Background: This study explores effective fixation methods for Pauwel type III femoral neck fractures by evaluating the biomechanical benefits of adding a screw to the Femoral Neck System (FNS). Methods: Computed tomography (CT) scans of an 82-year-old female patient with an intertrochanteric fracture were used to establish a finite element femur model with heterogeneous material properties. Finite element models of Pauwel type III fractures were created with and without an additional screw. The central and inferior trajectories of the FNS bolt were examined separately and combined with an additional screw for virtual fixation. Walking and stair-climbing loads were applied. Results: With the addition of a screw, both peak maximum and minimum principal strains consistently stayed comparable or decreased in models with both central and inferior bolt trajectories, while the volume of elements with principal strain exceeding 1% decreased by more than half. The peak von Mises stress observed in the implants ranged from 215.7 to 359.3 MPa, remaining below the titanium alloy's yield strength of 800 MPa. For normal walking, the addition of a screw to the central bolt trajectory model decreased the fracture gap by 50.6% and reduced sliding distance by 8.6%. For the inferior bolt trajectory, the gap was reduced by 57.9% and sliding distance by 25.0%.Under stair-climbing conditions, these improvements were also evident; the central trajectory model saw a halved fracture gap and a 7.9% decrease in sliding distance, while the inferior trajectory model experienced a 55.7% gap reduction and a 27.2% decrease in sliding distance. The additional screw increased the area ratio of the fracture site experiencing interfragmentary compression 34%–39%, while the additional screw alleviated peak interfragmentary compression by 12%–18% under both normal walking and stair-climbing conditions. Conclusions The addition of a screw reduced the fracture gap, sliding distance, and peak interfragmentary compression, while increasing the area ratio of interfragmentary compression under both walking and stair-climbing loads, regardless of the FNS bolt trajectory, suggesting a better mechanical environment for fracture healing.

Background: The removal of a well-fixed acetabular cup is a challenging, labor-intensive, and time-consuming step during revision hip arthroplasty. Although the advent of the manual osteotome, Explant, has simplified the procedure, it is still a stressful process as it dissipates the surgeon’s strength and time and risks an iatrogenic pelvic fracture. Recently, EZX, a powered tool for extraction of well-fixed acetabular cups with semicircular blade was invented. This study aimed to compare Explant and EZX in an experimental condition for their efficacy and safety. Methods: Cementless acetabular cups were press-fitted to 20 hemipelvic polyurethane models using foam adhesives. Ten cups were removed with each tool for comparison of the elapsed time, loads on the entire hemipelvis, periacetabular strain and temperature, volume of periacetabular bone removed, and diameter of the remaining acetabular rim. Strains and loads were quantitatively assessed using strain gauges and load cells for precise and reliable measurements. Results: The mean duration required to remove a well-fixed cup with EZX was 38.5 seconds (range, 25–55), whereas that with Explant was 543.7 seconds (range, 214–1,051) (p < 0.001). The load on the entire hemipelvis with EZX (mean, 9.1 kgf; range, 6.4–11.3) was 33% lower than that with Explant (mean, 13.6 kgf; range, 9.2–17.1) (p < 0.001). The periacetabular peak strains at the 3 positions with EZX were significantly lower than those with Explant (p < 0.001). The temperature during the removal did not differ significantly between the 2 tools. Although the mean volume of bone loss with Explant was 2.4 mL more than that with EZX (p < 0.001), the mean diameters of the remaining acetabular rim were not significantly different, measuring 54.1 mm with both tools. Conclusions The present experiment revealed that a well-fixed cup could be removed using a powered tool with less strength and time and less load on the entire pelvis. Although the powered tool removed a larger volume of bone, the diameters of the remaining acetabular rims were equivalent. This tool may help surgeons remove well-fixed cups in a short time and reduce the deforming load on the bone around the cup without increasing the size of the subsequent reconstruction cup.

Background: This study explores effective fixation methods for Pauwel type III femoral neck fractures by evaluating the biomechanical benefits of adding a screw to the Femoral Neck System (FNS). Methods: Computed tomography (CT) scans of an 82-year-old female patient with an intertrochanteric fracture were used to establish a finite element femur model with heterogeneous material properties. Finite element models of Pauwel type III fractures were created with and without an additional screw. The central and inferior trajectories of the FNS bolt were examined separately and combined with an additional screw for virtual fixation. Walking and stair-climbing loads were applied. Results: With the addition of a screw, both peak maximum and minimum principal strains consistently stayed comparable or decreased in models with both central and inferior bolt trajectories, while the volume of elements with principal strain exceeding 1% decreased by more than half. The peak von Mises stress observed in the implants ranged from 215.7 to 359.3 MPa, remaining below the titanium alloy's yield strength of 800 MPa. For normal walking, the addition of a screw to the central bolt trajectory model decreased the fracture gap by 50.6% and reduced sliding distance by 8.6%. For the inferior bolt trajectory, the gap was reduced by 57.9% and sliding distance by 25.0%.Under stair-climbing conditions, these improvements were also evident; the central trajectory model saw a halved fracture gap and a 7.9% decrease in sliding distance, while the inferior trajectory model experienced a 55.7% gap reduction and a 27.2% decrease in sliding distance. The additional screw increased the area ratio of the fracture site experiencing interfragmentary compression 34%–39%, while the additional screw alleviated peak interfragmentary compression by 12%–18% under both normal walking and stair-climbing conditions. Conclusions The addition of a screw reduced the fracture gap, sliding distance, and peak interfragmentary compression, while increasing the area ratio of interfragmentary compression under both walking and stair-climbing loads, regardless of the FNS bolt trajectory, suggesting a better mechanical environment for fracture healing.

