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PubMed1980

[Area of contact between osteosynthesis plate and bone in internal fixation (author's transl)].

The bone can be protected against excessive stress if the plate is properly adapted to the surface of the contact area between plate and bone, thus ensuring good and longlasting repositioning of the fracture. The article describes an in-vitro method for the quantitative evaluation of the contact area between plate and bone in osteosynthesis. With four different bones and the requisite plates, six expert surgeons were able to obtain an area of contact between plate and bone which varied between 13 and 60%, the average being 32%. The available data allow us to conclude that the peak loads of pressure occurring with small contact areas may be so great that they exceed the maximum compressive strength of the bone.

Bone Plates↗
PubMed1986

Fatigue fracture of a forearm plate within a long-arm cast.

Open fractures of both left ulna and radius, in which a segment of the radius was found to be missing, occurred in a 27-year-old man. The fractures were treated by open reduction, internal fixation with ASIF semitubular plates, and bone graft. Because of slow radiological union, regrafting was required twice. Approximately six months after the third operation, roentgenograms showed that the bone plate was broken, even though the fractures had been protected in a long-arm cast. The fatigue fracture of the plate, positioned on the posterior surface of the ulna, was presumably caused by the force of the finger flexors, most of which originate above the fracture site, and which were still able to contract because the fingers were not immobilized.

Adult↗
PubMed1984

Changes in long-bone structural properties during the first 8 weeks of plate implantation.

The midplate structural rigidities of metal- and plastic-plated intact canine femora were experimentally determined after initial plate application and 8 weeks after in vivo implantation. Composite beam theory significantly overestimated the bending rigidities of the metal-plated bones. The rigidities of the plastic-plated bones were nearly identical to that of the isolated bone, as composite beam theory predicted. Plating with either plate increased the intracortical porosity and caused the deposition of periosteal new bone, which was greater with plastic than with metal plates. The increased rigidities provided by the attachment of the metal plates and, hence, the degree of bone strain shielding were variable. Platings for 8 weeks which provided little strain shielding with either metal or plastic plates caused an increase in bone flexural rigidity (measured after plate removal) with respect to the contralateral control. Platings that provided increasing amounts of strain shielding caused a decreasing midplate bone rigidity (measured after plate removal) and increasing bone deposition at the outer screws. These findings suggest that the surgical implantation of any plate (metal or plastic) will provide a net stimulus to bone formation and consequently increased bone structural rigidity, even though intracortical porosity is increased. If the plate significantly reduces the normal loads borne by the bone, however, there is a net stimulus to remove bone, resulting in a loss of midplate structural rigidity within 8 weeks of implantation.

Animals↗
PubMed1993

An alternative to screws for plating osteoporotic bone.

There are several problems with existing techniques used to plate broken bones. One of the most serious is that of screws pulling out during insertion or healing in patients suffering from osteoporosis. This paper investigates the mechanism of this pulling out, and proposes an alternative device to attach plates to weak bones.

Biomechanical Phenomena↗
PubMed2002

Bone blood flow response to surgical trauma.

The evolution of bone plate design has been with a view to reducing the interface contact between the plate and the underlying bone thereby limiting the perfusion deficiency that develops. Little consequence, however, has been attributed to the drilling of holes in the steps prior to bone plate application; the work present herein attempts to define the vascular response of bone to the trauma of drilling holes. Anaesthetized sheep underwent the creation of drill holes in both tibiae and metatarsi. Animals were then heparinized and euthanatized. Utilizing femoral cannula, perfusion of the vasculature ensued; spalteholz (India ink), disulphine blue and radiocontrast material (barium sulfate). Decalcified histology was performed and correlated with the perfusion studies. Regions of perfusion deficiency were observed immediately adjacent to, and removed from, the drill hole site. Radiographic images showed substantial haematoma formation and vascular disruption in the vicinity of the drill hole site. Histologically, blood vessels immediately adjacent and distal to the drill hole site, contained a proteinaceous/cellular material occluding the vascular space. Our findings support the proposal of a short-term obstruction in cortical blood flow which may contribute to later adaptational osteopaenia following bone plate application. We have observed an acute vascular insufficiency in cortical bone directly related to the trauma of drilling screw holes.

Animals↗
PubMed2002

Sacral and iliac articular cartilage thickness and cellularity: relationship to subchondral bone end-plate thickness and cancellous bone density.

