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The effect of contouring on fatigue resistance of three types of fracture fixation plates

View Article: PubMed Central - PubMed

ABSTRACT

Background: Metallic reconstruction plates used for fracture stabilization typically require intraoperative contouring for patient-specific anatomical fit. Despite this, characterization of plate mechanical properties after contouring has previously been limited.

Background: The objective of this study was to assess whether contouring affects fatigue resistance for three types of Stryker seven-hole stainless steel (SS) 316LVM fracture fixation plates. The hypothesis was that for each plate type, more contouring repetitions would result in lower fatigue resistance.

Methods: Plates were contoured using a bench-top plate bender to ±20° either 0×, 3×, 6×, or 9× (n = 5 per group) and tested in the straight configuration. Cyclic four-point bending was applied in an incremental stepwise staircase approach (one step = 100,000 cycles, 10 Hz) until failure (defined as brittle fracture or plastic deformation of 10° permanent bend). Moment-cycle product (MCP) was computed as the summation of maximum moment × number of cycles and used as the primary measure of fatigue resistance.

Results: No significant differences in fatigue resistance were detected between contouring groups for Basic Fragment Set (BFS) Reconstruction Plates. Significantly lower fatigue resistance was measured for 9× contoured Matta Pelvic System (MPS) Straight Plates compared to 0× contoured plates (p = 0.023). MPS Flex Plates contoured 3× had greater fatigue resistance than 0× contoured (p = 0.031) and 9× contoured plates (p = 0.032).

Conclusions: This work provides fatigue resistance-based evidence that clinicians should avoid high repetitions of contouring for MPS Straight Plates. Meanwhile, BFS Reconstruction Plates and MPS Flex Plates are not negatively affected by contouring. These results allow for improved intraoperative decisions about using or discarding plates after multiple contouring repetitions.

No MeSH data available.


Related in: MedlinePlus

Each step consisted of 100,000 cycles at 10 Hz in the four-point bending configuration. Upper and lower load level targets for each cycle were Fmax and Fmin, respectively, where Fmin = 10 % Fmax for each step. Fmax was increased from one step to the next by a constant load increment corresponding to 10 % My,min, determined in preliminary tests to failure for each plate type. These Fmax load increase increments differed for the plate types due to geometry differences and are listed in Table 1. For example, for BFS Reconstruction Plates, Fmax,b+1 − Fmax,b = 12.5 N, where b = step number. Tests continued with subsequent steps of incrementally increased Fmax until conditions of failure were met (plate fracture or plastic deformation beyond 10° bend of the plate at 10-N load, applied between steps)
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Fig2: Each step consisted of 100,000 cycles at 10 Hz in the four-point bending configuration. Upper and lower load level targets for each cycle were Fmax and Fmin, respectively, where Fmin = 10 % Fmax for each step. Fmax was increased from one step to the next by a constant load increment corresponding to 10 % My,min, determined in preliminary tests to failure for each plate type. These Fmax load increase increments differed for the plate types due to geometry differences and are listed in Table 1. For example, for BFS Reconstruction Plates, Fmax,b+1 − Fmax,b = 12.5 N, where b = step number. Tests continued with subsequent steps of incrementally increased Fmax until conditions of failure were met (plate fracture or plastic deformation beyond 10° bend of the plate at 10-N load, applied between steps)

Mentions: Plates were subjected to cyclic loads in a stepwise staircase approach [12]. At each step, 100,000 cycles in four-point bending were applied at 10 Hz between 10 and 100 % of the maximum load designated for that step. Figure 2 shows an illustrative load vs. time plot describing the cyclic test procedure. Load corresponding to 10 % of the pre-determined minimum My was used as the incremental increase of Fmax between steps (12.5 N for BFS Reconstruction and MPS Straight Plates; 17 N for MPS Flex Plates, Table 1). To estimate failure load levels, preliminary cyclic fatigue testing was performed on one control plate of each type beginning at 20 % of the load corresponding to My and increasing stepwise as described (Fig. 2) until failure occurred. Based on these preliminary tests, subsequent plate cyclic testing began at initial Fmax levels such that failure would most likely be reached within eight steps (~24 h). See Table 1 and Fig. 2 for step details.Fig. 2


