Treatment of posterior pelvic ring injuries is frequently associated with pain or/and high mortal... more Treatment of posterior pelvic ring injuries is frequently associated with pain or/and high mortality rates. Percutaneous sacro-iliac (SI) screw fixation has proved to be one of the methods of choice, providing minimal operative time, blood loss and wound-related morbidity. However, fixation failures due to secondary fracture dislocation or screw backing out have been reported. There is a little knowledge regarding the impact of varying screw orientation and quality of reduction on the fixation strength. The purpose of the present study was biomechanical investigation of joint stability after SI screw fixation and its dependence on quality of reduction and screw orientation. Thirty-two artificial hemi-pelvices were assigned to four study groups and simulated SI dislocations were fixed with two SI screws in oblique or transverse screw orientation and anatomical or non-anatomical reduction in group A (oblique/anatomical), B (transverse/anatomical), C (oblique/non-anatomical) and D (tra...
Journal of orthopaedic research : official publication of the Orthopaedic Research Society, Jan 16, 2015
Femoral neck fractures in the elderly are a common problem in orthopedics. Augmentation of screw ... more Femoral neck fractures in the elderly are a common problem in orthopedics. Augmentation of screw fixation with bone cement can provide better stability of implants and lower the risk of secondary displacement. This study aimed to investigate whether cement augmentation of three cannulated screws in non-displaced femoral neck fractures could increase implant fixation. A femoral neck fracture was simulated in six paired human cadaveric femora and stabilized with three 7.3 mm cannulated screws. Pairs were divided into two groups: conventional instrumentation versus additional cement augmentation of screw tips with 2 ml TraumacemV+ each. Biomechanical testing was performed by applying cyclic axial load until failure. Failure cycles, axial head displacement, screw angle changes, telescoping and screw cut-out were evaluated. Failure (15 mm actuator displacement) occurred in the augmented group at 12,500 cycles (± 2,480) compared to 15,625 cycles (± 4,215) in the non-augmented group (p = 0...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Periprosthetic fractures are increasingly frequent. The fracture may be located over the shaft of... more Periprosthetic fractures are increasingly frequent. The fracture may be located over the shaft of the prosthesis, at its tip or below. The treatment of explosion fractures is difficult because the shaft blocks the application of implants, like screws, which need to penetrate the medullary cavity. The cerclage, as a simple periosteal loop, made of wire or more recently cable, does not only avoid the medullary cavity. Its centripetal mode of action is well suited for reducing and maintaining radially displaced fractures. Furthermore, the cerclage lends itself well for minimally invasive internal fixation. New insight challenges the disrepute of which the cerclage technology suffered for decades. The outcome of cerclage fixation benefits from an improved understanding of its technology, mechano-biology and periosteal blood supply. Preconceived and generally accepted opinions like "strangulation of blood supply" need to be re-examined. Recent mechanical evaluations demonstrate...
Bone cement augmentation of modified cannulated locking screws shows biomechanically and clinical... more Bone cement augmentation of modified cannulated locking screws shows biomechanically and clinically good results for osteoporotic fracture management. Nevertheless, complications need to be considered. Therefore implant removal should be tested for feasibility. Implant removal was simulated in 7 pairs of osteoporotic cadaveric humeri: During screw removal from an angular stable proximal humerus plate, we measured the maximum torque of 14 augmented screws and the corresponding 14 non-augmented screws on the contralateral humeri. After screw removal, specimens were cut along the screw axes to macroscopically investigate the impact of screw removal on the surrounding bone. In addition, we established a technique for cement removal in cases in which the screw head is obstructed with cement and therefore disables the insertion of the screwdriver. The screw extraction torque measurements showed no significant differences between the two groups regarding one screw (screw 4 augmented: 1.52N...
End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary naili... more End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary nailing. The aim of this study was to investigate the force at failure with and without end caps, and whether different insertion angles of nails and end caps would alter that force at failure. Simulated oblique fractures of the diaphysis were created in 15 artificial paediatric femurs. Titanium Elastic Nails with end caps were inserted at angles of 45°, 55° and 65° in five specimens for each angle to create three study groups. Biomechanical testing was performed with axial compression until failure. An identical fracture was created in four small adult cadaveric femurs harvested from two donors (both female, aged 81 and 85 years, height 149 cm and 156 cm, respectively). All femurs were tested without and subsequently with end caps inserted at 45°. In the artificial femurs, maximum force was not significantly different between the three groups (p = 0.613). Push-out force was significantly hig...
