Sheep Tibia Research Articles

Studies on the External Fixator Pin-Bone Interface: The Effect of Pin Design and Pin Cooling in an In Vivo Sheep Tibia Model

SummaryThe purpose of this study was to examine the effect of pin design and drill/pin cooling on the biological response of bone in the near (entry) and far (exit) cortices of mature intact sheep tibiae. Two pins with markedly different characteristics were used; the AO Schanz screw, a traditional pyramidal tipped design, and the fluted, tapered end Howmedica Apex pin. Our hypothesis was that cooling of hardware would reduce thermal necrosis of bone at the pin-bone interface (PBI). When the effect of pin design was controlled for, the cooled pins resulted in better pin bone interfaces at the near cortex but not the far cortex. It is possible that the drill bits and pins warmed significantly after traversing the more vascular bone marrow space, thus the cooling effect was lost before drilling the far cortex. Secondly, the Howmedica Apex pin resulted in more bone at the pin bone interface than the AO Schanz pin indicating that the former’s more advanced design follows the pilot hole and creates threads more accurately, resulting in a better pin-bone fit and less mechanical damage.The purpose of this study was to examine the effects of pin design and drill/pin cooling on the remodelling response of cortical bone at the pin-bone interface in an in vivo sheep tibia model. No significant differences were found between pin designs or between pins that were implanted at 4° C and those that were inserted at 20° C. More bone was retained at the near cortex pin-bone interface (PBI) than the far cortex PBI when the pins were cooled, but the opposite was true when the pins were not cooled.

Radiological sequences of healing in internal plates and splints of different contact surface to bone. (DCP, LC-DCP and PC-Fix)

For several years our attention has been directed towards the damage to the blood supply brought about by implant contact. The disturbance of the blood supply results in necrosis and consequent remodelling which then results in early temporary porosis and potentially in bone sequestration. Reduced resistance to local infection may follow. Locally delayed remodelling may give rise to stress concentrations and thus increase the danger of refracture. With this in mind a new approach to periosteal splinting has been developed which realizes minimal implant contact to preserve the blood supply to the bone. In order to elucidate the sequence of events in healing, time-lapse cinematography has been used to facilitate the comparison of conventional and new plates and internal splints. Fractures of the sheep tibia were recorded radiologically at short intervals Samples of these radiographs are displayed for comparison. The healing process after application of an internal fixator (PC-Fix) results in earlier solid union and a more homogeneous bone structure.

The implantation of cartilaginous and periosteal tissue into growth plate defects.

This experimental study reports the results of implantation of cartilaginous and periosteal tissues into growth plate defects in the tibiae of sheep. When no material was used, the defect rapidly filled with marrow-like tissue. When cartilage from the margin of the secondary centre of ossification was implanted, endochondral ossification continued and no shortening or deformity resulted. Implantation of periosteum with or without reconstructed peripheral tissues resulted in the formation of a bony bridge which led to a 32% inhibition of longitudinal growth and a 12 degrees varus deformity in the absence of peripheral connective tissues. After reconstruction with these tissues, the inhibition of longitudinal growth was 47% with a 28 degrees varus deformity. The chondroprogenitor cells in the implanted tissues cannot change phenotypic expression. Periosteum has a strong potential for bone formation after it has been implanted.

An assessment of postnatal growth after in utero long bone osteotomy with fixation.

Researchers have recently suggested that rigid fixation of the immature bony skeleton may restrict growth and development. This study assesses the effect on postnatal growth of an in utero tibial osteotomy fixed with a miniplate in fetal sheep. A midshaft osteotomy was performed on fetal sheep tibia (n = 5) at 95 days' gestation (term 145 days). One tibia was reduced and fixed with a titanium miniplate and screws, while the contralateral hindlimb served as a control. The newborns were vaginally delivered and sacrificed at 2 months of age. The hindlimbs, control and fractured, were harvested, stripped of soft tissue, and the tibia, femur, and distal metatarsal were each measured and weighed. Each tibia also underwent radiographic analysis and histologic examination (after decalcification) using hematoxylin and eosin, Sirius red, and Alcian blue stains. No prenatal, postnatal, or perioperative medical complications occurred. Apart from a slight angulation in one operated tibia, no gross morphologic differences, either visible or palpable, were found between the operated and control limbs. This was confirmed radiographically where no remnant of the osteotomy site was visible. Measurements of the operated and control tibias, femurs, and metatarsal bones were not statistically different. Histologic analysis showed a total incorporation of bone at the osteotomy site with appositional growth present. All bone was lamellar with longitudinal orientation. In the area of the screw sites, the surrounding bone shaft was the same width as its neighboring bone.(ABSTRACT TRUNCATED AT 250 WORDS)

