Fracture repair during external fixation. Torsion tests of rabbit osteotomies

Bone repair was studied in the rabbit tibiofibular bone after a midshaft transverse osteotomy stabilized by external fixation and heavy compression. Both subendosteal and subperiosteal callus formation with concomitant contact healing were observed within 3 weeks, and were further succeeded by subendosteal resorption and increased porosis resulting in atrophy of the cortical bone. Subjected to the torsion test, the bones exhibited restoration of strength within 3 weeks, with maximal energy absorption and elasticity at 6 weeks. The failure of the osteotomy in the torsion test, with radiographic visibility of the osteotomy, characterized the soft-tissue type of behavior of the bones. Hard-tissue like behaviour of the bones with resistance to torsion at the osteotomy site and radiographic obliteration of the osteotomy line occurred by 12 weeks, indicating complete union of the osteotomy. Our experiments demonstrate that elastic external fixation is preferable to the rigid compression plate.     

Stress shielding by rigid fixation studied in osteotomized rabbit tibiae

In 48 rabbits the bone-formation rates and strength in the tibial shaft, osteotomized and treated with rigid internal plate fixation, were compared with contralateral bones, which were treated with plate fixation without osteotomy. The plate fixation alone induced a 35 percent decrease in torsional strength after 12 weeks. The healing of the osteotomy counteracted the decrease in strength induced by stress protection of the rigid plate at 6 weeks, but this effect subsided within 12 weeks. The osteotomy also induced a 2-3-fold increase in the synthesis of bone matrix and mineral accretion of the bone underlying the plate at 6 and 9 weeks when compared with the contralateral side, which was plated but not osteotomized. The bone-formation levels returned to normal within 12 weeks; and the bone underlying the plate became subject to atrophy, resulting in decreased mechanical strength.     

Effect of compression on fracture healing. Plate fixation studied in rabbits

Bilateral osteotomies in rabbit tibiae were secured with six-hole rigid plates, using axial compression on the right and no compression on the left side. Histological, histomorphometric and torsiometric analysis was performed up to 24 weeks postoperatively. Histological analysis showed end-to-end primary bone healing regardless of treatment. The fracture gaps tended to be smaller in the compression osteotomies, but union was achieved within the same time on both sides, and at 6 weeks torsiometric analysis of the paired specimens revealed similar mechanical properties. By the time the fracture had united both groups of bones showed similar degrees of subendosteal resorption. As a result of this porotic transformation the strength of the cortical bone was slightly impaired from 6 weeks onward, whether or not compression had been applied. The results suggest that axial compression does not augment fracture healing of plated cortical bone.     

Comparison of the effects of compression plates and external fixators on early bone-healing

We used two mechanically dissimilar devices, compression bone-plates and unilateral-frame external fixators, in a standard canine osteotomy model; both methods were highly successful in achieving mature bone union. Bone union was studied by histological, physiological, and biomechanical means. At 120 days after injury, union was biomechanically less mature on the external fixator side. These tibiae had less intracortical new-bone formation (p less than 0.01), more bone resorption (p less than 0.045), and more bone porosity (p less than 0.04) when compared with paired tibiae that had been treated with compression plates. This higher level of bone turnover on the external fixator side was accompanied by an increase in blood flow (measured by clearance of 85Sr) (p less than 0.04). At the osteotomy site, pre-experimental or unlabeled bone and porosity were greater on the external fixator side and endosteal new-bone formation was greater on the plated side. Since the in vitro stiffness of the external fixator was less in all modes tested (compression, distraction, torsion, and anteroposterior bending) except lateral bending, it may be that the rigidity of the fixation is an important factor in early bone-remodeling of a healing osteotomy.     