The effect of contouring on fatigue resistance of three types of fracture fixation plates
Each step consisted of 100,000 cycles at 10 Hz in the four-point bending configuration. Upper and lower load level targets for each cycle were Fmax and Fmin, respectively, where Fmin = 10 % Fmax for each step. Fmax was increased from one step to the next by a constant load increment corresponding to 10 % My,min, determined in preliminary tests to failure for each plate type. These Fmax load increase increments differed for the plate types due to geometry differences and are listed in Table 1. For example, for BFS Reconstruction Plates, Fmax,b+1 − Fmax,b = 12.5 N, where b = step number. Tests continued with subsequent steps of incrementally increased Fmax until conditions of failure were met (plate fracture or plastic deformation beyond 10° bend of the plate at 10-N load, applied between steps)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5037585&req=5

Fig2: Each step consisted of 100,000 cycles at 10 Hz in the four-point bending configuration. Upper and lower load level targets for each cycle were Fmax and Fmin, respectively, where Fmin = 10 % Fmax for each step. Fmax was increased from one step to the next by a constant load increment corresponding to 10 % My,min, determined in preliminary tests to failure for each plate type. These Fmax load increase increments differed for the plate types due to geometry differences and are listed in Table 1. For example, for BFS Reconstruction Plates, Fmax,b+1 − Fmax,b = 12.5 N, where b = step number. Tests continued with subsequent steps of incrementally increased Fmax until conditions of failure were met (plate fracture or plastic deformation beyond 10° bend of the plate at 10-N load, applied between steps)
Mentions: Plates were subjected to cyclic loads in a stepwise staircase approach [12]. At each step, 100,000 cycles in four-point bending were applied at 10 Hz between 10 and 100 % of the maximum load designated for that step. Figure 2 shows an illustrative load vs. time plot describing the cyclic test procedure. Load corresponding to 10 % of the pre-determined minimum My was used as the incremental increase of Fmax between steps (12.5 N for BFS Reconstruction and MPS Straight Plates; 17 N for MPS Flex Plates, Table 1). To estimate failure load levels, preliminary cyclic fatigue testing was performed on one control plate of each type beginning at 20 % of the load corresponding to My and increasing stepwise as described (Fig. 2) until failure occurred. Based on these preliminary tests, subsequent plate cyclic testing began at initial Fmax levels such that failure would most likely be reached within eight steps (~24 h). See Table 1 and Fig. 2 for step details.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Background: Metallic reconstruction plates used for fracture stabilization typically require intraoperative contouring for patient-specific anatomical fit. Despite this, characterization of plate mechanical properties after contouring has previously been limited.

Background: The objective of this study was to assess whether contouring affects fatigue resistance for three types of Stryker seven-hole stainless steel (SS) 316LVM fracture fixation plates. The hypothesis was that for each plate type, more contouring repetitions would result in lower fatigue resistance.

Methods: Plates were contoured using a bench-top plate bender to ±20° either 0×, 3×, 6×, or 9× (n = 5 per group) and tested in the straight configuration. Cyclic four-point bending was applied in an incremental stepwise staircase approach (one step = 100,000 cycles, 10 Hz) until failure (defined as brittle fracture or plastic deformation of 10° permanent bend). Moment-cycle product (MCP) was computed as the summation of maximum moment × number of cycles and used as the primary measure of fatigue resistance.

Results: No significant differences in fatigue resistance were detected between contouring groups for Basic Fragment Set (BFS) Reconstruction Plates. Significantly lower fatigue resistance was measured for 9× contoured Matta Pelvic System (MPS) Straight Plates compared to 0× contoured plates (p = 0.023). MPS Flex Plates contoured 3× had greater fatigue resistance than 0× contoured (p = 0.031) and 9× contoured plates (p = 0.032).

Conclusions: This work provides fatigue resistance-based evidence that clinicians should avoid high repetitions of contouring for MPS Straight Plates. Meanwhile, BFS Reconstruction Plates and MPS Flex Plates are not negatively affected by contouring. These results allow for improved intraoperative decisions about using or discarding plates after multiple contouring repetitions.

No MeSH data available.


Related in: MedlinePlus