of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of... more of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of interfragmentary compression with the unreamed humeral nail. Unfallchirurg 2000; 103: 183-90. Dalton J E, Salkeld S L, Satterwhite Y E, Cook S D. A biomechanical comparison of intramedullary nailing systems
High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous sof... more High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep's femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed increasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.
Sildenafil, a cyclic guanosine monophosphate (cGMP)-dependent phospodiesterase-5 inhibitor, has b... more Sildenafil, a cyclic guanosine monophosphate (cGMP)-dependent phospodiesterase-5 inhibitor, has been shown to be a potent stimulator of angiogenesis through upregulation of pro-angiogenic factors and control of cGMP concentration. Herein, we determined whether sildenafil also influences angiogenic growth factor expression and bone formation during the process of fracture healing. Bone healing was studied in a murine closed femur fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analysis at 2 and 5 weeks after fracture. Thirty mice received 5 mg/kg body weight sildenafil p.o. daily. Controls (n = 30) received equivalent amounts of vehicle. After 2 weeks of fracture healing sildenafil significantly increased osseous fracture bridging, as determined radiologically and histologically. This resulted in an increased biomechanical stiffness compared to controls. A smaller callus area with a slightly reduced amount of cartilaginous tissue indicated an accelerated healing process. After 5 weeks the differences were found blunted, demonstrating successful healing in both groups. Western blot analysis showed a significantly higher expression of the pro-angiogenic and osteogenic cysteine-rich protein (CYR) 61, confirming the increase of bone formation. We show for the first time that sildenafil treatment accelerates fracture healing by enhancing bone formation, most probably by a CYR61-associated pathway.
Objective: Plunging when drilling can be a detrimental factor in patient care. There is, although... more Objective: Plunging when drilling can be a detrimental factor in patient care. There is, although, a general lack of information regarding the surgeon's performance in this skill. The aim of this study was to determine the effect that using sharp or blunt instruments had on the drill bit's soft tissue penetration, using a simulator.
In order to develop effective therapies for bone regeneration, site-specific bone defect small an... more In order to develop effective therapies for bone regeneration, site-specific bone defect small animal models are frequently needed. However, publications on murine bone fixation devices suitable for the generation of critical-size segmental bone defects are sparse. Therefore, the aim of this study was to establish a reliable, easy-to-handle, critical-size bone defect model using immunodeficient mice.
Although the mouse has become a preferred species for molecular studies on fracture healing, gait... more Although the mouse has become a preferred species for molecular studies on fracture healing, gait analysis after fracture fixation and during bone healing has not yet been performed in mice. Herein, we introduce a novel technique for gait analysis in mice and report the change of motion pattern after fracture and fixation. A standardized femur fracture was stabilized by a common pin. The non-fractured tibia was additionally marked with a pin, allowing continuous analysis of the tibio-femoral angle by digital video-radiography. Dynamic gait analysis was performed at day fourteen after surgery in a radio-opaque running wheel. Fracture fixation resulted in a significantly reduced range and maximum of the tibio-femoral angle compared to non-fractured controls. This was associated with a significantly reduced stride length. Because stride frequency was slightly increased and, thus, stride time diminished, stride velocity was not significantly reduced compared to controls. Thus, our study demonstrates distinct alterations of the gait of mice at 2 weeks after femur fracture and stabilization. Our results support the need of gait analysis in fracture healing studies to assess the animals' well-being.
Delayed unions are a problematic complication of fracture healing whose pathophysiology is not we... more Delayed unions are a problematic complication of fracture healing whose pathophysiology is not well understood. Advanced molecular biology methods available with mice would be advantageous for investigation. In humans, decreased fixation rigidity and poor reduction are generally associated with delayed unions. In this study, these two factors were combined to observe their effect on bone healing in mice. Two plates with locking screws, one with 1 4 the bending stiffness of the other, were used to stabilize a 0.45 mm gap osteotomy. mCT, radiographs, 4pt-bending tests and histological analysis demonstrated that the different plate types led to two different healing pathways. The less flexible bridging plate induced only intramembranous ossification whereas the more flexible bridging plate induced a mixture of endochondral and intramembranous ossification. However, the different plates led to a delay in healing of only 3-5 days in the period between 14 and 21 post-operative days. In mice, considerable fixation flexibility is necessary to induce secondary bone healing similar to that which occurs in humans, but this was not sufficient to induce a substantial delay in bone healing as would be expected in humans.
Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for... more Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for standardized models allowing for adjustment of the mechanical conditions in the fracture gap. We introduced such a model using rigid and flexible external fixators with considerably different stiffness (axial stiffnesses of 18.1 and 0.82 N/mm, respectively). Both fixators were used to stabilize a 0.5 mm osteotomy gap in the femur of C57BL/6 mice (each n = 8). Three-point bending tests, CT, and histomorphometry demonstrated a different healing pattern after 21 days. Both fixations induced callus formation with a mixture of intramembranous and enchondral ossification. Under flexible conditions, the bending stiffness of the callus was significantly reduced, and a larger but qualitatively inferior callus with a significantly lower fraction of bone but a higher fraction of cartilage and soft tissue was formed. Monitoring of the animal movement and the ground reaction forces demonstrated physiological loading with no significant differences between the groups, suggesting that the differences in healing were not based on a different loading behavior. In summary, flexible external fracture fixation of the mouse femur led to delayed fracture healing in comparison to a more rigid situation.
The various molecular mechanisms of cell regeneration and tissue healing can best be studied in m... more The various molecular mechanisms of cell regeneration and tissue healing can best be studied in mouse models with the availability of a wide range of monoclonal antibodies and gene-targeted animals. The influence of the mechanical stability of individual stabilization techniques on the molecular mechanisms of fracture healing has not been completely elucidated yet. Although during recent years several osteosynthesis techniques have been introduced in mouse fracture models, no comparative study on fracture stabilization is available yet. We therefore analyzed herein in a standardized ex vivo setup the rotational stiffness of seven different osteosynthesis techniques using osteotomized right cadaver femora of CD-1 mice. Uninjured femora without osteotomy served as controls. Femur stabilization with a locking plate or an external fixator resulted in a rotational stiffness almost similar to the intact femur. The use of a "pin-clip" device, a "locking nail," a "mouse nail," or an "intramedullary screw" produced a lower torsional stiffness, which, however, was still significantly higher than that achieved with the widely applied conventional pin. By the use of the presented data a more specific choice of stabilization technique will be possible according to the various questions concerning molecular aspects in fracture healing.
The mechanical environment around the healing of broken bone is very important as it determines t... more The mechanical environment around the healing of broken bone is very important as it determines the way the fracture will heal. Over the past decade there has been great clinical interest in improving bone healing by altering the mechanical environment through the fixation stability around the lesion. One constraint of preclinical animal research in this area is the lack of experimental control over the local mechanical environment within a large segmental defect as well as osteotomies as they heal. In this paper we report on the design and use of an external fixator to study the healing of large segmental bone defects or osteotomies. This device not only allows for controlled axial stiffness on the bone lesion as it heals, but it also enables the change of stiffness during the healing process in vivo. The conducted experiments have shown that the fixators were able to maintain a 5 mm femoral defect gap in rats in vivo during unrestricted cage activity for at least 8 weeks. Likewise, we observed no distortion or infections, including pin infections during the entire healing period. These results demonstrate that our newly developed external fixator was able to achieve reproducible and standardized stabilization, and the alteration of the mechanical environment of in vivo rat large bone defects and various size osteotomies. This confirms that the external fixation device is well suited for preclinical research investigations using a rat model in the field of bone regeneration and repair.
Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of ... more Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of large bone defects resulting in atrophic nonunions, a severe medical problem and a financial health-care-related burden. Models of atrophic nonunions are usually achieved by providing a highly stable biomechanical environment. For this purpose, external fixators have been investigated, but plate osteosynthesis, despite its high clinical relevance, has not yet been considered in mice. We hereby proposed and investigated the use of an internal osteosynthesis for stabilizing large bone defects. To this aim, a 3.5-mm-long segmental bone defect was induced in the mid-shaft of the femur using a Gigli saw and a jig. Bone fixation was performed using a titanium microlocking plate with four locking screws. The bone defect was either left empty or filled with a syngenic bone graft or filled with a coralline scaffold. Healing was monitored using radiographs. The healing process was further assessed using microcomputed tomography and histology 10 weeks after surgery. With the exception of one mouse that died during the surgical procedure, no complications were observed. A stable and reproducible bone fixation as well as a reproducible fixation of the implanted materials with full weight bearing was obtained in all animals tested. Nonunion was consistently observed in the group in which the defects were left empty. Bone union was obtained with the syngenic bone grafts, providing evidence that, although such defects were of critical size, bone healing was possible when the gold-standard material was used to fill the defect. Although new bone formation was greater in the coralline scaffold group than in the left-empty animal group, it remained limited and localized close to the bony edges, a consequence of the critical size of such bone defect. Our study established a reproducible, clinically relevant, femoral, atrophic nonunion, critical-sized defect, low morbidity mouse model. The present study was successful in designing and testing in a small animal model, a novel surgical method for the assessment of bone repair; this model has the potential to facilitate investigations of the molecular and cellular events involved in bone regeneration in load-bearing, segmental-bone defects.