10. Cancellous bone graft for skeletal reconstruction Muscular versus periosteal bed — Preliminary report

The purpose of this project was to verify the value of perfused periosteum as a possibly ideal bed for autogenous cancellous bone graft. The model consisted of a 7 cm defect in the sheep tibia, stabilized with a locked intramedullary nail. The defect was filled with conventional cortico-cancellous bone graft covered either with a muscle or a perfused osteoperiosteal flap. The incorporation of the graft was analysed by a series of radiological and mechanical examinations. The graft embedded in perfused osteo-periosteum was rapidly remodelled to a strong, circular bone. Mechanical testing revealed even better values than for normal bone. The graft embedded in muscle showed an important resorptive phase before scanty, incomplete, reconstitution of bone appeared. Mechanical properties were poor. The study supports the hypothesis that perfused osteo-periosteum is an ideal bed for cancellous bone graft and that perfused muscle is not the ideal environment for incorporation of the graft.

Stability of the construction of the elastic external fixation of Ilizarov system used for the lengthening of limbs

Objective. To measure and compare the mechanical properties in bending of the four-ring, and three-ring/one-tube hybrid external fixation frames.Design. In vitro measurements of the mechanical behaviour of ring and ring-tubular external fixation frames. In the latter, one ring of the full circular frame was replaced by one tube and Schanz screws.Background. The mechanical properties of the classical Ilizarov four-ring external fixation frames has been compared to those of other external fixation frames by various authors. However, in clinical practice the hybrid fixation frame is being used with increasing frequency. Therefore the mechanical properties of the latter are of immediate interest and clinical value.Methods. On explanted sheep tibiae with single and double osteotomies, frame stiffness in the four-point bending mode was measured at different K-wire tensions, comparing the values obtained from four-ring frames, to those of three-ring-tubular hybrid frames. These measurements were made under conditions of (a) bone distraction (BD), and (b) segment transport (ST), both at the initial and final stages of this procedure.Results. In circular frames, frame stiffness in bending for increasing K-wire tension showed a Gaussian distribution both in distraction and post-ST with an optimum at 1000 N. In ring tubular hybrid frames, however, frame stiffness showed a more linear relationship to K-wire tension.Conclusions. In the four-ring Ilizarov external fixation frame, the exchange of one ring with one tube and one Schanz screw both reduced frame stiffness in bending and converted to linear its relationship to K-wire tension.

The role of corticotomy and osteotomy in the treatment of bone defects using the Ilizarov technique.

Posttraumatic bone defects are usually bridged using autogenous or exogenous cancellous bone grafts. These grafts consolidate to form a solid bone structure that is mechanically stiffer than natural bone. Likewise, the procedure of corticotomy and distraction is appropriate for treatment of bone defects. In our experiment, a 2-cm bone defect was created in 25 sheep tibiae. We performed corticotomy or osteotomy of the intact bone, thus creating a bone segment that was drawn across the defect using a specially designed traction device. The limb was stabilized using an external fixator. Four groups were formed for comparison: corticotomy and osteotomy with distraction at a rate of 1 mm/day; corticotomy and osteotomy with immediate transportation of the segment to the docking site. The animals were killed after 4, 8, 12, 16 and 52 weeks. Evaluation of the results was based on standard radiographs. In the two groups involving gradual transportation, spontaneous bone regeneration occurred in all cases whereby after corticotomy the new bone was tubular (around the medulla). Following osteotomy, bone regeneration occurred initially on the dorsal and lateral sides of the tibia leaving a defect on the ventral and medial sides. This defect subsequently closed. At the end of segment transportation, healing was observed at the docking site. In Groups 3 and 4, the bone did not regenerate at all. Therefore, this procedure, immediate transportation, was not investigated further because no clinical success could be expected from its application.

Acute Effects of Reamed Versus Unreamed Locked Nailing on Blood Flow in a Fractured Sheep Tibia Model

Acute Effects of Reamed Versus Unreamed Locked Nailing on Blood Flow in a Fractured Sheep Tibia Model