Rotator cuff tears are of increasing clinical impact in the physically active elderly patients. R... more Rotator cuff tears are of increasing clinical impact in the physically active elderly patients. Recent research revealed, that a high percentage of these patients present with significant loss of bone mineral density at the insertion site of the rotator cuff, thereby compromising suture anchorage for operative repair. We therefore hypothesized that augmentation of suture anchors improves biomechanical properties in low bone quality. 28 osteoporotic humeral heads were included in this biomechanical study. Bone quality at the anchor insertion sites (group 1: posterior-medial; group 2: anterior-lateral) within the greater tuberosity was analyzed using HR-pQCT (voxel size: 82μm). Anchor positions of identical quality were then randomized to either conventional screw anchorage or polymethylmethacrylat augmented screw anchorage. All anchors were cyclically ramp-loaded until pullout. Pullout strength accounted for 226N in group I for conventional anchorage and for 332N in augmented techniq...
International journal for numerical methods in biomedical engineering, 2015
Percutaneous vertebroplasty represents a current procedure to effectively reinforce osteoporotic ... more Percutaneous vertebroplasty represents a current procedure to effectively reinforce osteoporotic bone via the injection of bone cement. This contribution considers a continuum-mechanically based modelling approach and simulation techniques to predict the cement distributions within a vertebra during injection. To do so, experimental investigations, imaging data and image processing techniques are combined and exploited to extract necessary data from high-resolution μCT image data. The multiphasic model is based on the Theory of Porous Media, providing the theoretical basis to describe within one set of coupled equations the interaction of an elastically deformable solid skeleton, of liquid bone cement and the displacement of liquid bone marrow. The simulation results are validated against an experiment, in which bone cement was injected into a human vertebra under realistic conditions. The major advantage of this comprehensive modelling approach is the fact that one can not only pre...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca, 2011
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...
The increasing problems in the field of osteoporotic fracture fixation results in specialized imp... more The increasing problems in the field of osteoporotic fracture fixation results in specialized implants as well as new operation methods, for example, implant augmentation with bone cement. The aim of this study was to determine the biomechanical impact of augmentation in the treatment of osteoporotic distal femur fractures.Seven pairs of osteoporotic fresh frozen distal femora were randomly assigned to either an augmented or nonaugmented group. In both groups, an Orthopaedic Trauma Association 33 A3 fractures was fixed using the locking compression plate distal femur and cannulated and perforated screws. In the augmented group, additionally, 1 mL of polymethylmethacrylate cement was injected through the screw. Prior to mechanical testing, bone mineral density (BMD) and local bone strength were determined. Mechanical testing was performed by cyclic axial loading (100 N to 750 N + 0.05N/cycle) using a servo-hydraulic testing machine.As a result, the BMD as well as the axial stiffness did not significantly differ between the groups. The number of cycles to failure was significantly higher in the augmented group with the BMD as a significant covariate.In conclusion, cement augmentation can significantly improve implant anchorage in plating of osteoporotic distal femur fractures.
Previous studies have clearly demonstrated superior biomechanical behavior of augmented proximal ... more Previous studies have clearly demonstrated superior biomechanical behavior of augmented proximal femoral nail antirotation (PFNA) blades compared with nonaugmented ones with respect to implant cutout. Nevertheless, there is concern about thermal bone necrosis due to exothermic curing of polymethylmethacrylate (PMMA)-based bone cements. The objective of this study was to quantify the temperatures arising around perforated titanium PFNA blades when augmenting with PMMA. Cylindrical samples from six pairs of fresh frozen human cadaveric femoral heads implanted with a PFNA blade were placed in a 37°C water bath and augmented with 3 mL and 6 mL PMMA. During augmentation, temperatures were measured using six K-type thermocouples that were placed at controlled distances around the implant. With the help of high-resolution quantitative computed tomography images, the locations of all thermocouples with respect to the cement-bone interface were reconstructed. No temperatures higher than 45°C were measured in the interface region and the surrounding cement-free cancellous bone. In the same regions, the longest exposure time above 41°C was 8.5 minutes and was measured in a 6-mL sample. Average maximum temperature was significantly lower for the 3-mL group compared with the 6-mL group (p = 0.017). The results of this study suggest that augmentation of titanium PFNA blades is not associated with a risk of thermal bone necrosis when using up to 6 mL of PMMA. However, larger amounts of cement lead to higher temperatures. PMMA application should therefore be kept low to minimally alter the biological system.
