For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) pro... more For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) provides an ideal autologous bone graft. Combination of this with an intramedullary interlocking nail instead of an external fixator could improve patient comfort, because transport with a small external device takes only one-third of the total fixation period. Using 21 adult female sheep we created standardized tibia shaft defects 20 mm (medium size) and 45 mm (large size) in length. The tibiae were stabilized with non-reamed intramedullary interlocking nails. Following corticotomy by chisel, segments were transported using subcutaneous traction wires with a screw as a fulcrum to maintain stationary skin exit points without soft tissue problems. The external traction devices were removed after 12 or 16 weeks. Animals were sacrificed after 12 or 24 weeks with medium-size defects, and after 16 or 32 weeks with large defects. We evaluated the results clinically, by standardized weekly X-rays ...
Our continuously evolving understanding of bone biology has led to a new approach to plate fixati... more Our continuously evolving understanding of bone biology has led to a new approach to plate fixation. In comminuted fractures, anatomical reduction of all fragments is no longer a goal in itself. Preservation of the viability of the bone fragments seems to be the key to unimpaired fracture healing in internal fixation. The rapid integration of unreduced but vital fragments into the fracture callus functions as a bio-buttress system and prevents fatigue fracture of the implant. To realize the new concept of biological internal fixation, the limited contact dynamic compression plate, which minimizes vascular damage to the plated bone segment, has been developed.
Intramedullary nailing of shaft fractures of the femur and tibia is a recognized operative proced... more Intramedullary nailing of shaft fractures of the femur and tibia is a recognized operative procedure and its use has even been enlarged by the introduction of the so-called interlocking technique. In recent years case reports have been published describing peroperative pulmonary embolism during reamed femoral nailing, suggesting either an unfavorable effect of the reaming or the pressure increase in the medullary cavity while reaming and nailing. In an in vitro study on explanted human femora and tibiae we investigated the intramedullary pressure increase in reamed and unreamed nailing procedures of both bones. A lower pressure increase was noted in unreamed nailing compared to reamed nailing in the femur (289/496 mm Hg) and in the tibia (128/>833 mm Hg). The unreamed tibial nailing displayed significantly less pressure increase than the unreamed femoral nailing (p = 0.01). Opening of the medullary cavity with the so-called cheese cutter (cannulated cutter over a centering pin) s...
Resistance to infection may be influenced by foreign bodies such as devices for fracture fixation... more Resistance to infection may be influenced by foreign bodies such as devices for fracture fixation. It is known that stainless steel and commercially-pure titanium have different biocompatibilities. We have investigated susceptibility to infection after a local bacterial challenge using standard 2.0 dynamic compression plates of either stainless steel or titanium in rabbit tibiae. After the wounds had been closed, various concentrations of a strain of Staphylococcus aureus were inoculated percutaneously. Under otherwise identical experimental conditions the rate of infection for steel plates (75%) was significantly higher than that for titanium plates (35%) (p < 0.05).
The healing process of spiral fractures of the sheep tibia was investigated in an experiment with... more The healing process of spiral fractures of the sheep tibia was investigated in an experiment with simulated clinical conditions. The effects of conventional internal fixation techniques with the DCP and the intramedullary nail are compared with those of internal fixation with the spine fixator. The internal fixation techniques are described in terms of their bending stiffness when mounted on the fractured bone. The in vivo investigation was documented clinically and radiographically and the post mortem specimens were evaluated histologically. The bending stiffness of the healed bone was assessed in relation to the contralateral side. After application of the DCP, primary healing took place and extensive transcortical necrosis occurred in the implant bed. Intramedullary nailing led to secondary healing and to necrosis of the inner cortex close to the endosteum. After internal fixation with the spine fixator, gap healing took place and no cortical necrosis was observed. The clinical c...