Mathematically directed single-cut osteotomy for correction of tibial malunion

In 1986 and 1987, four patients with tibial malunion involving both angular and torsional misalignment underwent surgical correction by a single-cut technique based on a mathematical model of long bone deformity. The technique involved a single surgical cut, followed by rotation of the two fragments along the osteotomy plane. The orientation of the osteotomy is based on a computer-assisted design. The deformity is measured on radiographs, computed tomography, and clinical exam and is then plotted on graphs to find the osteotomy orientation. The deformity involved varus and extension in four cases, internal rotation in 2, and external rotation in two. The deformities ranged from 9 to 26 degrees. The cutting angle of the osteotomy ranged from 50 to 66 degrees as measured from the transverse plane. Actual lengthening of 1 cm and functional lengthening over 1.5 cm was obtained without the use of bone graft. As no wedge of bone was removed, all corrected bones were easily suited to rigid internal fixation across the cut surface. In all cases, the desired correction was obtained within measurable error, and union was obtained with minimal immobilization. There were no soft tissue or joint contractures, and no neurovascular complications. In one patient, who had had four prior surgical procedures on the involved limb, an infection developed 6 weeks postoperatively that required debridement and delayed primary closure. As the technique involves only one cut, no wedge of bone is removed, no shortening occurs, and the osteotomy is highly suitable for rigid internal fixation. The described technique is the first to integrate in a precise way the correction of torsion with the correction of angular deformity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Accelerating bone formation and earlier healing after using demineralized bone matrix for limb lengthening in rabbits.

We studied the effects of grafting with demineralized bone matrix during lengthening of the tibia in young Japanese White rabbits. The demineralized bone matrix was made from frozen cortical bone harvested from other rabbits. A 5-mm gap was created in the tibial diaphysis by a subperiosteal osteotomy; a maximum of 20 mm (2-3 mm/day) of tibial lengthening was reached in a week with use of an external fixator. The control group of 20 rabbits did not receive an implant; the group of 21 experimental rabbits received an implant of demineralized bone matrix in the surgical gap. The control group failed to demonstrate radiographic callus 5 weeks after surgery, and nonunion was persistent after 1 year. In the group with demineralized bone matrix, new radiodensity was demonstrated within the lengthening gap at 3 weeks, with a gradual increase in bone density to 85% that of the intact tibia after 12 weeks. Bone union was seen within 1 year for all experimental animals for whom the external fixator was removed 8 weeks after the procedure. These bones showed normal bone structure histologically. The lengthening was carried out at a rapid distraction rate of 2-3 mm/day; therefore, this method allows for satisfactory bone formation at a faster rate than normal.     

Bone healing after metal plate fixation and external fixation of the osteotomized rabbit tibia

Controversy still exists as to the best method of treatment of long bone fractures. The purpose of the present study was to compare the effects on the healing bone of external fixation and metal plate fixation. In an experimental model on the rabbit tibia the stiffness of the fixation corresponded intentionally to that of the same methods in human fracture treatment.

A transverse, midshaft osteotomy was made on one tibia, and fixed with a steel plate (45 × 5 × 1 mm) or external mini-fixation. The animals were killed after 4, 6 or 12 weeks. The bone healing was evaluated by radiography, histology and biomechanical testing in three-point bending. There were no significant differences between plate fixation and external fixation in the pattern of bone healing, as it occurred by periosteal, in-tramedullary and intercortical callus after both methods. The stiffness increased more rapidly than the strength, and reached normal values after about 6 weeks. No significant differences in stiffness between the two methods were found. The strength was significantly greater after plate fixation than after external fixation at 6 weeks, while no significant differences were found at either 4 or 12 weeks.

It is concluded that the speed of bone healing was more rapid after plate fixation. However, in the later stages of healing the plated bones were secondarily weakened because of the stress-protecting effect of the plate.     

Gene therapy to improve osteogenesis in bone lesions with severe soft tissue damage