Implant loosening is frequently detected after fixation of open book injuries. Though many author... more Implant loosening is frequently detected after fixation of open book injuries. Though many authors do not see this as a complication, it is often the reason for hardware removal or reinstrumentation in the case of remaining instability. We hypothesized that the flexibility of the implant has an influence on loosening and thus on failure of the construct. We used 6 fresh-frozen pelvic specimens and tested them with our recently introduced test setup for two-leg alternate loading. We subjected them to a non-destructive quasi-static test in the intact condition followed by a non-destructive cyclic test under axial sinusoidal loading with progressive amplitude. Afterwards we simulated an open book injury and performed fixation with three different configurations of a modular fixation system (1-, 2- or 4-rod configuration) in randomized order. Subsequently, the specimens were subjected to 3 cyclic tests with the same loading protocol as previously defined. Finally, each construct was cyclically tested to failure keeping the final rod configuration. We detected significantly greater mobility after 1-rod-fixation and no significant differences after 2-rod or 4-rod-fixation compared to the intact symphysis condition. In the destructive test series the 4-rod-fixation failed first followed by the 1-rod-fixation. The 2-rod-fixation sustained almost 3 times as many load cycles prior to failure as the 4-rod-fixation, whereas the 1-rod-fixation sustained twice as many cycles as the 4-rod-fixation. In conclusion, flexible fixation of the ruptured pubic symphysis in human specimens shows superior behavior with respect to load bearing capacity and ability to withstand cyclic loading compared to stiff constructs.
To compare locking screws with conventional screws inserted in the tibial plateau fragment for re... more To compare locking screws with conventional screws inserted in the tibial plateau fragment for reduction and stability of the construct after tibial plateau leveling osteotomy (TPLO), using a locking TPLO plate. Experimental biomechanical study. Cadaveric canine pelvic limbs (n=8 pairs). TPLO was stabilized with either conventional cortical screws or locking screws in a compressed osteotomy model. Titanium pins inserted into the tibial plateau and proximal metaphysis were used to track bone fragment location by computed tomography (CT) imaging. CT imaging was performed after osteotomy reduction, after plate stabilization, and after 30,000 cycles of axial compression testing. After 30,000 cycles, cyclic loading was continued with monotonically increasing peak-load until failure. The magnitude of rotation about the sawing axis was significantly greater for the conventional screw group because of plate application (P=.009). Translational movement of the tibial plateau fragment toward the plate was significantly greater for the conventional screw group (P=.006). There were no significant differences between groups in stiffness or number of cycles to failure. Maintenance of tibial plateau position was significantly superior for the locking screw group during plate application; however, screw type had no effect on fixation stability under cyclic loading. These results suggest that conventional screws and careful contouring of the TPLO plate can provide comparable mechanical stability to fixation with locking screws in the tibial plateau under load-sharing conditions, but potentially at the expense of osteotomy reduction.