Background: The removal of a well-fixed acetabular cup is a challenging, labor-intensive, and time-consuming step during revision hip arthroplasty. Although the advent of the manual osteotome, Explant, has simplified the procedure, it is still a stressful process as it dissipates the surgeon’s strength and time and risks an iatrogenic pelvic fracture. Recently, EZX, a powered tool for extraction of well-fixed acetabular cups with semicircular blade was invented. This study aimed to compare Explant and EZX in an experimental condition for their efficacy and safety. Methods: Cementless acetabular cups were press-fitted to 20 hemipelvic polyurethane models using foam adhesives. Ten cups were removed with each tool for comparison of the elapsed time, loads on the entire hemipelvis, periacetabular strain and temperature, volume of periacetabular bone removed, and diameter of the remaining acetabular rim. Strains and loads were quantitatively assessed using strain gauges and load cells for precise and reliable measurements. Results: The mean duration required to remove a well-fixed cup with EZX was 38.5 seconds (range, 25–55), whereas that with Explant was 543.7 seconds (range, 214–1,051) (p < 0.001). The load on the entire hemipelvis with EZX (mean, 9.1 kgf; range, 6.4–11.3) was 33% lower than that with Explant (mean, 13.6 kgf; range, 9.2–17.1) (p < 0.001). The periacetabular peak strains at the 3 positions with EZX were significantly lower than those with Explant (p < 0.001). The temperature during the removal did not differ significantly between the 2 tools. Although the mean volume of bone loss with Explant was 2.4 mL more than that with EZX (p < 0.001), the mean diameters of the remaining acetabular rim were not significantly different, measuring 54.1 mm with both tools. Conclusions The present experiment revealed that a well-fixed cup could be removed using a powered tool with less strength and time and less load on the entire pelvis. Although the powered tool removed a larger volume of bone, the diameters of the remaining acetabular rims were equivalent. This tool may help surgeons remove well-fixed cups in a short time and reduce the deforming load on the bone around the cup without increasing the size of the subsequent reconstruction cup.

Background: This study explores effective fixation methods for Pauwel type III femoral neck fractures by evaluating the biomechanical benefits of adding a screw to the Femoral Neck System (FNS). Methods: Computed tomography (CT) scans of an 82-year-old female patient with an intertrochanteric fracture were used to establish a finite element femur model with heterogeneous material properties. Finite element models of Pauwel type III fractures were created with and without an additional screw. The central and inferior trajectories of the FNS bolt were examined separately and combined with an additional screw for virtual fixation. Walking and stair-climbing loads were applied. Results: With the addition of a screw, both peak maximum and minimum principal strains consistently stayed comparable or decreased in models with both central and inferior bolt trajectories, while the volume of elements with principal strain exceeding 1% decreased by more than half. The peak von Mises stress observed in the implants ranged from 215.7 to 359.3 MPa, remaining below the titanium alloy's yield strength of 800 MPa. For normal walking, the addition of a screw to the central bolt trajectory model decreased the fracture gap by 50.6% and reduced sliding distance by 8.6%. For the inferior bolt trajectory, the gap was reduced by 57.9% and sliding distance by 25.0%.Under stair-climbing conditions, these improvements were also evident; the central trajectory model saw a halved fracture gap and a 7.9% decrease in sliding distance, while the inferior trajectory model experienced a 55.7% gap reduction and a 27.2% decrease in sliding distance. The additional screw increased the area ratio of the fracture site experiencing interfragmentary compression 34%–39%, while the additional screw alleviated peak interfragmentary compression by 12%–18% under both normal walking and stair-climbing conditions. Conclusions The addition of a screw reduced the fracture gap, sliding distance, and peak interfragmentary compression, while increasing the area ratio of interfragmentary compression under both walking and stair-climbing loads, regardless of the FNS bolt trajectory, suggesting a better mechanical environment for fracture healing.