The Radial Forearm Flap

The use of vascularized bone grafts to reconstruct extremity and mandibular defects is now commonplace in reconstructive surgery. Fibula, scapula, iliac crest, rib, and metatarsal as well as the radial forearm osseocutaneous flaps have all been utilized for this purpose. Troublesome spiral fractures of the distal radius are the most common fractures associated with the use of the distal radius as a vascularized bone-graft donor site. This study was proposed to investigate the effect of donor-site bone loss on the strength of the radius under torsional (rotational) loading. Previous clinical series and experimental studies have not examined this aspect of distal radius loading after harvesting the bone graft. Fifty pairs of sheep tibiae were utilized in the experiment. Five pairs were used in a pilot study and 45 pairs were used in the main experiment. Five pairs of human radii were used for the control in the pilot study. The pilot study attempted to make a comparison between the human radius and the sheep tibia for experimental purposes. For the biomechanical study of donor-site defects, four study groups were examined with random assignment and matched pairs. The control group (group 1) had no alteration to the bone. Each test condition included five matched pairs of sheep tibiae. Experiment 1 compared the difference in the depth of the osteotomy defect. In doing this, one-third of the total length of the bone was removed in each of the following specimens to include (1a) 30 percent of the cross-sectional area of the total bone, (1b) 37 percent of the cross-sectional area of the total bone, and (1c) 50 percent of the cross-sectional area of the total bone. In experiment 2, the osteotomy shape was varied. Instead of the ends of the cuts being squared, the ends were beveled or rounded. Experiment 3 compared different lengths of bone removed in the osteotomy defect and included the following: In experiment 3a the diameter of the sheep tibia was measured at the incisura fibularis. This dimension was one diameter of bone, and a one-diameter length of bone was removed. In experiment 3b, a two-diameter length of bone was removed. In experiment 3c, a three-diameter length of bone was removed. In experiment 3d, a four-diameter length of bone was removed.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction and Prevention of Pin Loosening in External

In external fixation of fractures, pin loosening is a major concern. Preloading the pins is generally done to ensure their stability within the bone cortex. The effect of radial preload and bending preload in reducing resorption at the pin/bone interface was tested. Schanz screws were fixed to live sheep tibiae using a pneumatically operated external fixator frame. Evaluation was based on radiological observation and fluorochrome histology using sequential labels. Though not completely absent, bone resorption was minimal in the radial preload group, compared with the two other groups. More important, the bone-to-pin contact surface in the radial preload group was found to be almost intact after 5 weeks. In this study, radial preload appears to be superior to bending preload in terms of minimizing the problems of pin loosening.

Internal Fixation with a Self-Compressing Plate and Lag Screw

A mechanically improved design of bone plate and screw was compared in vivo with conventional plate fixation. This method was investigated biologically in a standardized osteotomy model on sheep tibiae. It was found that maintenance of reduction of an osteotomy was facilitated and there was no adverse effect of this fracture fixation system on bone remodeling. The modified implant permits the reduced surgical approach to the bone through one plane and optimal fixation of the fracture or osteotomy.

Biomechanical Factors in the Metaphyseal- and Diaphyseal-Lengthening Osteotomy

A post hoc comparison of the mechanical factors that affected the outcome of experimental metaphyseal- and diaphyseal-lengthening osteotomies in sheep tibiae was performed. The resulting motions between bone segments at the metaphyseal and diaphyseal levels were estimated using measured fixator stiffnesses, postural muscle activity, ground reaction forces, and calculated internal and external loads. Relative displacements of bone segments of up to 2.8 degrees were estimated in postural activities; displacements were up to 4.9 times larger at the metaphyseal than at the diaphyseal osteotomy level. The results suggest that due to these increased motions, mechanically inferior conditions for healing at the metaphyseal-lengthening osteotomy level may counteract any supposedly superior biologic healing potential that the metaphyseal region of the bone may have compared with the diaphyseal region. These results correlate well with the clinical findings of the earlier animal study.

Significance of postoperative stability for bony reparation of comminuted fractures

The significance of postoperative mechanical stability to bone repair of comminuted fractures was investigated in an animal experimental study comparing four commonly employed operative methods of fracture stabilization: 1. Plate osteosynthesis combined with lag screw fixation; 2. Bridging plate osteosynthesis; 3. External fixation; 4. Static interlocking intramedullary nailing. As fracture model, a triple wedge osteotomy of the right sheep tibia was used. In regard to biomechanical strength, the method which gave best postoperative stability, plate osteosynthesis in combination with interfragmentary lag screws, did not result in the best bone repair. In this experimental setup, stabilization by bridging methods, inducing bone healing by secondary intention, gave better bone regeneration in the experimental fractures.

Measurement of bending and torsion with and without an intramedullary nail implanted in sheep tibia in vivo.

This report concerns the analysis of the dynamic measurements of torque and bending on nailed tibiae, using two sheep walking at different speeds on a treadmill, both before and after nailing. The amplitude and the period of the measured values are reported and discussed in relationship to the speed and duration of the experiment.

Three-dimensional strain fields in a uniform osteotomy gap.

Stable internal fixation usually results in a unique histological healing pattern which involves direct cortical reconstruction and an absence of periosteal bridging callus. While it has been suggested that longitudinal interfragmentary strain levels control this healing pattern, the complex, multiaxial strain fields in the interfragmentary region are not well understood. Based on an in-vivo study of gap healing in the sheep tibia by Mansmann et al., we used several finite element models of simplified geometry to: explore modeling assumptions on material linearity and deformation kinematics, and examine the strain distribution in a healing fracture gap subjected to known levels of interfragmentary strain. We found that a general nonlinear material, nonlinear geometric analysis is necessary to model an osteotomy gap subjected to a maximum longitudinal strain of 100 percent. The large displacement, large strain conditions which were used in the in-vivo study result in complex, multiaxial strain fields in the gap. Restricting the maximum longitudinal strain to 10 percent allows use of a linear geometric formulation without compromising the numerical results. At this reduced strain level a linear material model can be used to examine the extent of material yielding within a homogeneous osteotomy gap. Severe local strain variations occurred both through the thickness of the gap and radially from the endosteal to periosteal gap surfaces. The bone/gap interface represented a critical plane of high distortional and volumetric change and principal strain magnitudes exceeded the maximum longitudinal strains.

