Plate fixation of tibial fractures in the rabbit: Correlation of bone strength with duration of fixation

Bone healing after metal plate fixation of rabbit tibial osteotomies was studied in order to gain information as to the optimum time for plate removal. The fracture had regained almost normal biomechanical properties after 6 weeks. Significantly greater strength and stiffness of the healing tibiae were obtained at 12 weeks when the plate was removed after 4, 6 or 9 weeks and no further fixation was subsequently applied, compared to those plated for 12 weeks. The results indicate that a metal plate should be removed as soon as the fracture has regained normal biomechanical properties; i.e. before the stress-protecting effect has secondarily weakened the bone.

The findings suggest that metal plates should be removed at an earlier stage of the healing period than is usual in clinical practice.     

Stress-protection after external fixation on the intact rabbit tibia

Bone loss due to the stress-protecting effect of a metal plate on intact bone is a well-known phenomenon. The purpose of the present study was to find whether a similar effect is caused by external fixation. External mini-fixation was applied on the intact rabbit tibial diaphysis of one leg. The other tibia served as control. The animals were sacrificed after 6 or 12 weeks, and both tibiae biomechanically tested in three-point bending. The bone mineral content was measured by photon absorptiometry. No significant changes in bone strength, stiffness or mineral content were found after 6 weeks. The strength and stiffness were significantly reduced after 12 weeks. The median strength and stiffness at that time were 87 and 88 per cent, respectively, in relation to the control bones. The mineral content in the bone segment which had been stabilized by external fixation was significantly reduced after 12 weeks (median 90 per cent of the values for the control bones). No significant change in the mineral content occurred at a level in the tibial diaphysis distal to the external fixation device. It is concluded that the stress-protecting effect caused by external mini-fixation on the rabbit tibia occurs later, and is less pronounced, than that caused by metal plates.     

Stress-Protection After External Fixation on the Intact Rabbit Tibia

Bone loss due to the stress-protecting effect of a metal plate on intact bone is a well-known phenomenon. The purpose of the present study was to find whether a similar effect is caused by external fixation.

External mini-fixation was applied on the intact rabbit tibial diaphysis of one leg. The other tibia served as control. The animals were sacrificed after 6 or 12 weeks, and both tibiae biomechanically tested in three-point bending. The bone mineral content was measured by photon absorptiometry.

No significant changes in bone strength, stiffness or mineral content were found after 6 weeks. The strength and stiffness were significantly reduced after 12 weeks. The median strength and stiffness at that time were 87 and 88 per cent, respectively, in relation to the control bones. The mineral content in the bone segment which had been stabilized by external fixation was significantly reduced after 12 weeks (median 90 per cent of the values for the control bones). No significant change in the mineral content occurred at a level in the tibial diaphysis distal to the external fixation device.

It is concluded that the stress-protecting effect caused by external mini-fixation on the rabbit tibia occurs later, and is less pronounced, than that caused by metal plates.     

The Healing of Experimental Fractures by Compression Osteosynthesis: I. Torsional Strength

Biomechanical properties of osteotomized rabbit tibio-fibular bones fixed with 6-hole stainless steel AO/DCP plates were investigated with torsional loading 3 to 24 weeks postoperatively.

During the first 9 weeks maximum torque capacity, energy absorption and torsional rigidity increased, reflecting progressive bony union between the fractured bone ends. From 9 to 24 weeks the values of torque capacity and energy absorption decreased, whereas torsional rigidity seemed to reach a steady state without further significant changes. For the three parameters considered, the mean percentage differences between the osteotomized plated bones and their paired sham-operated controls were 69, 64 and 80 per cent, respectively.

The results suggest that internal fixation of fractured bones provides conditions for undisturbed fracture healing, but that subsequently the rigid nature of the implant has an adverse effect on the cortical bone, which slowly loses strength. Thus the optimal time for removal of the plate seems to be shortly after the fracture has healed and before the bony tissue has been weakened by secondary changes, such as cancellous transformation and spatial rearrangement of the tubular bone.     