Background Ex vivo gene therapy can induce bone formation when delivery cells carrying the bone morphogenetic protein (BMP) gene are used. The hypothesis for this study was that the cell-mediated gene therapy could improve the healing of bony lesions with severe soft tissue damage.Method An animal model with a femoral osteotomy lesion associated with soft tissue damage was developed in rats. Muscle-derived cells, genetically engineered to express BMP4, were inserted within the osteotomy gap. Cells genetically engineered to express LacZ were used for the control group. The groups were subdivided with regard to the fixation method: stable and unstable fixation. The rats were killed for histological and radiographic evaluation 3 and 6 weeks post-surgery.Results No callus formation was found in the control group at any time point, whereas sufficient callus formation appeared in the treatment group after 6 weeks. A bridging callus with woven bone and hypertrophic chondrocytes was achieved in the treatment group when a stable fixation was used, but failed to appear in unstable fixation.Conclusion The combination of muscle-derived cells expressing BMP4 and a stable fixation were able to bridge the bone defect within 6 weeks, but with prolonged osteochondral ossification. Therefore, the ex vivo gene therapy could be an efficient biological approach to improve the treatment of bone lesions with severe soft tissue damage.     

A retrospective analysis of medial opening wedge high tibial osteotomy for varus osteoarthritic knee

Background:

Medial opening wedge high tibial osteotomy (MOWHTO) has proven to be an effective treatment for varus osteoarthritic knees. Various methods of fixation with different implant types and using either bone grafts or bone substitutes have been reported. We performed non-locking T-buttress plate fixation with autologous iliac bone graft augmentation, which is defined here as the traditional method, and locking compression plate fixation without any bone graft or bone substitute. We aimed to compare bone union and complications of these two MOWHTO techniques.

Materials and Methods:

Between June 2005 and December 2007, 50 patients who underwent MOWHTO (a total of 60 knees) were retrospectively reviewed and classified into two groups: group A, which consisted of 26 patients (30 knees) was treated using T-buttress plate fixation with autologous iliac bone graft augmentation and group B, which consisted of 24 patients (30 knees) was operated upon using a medial high tibial locking compression plate without any augmentation. Demographic characteristics and radiographic outcomes, including union rate, time to union, medial osteotomy defects, and complications, were collected and compared between the two groups. The progress of all patients was followed for at least 2 years.

Results:

All osteotomies united within 12 weeks after surgery. Group B had slightly longer time to union than group A (10.3 weeks and 9.5 weeks, respectively; P = 0.125). A significantly higher incidence of medial defects after osteotomy was reported in the locking compression plate group (P = 0.001). A total of 5 (8.3%) knees had complications. In group A, one knee had a superficial wound infection and another knee had a lateral tibial plateau fracture without significant loss of correction. In group B, one knee had screw penetration into the knee joint and two knees had local irritation that required the removal of the hardware.

Conclusion:

Locking compression plate fixation without the use of bone grafts or bone substitutes provides a satisfactory union rate and an acceptable complication rate when compared to the traditional MOWHTO technique. Thus, we recommend using this technique for treating unicompartmental medial knee osteoarthritis.     

Lengthening osteotomy in the metaphysis and diaphysis. An experimental study in the ovine tibia

In 20 sheep, aged seven to eight months, a tibial lengthening osteotomy was performed to compare the process of repair of the metaphyseal and diaphyseal regions of the bone. Analogous to clinical lengthening, two frame configurations of a bilateral external fixation device were used to obtain adequate fixation of the bone segments in the metaphyseal and diaphyseal lengthening osteotomies. A daily distraction rate of 1 mm for 4.5 weeks yielded an average length increase of 2.6 cm (12.5%). After death at 4.5 weeks postdistraction, the elongated bones were tested mechanically with the contralateral tibiae as controls. No significant difference in relative torsional strength of the elongated tibiae was found between the two groups. Inferior mechanical stability of the bone segments in metaphyseal compared with diaphyseal lengthening (due to differences in frame rigidity and distribution of muscular moments) influenced healing to such an extent that any superior biologic, osteogenic potential in the metaphyseal bone region was nullified. With the clinical use of two configurations of a given external device necessary for fixation of the bone segments in a metaphyseal or diaphyseal lengthening osteotomy, the empirically accepted idea that metaphyseal healing is superior may not be correct.     