Langenbecks Archiv für Chirurgie. Supplement. Kongressband. Deutsche Gesellschaft für Chirurgie. Kongress
With a standardised model we investigated the influence of two different surgical approaches to t... more With a standardised model we investigated the influence of two different surgical approaches to the rabbit tibia for plate osteosynthesis on resistance to local infection after postoperative inoculation of graduated concentrations of staphylococcus aureus at the implant. The infection rate for the minimally invasive plate osteosynthesis with insertion of the implant in closed, soft tissue tunneling technique was 25% (3/12 animals; ID50 = 6.2 x 10(6) CFU) and for the conventional open approach 38% (5/13 animals; ID50 = 2 x 10(6) CFU). This difference is statistically not significant (with P < 0.05).
Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of... more Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of the surgical procedure are offset by improved recovery of blood supply across a fracture zone and by stimulation of callus formation due to (controlled and slight) instability (elastically flexible fixation). Biological internal fixation is a principle in its own right; its technique is to some extent incompatible with conventional compression fixation. Locked screws provide better anchorage of the implant in both biological and compression internal fixation techniques. This generally offers improved potential in the treating fractures in osteoporotic bone. Because locked screws offer improved anchorage, the use of unicortical screws is made possible with the effect that the medullary circulation is damaged less. Locked unicortical screws, especially if they are self-drilling and self-cutting, offer important surgical advantages in minimally invasive percutaneous osteosynthesis (MIPO) w...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Fractures of the bones of elderly people occur more often and have a more important effect becaus... more Fractures of the bones of elderly people occur more often and have a more important effect because of a generally diminished ability to coordinate stance and walking. These fractures occur at a lower level of load because of lack of strength of the porotic bone. Prompt recovery of skeletal support function is essential to avoid respiratory and circulatory complications in the elderly. To prevent elderly people from the risks of being bedridden, demanding internal fixation of fractures is required. The weak porotic bone and the high level of uncontrolled loading after internal fixation pose complex problems. A combination of several technical elements of design, application and aftercare in internal fixation are proposed. Internal fixators with locked screws improve the biology and the mechanics of internal fixation. When such fixators are used as elevated splints they may stimulate early callus formation because of their flexibility, the limit of flexibility being set by the demands...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
PURPOSE OF THE STUDY Twisting is clinically the most frequently applied method for tightening and... more PURPOSE OF THE STUDY Twisting is clinically the most frequently applied method for tightening and maintaining cerclage fixation. The twisting procedure is controversially discussed. Several factors during twisting affect the mechanical behaviour of the cerclage. This in vitro study investigated the influence of different parameters of the twisting procedure on the fixation strength of the cerclage in an experimental setup with centripetal force application. MATERIAL AND METHODS Cortical half shells of the femoral shaft were mounted on a testing fixture. 1.0 mm, 1.25 mm and 1.5 mm stainless steel wire cerclages as well as a 1.0 mm cable cerclage were applied to the bone. Pretension of the cerclage during the installation was measured during the locking procedure. Subsequently, cyclic testing was performed up to failure. RESULTS Higher pretension could be achieved with increasing wire diameter. However, with larger wire diameter the drop of pretension due to the bending and cutting th...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Twisting is clinically the most frequently applied method for tightening and maintaining cerclage... more Twisting is clinically the most frequently applied method for tightening and maintaining cerclage fixation. The twisting procedure is controversially discussed. Several factors during twisting affect the mechanical behaviour of the cerclage. This in vitro study investigated the influence of different parameters of the twisting procedure on the fixation strength of the cerclage in an experimental setup with centripetal force application. Cortical half shells of the femoral shaft were mounted on a testing fixture. 1.0 mm, 1.25 mm and 1.5 mm stainless ste- el wire cerclages as well as a 1.0mm cable cerclage were applied to the bone. Pretension of the cerclage during the installation was measured during the locking procedure. Subsequently, cyclic testing was performed up to failure. Higher pretension could be achieved with increasing wire diameter. However, with larger wire diameter the drop of pre- tension due to the bending and cutting the twist also increased. The cable cerclage show...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