Background: The removal of a well-fixed acetabular cup is a challenging, labor-intensive, and time-consuming step during revision hip arthroplasty. Although the advent of the manual osteotome, Explant, has simplified the procedure, it is still a stressful process as it dissipates the surgeon’s strength and time and risks an iatrogenic pelvic fracture. Recently, EZX, a powered tool for extraction of well-fixed acetabular cups with semicircular blade was invented. This study aimed to compare Explant and EZX in an experimental condition for their efficacy and safety. Methods: Cementless acetabular cups were press-fitted to 20 hemipelvic polyurethane models using foam adhesives. Ten cups were removed with each tool for comparison of the elapsed time, loads on the entire hemipelvis, periacetabular strain and temperature, volume of periacetabular bone removed, and diameter of the remaining acetabular rim. Strains and loads were quantitatively assessed using strain gauges and load cells for precise and reliable measurements. Results: The mean duration required to remove a well-fixed cup with EZX was 38.5 seconds (range, 25–55), whereas that with Explant was 543.7 seconds (range, 214–1,051) (p < 0.001). The load on the entire hemipelvis with EZX (mean, 9.1 kgf; range, 6.4–11.3) was 33% lower than that with Explant (mean, 13.6 kgf; range, 9.2–17.1) (p < 0.001). The periacetabular peak strains at the 3 positions with EZX were significantly lower than those with Explant (p < 0.001). The temperature during the removal did not differ significantly between the 2 tools. Although the mean volume of bone loss with Explant was 2.4 mL more than that with EZX (p < 0.001), the mean diameters of the remaining acetabular rim were not significantly different, measuring 54.1 mm with both tools. Conclusions The present experiment revealed that a well-fixed cup could be removed using a powered tool with less strength and time and less load on the entire pelvis. Although the powered tool removed a larger volume of bone, the diameters of the remaining acetabular rims were equivalent. This tool may help surgeons remove well-fixed cups in a short time and reduce the deforming load on the bone around the cup without increasing the size of the subsequent reconstruction cup.

Background: This study explores effective fixation methods for Pauwel type III femoral neck fractures by evaluating the biomechanical benefits of adding a screw to the Femoral Neck System (FNS). Methods: Computed tomography (CT) scans of an 82-year-old female patient with an intertrochanteric fracture were used to establish a finite element femur model with heterogeneous material properties. Finite element models of Pauwel type III fractures were created with and without an additional screw. The central and inferior trajectories of the FNS bolt were examined separately and combined with an additional screw for virtual fixation. Walking and stair-climbing loads were applied. Results: With the addition of a screw, both peak maximum and minimum principal strains consistently stayed comparable or decreased in models with both central and inferior bolt trajectories, while the volume of elements with principal strain exceeding 1% decreased by more than half. The peak von Mises stress observed in the implants ranged from 215.7 to 359.3 MPa, remaining below the titanium alloy's yield strength of 800 MPa. For normal walking, the addition of a screw to the central bolt trajectory model decreased the fracture gap by 50.6% and reduced sliding distance by 8.6%. For the inferior bolt trajectory, the gap was reduced by 57.9% and sliding distance by 25.0%.Under stair-climbing conditions, these improvements were also evident; the central trajectory model saw a halved fracture gap and a 7.9% decrease in sliding distance, while the inferior trajectory model experienced a 55.7% gap reduction and a 27.2% decrease in sliding distance. The additional screw increased the area ratio of the fracture site experiencing interfragmentary compression 34%–39%, while the additional screw alleviated peak interfragmentary compression by 12%–18% under both normal walking and stair-climbing conditions. Conclusions The addition of a screw reduced the fracture gap, sliding distance, and peak interfragmentary compression, while increasing the area ratio of interfragmentary compression under both walking and stair-climbing loads, regardless of the FNS bolt trajectory, suggesting a better mechanical environment for fracture healing.

Background: The removal of a well-fixed acetabular cup is a challenging, labor-intensive, and time-consuming step during revision hip arthroplasty. Although the advent of the manual osteotome, Explant, has simplified the procedure, it is still a stressful process as it dissipates the surgeon’s strength and time and risks an iatrogenic pelvic fracture. Recently, EZX, a powered tool for extraction of well-fixed acetabular cups with semicircular blade was invented. This study aimed to compare Explant and EZX in an experimental condition for their efficacy and safety. Methods: Cementless acetabular cups were press-fitted to 20 hemipelvic polyurethane models using foam adhesives. Ten cups were removed with each tool for comparison of the elapsed time, loads on the entire hemipelvis, periacetabular strain and temperature, volume of periacetabular bone removed, and diameter of the remaining acetabular rim. Strains and loads were quantitatively assessed using strain gauges and load cells for precise and reliable measurements. Results: The mean duration required to remove a well-fixed cup with EZX was 38.5 seconds (range, 25–55), whereas that with Explant was 543.7 seconds (range, 214–1,051) (p < 0.001). The load on the entire hemipelvis with EZX (mean, 9.1 kgf; range, 6.4–11.3) was 33% lower than that with Explant (mean, 13.6 kgf; range, 9.2–17.1) (p < 0.001). The periacetabular peak strains at the 3 positions with EZX were significantly lower than those with Explant (p < 0.001). The temperature during the removal did not differ significantly between the 2 tools. Although the mean volume of bone loss with Explant was 2.4 mL more than that with EZX (p < 0.001), the mean diameters of the remaining acetabular rim were not significantly different, measuring 54.1 mm with both tools. Conclusions The present experiment revealed that a well-fixed cup could be removed using a powered tool with less strength and time and less load on the entire pelvis. Although the powered tool removed a larger volume of bone, the diameters of the remaining acetabular rims were equivalent. This tool may help surgeons remove well-fixed cups in a short time and reduce the deforming load on the bone around the cup without increasing the size of the subsequent reconstruction cup.