OBJECTIVES: To measure the thickness and cellularity of adult human sacral and iliac articular cartilages and the thickness and density of the subchondral bones. METHODS: The right sacroiliac joints of 15 adult patients were examined post-mortem. HOME (Highly Optimized Microscope Environment) microscopy was used to measure articular cartilage and subchondral bone end-plate thickness. Conventional morphometric techniques were employed to estimate cartilage cellularity and cancellous bone density. RESULTS: Sacral articular cartilage was thicker than iliac (1.81 vs 0.80 mm, P<0.001). Iliac cartilage cell density in all zones was higher than sacral. The overall mean was 31.19 x 10(-3) vs. 23.23 x 10(-3)/mm(3), P<0.001. Superficial zones contained more cells than middle and deep zones but there were large differences between the cell numbers of the middle and deep zones of both sacral and iliac cartilages. Iliac subchondral bone end-plates were thicker than sacral (0.36 vs 0.23 mm, P<0.001). The thickness of these plates was related inversely to that of the overlying articular cartilages. Iliac subchondral cancellous bone was twice as dense as sacral (22.07 vs. 12.05%, P<0.001), a ratio recognized anteriorly, centrally and posteriorly. CONCLUSIONS: Adult human sacral cartilage is thick and of low cell density. It rests upon a thin bone end-plate supported by porous, cancellous bone. Iliac cartilage and bone display the converse proportions. The identification of these variables may assist understanding of normal sacroiliac joint function and the interpretation of tissue changes in the spondylarthropathies.

Adult↗
PubMed2000

Force transfer between the plate and the bone: relative importance of the bending stiffness of the screws friction between plate and bone.

Stability in plate fixation of fractures relates to the motionless fastening between plate and bone. When the plate is affixed to the bone, high shear force may appear between plate and bone, particularly near the end screws, which can lead to motion under weight-bearing. Two mechanisms might be involved in the prevention of motion: the bending stiffness of the screws or the friction between the screw and the plate. Experiments performed in vivo and in vitro show that with conventional plates, motion is prevented by friction and depends upon the axial force of the screw, pressing the plate onto the bone. The torque applied to the screws is crucial. Motion appears under smooth plates under relatively low physiological loads. With newly developed internal fixators, the motion is prevented by the structural stiffness of the plate-screw system.

Animals↗
PubMed1991

Mechanical effects of a cushioned plate on bone fixation.

In vitro and in vivo experiments were carried out to study mechanical effects of the cushioned plate fixation in which a cushion was placed between a metal plate and bone. The cushioned plate fixation was found to be flexible in the physiological stress range and to reduce the stick slip between bone and the plate. A blood-soaked compression test indicated that the cushion moderates the stress shielding effect which occurs in the vicinity of the rigid plate, this being consistent with the result of in vivo experiments.

Animals↗
PubMed2003

[In vivo study of degradation of poly-(D,L-) lactide and poly-(L-lactide-co-glycolide) osteosynthesis material].

AIMS: Comparison of the degradation of poly(D,L)lactide (Resorb X) or poly(lactide-co-glycolide) (LactoSorb) in vivo. MATERIAL AND METHODS: LactoSorb and Resorb X osteosynthesis plates were fixed at the lateral aspect of the femora of 26 Chinchilla rabbits using the respective osteosynthesis screws. After intraperitoneal injection of fluorochromes the screw plate bone blocks were resected after 1, 6, 12, 14, 16, 21, 26 months and radiologic, histologic as well as fluorescence microscopic examinations were carried out. RESULTS: Newly formed bone was detectable above and beneath the polymers 1 month after the implantation. The implants were totally covered by newly formed bone after 6 months. While the LactoSorb screws were found to be as birefringent as after 1 month, in the Resorb X screws a continuous resorption by phagocytizing marrow cells starting from the periphery was detectable. Resorb X was totally resorbed in histologic slides 12 months after implantation, while total resorption of LactoSorb lasted 14 months; both polymers were replaced by marrow cells. Bone remodeling was not finished 26 months after implantation in both polymers. CONCLUSION: Resorption of Resorb X was finished earlier than the resorption of LactoSorb. Both materials were found by fluorescence microscope to be completely resorbed after 12 or 14 months, but bone remodeling of the screw holes was not yet finished 26 months after implantation.

