Effects of graded reaming on fracture healing: Blood flow and healing studied in rat femurs

In 30 rats, closed bilateral fractures of the femur were produced. On the left side intramedullary reaming was performed to 1.6 mm, and the fracture fixed with a steel pin with a diameter of 1.6 mm. On the right side the femoral canal was reamed to 2.0 mm and a hollow steel tube with a diameter of 2.0 mm was used for fixation. An additional 8 rats were used to obtain mechanical, dimensional and flow data on intact femurs, and another 10 rats were used to study the acute flow changes caused by fracture and different degrees of reaming and fracture.

Fracture and reaming reduced total bone and cortical bone blood flows to about one third of normal flow, with no differences between the 1.6-mm and the 2.0-mm reamed bones. At 4 weeks, total bone flow was about double and cortical bone flow about 4 times increased in the 1.6-mm group. In the 2.0-mm reamed bones increases of approximately 5 times in total bone flow and of about 7 times in cortical flow were found. Callus flow was about twice the size of the respective cortical flow in both groups. Both total and cortical flows gradually subsided, without differences between the 2 groups. At 12 weeks, the callus area in the 2.0-mm group was greater than in the 1.6-mm group, while bone dimensions were greater in the 2.0-mm group at 4 and 12 weeks. Bending moment and rigidity were greater in the 1.6-mm group than in the 2.0-mm one at every time interval; no differences were found in fracture energy.

We conclude that, in terms of healing, modest reaming is preferable to extensive reaming. The adverse effect of extensive reaming is not due to excessive flow derangement at the acute stage or to impaired vascularity at the phase of remodeling.     

Blood flow and mechanical properties of healing bone. Femoral osteotomies studied in rats.

In male Wistar rats, a transverse osteotomy at the midshaft of the femur was made, and the acute effects on bone flow were measured before and after reaming. Flow and mechanical variables in the healing bones were measured at 4, 8, and 12 weeks following osteotomy. Osteotomy reduced total bone blood flow by about 50 percent, and cortical flow in the diaphysis by approximately 40 percent. Cortical flow was equally diminished in the mid-diaphysis and in the osteotomy area, and no differences between the proximal and distal diaphyseal flows were found. Reaming of the osteotomized bones did not lead to any further flow reduction. At 4 weeks, total bone flow was more than doubled; increases were found in every segment of the fractured bone, and a more than 10-fold increase in the callus area was seen. At the end of the experiment, the femurs had regained 83 percent of their normal strength, 88 percent of normal rigidity and 78 percent of normal fracture energy. At this time total bone flow was marginally increased, flows in the proximal and the distal diaphyses were almost normalized, while a nearly 3-fold increase was still found in the callus area. Flow in the callus area gradually decreased during healing, and regression analysis demonstrated a negative correlation between callus flow and mechanical properties.     

Closed versus open medullary nailing of femoral fractures. Blood flow and healing studied in rats.

In rats, bilateral closed femoral fractures were produced. On the left side, closed intramedullary nailing was done, and on the right side, the nail was inserted by an open procedure. The healing process of the fractures was evaluated at 4, 8, and 12 weeks, bone and muscle blood flows were also determined. Reaming had no acute impact on bone blood flow, while reaming and fracture halved total bone flow (P < 0.04), and reduced cortical diaphyseal flow to approximately one quarter (P < 0.01). No differences were found between the open and closed methods. At 4 weeks, the bending moment, rigidity, and fracture energy of the fractures treated by closed medullary nailing were greater than those treated by open nailing. The fracture energy was still greater at 8 weeks, while no differences were seen in bending moment and rigidity. At 12 weeks, however, there were no differences in the mechanical parameters. Bone blood flows in both the cortical diaphysis and callus area were increased at 4 and in the callus area at 8 weeks in bones treated by the open method. No differences were found at the end of the experiment. Muscle blood flow was not different in the two limbs, and was constant during the experimental period. We conclude that femoral fractures treated by closed nailing heal better in the initial phase compared with those that have been openly nailed. This difference cannot be explained by an impaired muscle or bone blood flow due to open surgery.     