The clinical case of figure 1 through figure 11 shows a series of impressive failures of plate fi... more The clinical case of figure 1 through figure 11 shows a series of impressive failures of plate fixation. The plates were repeatedly applied bridging a comminuted bone segment in a heavy patient. The biomechanical analysis elaborates why this happened and proposes an unconventional procedure to prevent this failure with a minimally invasive procedure. A plate bridging an open gap or a defect in a long bone diaphysis is exposed to full functional load. According to clinical observations such plate application often fails even without external load such as weight bearing. The plate risks to break through fatigue when exposed during a long time to cyclic loading. This type of failure has been observed even with broad plates as well in femoral as in tibiae. The first option to avoid such failure consists in protecting the plate by installing load sharing between plate and either bone or an additional implant. This reduces the load carried by the plate to a safe level. Load sharing with bone may be installed at surgery by establishing solid mechanical bridge between the two main fragments of the fractured bone. The optimal load sharing relies on a solid compressed contact between the main fragments. It can be established because the bone is able to take a large load which results in optimal protection of the plate. In the case of an extended comminuted bone segment it may be very difficult, traumatizing and inefficient to reconstruct the bone. In the present case it was impossible to establish load sharing through the bone. The second option protecting the plate is provided by callus bridging of the gap or defect. The formation of a solid callus bridge takes time but the fatigue failure of the plate also takes time. Therefore, the callus bridge may prevent a late fatigue failure. The surgeon may select one of several options: - Replacing the lack of bone support using a second plate which immediately alleviates plate loading. The drawback of application of a second conventional plate is the extent of surgical trauma at the critical site of healing. - Shingling and/or applying an autologous cancellous bone graft: This procedure provides initially no relevant load sharing but will do so after a couple of weeks. The mechanical coupling of the comparably soft graft and the main fracture fragments presents little problems. Applying a cortical bone graft: Such a graft does provide initial only small load sharing and does a less good job inducing callus than a cancellous graft. Furthermore, the coupling by callus between a somewhat rigid bone graft and the mobile main fracture fragments requires a solid maintained contact. If the cortical graft is fixed using implants with small contact area to the graft such as screws or cerclage loops, the local stress may be critical and the graft may break. When the cortical graft is fixed with cerclage wires the procedure must take into account the limited strength of the individual cerclage. Therefore multiple and well-spaced cerclages are required and may lead to success especially if an intramedullary component of the implant contributes to protection (6). The degree of unloading depends apparently on the stiffness of the material of the protecting splint. Though, more important is the effect of the dimensions of the splint. While titanium as a material is about 50% less stiff than steel, the thickness of the implant changes the stiffness with the third power. That is doubling the thickness results in eightfold increased stiffness. When considering the unloading by application of a second plate the leverage of the second plate plays an important role. The larger the distance between the axis of bending and the second implant the larger the protecting effect. The helical plate (2, 3, 7) as introduced by A.A.D. Fernandez offers biological and mechanical advantages. It can be applied without touching the fracture site maintaining the critical biology intact and provides mechanically efficient unloading. Its application is fairly simple: The helical plate is modified conventional long and small plate that is twisted between its ends about 90 degrees. The twist is applied using &amp;amp;quot;bending irons&amp;amp;quot; (4, 5, 8) whereby the force required is small and the exact degree of twist is not critical. Therefore the twist is applicable operating bending irons by hand. Assuming a situation where a plate bridging a defect or non-union has failed the broken plate is replaced by a similar implant: At the distal end of the bone fracture and opposite to the surgical approach a small incision allows to slide in the helical plate in such a way that proximally the plate ends on the same side of the limb as the replaced plate. Ideally the two plate ends meet and the application of the helical plate does not ask for an additional surgical exposure at this location. Otherwise a small minimally invasive exposure is required. The helical plate is then fixed to the main bone fragments…
Cannulated screws, along with guide wires, are typically used for surgical fracture treatment in ... more Cannulated screws, along with guide wires, are typically used for surgical fracture treatment in cancellous bone. Breakage or bending deformation of the guide wire is a clinical concern. Mechanically superior guide wires made of Co-Cr alloys such as MP35N and L605 may reduce the occurrence of mechanical failures when used in combination with conventional (316L stainless steel) cannulated screws. However the possibility of galvanic or crevice corrosion and adverse tissue reaction, exists when using dissimilar materials, particularly in the event that a guide wire breaks, and remains in situ. Therefore, we designed an experiment to determine the tissue reaction to such an in vivo environment. Implant devices were designed to replicate a clinical situation where dissimilar metals can form a galvanic couple. Histological and SEM analyses were used to evaluate tissue response and corrosion of the implants. In this experiment, no adverse in vivo effects were detected from the use of dissi...
