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Biomechanics of the Ilizarov fixator for fracture fixation.

Compression, distraction, and torsion stiffness of the Ilizarov external fixator was measured in two fracture models in autopsy specimens of tibia and fibula. A transverse model was tested in six frame constructions with the osteotomy site preloaded in four different positions. An oblique model was tested in four frame constructions also with four preloaded positions. Stiffness was more dependent on bone preload than wire number, wire type, or frame design. High stiffness was achieved by bone preloading, by compressing the rings together, by increasing the number of wires, and by using olive wires. The stiffness can be decreased (dynamization) by separating the rings and by removing wires. This data is helpful for frame design of the Ilizarov fixator.

Biomechanical Phenomena

The mechanics and biology of intramedullary fracture fixation.

Intramedullary (IM) fracture fixation serves to stabilize fracture fragments and maintains alignment, while permitting motion at the fracture site during functional activities. Acting as an internal splint, the implant serves as a load-sharing device and fracture healing progresses with the formation of peripheral callus. By allowing motion of adjacent joints, rehabilitation is concurrent with treatment, and stress-shielding is thought to be minimal using these techniques. Recently, IM nails have been introduced to widen indications for their use based on variations in the cross-sectional geometry, length and shape of nails, interlocking designs, and surgical techniques. Although the most important mechanical factors in the design of IM nails are strength, stiffness, and rigidity, anatomic constraints and surgical technique limit nail variations. Closed nailing is preferred to open procedures to preserve periosteal blood supply and minimize surgical trauma adjacent to the fracture. Blood flow to the fractured bone is elevated in nailing experiments, although callus maturation is somewhat delayed. However, the end result in terms of healing was similar to that of plate fixation.

Animals

Impact of the use of absorbable fracture fixation implants on consumption of hospital resources and economic costs.

Within a 6-year period (1984-1989) absorbable pins, rods, and screws made of polyglycolide, polylactide, or lactide-glycolide copolymer were used in the internal fixation of 881 fractures, 73.1% of which were displaced malleolar fractures of the ankle. During the last 3 years the patients treated using absorbable fracture fixation constituted 19.6% of all fracture patients managed by internal fixation at the department. The number of hardware removal procedures avoided during the 6-year period as a result of the use of the absorbable implants was estimated at approximately 700. By determining all direct and indirect costs associated with internal fracture fixation and the influence of the percentage of hardware removal, a cost coefficient was calculated for certain fracture types when treated using absorbable versus metallic internal fixation. In bimalleolar fractures, an optimal indication for absorbable fixation, the coefficient was 1.04 (cost of absorbable fixation 4% higher than that of metallic fixation) if the removal percentage with metallic fixation was zero and 0.91 (cost of absorbable fixation 9% lower than that of metallic fixation) if the removal percentage was 100%. The breakeven point was a removal rate of 31%.

Absorption

Biodegradable implants in fracture fixation: early results of treatment of fractures of the ankle.

Biodegradable polylactide-glycolide copolymer implants for fracture fixation were developed and tested in rabbits. In a prospective clinical study 44 patients with a displaced fracture of the ankle were randomly allocated to two groups; one was treated with conventional metallic implants and the other with the biodegradable implants. There were no differences between the two groups in the early results, but the biodegradable fixation method is advantageous because the removal procedure associated with metallic implants is avoided.

Adult

Parametric analyses of pin-bone stresses in external fracture fixation devices.

Problems occurring in the use of external fixators for bone fractures include pin-bone interface necrosis, infection, and loosening. These may be initiated and enhanced by pin-bone interface stress levels. Based on stress data from finite element method (FEM) models, an analytical "closed-form" model of the local pin-bone configuration in long-bone fracture fixation is developed. This model is relatively simple and useful for routine applications in combination with clinical studies and animal experiments. Although approximate, the most significant stress predictions in the pin-bone structure compare well with more sophisticated FEM analysis results. The analytical model is used for extensive parametric analyses, investigating the effects on the pin-bone interface stress distribution of frame configuration parameters, pin diameter and modulus, bone dimensions, and elastic characteristics. The results indicate that these stresses may reach very high levels under unfavorable circumstances but can be drastically reduced by increasing the bending rigidity of the pin, reducing the side-bar separation and applying full-pin configuration in favor of half-pins.

Bone and Bones

A preliminary analysis of the forces in screws in tibial fracture fixation.

If a fracture of the tibia is incorrectly reduced and a plate fixed across the fracture site, then all of the load during subsequent weight bearing can be considered to be taken by the screws fixing the plate to the bone. An analysis of this extreme situation and determination of the magnitude of the consequent forces on the screws indicate that the screws are in danger of failing due to the shear forces but are in little danger from the tensile forces.

Bone Plates

Timing of fracture fixation: a review.

The timing of fracture stabilization has received little attention in the current orthopaedic literature. The existing data on fracture fixation will be reviewed specifically with regard to early versus delayed stabilization. Timing relative to the multiple trauma patient, open fractures, periarticular fractures, and hip fractures requires special consideration.