Limb lengthening by diaphyseal corticotomy, callus distraction, and dynamic axial fixation. An experimental study in the ovine femur

Limb lengthening of the left femur was performed in 12 sheep, 7-8 months of age. After weakening of the cortex by drill holes, a controlled fracture was created in the diaphysis. The bone segments were fixed in reduced position using a unilateral external fixation device. The fixator was left in neutral position for 10 days postoperatively when lengthening started. By means of daily distraction at a rate of 1.0 mm once a day for 3 weeks, an average lengthening of 1.9 cm (11.9%) was obtained. Two weeks after distraction had been discontinued, distinct callus bridging of the lengthening zone was confirmed radiographically in all animals. At this time the rigid state of fixation was converted to a system allowing axial compression by loading in half the animals. The other half of the animals served as controls with the fixator remaining unchanged. The external device was left on until 5 weeks after the end of distraction. At this time the animals were killed. Both femora of all animals were tested mechanically in torsion. The average ultimate torsional strength of the elongated femur compared with control was 71% in the group with dynamic axial fixation and 65% in the control group. No significant difference in relative strength of the tested bones in the two groups was found. We conclude that intermittent axial compression by loading during consolidation had no significant effect on the bone-healing process evaluated by radiography and mechanical testing.     

Volar fixation for dorsally angulated extra-articular fractures of the distal radius: a biomechanical study

PURPOSE: To compare the biomechanical properties of 10 volar plate-fixation designs in 2 fracture models (dorsal wedge osteotomy, segmental resection osteotomy models). METHODS: Forty-eight radiuses were used in this study including 8 pairs. In 40 specimens a 15-mm dorsally based wedge osteotomy was performed and the volar cortex was fractured manually. They were arranged into 10 fixation groups with 5 different fixation designs (test 1). In the contralateral specimens of 8 paired radiuses a 10-mm segment of bone was excised (test 2). Four of the 10 fixation systems were chosen for these specimens. Cadaver hands and the proximal radiuses were potted in polymethylmethacrylate and tested with a servohydraulic materials testing machine with 300 N of axial compression load at 1 N/s initially and after each 1,000 cycles up to 5,000 cycles. After cyclic loading the specimens were loaded to failure in axial compression at 2 mm/min. The stiffness, failure peak load, and failure mode of each specimen were recorded. RESULTS: In test 1 in the wedge osteotomy specimens the T plate was the stiffest and the Synthes titanium plate was the least stiff; however, all specimens completed the 5,000 cycles of loading with no failures. There was no significant difference between the 10 fixation groups in failure peak load and only 7 of 40 failed at the distal portion of the hardware in the final load to failure testing. In test 2 the resection osteotomy specimens were less stiff and failed at a lower failure peak load compared with the wedge osteotomy specimens. Failure at the distal portion of the fixation system was seen in 7 of 8 specimens; nonlocking screws loosened and tines compressed the surrounding bone, resulting in tine-hole enlargement. CONCLUSIONS: All of the plate-fixation systems delivered sufficient stability to permit the simulated postoperative regimen of 1 week of immobilization followed by 5 weeks of early mobilization until expected union at 6 weeks after surgery. Based on these results a preferable volar fixation system would appear to benefit from the following: (1) sufficient plate strength to support the distal fragment from the volar side, (2) a locking system with sufficient strength to remain locked during the healing process, and (3) a distal design that does not affect the bone adversely. The anatomic reduction of the volar cortex in the wedge osteotomy specimens added stability to the construct.     

Fixation technique influences osteogenesis of comminuted fractures

Comminuted fractures most often are associated with compromised soft tissue conditions and diminished vascularization leading to a reduced osteogenesis. In contrast to stable fixation by compression plating with lag screws, the less stable but also less invasive techniques of external fixation, unreamed nailing, or bridging plates have become increasingly popular. The aim of this study was to compare the bone healing and osteogenesis of these fixation techniques. A triple wedge osteotomy of the sheep tibia was used as a bone healing model. Internal compression plate fixation of all fragments with lag screws was used in one group. In the other three groups, only the main proximal and distal fragments were fixed by external fixation, unreamed interlocking nail, or bridging plate. The sheep with compression plate fixation and lag screws showed the worst results after 12 weeks. The periosteal and endosteal osteogenesis and the apparent density of the newly formed bone in the fracture gaps were significantly lower than those seen in the sheep in the other three technique groups. The best results were found for the bridging plate and external fixator. From these results, it can be concluded that compression plate fixation should be avoided for treatment of comminuted fractures.     