Journal of materials science. Materials in medicine, 2000
Adhesion of tissues to biomaterials is desirable to prevent bacterial proliferation and for epith... more Adhesion of tissues to biomaterials is desirable to prevent bacterial proliferation and for epithelial/transmucosal sealing of transcutaneous appliances, but can be counter-productive elsewhere, e.g. implants contacting tendons or maxillofacial subcutaneous tissue. It is therefore important to gauge adhesion strength of tissues to biomaterials before clinical use. Peel-testing is widely used for industrial product adhesion monitoring, but has rarely been applied biomedically. Here we describe peel-testing instrumentation designed for testing adherence of soft tissues to biomaterials. It offers the advantage that a 90 degrees angle between peel and substrate is maintained, simplifying determination of applied normal forces separating tissue layers from material surfaces. The device is portable and can be brought directly to the specimen removal site. This minimizes time delays between explantation and testing, maintaining the tissue/biomaterial interface in the freshest possible stat...
Measurement of the bending stiffness a healing fracture represents a valid variable in the assess... more Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing. A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-p...
The Journal of bone and joint surgery. American volume, 1999
The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Pros... more The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Prospective studies comparing different repair techniques are difficult to design and carry out because of the many factors that influence structural and clinical outcomes. The objective of this study was to develop a suitable animal model for evaluation of the efficacy of different repair techniques for massive rotator cuff tears and to use this model to compare a new repair technique, tested in vitro, with the conventional technique. We compared two techniques of rotator cuff repair in vivo using the left shoulders of forty-seven sheep. With the conventional technique, simple stitches were used and both suture ends were passed transosseously and tied over the greater tuberosity of the humerus. With the other technique, the modified Mason-Allen stitch was used and both suture ends were passed transosseously and tied over a cortical-bone-augmentation device. This device consisted of a poly(L...
For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) pro... more For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) provides an ideal autologous bone graft. Combination of this with an intramedullary interlocking nail instead of an external fixator could improve patient comfort, because transport with a small external device takes only one-third of the total fixation period. Using 21 adult female sheep we created standardized tibia shaft defects 20 mm (medium size) and 45 mm (large size) in length. The tibiae were stabilized with non-reamed intramedullary interlocking nails. Following corticotomy by chisel, segments were transported using subcutaneous traction wires with a screw as a fulcrum to maintain stationary skin exit points without soft tissue problems. The external traction devices were removed after 12 or 16 weeks. Animals were sacrificed after 12 or 24 weeks with medium-size defects, and after 16 or 32 weeks with large defects. We evaluated the results clinically, by standardized weekly X-rays ...
Our continuously evolving understanding of bone biology has led to a new approach to plate fixati... more Our continuously evolving understanding of bone biology has led to a new approach to plate fixation. In comminuted fractures, anatomical reduction of all fragments is no longer a goal in itself. Preservation of the viability of the bone fragments seems to be the key to unimpaired fracture healing in internal fixation. The rapid integration of unreduced but vital fragments into the fracture callus functions as a bio-buttress system and prevents fatigue fracture of the implant. To realize the new concept of biological internal fixation, the limited contact dynamic compression plate, which minimizes vascular damage to the plated bone segment, has been developed.
Intramedullary nailing of shaft fractures of the femur and tibia is a recognized operative proced... more Intramedullary nailing of shaft fractures of the femur and tibia is a recognized operative procedure and its use has even been enlarged by the introduction of the so-called interlocking technique. In recent years case reports have been published describing peroperative pulmonary embolism during reamed femoral nailing, suggesting either an unfavorable effect of the reaming or the pressure increase in the medullary cavity while reaming and nailing. In an in vitro study on explanted human femora and tibiae we investigated the intramedullary pressure increase in reamed and unreamed nailing procedures of both bones. A lower pressure increase was noted in unreamed nailing compared to reamed nailing in the femur (289/496 mm Hg) and in the tibia (128/>833 mm Hg). The unreamed tibial nailing displayed significantly less pressure increase than the unreamed femoral nailing (p = 0.01). Opening of the medullary cavity with the so-called cheese cutter (cannulated cutter over a centering pin) s...