of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of... more of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of interfragmentary compression with the unreamed humeral nail. Unfallchirurg 2000; 103: 183-90. Dalton J E, Salkeld S L, Satterwhite Y E, Cook S D. A biomechanical comparison of intramedullary nailing systems
Tissue engineered constructs should be tested for their efficacy not only in normal but also in o... more Tissue engineered constructs should be tested for their efficacy not only in normal but also in osteoporotic bone. The rat is an established animal model for osteoporosis and is used often for bone healing studies. In this study a defined and standardized critical size defect model in the rat suitable for screening new tissue engineered constructs in normal and osteoporotic bone is described and validated. Normal and ovariectomised Wistar rats received a unilateral middiaphyseal 5 mm defect in the femur, which was instrumented with a radiolucent PEEK plate fixed with angular stable titanium screws and left untreated. All animals were euthanized eight weeks after defect surgery and the bone healing was evaluated using radiographs, computed tomography measurements, and histology. The developed fixation system provided good stability, even in osteoporotic bone. The implants and ancillary instruments ensured consistent and facile placement of the PEEK plates. The untreated defects did not heal without intervention making the model a well-defined and standardized critical size defect model highly useful for evaluating tissue engineered solutions in normal and osteoporotic bone.
In most murine fracture models, the femur is stabilized by an intramedullary implant and heals pr... more In most murine fracture models, the femur is stabilized by an intramedullary implant and heals predominantly through endochondral ossification. The aim of the present study was to establish a mouse model in which fractures heal intramembranously. Femur fractures of 16 SKH-mice were stabilized by an internal locking plate. Femur fractures of another 16 animals were stabilized by an intramedullary screw. Bone repair was analyzed by radiographic, biomechanical, and histological methods. At 2 weeks, histological analysis showed a significantly smaller callus diameter and callus area after locking plate fixation. Cartilage formation within the callus could only be observed after screw fixation, but not after fracture stabilization with the locking plate. Radiological and biomechanical analysis after 2 and 5 weeks showed a significantly improved healing and a higher bending stiffness of fractures stabilized by the locking plate. Fractures stabilized by the locking plate healed exclusively by intramembranous ossification, which is most probably a result of the anatomical reduction and stable fixation. The fractures that healed by intramembranous ossification showed an increased stiffness compared to fractures that healed by endochondral ossification. This model may be used to study molecular mechanisms of intramembranous bone healing. ß
Knockout techniques enable us to expand our knowledge about bonerepair processes. Since they requ... more Knockout techniques enable us to expand our knowledge about bonerepair processes. Since they require the use of mice, such studies necessitate the development of special technologies. Mechano-biological reactions play a determining role in fracture healing, and therefore controlled conditions of stability are essential. Achieving fixation with a low-mass implant avoids uncontrolled inertial loading and enables free ambulation. A miniaturised version of conventional internal fixation as used in humans has been developed. The method consists of a plate-like internal fixator with locked screws. It permits compression fixation or splinting fixation at selectable levels of flexibility. A guide is used for standardised application of the fixator, the screws and the osteotomy. Locking the screws to the plate enables elevation of the fixator from the bone surface; therefore, minimal contact damage to the periosteal blood supply can be expected. The technology is now in use in several laboratories.
Metaphyseal osteotomy Mice Animal model Bone repair a b s t r a c t Background: Despite the incre... more Metaphyseal osteotomy Mice Animal model Bone repair a b s t r a c t Background: Despite the increasing clinical problems with metaphyseal fractures, most experimental studies investigate the healing of diaphyseal fractures. Although the mouse would be the preferable species to study the molecular and genetic aspects of metaphyseal fracture healing, a murine model does not exist yet. Using a special locking plate system, we herein introduce a new model, which allows the analysis of metaphyseal bone healing in mice.
of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of... more of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of interfragmentary compression with the unreamed humeral nail. Unfallchirurg 2000; 103: 183-90. Dalton J E, Salkeld S L, Satterwhite Y E, Cook S D. A biomechanical comparison of intramedullary nailing systems
High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous sof... more High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep's femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed increasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.