Trans-styloid fixation of fractures of the distal radius: A prospective randomized comparison between 6- and 1 -week postoperative immobilization in 60 fractures

We performed a prospective randomized study on 60 patients with dorsally displaced extra-articular or noncomminuted intraarticular fractures of the distal radius. All 60 fractures were treated by closed reduction and Kirchner wire trans-styloid fixation. 30 patients had 1 weeks' postoperative immobilization and 30 patients had 6 weeks' immobilization.

All patients had a clinical and radiographic review at 6 weeks and at 1 year after the operation. Pain, range of movement and grip strength were tested clinically, and changes in dorsal tilt, frontal radial deviation, ulnar variance, and radial shortening were assessed radiographically.

Rates of complications were the same in both groups. At follow-up, pain was similar in both groups and range of motion and grip strength were somewhat better after early mobilization-in comparison with the opposite wrist-but this was statistically significant only for ulnar deviation. The postoperative radiographic reductions were similar in both groups, with no differences in loss of reduction after bone healing.

Therefore, in Colles' fractures, trans-styloid fixation with two K-wires seems to give a stable osteosynthesis, which does not need additional immobilization with a plaster cast.     

In vitro Effects of External Fixation on Intact and Osteotomized Tibiae: A Biomechanical Study

In order to study the in vitro mechanical effects of external fixation on intact and osteotomized bone, human and rabbit tibiae were tested in three-point bending in an Instron testing machine. Intact tibiae were loaded in the elastic range before and after application of an external fixation device. in the human specimens the Vidal-Adrey double frame was used, and in the rabbit specimens the external mini-fixation. the bone deformation in the anteroposterior direction was measured with a linear voltage differential transformer. After application of external fixation a median bone elastic stiffness of 110.2 per cent in human tibiae and of 106.1 per cent in rabbit tibiae was found, in relation to the stiffness of intact tibiae without external fixation. the stiffness increase was significant in human specimens, but not significant in rabbit specimens.

In osteotomized human tibiae fixed with the Vidal-Adrey double frame a median stiffness of 8.5 per cent of the stiffness of intact bones was found when compression was not applied, compared to 19.9 per cent when compression was applied. in rabbit tibiae a median stiffness of osteotomized bones with external mini-fixation was 8.9 per cent of the stiffness of intact bones. There was a good agreement between the results in rabbit tibiae with the mini-fixation and human tibiae with external fixation without compression. the external mini-fixation thus seems to be a suitable model for the study of bone healing in rabbit tibiae.     

有限内固定结合外固定支架与钢板治疗胫骨平台骨折的疗效分析

[目的]探讨有限内固定结合外固定支架与钢板在胫骨平台骨折治疗中的应用及其疗效.[方法]2007年1月～2011年1月从胫骨平台骨折患者中选取58例,男38例,女20例;年龄19～ 54岁,平均(42.7±8.9)岁,按Schatzker分型:Ⅳ型17例,Ⅴ型31例,Ⅵ10例,其中外支架组31例,钢板内固定组27例,术后随访6～17个月,平均14.1个月.[结果]有限内固定结合外支架固定组平均手术时间(57.4±12.1)min,平均术中出血量(161.3±17.0) ml,平均骨折愈合时间为(12.4±1.5)周,切口感染率为6％,针道感染率为9％,Lysholm评分:优21例,占67％,良8例,占25％,差2例.钢板内固定治疗组平均手术时间(105.4±23.8) min,平均术中出血量(252.4±28.9)ml,平均骨折愈合时间为(15.5±2.5)周,切口感染率为4％,Lyshol评分:优16例,占60％,良10例,占37％,差1例.手术时间、术中出血量、骨折愈合时间,评分组间比较有显著差异(P＜0.05),切口感染率、Lysholm评分组间无显著差异(P＞0.05).[结论]两种方法治疗胫骨平台骨折,功能恢复佳,疗效满意,外固定架是目前治疗胫骨平台开放性骨折较为理想的治疗方式,尤其适用于胫骨平台骨折合并有严重的软组织损伤与缺损患者.     