Resistance to infection may be influenced by foreign bodies such as devices for fracture fixation... more Resistance to infection may be influenced by foreign bodies such as devices for fracture fixation. It is known that stainless steel and commercially-pure titanium have different biocompatibilities. We have investigated susceptibility to infection after a local bacterial challenge using standard 2.0 dynamic compression plates of either stainless steel or titanium in rabbit tibiae. After the wounds had been closed, various concentrations of a strain of Staphylococcus aureus were inoculated percutaneously. Under otherwise identical experimental conditions the rate of infection for steel plates (75%) was significantly higher than that for titanium plates (35%) (p < 0.05).
The healing process of spiral fractures of the sheep tibia was investigated in an experiment with... more The healing process of spiral fractures of the sheep tibia was investigated in an experiment with simulated clinical conditions. The effects of conventional internal fixation techniques with the DCP and the intramedullary nail are compared with those of internal fixation with the spine fixator. The internal fixation techniques are described in terms of their bending stiffness when mounted on the fractured bone. The in vivo investigation was documented clinically and radiographically and the post mortem specimens were evaluated histologically. The bending stiffness of the healed bone was assessed in relation to the contralateral side. After application of the DCP, primary healing took place and extensive transcortical necrosis occurred in the implant bed. Intramedullary nailing led to secondary healing and to necrosis of the inner cortex close to the endosteum. After internal fixation with the spine fixator, gap healing took place and no cortical necrosis was observed. The clinical c...
Langenbecks Archiv für Chirurgie. Supplement. Kongressband. Deutsche Gesellschaft für Chirurgie. Kongress
With a standardised model we investigated the influence of two different surgical approaches to t... more With a standardised model we investigated the influence of two different surgical approaches to the rabbit tibia for plate osteosynthesis on resistance to local infection after postoperative inoculation of graduated concentrations of staphylococcus aureus at the implant. The infection rate for the minimally invasive plate osteosynthesis with insertion of the implant in closed, soft tissue tunneling technique was 25% (3/12 animals; ID50 = 6.2 x 10(6) CFU) and for the conventional open approach 38% (5/13 animals; ID50 = 2 x 10(6) CFU). This difference is statistically not significant (with P < 0.05).
Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of... more Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of the surgical procedure are offset by improved recovery of blood supply across a fracture zone and by stimulation of callus formation due to (controlled and slight) instability (elastically flexible fixation). Biological internal fixation is a principle in its own right; its technique is to some extent incompatible with conventional compression fixation. Locked screws provide better anchorage of the implant in both biological and compression internal fixation techniques. This generally offers improved potential in the treating fractures in osteoporotic bone. Because locked screws offer improved anchorage, the use of unicortical screws is made possible with the effect that the medullary circulation is damaged less. Locked unicortical screws, especially if they are self-drilling and self-cutting, offer important surgical advantages in minimally invasive percutaneous osteosynthesis (MIPO) w...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Fractures of the bones of elderly people occur more often and have a more important effect becaus... more Fractures of the bones of elderly people occur more often and have a more important effect because of a generally diminished ability to coordinate stance and walking. These fractures occur at a lower level of load because of lack of strength of the porotic bone. Prompt recovery of skeletal support function is essential to avoid respiratory and circulatory complications in the elderly. To prevent elderly people from the risks of being bedridden, demanding internal fixation of fractures is required. The weak porotic bone and the high level of uncontrolled loading after internal fixation pose complex problems. A combination of several technical elements of design, application and aftercare in internal fixation are proposed. Internal fixators with locked screws improve the biology and the mechanics of internal fixation. When such fixators are used as elevated splints they may stimulate early callus formation because of their flexibility, the limit of flexibility being set by the demands...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