Closed versus open medullary nailing of femoral fractures

In rats, bilateral closed femoral fractures were produced. On the left side, closed intramedullary nailing was done, and on the right side, the nail was inserted by an open procedure. The healing process of the fractures was evaluated at 4, 8, and 12 weeks, bone and muscle blood flows were also determined. Reaming had no acute impact on bone blood flow, while reaming and fracture halved total bone flow (P < 0.04), and reduced cortical diaphyseal flow to approximately one quarter (P < 0.01). No differences were found between the open and closed methods. At 4 weeks, the bending moment, rigidity, and fracture energy of the fractures treated by closed medullary nailing were greater than those treated by open nailing. The fracture energy was still greater at 8 weeks, while no differences were seen in bending moment and rigidity. At 12 weeks, however, there were no differences in the mechanical parameters. Bone blood flows in both the cortical diaphysis and callus area were increased at 4 and in the callus area at 8 weeks in bones treated by the open method. No differences were found at the end of the experiment. Muscle blood flow was not different in the two limbs, and was constant during the experimental period.

We conclude that femoral fractures treated by closed nailing heal better in the initial phase compared with those that have been openly nailed. This difference cannot be explained by an impaired muscle or bone blood flow due to open surgery.     

Graded exchange reaming and nailing of non-unions

The effect of graded exchange reaming and intramedullary nailing on a non-union model in the rat femur was studied by clinical, radiological, bone mineralisation and biomechanical methods. A standardised procedure was first developed to create a non-union that did not heal and in which non-union developed consistently. In 30 male Wistar rats a standardised osteotomy was produced in the left femur diaphysis. The fractures were reamed to 1.5 mm and nailed with a soft polyethylene nail for 12 weeks. After 1 week the fractures were manipulated in bending and rotation every 2nd day for 5 weeks. At 12 weeks radiographs demonstrated a hypertrophic non-union in all fractures, and the rats were randomly divided into three groups. In the control group no reoperation was performed (group C). In group 1.6 exchange reaming to 1.6 mm and medullary nailing were performed, and reaming and nailing to 2.0 mm in group 2.0. The effect of extensive versus modest reaming and nailing on bone repair was then assessed 12 weeks later. Physical examination, radiographs, bone mineralisation measurements by dual energy X-ray absorptiometry (DEXA) and biomechanical femures evaluated by a three-point bending test in a Mini Bionix (MTS) testing system were employed. In the control group radiographs revealed a state of non-union in all fractures, and the mechanical strength was significantly reduced compared with both intervention groups. Bone mineral content (BMC) and bone mineral density (BMD) were reduced in the callus region compared with group 2.0. In the intervention groups radiographs showed various degrees of union. Mechanical testing showed that the fracture energy was significantly higher in group 2.0 than in group 1.6. The finding that extensive exchange reaming and nailing seems favourable in non-unions of diaphyseal fractures compared with modest reaming may have clinical implications. Received: 18 December 1997     

Effect of Instability on Experimental Fracture Healing

Bilateral tibial osteotomy with fracturing of the fibula was performed on ten Wistar rats weighing 300-350 g. Intramedullary nailing was performed with 1.4 mm nails after reaming. On the left side solid stainless rods were used, while on the right side the nails had a middle part made of titanium-nickel wire covered with polyvinyl-chloride (PVC), giving the nail a high degree of flexibility.

After 8 weeks, nine of the ten flexible nails showed fracture of the central wire. The continuity was, however, maintained by the PVC tube. The bones with flexible nailing always showed hypertrophic callus while there was only scanty callus on the side with rigid nailing.

Strength, deformation at fracture and stiffness were measured in a three-point bending test after removal of the solid nails and the fibulae. The strength of the tibiae was greatest on the side with flexible nailing, as was the deformation at fracture. The mean stiffness was higher in the bones with rigid nails, but the difference here was not statistically discernible.     