To compare tibial plateau rotation after tibial plateau leveling osteotomy with the radiographica... more To compare tibial plateau rotation after tibial plateau leveling osteotomy with the radiographically planned rotation and to determine the effect of translations and rotations of the tibial plateau fragment on the biomechanical stability of the construct under cyclic loading. Experimental biomechanical study. Cadaveric canine pelvic limbs (n=10). Titanium pins were inserted into the tibial plateau and the proximal metaphysis to track the fragment movements by means of computed tomography (CT) imaging. CT scans were performed (1) before osteotomy, (2) after osteotomy and tibial plateau rotation, and (3) after stabilization with plate and screws. The bones were then cyclically loaded in axial compression. The radiographically planned tibial plateau rotation correlated significantly with the achieved rotation (r=0.73, P=.016), although deviations of up to 4.7 degrees were observed. A significant positive correlation between the amount of rotation about the sawing axis and the plastic deformation of the construct after 30,000 test cycles could be found (r=0.81, P=.005). Considerable deviation occurred between planned and achieved rotation of the tibial plateau fragment. Lower degrees of rotation were beneficial for biomechanical stability. Dogs with larger tibial plateau angles may be at a relatively higher risk for fixation failure, but further studies are needed to establish a safe margin of tibial plateau rotation.
Cadaver study. To determine bone strength in vertebrae by measuring peak breakaway torque or inde... more Cadaver study. To determine bone strength in vertebrae by measuring peak breakaway torque or indentation force using custom-made pedicle probes. Screw performance in dorsal spinal instrumentation is dependent on bone quality of the vertebral body. To date no intraoperative measuring device to validate bone strength is available. Destructive testing may predict bone strength in transpedicular instrumentations in osteoporotic vertebrae. Insertional torque measurements showed varying results. Ten human cadaveric vertebrae were evaluated for bone mineral density (BMD) measurements by quantitative computed tomography. Peak torque and indentation force of custom-made probes as a measure for mechanical bone strength were assessed via a transpedicular approach. The results were correlated to regional BMD and to biomechanical load testing after pedicle screw implementation. Both methods generated a positive correlation to failure load of the respective vertebrae. The correlation of peak breakaway torque to failure load was r = 0.959 (P = 0.003), therewith distinctly higher than the correlation of indentation force to failure load, which was r = 0.690 (P = 0.040). In predicting regional BMD, measurement of peak torque also performed better than that of indentation force (r = 0.897 [P = 0.002] vs. r = 0.777 [P = 0.017]). Transpedicular measurement of peak breakaway torque is technically feasible and predicts reliable local bone strength and implant failure for dorsal spinal instrumentations in this experimental setting.
Treatment of posterior pelvic ring injuries is frequently associated with pain or/and high mortal... more Treatment of posterior pelvic ring injuries is frequently associated with pain or/and high mortality rates. Percutaneous sacro-iliac (SI) screw fixation has proved to be one of the methods of choice, providing minimal operative time, blood loss and wound-related morbidity. However, fixation failures due to secondary fracture dislocation or screw backing out have been reported. There is a little knowledge regarding the impact of varying screw orientation and quality of reduction on the fixation strength. The purpose of the present study was biomechanical investigation of joint stability after SI screw fixation and its dependence on quality of reduction and screw orientation. Thirty-two artificial hemi-pelvices were assigned to four study groups and simulated SI dislocations were fixed with two SI screws in oblique or transverse screw orientation and anatomical or non-anatomical reduction in group A (oblique/anatomical), B (transverse/anatomical), C (oblique/non-anatomical) and D (tra...
Journal of orthopaedic research : official publication of the Orthopaedic Research Society, Jan 16, 2015
Femoral neck fractures in the elderly are a common problem in orthopedics. Augmentation of screw ... more Femoral neck fractures in the elderly are a common problem in orthopedics. Augmentation of screw fixation with bone cement can provide better stability of implants and lower the risk of secondary displacement. This study aimed to investigate whether cement augmentation of three cannulated screws in non-displaced femoral neck fractures could increase implant fixation. A femoral neck fracture was simulated in six paired human cadaveric femora and stabilized with three 7.3 mm cannulated screws. Pairs were divided into two groups: conventional instrumentation versus additional cement augmentation of screw tips with 2 ml TraumacemV+ each. Biomechanical testing was performed by applying cyclic axial load until failure. Failure cycles, axial head displacement, screw angle changes, telescoping and screw cut-out were evaluated. Failure (15 mm actuator displacement) occurred in the augmented group at 12,500 cycles (± 2,480) compared to 15,625 cycles (± 4,215) in the non-augmented group (p = 0...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca
Periprosthetic fractures are increasingly frequent. The fracture may be located over the shaft of... more Periprosthetic fractures are increasingly frequent. The fracture may be located over the shaft of the prosthesis, at its tip or below. The treatment of explosion fractures is difficult because the shaft blocks the application of implants, like screws, which need to penetrate the medullary cavity. The cerclage, as a simple periosteal loop, made of wire or more recently cable, does not only avoid the medullary cavity. Its centripetal mode of action is well suited for reducing and maintaining radially displaced fractures. Furthermore, the cerclage lends itself well for minimally invasive internal fixation. New insight challenges the disrepute of which the cerclage technology suffered for decades. The outcome of cerclage fixation benefits from an improved understanding of its technology, mechano-biology and periosteal blood supply. Preconceived and generally accepted opinions like "strangulation of blood supply" need to be re-examined. Recent mechanical evaluations demonstrate...