PURPOSE OF THE STUDY Twisting is clinically the most frequently applied method for tightening and... more PURPOSE OF THE STUDY Twisting is clinically the most frequently applied method for tightening and maintaining cerclage fixation. The twisting procedure is controversially discussed. Several factors during twisting affect the mechanical behaviour of the cerclage. This in vitro study investigated the influence of different parameters of the twisting procedure on the fixation strength of the cerclage in an experimental setup with centripetal force application. MATERIAL AND METHODS Cortical half shells of the femoral shaft were mounted on a testing fixture. 1.0 mm, 1.25 mm and 1.5 mm stainless steel wire cerclages as well as a 1.0 mm cable cerclage were applied to the bone. Pretension of the cerclage during the installation was measured during the locking procedure. Subsequently, cyclic testing was performed up to failure. RESULTS Higher pretension could be achieved with increasing wire diameter. However, with larger wire diameter the drop of pretension due to the bending and cutting th...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Twisting is clinically the most frequently applied method for tightening and maintaining cerclage... more Twisting is clinically the most frequently applied method for tightening and maintaining cerclage fixation. The twisting procedure is controversially discussed. Several factors during twisting affect the mechanical behaviour of the cerclage. This in vitro study investigated the influence of different parameters of the twisting procedure on the fixation strength of the cerclage in an experimental setup with centripetal force application. Cortical half shells of the femoral shaft were mounted on a testing fixture. 1.0 mm, 1.25 mm and 1.5 mm stainless ste- el wire cerclages as well as a 1.0mm cable cerclage were applied to the bone. Pretension of the cerclage during the installation was measured during the locking procedure. Subsequently, cyclic testing was performed up to failure. Higher pretension could be achieved with increasing wire diameter. However, with larger wire diameter the drop of pre- tension due to the bending and cutting the twist also increased. The cable cerclage show...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
The clinical case of figure 1 through figure 11 shows a series of impressive failures of plate fi... more The clinical case of figure 1 through figure 11 shows a series of impressive failures of plate fixation. The plates were repeatedly applied bridging a comminuted bone segment in a heavy patient. The biomechanical analysis elaborates why this happened and proposes an unconventional procedure to prevent this failure with a minimally invasive procedure. A plate bridging an open gap or a defect in a long bone diaphysis is exposed to full functional load. According to clinical observations such plate application often fails even without external load such as weight bearing. The plate risks to break through fatigue when exposed during a long time to cyclic loading. This type of failure has been observed even with broad plates as well in femoral as in tibiae. The first option to avoid such failure consists in protecting the plate by installing load sharing between plate and either bone or an additional implant. This reduces the load carried by the plate to a safe level. Load sharing with bone may be installed at surgery by establishing solid mechanical bridge between the two main fragments of the fractured bone. The optimal load sharing relies on a solid compressed contact between the main fragments. It can be established because the bone is able to take a large load which results in optimal protection of the plate. In the case of an extended comminuted bone segment it may be very difficult, traumatizing and inefficient to reconstruct the bone. In the present case it was impossible to establish load sharing through the bone. The second option protecting the plate is provided by callus bridging of the gap or defect. The formation of a solid callus bridge takes time but the fatigue failure of the plate also takes time. Therefore, the callus bridge may prevent a late fatigue failure. The surgeon may select one of several options: - Replacing the lack of bone support using a second plate which immediately alleviates plate loading. The drawback of application of a second conventional plate is the extent of surgical trauma at the critical site of healing. - Shingling and/or applying an autologous cancellous bone graft: This procedure provides initially no relevant load sharing but will do so after a couple of weeks. The mechanical coupling of the comparably soft graft and the main fracture fragments presents little problems. Applying a cortical bone graft: Such a graft does provide initial only small load sharing and does a less good job inducing callus than a cancellous graft. Furthermore, the coupling by callus between a somewhat rigid bone graft and the mobile main fracture fragments requires a solid maintained contact. If the cortical graft is fixed using implants with small contact area to the graft such as screws or cerclage loops, the local stress may be critical and the graft may break. When the cortical graft is fixed with cerclage wires the procedure must take into account the limited strength of the individual cerclage. Therefore multiple and well-spaced cerclages are required and may lead to success especially if an intramedullary component of the implant contributes to protection (6). The degree of unloading depends apparently on the stiffness of the material of the protecting splint. Though, more important is the effect of the