The significance of postoperative stability for osseous repair of a multiple fragment fracture. Animal experiment studies

The significance of postoperative mechanical stability for bony repair of a comminuted fracture was investigated in an animal experimental study comparing four commonly applied operative methods of stabilizing fractures: (1) flate osteosynthesis combined with lag screw fixation after reduction of the fragments; (2) bridging plate osteosynthesis; (3) external fixation; (4) static interlocking intramedullary nailing. As the fracture model, a triple-wedge osteotomy of the right sheep tibia was used. The results of in vitro testing of stiffness (N/mm) of each of the four osteosyntheses was as follows: anatomical plate: 746 N/mm; bridging plate 434 N/mm; external fixation 625 N/mm; nailing 416 N/mm. Eight weeks after the operation, the tibiae were explanted and the contralateral tibiae of six sheep were taken as a control group. The three-point bending test revealed no significant difference in bending deviation: anatomical plate 47.58 +/- 22.57 microns; bridging plate 33.93 +/- 7.67 microns; external fixation 33.83 +/- 8.02 microns; nailing 33.0 +/- 17.23 microns. However, it was noted that there was a slightly higher tendency towards stiffness of the bones after bridging plate osteosynthesis, external fixation and interlocking intramedullary nailing and that the amount of stiffness resembled that in non-operated control animals (25.56 +/- 6.66 microns). On the other hand, anatomical plate osteosynthesis showed less stiffness. To assess the tensile strength at the osteotomy area, bone samples were prepared and tested for failure on a material testing machine. The tensile strength of the bone samples showed a distinct difference in all experimental groups according to their anatomical location.(ABSTRACT TRUNCATED AT 250 WORDS)     

Primary bone grafting does not improve the results in severely displaced distal radius fractures

We prospectively randomised 45 patients ages 20-70 years with distal radius fractures of Older type III and IV to one of two treatment groups. One group was treated with closed reduction, primary bone grafting, and external fixation for 3 weeks, followed by a plaster cast that allowed volar flexion, for an additional 3 weeks. The other group was treated with closed reduction and external fixation for 6 weeks. The functional and radiographic results were evaluated. There was no difference between the two groups in either clinical or radiographic outcome. We do not recommend external fixation and primary bone grafting as a routine method in these fractures.     

点式接触动力加压接骨板与动力加压钢板固定后板下的骨质变化

目的观察点式接触动力加压接骨板(PC-DCP)与动力加压钢板(DCP)内固定后板下骨质改变情况并进行对照。方法采用性成熟山羊10只,在左右侧完整胫骨中段分别用PC-DCP与DCP固定。固定术后12、24周分批处死动物,每批5只,解剖出双侧胫骨。取3对胫骨进行CT扫描与生物力学测试,对照研究两种钢板固定术后固定骨段皮质骨厚度和生物力学强度改变;取剩余两对胫骨,截取接骨板下皮质骨骨段,进行板下骨的组织学观察。结果固定术后12周,DCP组板下皮质骨呈明显松质骨样改变,PC-DCP组板下皮质骨厚度和骨抗扭力学强度均明显大于DCP组,差异有统计学意义(P<0.05)。固定术后24周,DCP组和PC-DCP组骨皮质均变薄,骨髓腔扩大,板下皮质骨松质骨样改变,两组板下皮质骨厚度和抗扭力学强度间差异无统计学意义(P>0.05)。结论传统坚硬接骨板固定后板下骨质疏松是血运障碍和应力遮挡共同作用的结果,但血运损害在固定的较早期是其主要原因。PC-DCP可以明显减轻因血运损害导致的骨质疏松。     

Loss of bone strength after intramedullary nailing: Torsion tests of tibial osteotomies in rabbits

