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The best location for proximal locking screw for femur interlocking nailing: A biomechanical study.

Karaarslan AA, Karakaşli A, Aycan H, Çeçen B, Yildiz DV, Sesli E - Indian J Orthop (2016 Jan-Feb)

Bottom Line: Which means 103% increase of screw resistance between two levels (P = 0.000).According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels.To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Şifa University, İzmir, Turkey.

ABSTRACT

Background: Proximal locking screw deformation and screw fracture is a frequently seen problem for femur interlocking nailing that affects fracture healing. We realized that there is lack of literature for the right level for the proximal locking screw. We investigated the difference of locking screw bending resistance between the application of screws on different proximal femoral levels.

Materials and methods: We used a total of 80 proximal locking screws for eight groups, 10 screws for each group. Three-point bending tests were performed on four types of screws in two different trochanteric levels (the lesser trochanter and 20 mm proximal). We determined the yield points at three-point bending tests that a permanent deformation started in the locking screws using an axial compression testing machine.

Results: The mean yield point value of 5 mm threaded locking screws applied 20 mm proximal of lesser trochanter was 1022 ± 49 (range 986-1057) (mean ± standard deviation, 95% confidence interval). On the other hand, the mean yield point value of the same type of locking screws applied on the lesser trochanteric level was 2089 ± 249 (range 1911-2268). Which means 103% increase of screw resistance between two levels (P = 0.000). In all screw groups, on the lesser trochanter line we determined 98-174% higher than the yield point values of the same type of locking screws in comparison with 20 mm proximal to the lesser trochanter (P = 0.000).

Conclusion: According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

No MeSH data available.


Related in: MedlinePlus

Proximal locking screw three-point bending test
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Figure 1: Proximal locking screw three-point bending test

Mentions: We used 80 medical stainless steel (316 L) (manufactured by Hipokrat Medical Devices, Izmir, Turkey) proximal locking screws for eight groups, ten screws for each group [Table 1]. Smooth screws were only 17 mm tip threaded. All fully threaded screws had a low profile high pitch thread. We used two metal cylinders, one of them representing trochanteric level and the other representing 20 mm proximal of it. The inner and outer femoral cortex diameters were 30–45 mm on the level of lesser trochanter and 45–55 mm 20 mm proximal of lesser trochanter according to previous studies.14151617 We designed the inner and outer diameters of these two metal cylinders according to femur measurements on previous studies. In groups 1, 3, 5, and 7 a metallic stainless steel cylinder (inner diameter of 45 mm, outer diameter 55 mm and length 440 mm) that mimicked the level of the femur, 2 cm above the lesser trochanter was used. In the second, fourth, sixth and eighth groups, a second metallic cylinder (inner diameter 30 mm, outer diameter 45 mm and length 440 mm) that mimicked the level of the femur on the lesser trochanter was used. 2 cm below their tip were two opposite holes with a diameter of 6.5 mm. A locked nail (Tıpsan Medical Devices Company, Izmir, Turkey) that was 380 mm in length, the proximal part of which was 13 mm in diameter with a 12 mm body diameter, was used for the three-point bending test. There is an oblong proximal locking screw hole which is 12 mm long and 6 mm wide 60 mm distal from the locked nail proximal edge. The nail was supported by two rings proximally and distally in case the locking nail should not move to the sides in the metal cylinder [Figure 1]. The rings, of which the outer diameter was 2 mm smaller than the inner diameter of the cylinder, had 15 mm inner diameter, with a height of 10 mm. After two rings had been put on the nail by three screws, their free movement distally and proximally in the cylinder was checked. The screws to be tested were passed through metal cylinder holes which had a 6.5 mm diameter and a proximal locking screw hole of the nail [Figures 1 and 2]. The whole load is transferred from the proximal to distal in this experiment assembly through the proximal locking screw. There is no load sharing situation, instead a load bearing condition that imitate comminuted femur fractures.


