Early Stages Of Fracture Healing Research Articles

Expression of bone morphogenetic proteins in fracture healing.

Fracture healing involves a complex interaction of many local and systemic regulatory factors. Recently, the presence of several bone morphogenetic proteins and their receptors in the fracture healing process has been described. During the early stages of fracture healing, only a minimum number of primitive cells are expressing bone morphogenetic proteins in the fracture callus. As the process of endochondral ossification proceeds, the presence of bone morphogenetic proteins and their receptors increases dramatically, especially in the primitive mesenchymal and chondrocytic cells. While the cartilaginous component of the callus matures with a concomitant decrease in the number of primitive cells, there is a concomitant decrease in presence of bone morphogenetic protein expressing cells. As osteoblasts start to lay down woven bone on the chondroid matrix, these osteoblastic cells express bone morphogenetic proteins and their receptors. The presence of bone morphogenetic proteins decreases, however, as lamellar bone replaces the primitive woven bone. A similar observation is seen in the areas of the callus undergoing intramembranous ossification. Initially, within several days after the fracture, periosteal cells and osteoblasts show intense expression of bone morphogenetic proteins and their receptors. As the woven bone is replaced with mature lamellar bone, the expression of bone morphogenetic protein decreases. These data and the knowledge of bone morphogenetic proteins' strong osteoinductive capacities suggest that individual bone morphogenetic proteins play important yet different roles during fracture repair.

Cloning of a Novel cDNA Expressed during the Early Stages of Fracture Healing

Using differential mRNA display (DD-PCR), a novel cDNA, FxC1 (Fracture Callus 1) was isolated from the early stages of a healing fractured femur. Utilizing 5′ RACE PCR, a 598-bp full-length cDNA was obtained for FxC1 that contains an open reading frame (ORF) of 243 bp, encoding for an 80 amino acid protein. Within this ORF, a leucine zipper motif was present.In vitrotranscription/translation of the full-length cDNA generated the expected 9-kDa protein. Northern analysis reveals that this gene is expressed in calluses harvested from post-fracture day 5, 7 and 10, as well as in several other tissues and bone-derived cell lines. During the differentiation of MC3T3 cells along the osteoblast lineage, FxC1 expression increases 3- to 4-fold during the production and deposition of matrix proteins, suggesting a possible role for this protein in cell differentiation.

Osteoblasts express types I and II activin receptors during early intramembranous and endochondral bone formation.

Increasing evidence suggests a potential role for activin in bone formation. However, the cognate receptors through which activins function with respect to skeletal tissues have not yet been identified. Identification and regulation of expression of these receptors are necessary prerequisites to understanding the role of activins in bone metabolism. We detected mRNAs for three activin receptors, type I (ActRI), type II (ActRII), and type IIB (ActRIIB), in multiple skeletal tissues in rat, including tibia and costochondral growth plate, and also in cultured osteoblasts. To gain information about the relationship between receptor expression and different skeletal cell functions, we evaluated expression of the three receptors in a semiquantitative manner during the early stages of fracture healing, a model for rapid bone formation. Relatively high levels of ActRI and ActRII expression were detected in the callus at 7, 10, and 14 days after fracture, times that correlate with the interval of rapid intramembranous bone formation and the initiation of endochondral bone formation. Expression of the ActRIIB in the fracture callus was strikingly lower than either ActRI or ActRII. Immunostaining of the fracture callus and the newborn rat femur with an anti-ActRII antibody localized the receptor to osteoblasts at regions of membranous and endochondral bone formation. No staining of osteoblasts in fracture callus or bone was seen with an anti-ActRIIB antibody. These results provide strong evidence of the identification of the principal receptors through which activins could function in the skeletal system and further shed light on activin's mechanism of action in bone formation.

Immunolocalization and expression of bone morphogenetic proteins 2 and 4 in fracture healing

Recently, it has become increasingly evident that fracture healing involves a complex interaction of many local and systemic regulatory factors. The roles of some of these growth factors have been described; however, little is understood about the presence of the bone morphogenetic proteins in fracture repair, despite the fact that they are the most potent osteoinductive proteins known. This study defines and characterizes the physiologic presence, localization, and chronology of the bone morphogenetic proteins in fracture healing with an established rat fracture healing model. With use of a recently developed monoclonal antibody against bone morphogenetic proteins 2 and 4 developed with standard avidin-biotin complex/immunoperoxidase protocols, frozen undecalcified fracture calluses were analyzed semiquantitatively for the percentage of various types of fracture cells staining positively. During the early stages of fracture healing, only a minimum number of primitive cells stained positively in the fracture callus. As the process of endochondral ossification proceeded, the presence of bone morphogenetic proteins 2 and 4 increased dramatically, especially in the primitive mesenchymal and chondrocytic cells. While the cartilaginous component of the callus matured with a concomitant decrease in the number of primitive cells, there was a concomitant decrease in both the intensity and the number of positively staining cells. As osteoblasts started to lay down woven bone on the chondroid matrix, these osteoblastic cells exhibited strong positive staining. The intensity of this staining decreased, however, as lamellar bone replaced the primitive woven bone. A similar observation was noted for the areas of the callus undergoing intramembranous ossification. Initially, within several days after the fracture, periosteal cells and osteoblasts exhibited intense staining for bone morphogenetic proteins 2 and 4. As the woven bone was replaced with mature lamellar bone, this staining decreased. These data, and the awareness of the strong osteoinductive capacities of bone morphogenetic protein, suggest that bone morphogenetic proteins 2 and 4 are important regulators of cell differentiation during fracture repair.

