组骨折端骨外膜骨痂面积平均值分别为(1.38±0.31)、(2.09±0.23)、(2.69±0.28)、(2.71±0.31)cm~2,A、B、C组分别与对照组比较,B、C组分别与A组比较,差异均有统计学意义(P<0.05). 结论 骨折端施加轴向应力时能促进骨折端骨痂生长,较大的应力强度能更好地促进骨折端骨痂生长,但同时会造成骨折愈合成角畸形发生率增高.骨折端施加自身体质量的1/3应力时骨折端成角畸形发生率较低,最适宜促进骨折端骨痂生长.     

A study of diaphyseal fracture repair using tissue isolation techniques.

The repair of an osteotomy of the rabbit tibia was studied by arterial radiography and by histology following selective isolation of the potential sources of the fracture callus. The periosteum was isolated by reaming and nailing the medullary cavity and the bone marrow was isolated by applying a Silastic sheath around the shaft. The results revealed certain features of periosteal and medullary healing.     

Percutaneous autologous bone marrow transplantation for nonunion of the femur.

Percutaneous bone marrow injections were performed on 7 nonunions of the femur. There were 6 hypervascular nonunions and one avascular nonunion. Two nonunions presented with active infections. One other patient had a history of infection which had subsided. One nonunion received the injection twice. After the site of nonunion was curetted and the bone surface was scored, 150 ml of bone marrow aspirated from the iliac bone was injected. Complete union occurred in 4 patients within 9 months; all of them were uninfected hypervascular nonunions following intramedullary nail fixation. One nonunion with a bone defect united partially leaving a 1 x 1 cm defect. The two infected femoral nonunions failed to unite. The results show that percutaneous autologous bone marrow injection for femoral nonunions can be considered for uninfected hypervascular nonunions following intramedullary nail fixation. In these cases stimulation of healing processes of fracture leading to consolidation can be expected from bone marrow injection. However, femoral nonunion with an active infection and loss of fixation is considered to be a contraindication for this technique.     

Augmentation of fracture healing by hydroxyapatite/collagen paste and bone morphogenetic protein‐2 evaluated using a rat femur osteotomy model

In fracture treatment, biological bone union generally depends on the bone's natural fracture healing capacity, even in surgically treated cases. Hydroxyapatite/collagen composite (HAp/Col) has high osteoconductivity and stimulates osteogenic progenitors. Furthermore, it has the potent capacity to adsorb bone morphogenetic proteins (BMPs). In this study, we prepared an injectable HAp/Col paste and evaluated its augmentation of bone union. Furthermore, the effect of HAp/Col paste combined with BMP‐2 was also evaluated. We used a rat femur osteotomy model with a defect size of 1 mm. Male Wistar rats were assigned to one of the following four groups; a control group without any implant, a HAp/Col implant group, a group that received an absorbable collagen sponge (ACS) implant impregnated with BMP‐2 (1 μg), and a group that received a HAp/Col implant impregnated with BMP‐2 implant. Micro‐CT analysis, three‐point bending tests, and histological evaluation were performed. Bone union was achieved in two of eight cases in the HAp/Col group, five of eight cases in the ACS + BMP‐2 group, and all cases in the HAp/Col + BMP‐2 group at 8 weeks post‐surgery. The control group did not achieve bone union. In addition, in the HAp/Col + BMP‐2 group, the biomechanical strength of the fused femurs was comparable to that of the contralateral intact femur; the ratio of the mechanical load at the breaking point of the osteotomy side relative to that of the contralateral side was 1.00 ± 0.151 (SD). These results indicate that HAp/Col paste with or without BMP‐2 augments bone union. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:129–137, 2018.     

四肢难治性骨不连的三种治疗策略疗效分析

[目的] 比较分析3种方法治疗四肢难治性骨不连的临床疗效.[方法] 2003年4月-2008年2月,共收治四肢难治性骨不连36例39肢,男22例,女14例;年龄15～71岁,平均51.5岁;胫骨19肢,肱骨9肢,股骨7肢,尺、桡骨4肢;治疗骨不连手术次数1～4次,平均2.5次;术前X线片骨不连骨断端距离:4.5～36 mm,平均16.5 mm;下肢短缩距离:5～40 mm,平均21 mm.自体骨髓复合人工骨联合髂骨骨膜移植19肢(联合组),自体骨髓移植联合人工骨9肢(骨髓组),自体髂骨移植治疗11肢(髂骨组).[结果] 39肢最终均达骨性愈合,均获随访12～28个月,平均18.5个月.骨愈合时间、固定物取出1个月患肢功能评分和术后X线片评分,联合组疗效优越(P＜0.05).联合组骨愈合时间(5.5±1.5)个月,骨髓组骨愈合时间(6.6±1.8)个月,髂骨组骨愈合时间(7.4±2.1)个月.[结论] 自体骨髓复合人工骨联合髂骨骨膜移植治疗四肢难治性骨不连临床疗效优越.     