Sildenafil, a cyclic guanosine monophosphate (cGMP)-dependent phospodiesterase-5 inhibitor, has b... more Sildenafil, a cyclic guanosine monophosphate (cGMP)-dependent phospodiesterase-5 inhibitor, has been shown to be a potent stimulator of angiogenesis through upregulation of pro-angiogenic factors and control of cGMP concentration. Herein, we determined whether sildenafil also influences angiogenic growth factor expression and bone formation during the process of fracture healing. Bone healing was studied in a murine closed femur fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analysis at 2 and 5 weeks after fracture. Thirty mice received 5 mg/kg body weight sildenafil p.o. daily. Controls (n = 30) received equivalent amounts of vehicle. After 2 weeks of fracture healing sildenafil significantly increased osseous fracture bridging, as determined radiologically and histologically. This resulted in an increased biomechanical stiffness compared to controls. A smaller callus area with a slightly reduced amount of cartilaginous tissue indicated an accelerated healing process. After 5 weeks the differences were found blunted, demonstrating successful healing in both groups. Western blot analysis showed a significantly higher expression of the pro-angiogenic and osteogenic cysteine-rich protein (CYR) 61, confirming the increase of bone formation. We show for the first time that sildenafil treatment accelerates fracture healing by enhancing bone formation, most probably by a CYR61-associated pathway.
Objective: Plunging when drilling can be a detrimental factor in patient care. There is, although... more Objective: Plunging when drilling can be a detrimental factor in patient care. There is, although, a general lack of information regarding the surgeon's performance in this skill. The aim of this study was to determine the effect that using sharp or blunt instruments had on the drill bit's soft tissue penetration, using a simulator.
In order to develop effective therapies for bone regeneration, site-specific bone defect small an... more In order to develop effective therapies for bone regeneration, site-specific bone defect small animal models are frequently needed. However, publications on murine bone fixation devices suitable for the generation of critical-size segmental bone defects are sparse. Therefore, the aim of this study was to establish a reliable, easy-to-handle, critical-size bone defect model using immunodeficient mice.
Although the mouse has become a preferred species for molecular studies on fracture healing, gait... more Although the mouse has become a preferred species for molecular studies on fracture healing, gait analysis after fracture fixation and during bone healing has not yet been performed in mice. Herein, we introduce a novel technique for gait analysis in mice and report the change of motion pattern after fracture and fixation. A standardized femur fracture was stabilized by a common pin. The non-fractured tibia was additionally marked with a pin, allowing continuous analysis of the tibio-femoral angle by digital video-radiography. Dynamic gait analysis was performed at day fourteen after surgery in a radio-opaque running wheel. Fracture fixation resulted in a significantly reduced range and maximum of the tibio-femoral angle compared to non-fractured controls. This was associated with a significantly reduced stride length. Because stride frequency was slightly increased and, thus, stride time diminished, stride velocity was not significantly reduced compared to controls. Thus, our study demonstrates distinct alterations of the gait of mice at 2 weeks after femur fracture and stabilization. Our results support the need of gait analysis in fracture healing studies to assess the animals' well-being.
Delayed unions are a problematic complication of fracture healing whose pathophysiology is not we... more Delayed unions are a problematic complication of fracture healing whose pathophysiology is not well understood. Advanced molecular biology methods available with mice would be advantageous for investigation. In humans, decreased fixation rigidity and poor reduction are generally associated with delayed unions. In this study, these two factors were combined to observe their effect on bone healing in mice. Two plates with locking screws, one with 1 4 the bending stiffness of the other, were used to stabilize a 0.45 mm gap osteotomy. mCT, radiographs, 4pt-bending tests and histological analysis demonstrated that the different plate types led to two different healing pathways. The less flexible bridging plate induced only intramembranous ossification whereas the more flexible bridging plate induced a mixture of endochondral and intramembranous ossification. However, the different plates led to a delay in healing of only 3-5 days in the period between 14 and 21 post-operative days. In mice, considerable fixation flexibility is necessary to induce secondary bone healing similar to that which occurs in humans, but this was not sufficient to induce a substantial delay in bone healing as would be expected in humans.
Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for... more Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for standardized models allowing for adjustment of the mechanical conditions in the fracture gap. We introduced such a model using rigid and flexible external fixators with considerably different stiffness (axial stiffnesses of 18.1 and 0.82 N/mm, respectively). Both fixators were used to stabilize a 0.5 mm osteotomy gap in the femur of C57BL/6 mice (each n = 8). Three-point bending tests, CT, and histomorphometry demonstrated a different healing pattern after 21 days. Both fixations induced callus formation with a mixture of intramembranous and enchondral ossification. Under flexible conditions, the bending stiffness of the callus was significantly reduced, and a larger but qualitatively inferior callus with a significantly lower fraction of bone but a higher fraction of cartilage and soft tissue was formed. Monitoring of the animal movement and the ground reaction forces demonstrated physiological loading with no significant differences between the groups, suggesting that the differences in healing were not based on a different loading behavior. In summary, flexible external fracture fixation of the mouse femur led to delayed fracture healing in comparison to a more rigid situation.
The various molecular mechanisms of cell regeneration and tissue healing can best be studied in m... more The various molecular mechanisms of cell regeneration and tissue healing can best be studied in mouse models with the availability of a wide range of monoclonal antibodies and gene-targeted animals. The influence of the mechanical stability of individual stabilization techniques on the molecular mechanisms of fracture healing has not been completely elucidated yet. Although during recent years several osteosynthesis techniques have been introduced in mouse fracture models, no comparative study on fracture stabilization is available yet. We therefore analyzed herein in a standardized ex vivo setup the rotational stiffness of seven different osteosynthesis techniques using osteotomized right cadaver femora of CD-1 mice. Uninjured femora without osteotomy served as controls. Femur stabilization with a locking plate or an external fixator resulted in a rotational stiffness almost similar to the intact femur. The use of a "pin-clip" device, a "locking nail," a "mouse nail," or an "intramedullary screw" produced a lower torsional stiffness, which, however, was still significantly higher than that achieved with the widely applied conventional pin. By the use of the presented data a more specific choice of stabilization technique will be possible according to the various questions concerning molecular aspects in fracture healing.
The mechanical environment around the healing of broken bone is very important as it determines t... more The mechanical environment around the healing of broken bone is very important as it determines the way the fracture will heal. Over the past decade there has been great clinical interest in improving bone healing by altering the mechanical environment through the fixation stability around the lesion. One constraint of preclinical animal research in this area is the lack of experimental control over the local mechanical environment within a large segmental defect as well as osteotomies as they heal. In this paper we report on the design and use of an external fixator to study the healing of large segmental bone defects or osteotomies. This device not only allows for controlled axial stiffness on the bone lesion as it heals, but it also enables the change of stiffness during the healing process in vivo. The conducted experiments have shown that the fixators were able to maintain a 5 mm femoral defect gap in rats in vivo during unrestricted cage activity for at least 8 weeks. Likewise, we observed no distortion or infections, including pin infections during the entire healing period. These results demonstrate that our newly developed external fixator was able to achieve reproducible and standardized stabilization, and the alteration of the mechanical environment of in vivo rat large bone defects and various size osteotomies. This confirms that the external fixation device is well suited for preclinical research investigations using a rat model in the field of bone regeneration and repair.
Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of ... more Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of large bone defects resulting in atrophic nonunions, a severe medical problem and a financial health-care-related burden. Models of atrophic nonunions are usually achieved by providing a highly stable biomechanical environment. For this purpose, external fixators have been investigated, but plate osteosynthesis, despite its high clinical relevance, has not yet been considered in mice. We hereby proposed and investigated the use of an internal osteosynthesis for stabilizing large bone defects. To this aim, a 3.5-mm-long segmental bone defect was induced in the mid-shaft of the femur using a Gigli saw and a jig. Bone fixation was performed using a titanium microlocking plate with four locking screws. The bone defect was either left empty or filled with a syngenic bone graft or filled with a coralline scaffold. Healing was monitored using radiographs. The healing process was further assessed using microcomputed tomography and histology 10 weeks after surgery. With the exception of one mouse that died during the surgical procedure, no complications were observed. A stable and reproducible bone fixation as well as a reproducible fixation of the implanted materials with full weight bearing was obtained in all animals tested. Nonunion was consistently observed in the group in which the defects were left empty. Bone union was obtained with the syngenic bone grafts, providing evidence that, although such defects were of critical size, bone healing was possible when the gold-standard material was used to fill the defect. Although new bone formation was greater in the coralline scaffold group than in the left-empty animal group, it remained limited and localized close to the bony edges, a consequence of the critical size of such bone defect. Our study established a reproducible, clinically relevant, femoral, atrophic nonunion, critical-sized defect, low morbidity mouse model. The present study was successful in designing and testing in a small animal model, a novel surgical method for the assessment of bone repair; this model has the potential to facilitate investigations of the molecular and cellular events involved in bone regeneration in load-bearing, segmental-bone defects.