Material properties are related to stress fracture callus and porosity of cortical bone tissue at affected and unaffected sites

Stress fractures are overuse injuries of bone that affect elite athletes and military recruits. One response of cortical bone to stress fracture is to lay down periosteal callus. The objectives of this study were to determine if material properties are different among bones with different stages of stress fracture callus, at both a callus site and at a distal site. Cortical specimens were mechanically tested to determine their stress–strain response. Material property differences were examined using nonparametric and regression analyses. At the callus site, material properties were low during the earliest stages of callus, higher with increasing callus maturity, but dropped at the late stage of callus. At the distal site, the material properties were low during early stages of callus and approached, or returned to, those of bones without callus during the late stages of callus. The effects of stress fracture and bone callus are not limited to the focal site of stress fracture. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1272–1279, 2009     

Intramedullary reaming for press-fit fixation of a humeral component removes cortical bone asymmetrically

Periprosthetic humeral fractures are major complications of shoulder arthroplasty. Bone removal during surgical reaming is a risk factor for these fractures. Although it is recognized that the endosteal surface of the humerus is asymmetrical whereas the reamers are symmetrical, to our knowledge, the effect of cylindrical reaming on the pattern of cortical bone removal during reaming has not been previously studied. The medullary canals of 10 cadaveric humeri (mean age, 73 years) were reamed in a manner similar to that used during humeral arthroplasty. Cortical dimensions were obtained from computed tomography scans before and after reaming. In unreamed humeri, the anterior-posterior endocortical diameter was 20% smaller than the medial-lateral diameter. The average medial-lateral diameter (15.6 +/- 2.3 mm) was significantly greater than the anterior-posterior diameter (12.5 +/- 1.9 mm) at 13 cm distal to the tuberosity (P < .00005). Successive cylindrical reaming preferentially thinned the anterior and posterior cortices. This bone loss would not be apparent on anterior-posterior radiographs. Intramedullary reaming to obtain substantial cortical contact asymmetrically removes cortical bone in a manner that may increase the risk of periprosthetic fracture.     

Viable osteoblastic potential of cortical reamings from intramedullary nailing.

To analyze the effect of intramedullary reaming on fracture healing, we investigated whether or not cortical reamings contain viable bone cells. There are several tissue components contained in medullary reamings including blood, bone marrow and cortical bone. This study is focused on the cortical reamings, which are produced during reaming of the medullary cavity. They may stimulate fracture healing but it is still unclear if they contain vital bone cells. We tested the hypothesis that these cortical reamings are a source of viable bone cells and compared cell cultures with cultivated cells from iliac crest biopsies. Responses of protein content and ALP activity to vitD stimulation in the cells were considered as properties of viability. Ten in tact living sheep femora were fully reamed and the cortical reamings were cultivated in a standard manner and compared with cultivated cells from ipsi-lateral iliac crest biopsies from the same animals. Cells started to grow from the reamings as well as the iliac crest within 2-5 days, and covered the entire culture flask within 9-13 days. Protein content and ALP activity in cells from both reamings and iliac crest were significantly responsive to vitD stimulation. Cortical reamings from intramedullary nailing have osteoblastic potential and contain living bone cells similar to bone cells from the iliac crest. These findings may further explain the superior healing of fractures, treated with reamed nailing.     

Vascular and structural changes in rat femora following nailing and intramedullary occlusion

The purpose of this study was to evaluate biomechanical, structural, and blood flow changes of the femoral canal in rats 12 weeks after intramedullary reaming, nailing, or occlusion. In one group, reaming alone was performed. In a second group, reaming was followed by use of a tight-fit steel nail. In a third group, reaming was followed by use of inert silicone that totally plugged the medullary cavity. A fourth group served as the control. The acute mechanical and vascular effects caused by reaming and nailing were determined in a separate group. Reaming and nail insertion reduced blood flow in femoral bone to about one-third. Reaming reduced bending moment by approximately 40%, whereas bending rigidity was unchanged. After 12 weeks, the cortical bone blood flow was significantly increased in both the nailed and the silicone-plugged bones compared with the reamed and control groups. The bending moment and energy absorption in the silicone group were inferior to those of the other groups. There were no differences in either the external or internal diameter or the medullary and net bone areas. In the silicone group, both the number and the area of large pores (larger than 10 μm) significantly increased in comparison with the other groups; hence, bone porosity was increased. This increment was confined to large pores. It is concluded that medullary occlusion contributes to structural and blood flow changes in bone.     