Bone cement augmentation of modified cannulated locking screws shows biomechanically and clinical... more Bone cement augmentation of modified cannulated locking screws shows biomechanically and clinically good results for osteoporotic fracture management. Nevertheless, complications need to be considered. Therefore implant removal should be tested for feasibility. Implant removal was simulated in 7 pairs of osteoporotic cadaveric humeri: During screw removal from an angular stable proximal humerus plate, we measured the maximum torque of 14 augmented screws and the corresponding 14 non-augmented screws on the contralateral humeri. After screw removal, specimens were cut along the screw axes to macroscopically investigate the impact of screw removal on the surrounding bone. In addition, we established a technique for cement removal in cases in which the screw head is obstructed with cement and therefore disables the insertion of the screwdriver. The screw extraction torque measurements showed no significant differences between the two groups regarding one screw (screw 4 augmented: 1.52N...
End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary naili... more End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary nailing. The aim of this study was to investigate the force at failure with and without end caps, and whether different insertion angles of nails and end caps would alter that force at failure. Simulated oblique fractures of the diaphysis were created in 15 artificial paediatric femurs. Titanium Elastic Nails with end caps were inserted at angles of 45°, 55° and 65° in five specimens for each angle to create three study groups. Biomechanical testing was performed with axial compression until failure. An identical fracture was created in four small adult cadaveric femurs harvested from two donors (both female, aged 81 and 85 years, height 149 cm and 156 cm, respectively). All femurs were tested without and subsequently with end caps inserted at 45°. In the artificial femurs, maximum force was not significantly different between the three groups (p = 0.613). Push-out force was significantly hig...
Rotator cuff tears are of increasing clinical impact in the physically active elderly patients. R... more Rotator cuff tears are of increasing clinical impact in the physically active elderly patients. Recent research revealed, that a high percentage of these patients present with significant loss of bone mineral density at the insertion site of the rotator cuff, thereby compromising suture anchorage for operative repair. We therefore hypothesized that augmentation of suture anchors improves biomechanical properties in low bone quality. 28 osteoporotic humeral heads were included in this biomechanical study. Bone quality at the anchor insertion sites (group 1: posterior-medial; group 2: anterior-lateral) within the greater tuberosity was analyzed using HR-pQCT (voxel size: 82μm). Anchor positions of identical quality were then randomized to either conventional screw anchorage or polymethylmethacrylat augmented screw anchorage. All anchors were cyclically ramp-loaded until pullout. Pullout strength accounted for 226N in group I for conventional anchorage and for 332N in augmented techniq...
International journal for numerical methods in biomedical engineering, 2015
Percutaneous vertebroplasty represents a current procedure to effectively reinforce osteoporotic ... more Percutaneous vertebroplasty represents a current procedure to effectively reinforce osteoporotic bone via the injection of bone cement. This contribution considers a continuum-mechanically based modelling approach and simulation techniques to predict the cement distributions within a vertebra during injection. To do so, experimental investigations, imaging data and image processing techniques are combined and exploited to extract necessary data from high-resolution μCT image data. The multiphasic model is based on the Theory of Porous Media, providing the theoretical basis to describe within one set of coupled equations the interaction of an elastically deformable solid skeleton, of liquid bone cement and the displacement of liquid bone marrow. The simulation results are validated against an experiment, in which bone cement was injected into a human vertebra under realistic conditions. The major advantage of this comprehensive modelling approach is the fact that one can not only pre...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca, 2011
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...