Absorbable Implants↗
PubMed1989

Bacterial growth associated with metallic implants in dogs.

Tissue and swab specimens for bacteriologic culture were obtained from the operative wound in 40 dogs in which plates and screws were applied and then removed from the sites of healed fractures or arthrodeses. Implants were removed after a mean (+/- SD) application period of 15.7 +/- 9.3 months. Bacteria were isolated from the plate-bone interface in 17 dogs. Of the 17 dogs, 9 had had complications associated with initial management (eg, osteomyelitis, open fractures, or multiple surgical procedures). Control specimens were obtained from 30 dogs that had clean elective orthopedic procedures that did not involve implantation of metallic prostheses. None of the dogs of the control group were given antibiotics. Bacteria were isolated from 2 of 30 specimens obtained from control dogs. The difference between the number of culture-positive specimens from dogs of the implant group and those from dogs of the control group was significant (P less than 0.01).

Animals↗
PubMed1994

The stability of the downgrafted maxilla in the cleft lip and palate patient.

Vertical stability following maxillary downgrafting in cleft patients is poor with an average relapse of 42 per cent (ranged 0-100 per cent). Overcompensation should, therefore, be undertaken with 2 mm added to the downgraft movement for bony relapse and 1 mm added to the downgraft movement for upper lip lengthening. The Tideman et al. method for advancement of the lesser maxillary segment is a very stable procedure (less than 8 per cent relapse). Semi-rigid fixation with plates, bone grafting and 'ramping' enhances stability; and freeway space assessment preoperatively is an important guide to relapse potential in the downgrafted cleft maxilla. All surgical prediction tracings should be done with the patient at the occlusal vertical dimension to prevent inadequate maxillary advancement and subsequent reverse overjet or excessive anterior incisor proclination developing with vertical relapse.

Bone Plates↗
PubMed1985

Reconstruction of the edentulous mandible.

Three techniques, the subperiosteal mandibular bone plate, the mandibular staple bone plate and the titanium plasma screw implant system, used in the reconstruction of the edentulous mandible, are reviewed. The surgical and prosthetic techniques for each type of implant are described. A first attempt at gathering statistics on the results obtained with these implants is reported.

Bone Plates↗
PubMed1997

[The structural changes of cortical bone beneath plate after rigid platefixation and removal].

We investigated the structural changes of bone under the plate after plate fixation and removal. Twenty-four New Zealand white rabbits were plated on their intact left tibiae with stainless steel plates and 4 animals served as controls. The plates were removed 2 months after implantation in 20 plated animals, of which, 4 were sacrificed immediately after plate removal and the other were killed in successive groups of 4 each at 1, 2, 3 and 4 months after plate removal respectively. The remaining 4 plated animals were killed at 6 months after implantation. Bone samples were harvested and prepared for scanning microscopic observation. Internal fixation with a rigid plate may lead not only to osteopenia of the cortex under the plate, but also to disorganization of the cortex, in which the mineral column and collagen fibers were oriented in a randomized pattern. The regional osteoporosis could recover gradually after removal of the rigid plate. However, the restoration of normal bone structure occurred later than that of the bone mass. Delayed restoration of bone structure might be one of the potential causes of refracture of the plated bone.

Animals↗
PubMed2003

Bone mineral density of lumbar vertebral end plates in the aging male sand rat spine.

STUDY DESIGN: Lumbar vertebral segments from young and old male sand rats were assessed for quantitative determination of lumbar end plate bone mineral density. OBJECTIVES: To determine whether bone mineral density increases in the lumbar end plate with age in the male sand rat and to investigate its relationship to disc degeneration. SUMMARY OF THE BACKGROUND DATA: Few basic science studies evaluated the end plate and disc degeneration. The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized. METHODS: Bone mineral density data on cranial and caudal lumbar end plates of young (mean age 6.8 months) and old (mean age 23.3 months) male sand rats were assessed for changes related to age, lumbar position, and radiologic features. RESULTS: Mean bone mineral density was significantly greater in end plates in older compared to younger males (P <or= 0.0018). Mean end plate bone mineral density within young animals was not significantly different in levels L5 to L7; in old animals, bone mineral density was significantly different (greater) progressing from L5 to L7 (P < 0.0001). In older animals, mean end plate bone mineral density for each disc showed a significant increase with lower lumbar sites (P = 0.0068). Mean end plate bone mineral density was significantly greater in animals with radiographic evidence of disc wedging (P = 0.006). End plate bone mineral density correlated positively with age. CONCLUSIONS: Results provide quantitative bone mineral density data on end plate sclerosis in male sand rats. Data reveal site specificities and show that in old animals, end plate bone mineral density is greater than in young animals. Mean end plate bone mineral density was significantly greater at sites with radiographic disc wedging (P = 0.006). Data support the hypothesis that end plate sclerosis may play a role in disc degeneration.