Effects of increased earth gravity and estrone treatment on intact and healing avian radii

Summary Estrone, 0.4 mg administered daily for 7 days to developing chicks at 2 weeks post hatching, increased total mass and accelerated the rate of growth of the diaphyseal and proximal epiphyseal diameters of intact radii. Fractured radii of animals subjected to the same hormonal treatment displayed decreased bone weight but increased rate of growth of the proximal epiphyseal diameters and longer but thinner and lighter calluses. Two-week-old chicks, which had received no estrone, when exposed to a week-long 2g environment showed decreased intact bone weight and, with the exception of length of fracture callus, a reduction of all measured parameters of fractured bones. Estrone treatments of 0.4 mg administered daily to hypergravity-exposed animals over a week-long period resulted in greater length of fracture callus and increased rate of growth of the proximal epiphyseal diameter of both intact and fractured bones. The same treatments decreased weight and linear growth of fractured bones and width and weight of the fracture callus.This paper is dedicated to the memory of my friend, John Camiscioni, Division of Research and Evaluation in Medical Education.     

单侧骨皮质缺损对长管状骨生物力学的影响

目的探讨长管状骨骨干不同大小的单侧骨皮质缺损对长管状骨生物力学性质的影响。方法取76根三黄鸡胫骨,随机分7组(1.5mm组n=11,2.0mm组n=9,2.5mm组n=13,3.0mm组n=12,3.5mm组n=8,4.5mm组n=11,皮质完整组即正常对照组n=12),于后侧骨皮质造成直径分别为1.5～4.5mm的环形骨缺损,进行三点弯曲单一实验,皮质完整组作为正常组对照。结果缺损直径为1.5mm及2.0mm组鸡胫骨达到结构破坏时的最大载荷与正常组差异无统计学意义(P=0.824,0.865),2.5mm、3.0mm、3.5mm组的最大载荷较正常组降低14%左右,差异有统计学意义(P=0.015,0.010,0.021);4.5mm组较正常组降低23%左右,差异有统计学意义(P=0.001)。结论单侧皮质缺损直径在长管状骨外径的(22.6±1.4)%以内时,不影响其抗弯曲性能;当其超过长管状骨外径的(29.4±2.1)%时,将降低长管状骨的抗弯曲性能,但降低的幅度跟缺损大小并不完全呈正比。     

Comparison of the effect of reamed and unreamed locked intramedullary nailing on blood flow in the callus and strength of union following fracture of the sheep tibia

This study was performed to compare the effects of reamed and unreamed locked intramedullary nailing on blood flow in the callus and early strength of union in a fractured sheep tibia model. After the creation of a standardized short spiral fracture by three-point bending with torsion, each tibia was stabilized by the insertion of a locked intramedullary nail. Ten animals were allocated randomly into two groups: one that had reaming prior to nail insertion and one that did not. Blood flow was measured in real time with use of laser Doppler flowmetry. Endosteal perfusion was determined at the fracture site before and after nail insertion. Perfusion of the callus was measured at three locations (proximal diaphysis, fracture site, and distal diaphysis) and at three time intervals (2, 6, and 12 week follow-up). All animals were killed 12 weeks postoperatively, and the tibiae were tested to failure in four-point bending. Nailing with reaming resulted in a larger decrease in overall endosteal perfusion than nailing without reaming (p < 0.015). The presence or absence of reaming did not affect blood flow within fracture callus. Perfusion of callus was greatest at 6 weeks of follow-up. Bending strength and stiffness were the same in both groups at 12 weeks. The study demonstrated that perfusion of callus and early strength of union are similar following intramedullary nailing with or without reaming.     