The effect of induced electric currents on bone after experimental osteotomy in sheep.

We have investigated the effect of currents induced by electromagnetic fields on the healing of the tibia of sheep after osteotomy, using objective and quantifiable criteria wherever possible. A battery-powered, induction apparatus was developed and was enclosed within the cast applied to the limb, so that the treated fractures received pulsed magnetic fields for 24 hours a day while the animals were freely mobile. In all, 13 sheep were treated and 13 were used as controls. The response was assessed by radiography of the limb and of the excised bone, by histology, including measurement of the areas of callus, fibrocallus and cortical bone, and by measurement of the uptake and extraction of bone-seeking mineral. All the bones healed and no statistically significant differences between the treated animals and the controls were discovered except (at only P less than 0.05) in the uptake of bone-seeking mineral; this increased more rapidly in treated animals over the two to three weeks after osteotomy, although at six weeks the uptake in both groups was the same.

The effect of impact on the marrow pressure of long bones in vitro

Intact fresh sheep tibiae were subjected to non-destructive impact loads while maintained in an environment like that encountered in life. Under a maximum load of 2.5 kN, and loading rate of 500N ms −1, marrow pressures no higher than 50 k Pa were recorded. Such low pressures would provide only a trivial amount of hydraulic strengthening, and are consistent with results from other workers carried out at lower rates of loading.

Quantitative investigations on newly-built bone in defects Its time-dependent changes of morphological and biomechanical properties

Bone growth in drillholes in sheep tibiae were examined morphologically and biomechanically after 4, 6, 9, and 12 weeks. Selected bone specimens were removed from the defective areas and used to determine the strength and, with the aid of microradiographs, the volume of new bone. Strength as well as volume of new bone increased in the defects within the healing time. However, the strength of the newly-formed bone reached only 20% of the strength of normal cortical bone. This is caused by the random structure of new bone which, despite the repair of the defect and the nearly normal mineralization, is not yet adapted to the adjacent normal cortical bone.

Distraction Epiphysiolysis as a Method of Limb Lengthening

Distraction epiphysiolysis as a means of lengthening bone has been studied in sheep tibiae by histologic, histochemical and microradiographic and electron microscopic methods. The tibiae have been studied 1, 2, 3 and 4 weeks and 2, 4, 6 and 12 months after the induction of this procedure. Distraction epiphysiolysis occurs in the following stages: development of a fracture along a line dividing the maturing from the hypertrophic chondrocytes, with the formation of a hematoma between the fracture surfaces; downward displacement of the metaphyseal cartilaginous fragment and gradual resorption of the hematoma, which is replaced by fibrous tissue; elongation of the fibrous tissue; with the formation of collagen bundles oriented parallel to the tensile force of distraction; calcification and ossification of these bundles, with the formation of longitudinal and parallel bone trabeculae; development of periosteal bone, which becomes a new diaphyseal shaft. The results show that distraction epiphysiolysis actually lengthens the bone segments; bone structure is completely restored, without serious changes occurring in the soft tissues. Restoration of endochondral ossification in the epiphysis tends to be unpredictable, however, so that the procedure is reliable only in subjects that have almost reached skeletal maturity.

Porous ceramics as a bone substitute in the medial condyle of the tibia. An experimental study in sheep. Long-term observations.

A recent 3-month implantation study indicated that a new porous ceramic material might be suitable as a bone substitute in regions exposed mainly to compressive forces. The porous ceramics were implanted into the medial condyle of the tibia of sheep. In the present study the implants were left for 10 months in three animals, and 12 months in two. In the two animals with 12 months' observation, the plate which had been used to stabilize the implant was removed at 10 months. The implants and the adjacent bone tissue were studied macroscopically, radiographically and by microradiography and transmitted light microscopy. All the implants were bound to the adjacent bone by ingrowth of bony tissue. The depth of the bony invasion was slightly greater than that observed at 3 months, being maximally 3-4 mm. Some signs of ossification were still seen within the pores. The bony bridges between the implants and the surrounding bone were particularly well developed in regions of maximal stress. This was interpreted as a sign of active adaption of the bone formation to the actual stress to which the shearing surfaces were exposed. It is concluded that the properties of the porous ceramic implants justify a clinical trial in man.