The increasing problems in the field of osteoporotic fracture fixation results in specialized imp... more The increasing problems in the field of osteoporotic fracture fixation results in specialized implants as well as new operation methods, for example, implant augmentation with bone cement. The aim of this study was to determine the biomechanical impact of augmentation in the treatment of osteoporotic distal femur fractures.Seven pairs of osteoporotic fresh frozen distal femora were randomly assigned to either an augmented or nonaugmented group. In both groups, an Orthopaedic Trauma Association 33 A3 fractures was fixed using the locking compression plate distal femur and cannulated and perforated screws. In the augmented group, additionally, 1 mL of polymethylmethacrylate cement was injected through the screw. Prior to mechanical testing, bone mineral density (BMD) and local bone strength were determined. Mechanical testing was performed by cyclic axial loading (100 N to 750 N + 0.05N/cycle) using a servo-hydraulic testing machine.As a result, the BMD as well as the axial stiffness did not significantly differ between the groups. The number of cycles to failure was significantly higher in the augmented group with the BMD as a significant covariate.In conclusion, cement augmentation can significantly improve implant anchorage in plating of osteoporotic distal femur fractures.
Previous studies have clearly demonstrated superior biomechanical behavior of augmented proximal ... more Previous studies have clearly demonstrated superior biomechanical behavior of augmented proximal femoral nail antirotation (PFNA) blades compared with nonaugmented ones with respect to implant cutout. Nevertheless, there is concern about thermal bone necrosis due to exothermic curing of polymethylmethacrylate (PMMA)-based bone cements. The objective of this study was to quantify the temperatures arising around perforated titanium PFNA blades when augmenting with PMMA. Cylindrical samples from six pairs of fresh frozen human cadaveric femoral heads implanted with a PFNA blade were placed in a 37°C water bath and augmented with 3 mL and 6 mL PMMA. During augmentation, temperatures were measured using six K-type thermocouples that were placed at controlled distances around the implant. With the help of high-resolution quantitative computed tomography images, the locations of all thermocouples with respect to the cement-bone interface were reconstructed. No temperatures higher than 45°C were measured in the interface region and the surrounding cement-free cancellous bone. In the same regions, the longest exposure time above 41°C was 8.5 minutes and was measured in a 6-mL sample. Average maximum temperature was significantly lower for the 3-mL group compared with the 6-mL group (p = 0.017). The results of this study suggest that augmentation of titanium PFNA blades is not associated with a risk of thermal bone necrosis when using up to 6 mL of PMMA. However, larger amounts of cement lead to higher temperatures. PMMA application should therefore be kept low to minimally alter the biological system.
Implant loosening is frequently detected after fixation of open book injuries. Though many author... more Implant loosening is frequently detected after fixation of open book injuries. Though many authors do not see this as a complication, it is often the reason for hardware removal or reinstrumentation in the case of remaining instability. We hypothesized that the flexibility of the implant has an influence on loosening and thus on failure of the construct. We used 6 fresh-frozen pelvic specimens and tested them with our recently introduced test setup for two-leg alternate loading. We subjected them to a non-destructive quasi-static test in the intact condition followed by a non-destructive cyclic test under axial sinusoidal loading with progressive amplitude. Afterwards we simulated an open book injury and performed fixation with three different configurations of a modular fixation system (1-, 2- or 4-rod configuration) in randomized order. Subsequently, the specimens were subjected to 3 cyclic tests with the same loading protocol as previously defined. Finally, each construct was cyclically tested to failure keeping the final rod configuration. We detected significantly greater mobility after 1-rod-fixation and no significant differences after 2-rod or 4-rod-fixation compared to the intact symphysis condition. In the destructive test series the 4-rod-fixation failed first followed by the 1-rod-fixation. The 2-rod-fixation sustained almost 3 times as many load cycles prior to failure as the 4-rod-fixation, whereas the 1-rod-fixation sustained twice as many cycles as the 4-rod-fixation. In conclusion, flexible fixation of the ruptured pubic symphysis in human specimens shows superior behavior with respect to load bearing capacity and ability to withstand cyclic loading compared to stiff constructs.