A finite element study of a fractured tibia treated with a unilateral external fixator: The effects of the number of pins and cortical thickness

IntroductionIn the early stage of fracture fixation, the aim of a unilateral external fixator (UEF) to stimulate healing and maintain stability may be suppressed by using inadequate number of pins. Cortical thinning due to age or osteoporosis endangers a successful fracture fixation.Materials and methodsThis study evaluates the initial strength and stability of the fracture fixation and tissue differentiation under the influences of variable cortical thickness (5 mm to 1 mm) and variable number of pins (1 to 4 in each bone fragment). A finite element program was utilised to develop 20 three-dimensional models of simplified diaphyseal tibia with fracture callus fixed with UEF. A mechano-regulation code based on the deviatoric strain theory was written and applied to simulate tissue differentiation. The values of von Mises stress, interfragmentary strain (IFS), and fibrocartilage index (FCI) were evaluated.ResultsCortical thinning from 5 mm to 1 mm increased IFS and FCI by an average of 30.3% and 18.7%, respectively, and resulted in higher stresses in the UEF and bone. Using 1 pin in each bone fragment produced excessive IFS in the models with 1 mm, 2 mm and 3 mm cortical thickness. Inserting the second pin into the bone fragment could considerably reduce the IFS and fibrocartilaginous tissue formation in the fracture site and improve load transmission to the fixator. Whereas inserting the fourth pin could minimally affect the mechano-biological environment of healing.ConclusionsThis study suggests that initial instability due to cortical thinning can be efficiently alleviated by adding the number of pins up to 3 in a UEF; additionally, it may improve the knowledge about applying UEFs adequately stable, whilst promoting inclination toward endochondral ossification, simultaneously.     

不同神经损伤对骨折前期愈合影响的实验研究

目的：研究脊髓和周围神经损伤对骨折前期修复的影响。方法：将实验大鼠分成3组，一组为T10脊髓横断伴股骨骨折，另两组分别为周围神经切断伴股骨骨折组和单纯股骨骨折组。骨折后2周和4周摄股骨X线片，4周处死大鼠行骨痂细胞和组织学检查。结果：骨折后2周3组均未出现明显骨痂，术后4周测量x线片骨痂大小显示周围神经切断组骨痂最多，其次分别为对照组和脊髓损伤组。组织学显示周围神经切断组骨痂量多，并有明显的皮质骨桥接断端，但其中类骨质较多，骨钙的沉积相对较少，而且骨痂缺乏血管和正常的骨小梁结构，骨化重建不够理想；而脊髓损伤组骨痂则表现为欠成熟，细胞种类多，分布紊乱，少部分仍处于纤维修复阶段。对照组的组织学改变介于两者之间，但其骨小梁结构良好而且骨钙沉着明显。结论：不同类型神经损伤对骨折愈合前期有着不同的影响。失周围神经支配对骨折修复有一定的加速作用，而脊髓损伤则延缓了骨折前期愈合，其发生机理仍需进一步研究。     

Immediate strain shielding after femoral reaming and nailing. An in vivo study in rat femora

Following intramedullary reaming and nailing of rat femora, in vivo changes in dynamic strain were correlated with in vitro measurements of the bones. Reaming and nailing procedures were performed 2 days after implantation of unidirectional strain gauges at the anterior, mid-diaphyseal level of the femur. Structural stiffness of polyacetal nails were three times as stiff as intact bone. Reaming only decreased the median strain value by 26 percent, and this value was not reduced by insertion of polyacetal nails. Steel nailing reduced the strain by 74 percent. Tested by three-point bending, reaming increased stiffness by 5 percent at the anterior aspect. The presence of nails gave stiffness values that were 9 percent (polyacetal) and 56 percent (steel) higher than the reamed only condition. Our results indicate that steel nailing following reaming causes marked reduction in strain at the anterior, mid-diaphyseal surface, whereas reduction in strain caused by polyacetal nails is negligible.     