Aged

[New information about the biomechanics of fracture fixation].

The better knowledge of the biomechanics of bone tissue and fracture healing resulted in the development of the AO principles and its methods of treatment. I have demonstrated on the femora of rabbits that the consequence of progressive dynamization versus the current unchanging stability of fracture fixation was a more rapid healing. According to our knowledge the more elastic, dynamizating or dynamizable fixation of the fracture are the methods of future. The new biodegradive implantates make not only their removal superfluous but help the fracture healing, too.

Biomechanical Phenomena

Lower extremity fracture fixation in head-injured patients.

Compared with nonsurgical management or delayed repair, early fracture fixation can reduce the incidence of pulmonary complications in patients with long-bone fractures of the lower extremities. Blunt trauma victims often have multiple nonskeletal injuries that might influence the risk of pulmonary complications, and when head injuries are present it has been a common practice to delay nonemergent operations for several days to protect the injured brain. We conducted a retrospective review of 114 patients with multiple trauma whose injuries included head trauma and a fracture of the neck or shaft of the femur or shaft of the tibia to determine if delayed stabilization of lower extremity fractures increased the risk of pulmonary complications or reduced the risk of cerebral complications. Forty-six patients underwent surgical fixation of their fractures within 24 hours of injury (early fixation), 26 patients had their fractures repaired more than 24 hours after injury (late fixation), and 42 patients did not undergo surgical fracture fixation. The risk of pulmonary complications was not related to the timing of surgical fracture fixation but was strongly influenced by the severity of injuries to the head and to the chest (p less than 0.001). Furthermore, a delay in fracture fixation did not protect the injured brain; the risk of CNS events was determined by the severity of the head injury (p less than 0.0001). Early fracture fixation in patients with head injury may be appropriate because it simplifies patient care and does not seem to worsen the head injury, but it does not prevent pulmonary complications in these high-risk patients.

Adolescent

[Development of synthetic bone models for the evaluation of fracture fixation devices].

Mechanical tests are indispensable for the research and development of internal devices used for fracture fixation. It is ideal to use fresh human bones even for in vitro experiments. However, fresh human bones are difficult to access, so that alternative materials have been developed. In this study, the applicability of synthetic tibia or femur models made from polyurethane resin (Hiprox) was studied, comparing the mechanical properties of both the synthetic models and the fresh human bones under fracture-fixation conditions using various fixation devices. When the models were designed to simulate the cortical bone with solid resin and the cancellous bone with porous resin, the mechanical properties can be fairly approximated to those of the fresh human bones. It was concluded that the Hiprox models are useful in for preliminary testing of fracture fixation devices.

Biomechanical Phenomena

Implant materials for fracture fixation: a clinical perspective.

The optimum management of traumatic skeletal fractures may involve the installation of high quality surgical implants by a skilled orthopedic surgeon. Satisfactory clinical results are very dependent on the ability to maintain stable fracture fixation. Well designed contemporary implants rely on precise control of material composition and properties to achieve a well tolerated level of biological response. Metallic materials, such as 316L stainless steel, pure titanium, and titanium alloys, demonstrate an acceptable combination of strength, ductility, corrosion resistance, and biocompatibility. Polymers, composites, and biodegradable materials may offer selected opportunities for fracture fixation. An understanding of relevant clinical factors is essential to evaluate potential applications for advanced materials.

Biocompatible Materials

Principles of fracture fixation in growing animals.

Changes in bone structure and conformation can occur very rapidly in growing animals. Injury to the bones or articular surfaces warrant special consideration because of the potential devastating consequences of secondary growth deformities in the animal. Disturbance of normal growth plate activity, imperfect fixation of an articular fracture, and conformational defects in long bones may create lifelong problems for the animal.

Animals

Biomechanics of fracture fixation failure.

This article reviews the physiologic forces, stresses, and strains in normal bones. Biomaterials used in implants for fracture fixation devices are described, and the mechanical properties of an implant are discussed. The common mechanisms of implant failure are included.

Animals

Mandibular fracture fixation and reconstruction using the lower-border threaded rod: an eleven-year follow-up study.

Twenty-five cases in which a lower border threaded rod was used for fracture fixation and mandibular reconstruction were reviewed. These cases were performed during the last 11 years and have been followed for periods of up to five years and ten months. The fixation technique, originally reported in 1978, is well tolerated and provides excellent mechanical stability when enhanced security of fixation is indicated. Three unusual cases are reported in detail.

Adolescent

[Method of fracture fixation using external fixation devices].

An improvement of the results of treatment can be reached, beside respecting the indication of external fixateurs, with correct tactics of the treatment. Because of the disadvantages of the fixateur externe, we strive to restrict their use, to the time by all means necessary, and if possible to use other methods of fixation. This is motivated especially by the effect on fracture healing and the hindering of the movements and activity of the patient.

Biomechanical Phenomena