Effects of fixation stiffness on fracture healing. External fixation of tibial osteotomy in the rabbit

In rabbit tibial osteotomies, the effects on bone healing of three different degrees of stiffness of external fixation were investigated. Redislocation occurred in one third of the osteotomies with the least rigid fixation, and the amount of external callus was greater in this group. At 6 weeks there were no significant differences between the groups regarding bending strength and stiffness of the bones.     

Effects of fixation stiffness on fracture healing: External fixation of tibial osteotomy in the rabbit

In rabbit tibial osteotomies, the effects on bone healing of three different degress of stiffness of external fixation were investigated. Redislocation occurred in one third of the osteotomies with the least rigid fixation, and the amount of external callus was greater in this group. At 6 weeks there were no significant differences between the groups regarding bending strength and stiffness of the bones.     

Recovery of Diaphyseal Bone Strength After Rigid Internal Plate Fixation: An Experimental Study in the Rabbit

The course of the recovery from the unfavourable effects of a rigid internal fixation plate on the strength of diaphyseal bone, measured as the maximum torque capacity, has been studied in rabbit tibiae. Due attention was paid to the screw holes. on removal of the plate, which had been applied for 12 weeks without prior osteotomy, the bone had decreased in strength by approximately 50 per cent.

Following removal of the plate, the bone regained its normal strength after only 6 weeks. the regaining of strength proceeded in a significantly non-linear manner and in accordance with the logistic function     

The influence of different degrees of stiffness of fixation plates on experimental bone healing

In order to throw some light on the controversial issue of the optimal stiffness in fracture fixation, the effects on bone healing of rabbit tibial osteotomies fixed by plates with four different degrees of stiffness were studied. The least stiff plate was made of glass fiber-reinforced epoxy; the other three were made of stainless steel. The median bending stiffness in vitro of tibial osteotomies fixed with the various plates were 13%, 17%, 61%, and 74%, related to the stiffness of intact tibiae. Transverse midshaft unilateral tibial osteotomies were fixed by the various plates, and the animals were killed after 6 weeks. The amount of periosteal callus was inversely related to the stiffness of the plates. A marked trend toward decreased strength and stiffness occurred in tibiae where the most rigid plate was used, compared with the values of those with the less rigid plates. This indicates that the stress-protecting effect of very stiff plates begins early in the healing period and is pronounced even at 6 weeks and that a steel plate of lower stiffness is more appropriate for bone healing. However, too flexible plates involve increased risk of redislocation and mechanical failure.     

Studies on Mechanical Strength of Bone: II. Torsional Strength of Cortical Bone after Rigid Plate Fixation with and without Compression

Biomechanical properties of intact rabbit tibio-fibulae were investigated with torsional loading 1 day to 36 weeks alter fixation using 4-hole stainless steel ASIF/DCP plates with and without compression.

During the first 12 weeks energy absorption and torque moment increased slightly as a result of subperiosteal new bone formation following application of the plates. There was a concomitant increase in the yielding properties of the bone, reflecting progressive porotic transformation. Thereafter, up to 36 weeks postoperatively, the values for energy absorption, torque moment and angular deformation gradually declined in both groups of bones. The differences between normal control bones and plated bones at 36 weeks were 70.1, 53.0 and 26.3 per cent, respectively. The decay of torsional strength was the same whether or not compression was used in the plate fixation.

The results suggest that even in normal bone rigid plates induce a considerable loss of strength due to the cancellous transformation they are known to cause in cortical bone.     

Biochemical Changes in Bone Grafts Stabilized with Rigid Plates: I. Cancellous Grafts

The effect of rigid plate fixation on the chemical composition of cancellous interposition grafts was studied in rabbit tibio-fibular bones.

The concentrations of hexosamines and, to a lesser degree, of hydroxyproline and nitrogen, were high in the graft for the first 6 weeks, decreased from weeks 6 to 12, but remained higher than the corresponding values for the controls throughout the experiment (52 weeks). The ratio of hexosamines to hydroxyproline was highest for the graft at 3 weeks, indicating formation of cartilage and osteoid.

The initially low calcium concentration of the graft increased by 35 per cent from weeks 1 to 6, decreased from weeks 6 to 12, and remained below normal thereafter in comparison with corresponding values for the cortical host bone. The ratio of calcium to hydroxyproline increased throughout the experiment, reflecting maturation of the graft to lamellar bone.