Rigid intramedullary nailing was used in 75 rabbits to stabilize a transverse osteotomy of the midshaft of the tibia. In 36 additional rabbits intramedullary nailing was performed without osteotomy. No additional external immobilization was used postoperatively. After removal of the nail the mechanical strength of the tibiofibular bones was tested torsiometrically in 30 osteotomized and 18 non-osteotomized animals from 3 to 24 weeks after the operation. At 3 weeks the torsional load fractured all osteotomized bones through the osteotomy line. At later stages a spiral fracture occurred either crossing or close to the osteotomy area, usually distal to the tibiofibular junction. The increase in mechanical strength of the osteotomized bones reached a maximum at 6 weeks and then decreased. The strength of the non-osteotomized nailed bones also decreased slightly. The results suggest that rigid intramedullary nailing, although providing good conditions for early consolidation of experimental osteotomy, leads secondarily to deterioration of the mechanical properties of tubular bone.     

Loss of bone strength after intramedullary nailing: Torsion tests of tibial osteotomies in rabbits

Rigid intramedullary nailing was used in 75 rabbits to stabilize a transverse osteotomy of the midshaft of the tibia. In 36 additional rabbits intramedullary nailing was performed without osteotomy. No additional external immobilization was used postoperatively. After removal of the nail the mechanical strength of the tibiofibular bones was tested torsiometrically in 30 osteotomized and 18 non-osteotomized animals from 3 to 24 weeks after the operation. At 3 weeks the torsional load fractured all osteotomized bones through the osteotomy line. At later stages a spiral fracture occurred either crossing or close to the osteotomy area, usually distal to the tibiofibular junction. The increase in mechanical strength of the osteotomized bones reached a maximum at 6 weeks and then decreased. The strength of the non-osteotomized nailed bones also decreased slightly. The results suggest that rigid intramedullary nailing, although providing good conditions for early consolidation of experimental osteotomy, leads secondarily to deterioration of the mechanical properties of tubular bone.     

Loss of bone strength after intramedullary nailing. Torsion tests of tibial osteotomies in rabbits

Rigid intramedullary nailing was used in 75 rabbits to stabilize a transverse osteotomy of the midshaft of the tibia. In 36 additional rabbits intramedullary nailing was performed without osteotomy. No additional external immobilization was used postoperatively. After removal of the nail the mechanical strength of the tibiofibular bones was tested torsiometrically in 30 osteotomized and 18 non-osteotomized animals from 3 to 24 weeks after the operation. At 3 weeks the torsional load fractured all osteotomized bones through the osteotomy line. At later stages a spiral fracture occurred either crossing or close to the osteotomy area, usually distal to the tibiofibular junction. The increase in mechanical strength of the osteotomized bones reached a maximum at 6 weeks and then decreased. The strength of the non-osteotomized nailed bones also decreased slightly. The results suggest that rigid intramedullary nailing, although providing good conditions for early consolidation of experimental osteotomy, leads secondarily to deterioration of the mechanical properties of tubular bone.     

Healing patterns of transverse and oblique osteotomies in the canine tibia under external fixation

Healing patterns were compared between transverse and 60 degrees oblique osteotomies in canine tibiae stabilized under external fixation. Under similar in vitro testing conditions (osteotomy ends in contact), the axial stiffness of the oblique osteotomy under external fixation was 45% of the paired transverse osteotomy. Under torsion and bending, the two sides exhibited similar fixation rigidity. The animals put significantly less weight on the oblique side than on the transverse side in the early phases of bone healing (p less than 0.05 for static and p = 0.024 for dynamic weight bearing). The osteotomy bending stiffness at 60 days (in vivo) and the torsional stiffness of osteotomy union measured after sacrifice at 90 days were significantly higher on the transverse side (p = 0.013 and p = 0.016, respectively). Intracortical new bone formation was significantly higher on the transverse side (p less than 0.01), indicating a difference in the rate of cortical healing and remodeling. The average pin removal torque was significantly lower on the oblique side (p less than 0.05), a sign of increased pin loosening. In the clinical situation, unstable oblique or spiral fractures should be protected from weight bearing even under stable external fixation due to the delayed recovery of bone union stiffness property as well as increased pin tract problems.