Calcitonin Producing Tumour: Effects on Fracture Repair and Normal Bone in Rats

The mechanical properties and the collagen metabolism of healing fractures and intact bones have been studied in rats with a transplanted, calcitonin (CT) secreting, medullary thyroid carcinoma (MCT). Sham operated animals served as controls. the MCT was transplanted beneath the kidney capsule. Seven months later, when the rats with MCT had increased circulating levels of CT, a standardized femoral fracture was produced in all the animals.

The serum levels of CT were 3-40 times higher in tumour bearing rats than in controls in the period following the fracture. the fracture strength of rats with MCT was reduced by about 60 per cent compared to controls at 16 weeks after the fracture. the strength of intact femora (ultimate torsional moment) seemed to be progressively impaired by increasing levels of circulating CT. Also the strength of bone as a material (ultimate torsional stress) was reduced in the rats with MCT. the collagen synthesis was reduced in MCT rats, but the amounts of collagen in fractured or intact bones were not changed compared to controls.

We conclude that chronic hypercalcitoninaemia due to MCT seems to have a negative influence both on fracture healing and on bone metabolism.     

Clodronate reduces plate osteopenia in the rabbit

An osteosynthesis with a four-hole AO/ASIF-DCP plate was performed on the right tibia of 40 rabbits. Clodronate (50 mg/kg s.c.) was given once a week, resulting in a mean bone concentration of 509 µg/g in 2 hours. Plate fixation caused a decrease in mean net cross-sectional area of compact cortical bone of 17 percent at 9 weeks and 46 percent at 18 weeks. This resulted from bone resorption in bone under the plate, from pronounced cavitation in the plated bone (about 5 percent of cortical bone area at 9 weeks and 15 percent at 18 weeks), and from the fact that the medullary space was increased by 15 percent at 18 weeks. The total cross-sectional area of the diaphysis was increased by 31 percent at 9 weeks and by 17 percent at 18 weeks.

Clodronate treatment reduced cortical porosity to about half of the mean values in the placebo group. Clodronate increased both the calcium content in the retained bone and the cross-sectional area of compact cortical bone, but induced only an insignificant increase in the area of periosteal new bone. Clodronate treatment seems not to be contraindicated in conjunction with rigid osteosynthesis, and may even slow down the osteopenic response occurring under the rigid plate.     

Effects of medullary reaming on fracture healing: Tibial osteotomies in rabbits

Unilateral, midshaft tibial osteotomy was made in 16 rabbits. Reaming of the medullary canal was performed in half the animals, while the other half were operated on without reaming. Intramedullary fixation was accomplished with multiple Kirschner pins in both groups. Bone healing occurred with abundant peripheral callus in both groups. Mechanical testing after 6 weeks revealed higher strength of the osteotomized bones where reaming had not been performed compared with bones with reaming.

We conclude that bone healing is delayed by medullary reaming, where-as the pattern of healing is similar in bones with and without reaming.     

Changes in Femoral Cortical Porosity After Reaming and Intramedullary Canal Preparation in a Canine Model

This study examined changes in femoral cortical porosity resulting from femoral canal preparation during cemented total hip arthroplasty (THA). Twenty-four canines were randomly assigned to 3 groups: (1) reaming only, (2) cementing without pressurization, and (3) cementing with pressurization. Femoral cortical porosity was measured from histologic samples of the femurs at 7 positions. Reaming during canal preparation significantly increased cortical porosity. Cementing further increased cortical porosity, whereas pressurization of cement helped to counteract the increase in cortical porosity caused by cementing alone. Cortical porosity was considered to be a marker for bone mineral density (BMD) during the early phase of peri-implant healing around cemented stems. To maximize bone mineral density after cemented total hip arthroplasty, we suggest using implants that do not require reaming and pressurizing cement appropriately.