Biomechanical consequences of callus development in Hoffmann, Wagner, Orthofix and Ilizarov external fixators

A theoretical analysis by a finite elements model (FEM) of some external fixators (Hoffmann, Wagner, Orthofix and Ilizarov) was carried out. This study considered a logarithmic progress of callus elastic characteristics. A standard configuration of each fixator was defined where design and application characteristics were modified. A comparison among standard configurations and influence of every variation was made with regard to displacement and load transmission at the fracture site. An experimental evaluation of standard configurations was performed with a testing machine. After experimental validation of the theoretical model was achieved, an application of physiological loads which act on a fractured limb during normal gait was analysed.A minimal contribution from an external fixator to the total rigidity of the bone-callus-fixator system was assessed when a callus showing minimum elastic characteristics had just been established. Insufficient rigidity from the fixation devices to assure an adequate immobilization during the early stages of fracture healing was verified. However, regardless of the external fixator, callus development was the overriding element for the rigidity of the fixator-bone system.

The design and analysis of a laminated partially degradable composite bone plate for fracture fixation

During the early stages of fracture healing, rigid internal fixation maintains alignment and promotes primary osseous union. Unfortunately, as healing progresses rigid fixation from bone plating can cause bone in the region of the plate to undergo stress protection atrophy. This can result in significant loss of bone mass and osteoporosis. Refracture of the bone upon device removal is a widely reported complication. In an effort to minimize or eliminate stress protection atrophy, we have designed a partially absorbable, fiber‐reinforced bone plate. Ideally, such a plate gradually loses rigidity as the fracture heals, increasingly transferring stress to the bone. Stress protection may be avoided and removal or the device after healing may be unnecessary. Composite theory was used to determine an optimum fiber layup for a composite bone plate. Composite analysis suggested the mechanical superiority of a 0°/ $pM45° laminae layup. Given this laminated design, a thermoplastic absorbable polymer (polylactic acid polymer) was reinforced with high‐modulus carbon fiber to produce a semiabsorbable composite. Implant evaluation included optimizing fabrication techniques, thorough mechanical device testing, and implantation on canine femurs to determine biocompatibility and efficacy. The composite design proved to have superior static and fatigue properties to laminated or random fiber designs used previously. Two techniques for hole fabrication were tested. The production of screw holes during the molding process rather than machining postmolding, improved the mechanical integrity of the finished plate. Although the 0°/±45° carbon/polylactic acid composite possessed superior mechanical properties, it was unsuccessful in the in vivo environment. Water absorption and subsequent delamination made the plate flexible. Hypertrophic nonunions developed. Further development to prevent water intrusion and premature loss of mechanical properties is necessary.

Biochemical characterization of fracture callus proteoglycans.

The changes in proteoglycan molecules during the initial stages of fracture healing in rats were characterized. Following extraction of callus proteoglycan components with dissociative solvents, the components were purified in a cesium chloride density gradient. The recovered proteoglycans were characterized with respect to their molecular size distribution using gel filtration chromatography and a centrifugal transport methodology. During this early healing period, a decrease was observed in the relative proportion of the aggregate and in the hydrodynamic size and sedimentation coefficients of these molecules. While some molecular degradation could have occurred during the early stages of fracture healing, the dominant change of the proteoglycan molecules seemed to be disaggregation. No significant difference was observed in the proportion of aggregates reformed when exogenous hyaluronate and link glycoproteins were allowed to interact with the two corresponding monomer preparations. The molecular changes of the proteoglycan molecules seem to parallel those occurring during endochondral calcification of rat epiphyseal cartilage.

Osteolytic Retardation of Early Stages of Fracture Healing Induced by Vitamin B6—Deficiency

Osteolytic Retardation of Early Stages of Fracture Healing Induced by Vitamin B6—Deficiency

An engineering evaluation of the Oxford External Fixator with sliding clamps: fixator stiffness and fracture healing assessment.

A theoretical and experimental evaluation of the Mark II Oxford External Fixator with sliding clamps has shown that: the effective axial stiffness may readily be varied over a wide range; significant load-bearing may be achieved on the fractured bone while maintaining adequate fracture alignment and stability; the axial sliding facility is likely to be of greatest benefit in the early stages of fracture healing. Sliding decreases rapidly as fracture stiffness increases and ceases altogether at a relatively early stage in the healing process; the effects of bone pin loosening are similar to those previously reported for the fixed-clamp Oxford External Fixator; bone healing assessment using a strain-gauge transducer clamped to the fixator column may become difficult and inaccurate when sliding of the clamps occurs. Temporary locking of the clamps is recommended during the assessment procedure to ensure that sequential tests are strictly comparable.

VASCULAR RESPONSE TO FRACTURE HEALING IN THE BOVINE

Angiography during metatarsal fracture healing following simple coaptation, stainless steel plating, and allogeneic onlay bone plating was performed in 24 calves. Angiograms obtained during the early stage of fracture healing demonstrated enhanced extraosseous vascularity at and around the fracture site regardless of the technique used for immobilization. However, the increased soft tissue vascularity was more intense in animals with simple coaptation than with metallic or allogeneic onlay bone plating. From four to six weeks the fracture site was vascularized, with visualization of crossover vascular contacts and ramification of vessels supplying the bridging callus. These changes were observed earlier and were more intense following plating. Enhanced soft tissue vascularity persisted longer in animals with delayed union and infection, whereas it regressed to nearly normal by the tenth week in normally healing fractures.