Modification of the screw hole structures to improve the fatigue strength of locking plates

Lin, Chen-Huei; Chao, Ching‐Kong; Ho, Yu-Jou; Lin, Jinn

doi:10.1016/j.clinbiomech.2018.03.011

Cited by 8 publications

(11 citation statements)

References 24 publications

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“… 9 , 15 However, if the threads are partially removed from the tension side of a titanium plate, then the fatigue strength of the plate can be restored. 3 It has also been found that removing half of the threads is more effective than removing one-third of the threads. As noted in the present report, the stiffness and yield strength of the A and B plates was very similar because the influence of the threads was negligible.…”

Section: Discussionmentioning

confidence: 99%

“…The plates were prevented from moving during the cyclic loading tests by two bars inserted into the slots at the ends of the plates. 3 , 9 In this experiment, according to the torques suggested in the operation instructions of the commercial locking plates, the screw heads were inserted orthogonally into the screw holes on the type I, II, and III plates with maximum torques of 4 Nm, 4 Nm, and 2 Nm, respectively, using a torque limited driver. Firstly, three plates of each type were tested to determine the stiffness and yield strength using a single ramp type load at a loading rate of 1 mm per minute in displacement control mode.…”

Section: Methodsmentioning

confidence: 99%

“…Then, with the same test setup, ten new plates of each type were tested with sinusoidal cyclic loading at a rate of 10 Hz using a fatigue-rated load cell. The maximum load applied during cyclic loading was estimated from a previous study, 3 and the stress ratio between the minimum and maximum loads was 10%. The plates were loaded cyclically to failure until cracks were visible.…”

Section: Methodsmentioning

confidence: 99%

“…Locking plates provide a minimally invasive means of treating long bone fractures in the body when intramedullary nails cannot provide stable fixation. 1 - 3 However, implant failure, especially fatigue fractures of the plates or screws, may cause severe patient disability. 4 …”

Section: Introductionmentioning

confidence: 99%

“…However, it has been shown using a thick femoral plate model that thread removal from the tension side of the holes may reduce the notch sensitivity and increase the fatigue strength. 3 Nevertheless, the effects of thread number reduction on plates in other regions of the body and on screw stability remain unknown.…”

Section: Introductionmentioning

confidence: 99%

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Half-threaded holes markedly increase the fatigue life of locking plates without compromising screw stability

Chao

Chen

Lin

2020

Bone & Joint Research

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Aims To determine whether half-threaded screw holes in a new titanium locking plate design can substantially decrease the notch effects of the threads and increase the plate fatigue life. Methods Three types (I to III) of titanium locking plates were fabricated to simulate plates used in the femur, tibia, and forearm. Two copies of each were fabricated using full- and half-threaded screw holes (called A and B, respectively). The mechanical strengths of the plates were evaluated according to the American Society for Testing and Materials (ASTM) F382-14, and the screw stability was assessed by measuring the screw removal torque and bending strength. Results The B plates had fatigue lives 11- to 16-times higher than those of the A plates. Before cyclic loading, the screw removal torques were all higher than the insertion torques. However, after cyclic loading, the removal torques were similar to or slightly lower than the insertion torques (0% to 17.3%), although those of the B plates were higher than those of the A plates for all except the type III plates (101%, 109.8%, and 93.8% for types I, II, and III, respectively). The bending strengths of the screws were not significantly different between the A and B plates for any of the types. Conclusion Removing half of the threads from the screw holes markedly increased the fatigue life of the locking plates while preserving the tightness of the screw heads and the bending strength of the locking screws. However, future work is necessary to determine the relationship between the notch sensitivity properties and titanium plate design. Cite this article: Bone Joint Res 2020;9(10):645–652.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%