Thus, biochemically the early incorporation of rigidly fixed cancellous interposition grafts resembles the healing of unimmobilized fractures by callus formation.     

Timely fracture-healing requires optimization of axial fixation stability

BACKGROUND: Bone-healing is known to be sensitive to the mechanical stability of fixation. However, the influence on healing of the individual components of fixation stiffness remains unclear. The aim of this study was to investigate the relationship between the initial in vitro fixation stiffness and the strength and stiffness of the callus after nine weeks. We hypothesized that axial stiffness would determine the healing outcome. METHODS: A standardized midshaft osteotomy of the right tibia was performed on Merino-mix sheep and was stabilized with either one of four monolateral external fixators or one of two tibial nails inserted without reaming. The in vitro stiffness of fixation was determined in six loading conditions (axial compression, torsion, as well as bending and shear in the anteroposterior and mediolateral planes) on ovine tibial specimens. Stiffness was calculated by relating displacements of the fracture fragments, determined by means of attached optical markers, and the loads applied by a materials testing machine. Torsional testing until failure of the explanted tibiae was performed with use of a standard materials testing machine after nine weeks of healing to determine the failure moment and the torsional stiffness of the healed tibia. RESULTS: External fixation in sheep generally resulted in higher fixation stiffness than did conventional unreamed tibial nailing. The use of angle-stable locking screws in tibial nailing resulted in fixation stiffness comparable with that of external fixation. The highest torsional moment to failure was observed for the external fixator with moderate axial stiffness and high shear stiffness. The fixator with the highest axial stability did not result in the highest failure moment. Low axial stability in combination with low shear stability resulted in the lowest failure moment. CONCLUSIONS: In this study, a clear relationship between the stability of fixation and the mechanical strength of the healing tibia was seen. Moderate levels of axial stability were associated with the highest callus strength and stiffness.     

External fixation of the pelvic ring: an experimental study on the role of pin diameter, pin position, and parasymphyseal fixator pins

Background The mechanical properties of current external fixator systems for unstable (type C) pelvic ring fractures are inferior to internal fixation, and are not optimal for definitive treatment. We explored methods to increase stability of external fixator constructs.

Methods An experimental model was used for load tests. The same pelvic fixator was used while different pin diameters, pin positions, and modes of pubic symphysis fixation were tested.

Results Changing of the pin diameter of the unthreaded part from 6 to 8 mm resulted in an increase in stiffness of 20%. An increase in stiffness by a factor of 1.9 was found by placing a pin on the iliac crest and one supra-acetabular. An additional increase by a factor of 3.6 was obtained by adding pubic symphysis plate fixation. Parasymphyseal pin fixation instead reduced stiffness, but not so much as when parasymphyseal pins were connected to the external fixator of the pelvic ring. The final configuration was at least 6 times stiffer than the initial configuration.

Interpretation The new concept of parasymphyseal pin fixation connected to an external fixator of the pelvic ring produces a considerable increase in stability for the treatment of type C pelvic ring injuries, as does an increase in pin diameter and alternative pin positioning.     

Cement augmentation of intertrochanteric fracture fixation:A cadaver comparison of 2 techniques

We evaluated 2 techniques of cement augmentation to enhance fixation of intertrochanteric hip fractures. 4 fixation groups with 6 cadaver femurs in each group were compared: stainless steel lag screw and side plate with and without cement augmentation and a titanium alloy expandable dome plunger and side plate with and without cement augmentation. Gauges were used to establish the mechanical behavior of intact and then fractured femurs to simple uniaxial loads. Subsequent loading to failure allowed determination of maximum fixation strengths and modes of failure

Cement augmentation of each device increased its load to failure. There was no significant difference between the cemented lag screw and the uncemented dome plunger groups with average loads to failure of 4.0 × 10³ N. The greatest average load to failure was in the cemented dome plunger group (5.6 × 10³ N) with the lowest in the uncemented sliding hipscrew group (3.6 × 10³ N). Device cut-out as a cause of failure occurred mostly in the uncemented lag screw group. Sliding was enhanced by those methods that increased the fixation surface area within the femoral head, unless cement encroached in the region of the barrel-screw junction. Strain analysis showed that the dome plunger unloaded the bone at the calcar, regardless of cement augmentation, while the sliding hip screw allowed for compressive stresses in this area.