To compare locking screws with conventional screws inserted in the tibial plateau fragment for re... more To compare locking screws with conventional screws inserted in the tibial plateau fragment for reduction and stability of the construct after tibial plateau leveling osteotomy (TPLO), using a locking TPLO plate. Experimental biomechanical study. Cadaveric canine pelvic limbs (n=8 pairs). TPLO was stabilized with either conventional cortical screws or locking screws in a compressed osteotomy model. Titanium pins inserted into the tibial plateau and proximal metaphysis were used to track bone fragment location by computed tomography (CT) imaging. CT imaging was performed after osteotomy reduction, after plate stabilization, and after 30,000 cycles of axial compression testing. After 30,000 cycles, cyclic loading was continued with monotonically increasing peak-load until failure. The magnitude of rotation about the sawing axis was significantly greater for the conventional screw group because of plate application (P=.009). Translational movement of the tibial plateau fragment toward the plate was significantly greater for the conventional screw group (P=.006). There were no significant differences between groups in stiffness or number of cycles to failure. Maintenance of tibial plateau position was significantly superior for the locking screw group during plate application; however, screw type had no effect on fixation stability under cyclic loading. These results suggest that conventional screws and careful contouring of the TPLO plate can provide comparable mechanical stability to fixation with locking screws in the tibial plateau under load-sharing conditions, but potentially at the expense of osteotomy reduction.
To compare tibial plateau rotation after tibial plateau leveling osteotomy with the radiographica... more To compare tibial plateau rotation after tibial plateau leveling osteotomy with the radiographically planned rotation and to determine the effect of translations and rotations of the tibial plateau fragment on the biomechanical stability of the construct under cyclic loading. Experimental biomechanical study. Cadaveric canine pelvic limbs (n=10). Titanium pins were inserted into the tibial plateau and the proximal metaphysis to track the fragment movements by means of computed tomography (CT) imaging. CT scans were performed (1) before osteotomy, (2) after osteotomy and tibial plateau rotation, and (3) after stabilization with plate and screws. The bones were then cyclically loaded in axial compression. The radiographically planned tibial plateau rotation correlated significantly with the achieved rotation (r=0.73, P=.016), although deviations of up to 4.7 degrees were observed. A significant positive correlation between the amount of rotation about the sawing axis and the plastic deformation of the construct after 30,000 test cycles could be found (r=0.81, P=.005). Considerable deviation occurred between planned and achieved rotation of the tibial plateau fragment. Lower degrees of rotation were beneficial for biomechanical stability. Dogs with larger tibial plateau angles may be at a relatively higher risk for fixation failure, but further studies are needed to establish a safe margin of tibial plateau rotation.
Cadaver study. To determine bone strength in vertebrae by measuring peak breakaway torque or inde... more Cadaver study. To determine bone strength in vertebrae by measuring peak breakaway torque or indentation force using custom-made pedicle probes. Screw performance in dorsal spinal instrumentation is dependent on bone quality of the vertebral body. To date no intraoperative measuring device to validate bone strength is available. Destructive testing may predict bone strength in transpedicular instrumentations in osteoporotic vertebrae. Insertional torque measurements showed varying results. Ten human cadaveric vertebrae were evaluated for bone mineral density (BMD) measurements by quantitative computed tomography. Peak torque and indentation force of custom-made probes as a measure for mechanical bone strength were assessed via a transpedicular approach. The results were correlated to regional BMD and to biomechanical load testing after pedicle screw implementation. Both methods generated a positive correlation to failure load of the respective vertebrae. The correlation of peak breakaway torque to failure load was r = 0.959 (P = 0.003), therewith distinctly higher than the correlation of indentation force to failure load, which was r = 0.690 (P = 0.040). In predicting regional BMD, measurement of peak torque also performed better than that of indentation force (r = 0.897 [P = 0.002] vs. r = 0.777 [P = 0.017]). Transpedicular measurement of peak breakaway torque is technically feasible and predicts reliable local bone strength and implant failure for dorsal spinal instrumentations in this experimental setting.
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Papers by Markus Windolf