Head‐locking durability of fixed and variable angle locking screws under repetitive loading

Lenz, Mark; Wahl, D.; Gueorguiev, Boyko; Jupiter, Jesse B.; Perren, Stephan M.

doi:10.1002/jor.23108

Cited by 9 publications

(7 citation statements)

References 13 publications

(43 reference statements)

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“…In the former method, the tightness of the screws is assessed as a prerequisite to maintaining the screw holding power, whereas in the latter approach, the screw holding power required to support the bone under load is utilized. The removal torque tended to be higher than the insertion torque before cyclic loading, 22 although it could be lower afterwards. 23 In the present study, the thread counts for the fully threaded plates were approximately ten, eight, and six, and those for the half-threaded plates were five, four, and three for plate types I, II, and III, respectively.…”

Section: Discussionmentioning

confidence: 82%

“…In the literature, two methods have been used to assess the stability of locking screws. 19 , 21 , 22 The first involved measuring the removal torque of the screws before or after cyclic loading, and the second involved the bending strength of the screws. In the former method, the tightness of the screws is assessed as a prerequisite to maintaining the screw holding power, whereas in the latter approach, the screw holding power required to support the bone under load is utilized.…”

Section: Discussionmentioning

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: 82%

Section: Discussionmentioning

confidence: 99%

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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“…titanium polyaxial locking screws inserted in different angels, head loosening was not observed after cyclic testing. 15 In this publication 15 authors concluded that screws inserted up to 15 degrees and orthogonally inserted fixed angle locking screws offer a stable locking mechanism. In another study authors concluded that inclination of polyaxial locking screws up to 15 degrees is comparable to orthogonally placed fixed angle locking screws.…”

Section: Discussionmentioning

confidence: 99%

“…In these studies, the connection between the screw head and the plate hole was investigated using destructive mechanical tests. 2,4,[13][14][15] In this study, we introduce micro-CT as a novel nondestructive quantitative method investigating locking systems. In this experiment, 3.5 mono-and 3.5 polyaxial locking plates were used.…”

Section: Introductionmentioning

confidence: 99%

How Do the Locking Screws Lock? A Micro-CT Study of 3.5-mm Locking Screw Mechanism

Kaczmarek¹,

Bartkowiak

Paczos

et al. 2020

Vet Comp Orthop Traumatol

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Objective To quantify the amount of the screw head thread and the plate hole thread connection in two 3.5 mm locking plates: Locking Compression Plate (LCP) and Polyaxial Locking System (PLS). Materials and Methods A micro - CT scan of a screw head - plate hole connection was performed pre- and post destructive tests. Tests were performed on bone surrogates in a fracture gap model. The 3.5 LCP and 3.5 PLS plates, with 3 perpendicular screws per segment were used in a destructive static test. The 3.5 PLS plates with mono- and polyaxial screws were compared in a cyclic fatigue tests in two orthogonal directions. Pre - and post - test scan datasets were compared. Each dataset was converted into serial images depicting sections cut orthogonally to locking screw axis. The amount of engagement was detected through automated image postprocessing. Results The mean amount of the thread connection for the LCP was 28.85% before and 18.55% after destructive static test. The mean amount of the connection for the PLS was 16.20% before and 14.55% after destructive static test. When inserted monoaxially, the mean amount of the connection for the PLS screws was 14.4% before and 19.24% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate thickness was 2.99% before and 2.08% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate width was 3.36% before and 3.93% after destructive cyclic test. The 3D visualization of the thread connection showed that the initial interface points between screw head and plate hole are different for both LCP and PLS after the destructive testing. Depending on the type of applied force, there was either loss or increase of the contact. Clinical Relevance Micro-CT offers news possibilities in locking implant investigation. It might be helpful in better understanding the nature of locking mechanism and prediction of possible mode of failure in different systems.

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“…The harmful effect of off-axis screw insertion has been demonstrated and discussed in previous biomechanical studies. 13,[22][23][24][25] The exclusive failure mode in the present study was cut-out of the 2 proximal screws through cancellous bone. This is reflected by the fact that mechanical failure, defined by abrupt change in the machine and radiological data, was reached significantly earlier than the clinical failure defined by 5 degrees varus tilting of the femoral head.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical Analysis of the Proximal Femoral Locking Compression Plate: Do Quality of Reduction and Screw Orientation Influence Construct Stability?

Stoffel²,

Sommer

et al. 2018

Journal of Orthopaedic Trauma

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Generally, malreduction led to significantly earlier construct failure. The observed failures were cut-out of the proximal screws in the femoral head, followed by either screw bending, screw loosening, or screw fracture. Proper placement of the proximal screws in anatomically reduced fractures led to significantly higher construct stability. Our data also indicate that once the screws are placed off-axis (>5 degrees), the benefit of an anatomic reduction is lost.

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Head‐locking durability of fixed and variable angle locking screws under repetitive loading

Cited by 9 publications

References 13 publications

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

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

How Do the Locking Screws Lock? A Micro-CT Study of 3.5-mm Locking Screw Mechanism

Biomechanical Analysis of the Proximal Femoral Locking Compression Plate: Do Quality of Reduction and Screw Orientation Influence Construct Stability?

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