The best location for proximal locking screw for femur interlocking nailing: A biomechanical study.

Karaarslan AA, Karakaşli A, Aycan H, Çeçen B, Yildiz DV, Sesli E - Indian J Orthop (2016 Jan-Feb)

Proximal locking screw three-point bending test
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4759882&req=5

Figure 1: Proximal locking screw three-point bending test
Mentions: We used 80 medical stainless steel (316 L) (manufactured by Hipokrat Medical Devices, Izmir, Turkey) proximal locking screws for eight groups, ten screws for each group [Table 1]. Smooth screws were only 17 mm tip threaded. All fully threaded screws had a low profile high pitch thread. We used two metal cylinders, one of them representing trochanteric level and the other representing 20 mm proximal of it. The inner and outer femoral cortex diameters were 30–45 mm on the level of lesser trochanter and 45–55 mm 20 mm proximal of lesser trochanter according to previous studies.14151617 We designed the inner and outer diameters of these two metal cylinders according to femur measurements on previous studies. In groups 1, 3, 5, and 7 a metallic stainless steel cylinder (inner diameter of 45 mm, outer diameter 55 mm and length 440 mm) that mimicked the level of the femur, 2 cm above the lesser trochanter was used. In the second, fourth, sixth and eighth groups, a second metallic cylinder (inner diameter 30 mm, outer diameter 45 mm and length 440 mm) that mimicked the level of the femur on the lesser trochanter was used. 2 cm below their tip were two opposite holes with a diameter of 6.5 mm. A locked nail (Tıpsan Medical Devices Company, Izmir, Turkey) that was 380 mm in length, the proximal part of which was 13 mm in diameter with a 12 mm body diameter, was used for the three-point bending test. There is an oblong proximal locking screw hole which is 12 mm long and 6 mm wide 60 mm distal from the locked nail proximal edge. The nail was supported by two rings proximally and distally in case the locking nail should not move to the sides in the metal cylinder [Figure 1]. The rings, of which the outer diameter was 2 mm smaller than the inner diameter of the cylinder, had 15 mm inner diameter, with a height of 10 mm. After two rings had been put on the nail by three screws, their free movement distally and proximally in the cylinder was checked. The screws to be tested were passed through metal cylinder holes which had a 6.5 mm diameter and a proximal locking screw hole of the nail [Figures 1 and 2]. The whole load is transferred from the proximal to distal in this experiment assembly through the proximal locking screw. There is no load sharing situation, instead a load bearing condition that imitate comminuted femur fractures.

Bottom Line: Which means 103% increase of screw resistance between two levels (P = 0.000).According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels.To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Şifa University, İzmir, Turkey.

ABSTRACT

Background: Proximal locking screw deformation and screw fracture is a frequently seen problem for femur interlocking nailing that affects fracture healing. We realized that there is lack of literature for the right level for the proximal locking screw. We investigated the difference of locking screw bending resistance between the application of screws on different proximal femoral levels.

Materials and methods: We used a total of 80 proximal locking screws for eight groups, 10 screws for each group. Three-point bending tests were performed on four types of screws in two different trochanteric levels (the lesser trochanter and 20 mm proximal). We determined the yield points at three-point bending tests that a permanent deformation started in the locking screws using an axial compression testing machine.

Results: The mean yield point value of 5 mm threaded locking screws applied 20 mm proximal of lesser trochanter was 1022 ± 49 (range 986-1057) (mean ± standard deviation, 95% confidence interval). On the other hand, the mean yield point value of the same type of locking screws applied on the lesser trochanteric level was 2089 ± 249 (range 1911-2268). Which means 103% increase of screw resistance between two levels (P = 0.000). In all screw groups, on the lesser trochanter line we determined 98-174% higher than the yield point values of the same type of locking screws in comparison with 20 mm proximal to the lesser trochanter (P = 0.000).

Conclusion: According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

No MeSH data available.


Related in: MedlinePlus