of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of... more of interlocked nailing in humeral shaft fractures. Comparison of 2 nail systems and the effect of interfragmentary compression with the unreamed humeral nail. Unfallchirurg 2000; 103: 183-90. Dalton J E, Salkeld S L, Satterwhite Y E, Cook S D. A biomechanical comparison of intramedullary nailing systems
Tissue engineered constructs should be tested for their efficacy not only in normal but also in o... more Tissue engineered constructs should be tested for their efficacy not only in normal but also in osteoporotic bone. The rat is an established animal model for osteoporosis and is used often for bone healing studies. In this study a defined and standardized critical size defect model in the rat suitable for screening new tissue engineered constructs in normal and osteoporotic bone is described and validated. Normal and ovariectomised Wistar rats received a unilateral middiaphyseal 5 mm defect in the femur, which was instrumented with a radiolucent PEEK plate fixed with angular stable titanium screws and left untreated. All animals were euthanized eight weeks after defect surgery and the bone healing was evaluated using radiographs, computed tomography measurements, and histology. The developed fixation system provided good stability, even in osteoporotic bone. The implants and ancillary instruments ensured consistent and facile placement of the PEEK plates. The untreated defects did not heal without intervention making the model a well-defined and standardized critical size defect model highly useful for evaluating tissue engineered solutions in normal and osteoporotic bone.
In most murine fracture models, the femur is stabilized by an intramedullary implant and heals pr... more In most murine fracture models, the femur is stabilized by an intramedullary implant and heals predominantly through endochondral ossification. The aim of the present study was to establish a mouse model in which fractures heal intramembranously. Femur fractures of 16 SKH-mice were stabilized by an internal locking plate. Femur fractures of another 16 animals were stabilized by an intramedullary screw. Bone repair was analyzed by radiographic, biomechanical, and histological methods. At 2 weeks, histological analysis showed a significantly smaller callus diameter and callus area after locking plate fixation. Cartilage formation within the callus could only be observed after screw fixation, but not after fracture stabilization with the locking plate. Radiological and biomechanical analysis after 2 and 5 weeks showed a significantly improved healing and a higher bending stiffness of fractures stabilized by the locking plate. Fractures stabilized by the locking plate healed exclusively by intramembranous ossification, which is most probably a result of the anatomical reduction and stable fixation. The fractures that healed by intramembranous ossification showed an increased stiffness compared to fractures that healed by endochondral ossification. This model may be used to study molecular mechanisms of intramembranous bone healing. ß
Knockout techniques enable us to expand our knowledge about bonerepair processes. Since they requ... more Knockout techniques enable us to expand our knowledge about bonerepair processes. Since they require the use of mice, such studies necessitate the development of special technologies. Mechano-biological reactions play a determining role in fracture healing, and therefore controlled conditions of stability are essential. Achieving fixation with a low-mass implant avoids uncontrolled inertial loading and enables free ambulation. A miniaturised version of conventional internal fixation as used in humans has been developed. The method consists of a plate-like internal fixator with locked screws. It permits compression fixation or splinting fixation at selectable levels of flexibility. A guide is used for standardised application of the fixator, the screws and the osteotomy. Locking the screws to the plate enables elevation of the fixator from the bone surface; therefore, minimal contact damage to the periosteal blood supply can be expected. The technology is now in use in several laboratories.
Metaphyseal osteotomy Mice Animal model Bone repair a b s t r a c t Background: Despite the incre... more Metaphyseal osteotomy Mice Animal model Bone repair a b s t r a c t Background: Despite the increasing clinical problems with metaphyseal fractures, most experimental studies investigate the healing of diaphyseal fractures. Although the mouse would be the preferable species to study the molecular and genetic aspects of metaphyseal fracture healing, a murine model does not exist yet. Using a special locking plate system, we herein introduce a new model, which allows the analysis of metaphyseal bone healing in mice.
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Papers by Romano Matthys