Proper cement augmentation increases load to failure and minimizes nail cut-out for both devices studied. However, the dome plunger, a device with a large fixation area in the femoral head, was equally effective and eliminated potential cement encroachment. Failure of intertrochanteric fracture fixation in osteoporotic bone may be minimized by an appropriate choice of device or cement augmentation.     

Staged method using antibiotic beads and subsequent autografting for large traumatic tibial bone loss: 22 of 23 fractures healed after 5-20 months

Introduction The vascularity of surrounding soft tissues, which is related to muscle cover, is important for the healing of traumatic bone loss. Muscle cover on the distal tibia is limited compared to the diaphyseal and proximal tibia, and delayed healing of fractures in this area is common. We evaluated the healing of traumatic bone loss in the proximal, diaphyseal, and distal tibia.

Patients and methods 23 open tibial fractures with substantial bone loss (mean 52 (34-104) mm) were treated using a staged method with antibiotic-impregnated beads and later autologous bone grafting at second-stage surgery on average 8 weeks after the injury.

Results 22 fractures healed after mean 40 (20-79) weeks. The average healing time in the distal tibia (mean 30 weeks) was 7 weeks shorter (95% CI: 12-26 weeks) than in the proximal tibia (37 weeks), and 16 weeks shorter (95% CI: 3-29 weeks) than in the tibial shaft (47 weeks). The length of the bone and the type of soft tissue cover (free muscle or secondary suture) had no effect on healing time.

Interpretation Our study suggests that the method we used is applicable in all parts of the tibia, although the healing of bone loss is slower in the diaphyseal tibia than in the proximal and distal tibia.     

Plate fixation of tibial fractures in the rabbit: Correlation of bone strength with duration of fixation

Bone healing after metal plate fixation of rabbit tibial osteotomies was studied in order to gain information as to the optimum time for plate removal. The fracture had regained almost normal biomechanical properties after 6 weeks. Significantly greater strength and stiffness of the healing tibiae were obtained at 12 weeks when the plate was removed after 4, 6 or 9 weeks and no further fixation was subsequently applied, compared to those plated for 12 weeks. The results indicate that a metal plate should be removed as soon as the fracture has regained normal biomechanical properties; i.e. before the stress-protecting effect has secondarily weakened the bone.

The findings suggest that metal plates should be removed at an earlier stage of the healing period than is usual in clinical practice.     

Plate fixation of tibial fractures in the rabbit. Correlation of bone strength with duration of fixation

Bone healing after metal plate fixation of rabbit tibial osteotomies was studied in order to gain information as to the optimum time for plate removal. The fracture had regained almost normal biomechanical properties after 6 weeks. Significantly greater strength and stiffness of the healing tibiae were obtained at 12 weeks when the plate was removed after 4, 6 or 9 weeks and no further fixation was subsequently applied, compared to those plated for 12 weeks. The results indicate that a metal plate should be removed as soon as the fracture has regained normal biomechanical properties; i.e. before the stress-protecting effect has secondarily weakened the bone. The findings suggest that metal plates should be removed at an earlier stage of the healing period than is usual in clinical practice.     

Bone repair inhibited by indomethacin: Effects on bone metabolism and strength of rabbit osteotomies

We measured mineral content, maximum bending strength, and regional blood flow after tibial osteotomy fixed with a small metal plate in 38 rabbits. Half of the animals were treated with indomethacin (10 mg/kg/day) while the other half served as controls.

After 2 and 6 weeks, the bone mineral content and maximum bending strength were lower in the indomethacin group when compared with the controls. Compared with the controls, the blood flow at the osteotomy site was decreased after 2 weeks and increased after 6 weeks in the indomethacin-treated animals.

Inhibition of blood flow increase by indomethacin medication in the early period following osteotomy, as well as retarded bone healing, are probably caused by inhibition of the inflammatory reaction.