Aging↗
PubMed2003

A finite element model of an idealized diarthrodial joint to investigate the effects of variation in the mechanical properties of the tissues.

The stiffness of articular cartilage increases dramatically with increasing rate of loading, and it has been hypothesized that increasing the stiffness of the subchondral bone may result in damaging stresses being generated in the articular cartilage. Despite the interdependence of these tissues in a joint, little is understood of the effect of such changes in one tissue on stresses generated in another. To investigate this, a parametric finite element model of an idealized joint was developed. The model incorporated layers representing articular cartilage, calcified cartilage, the subchondral bone plate and cancellous bone. Taguchi factorial design techniques, employing a two-level full-factorial and a four-level fractional factorial design, were used to vary the material properties and thicknesses of the layers over the wide range of values found in the literature. The effects on the maximum values of von Mises stress in each of the tissues are reported here. The stiffness of the cartilage was the main factor that determined the stress in the articular cartilage. This, and the thickness of the cartilage, also had the largest effect on the stresses in all the other tissues with the exception of the subchondral bone plate, in which stresses were dominated by its own stiffness. The stiffness of the underlying subchondral bone had no effect on the stresses generated in the cartilage. This study shows how stresses in the various tissues are affected by changes in their mechanical properties and thicknesses. It also demonstrates the benefits of a structured, systematic approach to investigating parameter variation in finite element models.

Adaptation, Physiological↗
PubMed1989

Histomorphometric evaluation of stress shielding in mandibular continuity defects treated with rigid fixation plates and bone grafts.

Histomorphometric techniques were used to evaluate the stress shielding effect in bilateral bone grafts in 4 Macaca fascicularis monkeys. Bilateral continuity defects were created and grafted by replacing the resected portion of the mandible and iliac crest bone into the defect area. Both sides were plated with rigid internal fixation plates. Three months after bone grafting, the plate was removed from one side while the other plate was left in place. The animals were sacrificed at 1, 4, 6, and 8 months after plate removal and the grafted areas removed for histomorphometric analysis. This study documents decreased bone volume as well as smaller interlabel width on the plated side, suggesting a stress shielding effect as a result of the rigid internal fixation plate.

Animals↗
PubMed2000

Influence of decortication of the donor bone on guided bone augmentation. An experimental study in the rabbit skull bone.

The aim of the present study was to evaluate if early access to the endosteal bone compartment by removal of the outer cortical bone plate will enhance bone augmentation in a secluded space. Two titanium cylinders were placed on the skull of each of 8 rabbits. Each cylinder was placed into a circular slit, secured to the skull bone via two mini-screws and supplied with a titanium lid. On the test side, the outer plate of the cortical bone, demarcated by the slit, was removed. The subsequent bleeding resulted in blood fill of the cylinders to various degrees. On the control side, the corfical bone plate was left intact and no bleeding was observed at the time of the placement of the titanium lids. After 3 months, the animals were sacrificed to obtain histology and histomorphometry. No differences in the total amount of augmented bone tissue, in relation to the total experimental area (75.5% +/- 10.9% at the test sites and 71.2% +/- 13.5% at the control sites) or of the augmented mineralized bone tissue in relation to the total amount of augmented bone tissue, was revealed (17.8% +/- 3.0% and 16.0% +/- 4.9% respectively). There was no difference in the morphological appearance of the augmented bone between test and control sites and there were no obvious similarities in the appearance between the newly formed bone tissue and the donor bone. The augmented bone consisted of slender bone trabeculae, distributed in abundant marrow spaces. A conspicuous finding was that the bone trabeculae tended to climb along the inner walls of the titanium cylinder. It is concluded that decortication of the calvarial bone in the rabbit does not result in more bone formation beyond the skeletal envelope after a healing period of 3 months compared to no removal of the cortical bone plate inside a secluded experimental area.

Animals↗