A 5-mm femoral defect in female but not in male rats leads to a reproducible atrophic non-union

Introduction  

The objectives of this study were to (1) establish a reproducible atrophic non-union model in rats by creation of a segmental femoral bone defect that allows, (2) in-depth characterization of impaired healing, and (3) contrast its healing patterns to the normal course. Hypothesis was that a 5-mm bone defect in male rats would deviate from uneventful healing patterns and result in an atrophic non-union.     

A novel model to study metaphyseal bone healing under defined biomechanical conditions

Introduction  Experimental studies on metaphyseal fractures are rare and do not control the biomechanical conditions in the healing zone. This study aimed to develop an improved experimental model, which characterizes and controls the biomechanical condition in the fracture gap of a metaphyseal fracture. Materials and methods  A partial osteotomy model in the distal femur of the sheep was developed. The osteotomy was located in the region of the trochlea groove. The osteotomy gap was 3 mm wide. The retro-patellar force acting on the joint in vivo causes a bending of the trochlea resulting in a narrowing of the osteotomy gap. To limit and control this interfragmentary movement, stainless steel plates of various thicknesses were implanted into the osteotomy gap. Forces acting on the trochlea were analyzed and a load-deflection curve of the model was determined in vitro. A pilot study on two sheep was performed using the new model with two different interfragmentary movements of 0.3 or 1 mm. Eight weeks, post-operatively, the sheep were sacrificed and undecalcified histology was performed. Results  The biomechanical analysis of the joint forces and the in vitro load-deflection behavior of the trochlea revealed that the forces acting on the trochlea were high enough to cause an interfragmentary movement of 1 mm in the osteotomy gap. This was confirmed by an X-ray of the sheep, which showed a closing of the proximal osteotomy gap under weight-bearing conditions. The histological section revealed no external callus formation. The sheep with the 0.3 mm interfragmentary movement showed almost complete bridging of the osteotomy gap with woven bone whereas the sheep with the 1 mm interfragmentary movement exhibited new bone formation only at the borderline of the osteotomy but larger areas with connective tissue or even fibrous cartilage in the center of the gap. Conclusion  This metaphyseal bone-healing model provides defined and adjustable biomechanical conditions. The histological images demonstrated intramembranous and endochondral bone healing in the osteotomy gap without callus formation. The model therefore seems appropriate to study metaphyseal bone healing under differing mechanical conditions.     

Local delivery of growth factors from coated titanium plates increases osteotomy healing in rats

Different methods for the stabilization of long bone fractures are used in clinic. Besides the development of further stabilization devices, the use of new materials, the modification of the surfaces, and the local application of stimulating factors for enhancement of healing are from great interest. Previous studies successfully used a biodegradable poly(d,l-lactide) coating as a local drug delivery system of growth factors from intramedullary (IM) implants to enhance fracture healing. In this study, we developed a new rat model (n = 60) for plate osteosynthesis and used a plate for stabilization and as a local drug delivery system for the growth factors IGF-I and TGF-beta1. A four-hole titanium plate was used for stabilization of a 0.6-mm osteotomy gap of the femur. The space between the inner holes was coated with 50 microg IGF-I and 10 microg TGF-beta1 incorporated in the poly(d,l-lactide) coating or with the coating alone. After 42 days, biomechanical tests and histomorphological analyses were performed to investigate osteotomy healing. Radiologically small differences were detectable between the groups. The biomechanical torsional testing revealed a significantly higher maximum load of the osteotomized femura after treatment with growth factors compared to the uncoated group. In the histomorphometric analyses measuring the callus composition, a significantly higher percentage of mineralized tissue in the osteotomy callus was assessed in the growth factor treated group compared to the uncoated. In conclusion, the local application of IGF-I and TGF-beta1 from a biodegradable coating enhances the osteotomy healing as shown in the biomechanical testing and the histomorphometry. Bioactive plates could be used in clinic for fracture stabilization and for local and controlled application of growth factors to stimulate bone healing.