dimensions of the splint. While titanium as a material is about 50% less stiff than steel, the thickness of the implant changes the stiffness with the third power. That is doubling the thickness results in eightfold increased stiffness. When considering the unloading by application of a second plate the leverage of the second plate plays an important role. The larger the distance between the axis of bending and the second implant the larger the protecting effect. The helical plate (2, 3, 7) as introduced by A.A.D. Fernandez offers biological and mechanical advantages. It can be applied without touching the fracture site maintaining the critical biology intact and provides mechanically efficient unloading. Its application is fairly simple: The helical plate is modified conventional long and small plate that is twisted between its ends about 90 degrees. The twist is applied using &amp;amp;quot;bending irons&amp;amp;quot; (4, 5, 8) whereby the force required is small and the exact degree of twist is not critical. Therefore the twist is applicable operating bending irons by hand. Assuming a situation where a plate bridging a defect or non-union has failed the broken plate is replaced by a similar implant: At the distal end of the bone fracture and opposite to the surgical approach a small incision allows to slide in the helical plate in such a way that proximally the plate ends on the same side of the limb as the replaced plate. Ideally the two plate ends meet and the application of the helical plate does not ask for an additional surgical exposure at this location. Otherwise a small minimally invasive exposure is required. The helical plate is then fixed to the main bone fragments…
Cannulated screws, along with guide wires, are typically used for surgical fracture treatment in ... more Cannulated screws, along with guide wires, are typically used for surgical fracture treatment in cancellous bone. Breakage or bending deformation of the guide wire is a clinical concern. Mechanically superior guide wires made of Co-Cr alloys such as MP35N and L605 may reduce the occurrence of mechanical failures when used in combination with conventional (316L stainless steel) cannulated screws. However the possibility of galvanic or crevice corrosion and adverse tissue reaction, exists when using dissimilar materials, particularly in the event that a guide wire breaks, and remains in situ. Therefore, we designed an experiment to determine the tissue reaction to such an in vivo environment. Implant devices were designed to replicate a clinical situation where dissimilar metals can form a galvanic couple. Histological and SEM analyses were used to evaluate tissue response and corrosion of the implants. In this experiment, no adverse in vivo effects were detected from the use of dissi...
Journal of materials science. Materials in medicine, 2000
Adhesion of tissues to biomaterials is desirable to prevent bacterial proliferation and for epith... more Adhesion of tissues to biomaterials is desirable to prevent bacterial proliferation and for epithelial/transmucosal sealing of transcutaneous appliances, but can be counter-productive elsewhere, e.g. implants contacting tendons or maxillofacial subcutaneous tissue. It is therefore important to gauge adhesion strength of tissues to biomaterials before clinical use. Peel-testing is widely used for industrial product adhesion monitoring, but has rarely been applied biomedically. Here we describe peel-testing instrumentation designed for testing adherence of soft tissues to biomaterials. It offers the advantage that a 90 degrees angle between peel and substrate is maintained, simplifying determination of applied normal forces separating tissue layers from material surfaces. The device is portable and can be brought directly to the specimen removal site. This minimizes time delays between explantation and testing, maintaining the tissue/biomaterial interface in the freshest possible stat...
Measurement of the bending stiffness a healing fracture represents a valid variable in the assess... more Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing. A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-p...
The Journal of bone and joint surgery. American volume, 1999
The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Pros... more The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Prospective studies comparing different repair techniques are difficult to design and carry out because of the many factors that influence structural and clinical outcomes. The objective of this study was to develop a suitable animal model for evaluation of the efficacy of different repair techniques for massive rotator cuff tears and to use this model to compare a new repair technique, tested in vitro, with the conventional technique. We compared two techniques of rotator cuff repair in vivo using the left shoulders of forty-seven sheep. With the conventional technique, simple stitches were used and both suture ends were passed transosseously and tied over the greater tuberosity of the humerus. With the other technique, the modified Mason-Allen stitch was used and both suture ends were passed transosseously and tied over a cortical-bone-augmentation device. This device consisted of a poly(L...
Uploads
Papers by Stephan Perren