Fig 1.
The shown screws were used for the test series: Acutrak®2mini (Acumed) (Fig 1a), Twinfix® (Stryker) (Fig 1b), HCS® 3.0 (Synthes) (Fig 1c), and prototypes of the two new BSS sets with an additional crosswise drill hole with an inner thread in oblique type (BSS-obl.) (Fig 1d) and with a longitudinal groove with an inner thread and longitudinal screw as a longitudinal type (BSS-long.) (Fig 1e).
Fig 2.
The scaphoid bones were clamped into the steel bracket in a fitted plastic form which was produced using the stereolithography technique. They were embedded in a device which permitted the correct orientation of the scaphoid bone for the osteotomy and screw insertion. In this illustration, the circular saw which was used for the osteotomy has already been removed, and the guide sheaths for the drill wire as well as the targeting drilling wire are visible. The osteosynthesized scaphoid bone was removed from the clamping device with its holders and clamped into the test array (Fig 3).
Fig 3.
Draft of the test array for cyclic load to the scaphoid bone osteosyntheses, which were clamped into the holder.
Fig 4.
a-d. Sample of a force/angle diagram.
Force/angle diagrams of the cyclic load of a scaphoid bone with a torque load from 150 to 300 mNm and resulting loss of stability. In Fig 4d loosening of the screw fastening is clearly visible by the curves which run out to the right and the line up to 10°.
Fig 5.
Observed Cycles until failure by Implant. Median of maximum attained cycles of the respective screw models with average parameter and standard deviation. Box plot of maximum cycles per screw type. Median, 25% and 75% percentiles, the points correspond to the individual results per screw.
Table 1.
primary outcome (Statistics for primary outcome by implant): dataset on total cycles until failure for all tested screws.
Table 2.
Statistics for secondary outcome by implant.
Adjustment for Multiplicity: Holm- Simulated.
Fig 6.
Maximum rotational clearance at Torque level by Implant. Median of maximum attained cycles of the respective screw models with average parameter and standard deviation. Box plot of maximum displacement per screw type/load combination. Median, 25% and 75% percentiles, the points correspond to the individual results per screw. The number above the boxplots indicates the number of non-failing screws.
Table 3.
primary outcome (Least squares means estimates for screw comparisons): dataset on cycles until failure with reference to torque loads (restricted to load range, where majority of failures occurred); N stands for number of screws which didn’t fail at a previous torque level and a further tested in the indicated load range.