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Purpose: To investigate if the stability of minimally invasive screw osteosynthesis of displaced intra-articular calcaneal fractures (DIACF) can be effectively increased by an innovative approach to screw tip augmentation., Methods: In eight-paired human cadaver hindfoot specimens, DIACF of Sanders type IIB were treated with either standard screw osteosynthesis or with bone cement augmentation of the screw tips in the main fragments. The instrumented specimens were subjected to a cyclic loading protocol (9000 cycles, with stepwise increasing loads, 100-1000 N). The interfragment motions were quantified as tuber fragment tilt (TFT) and posterior facet inclination angle (PFIA) using a 3-D motion analysis system. Böhler's angle (BA) was evaluated from X-rays. A load-to-failure test was performed after the cyclic loading protocol., Results: All but one specimen of the augmented group withstood more cycles than the respective specimens of the non-augmented group. Mean cycles to failure for the failure criterion of 5° TFT were 7299 ± 1876 vs. 3864 ± 1810, corresponding to loads of 811 N ± 195 vs. 481 N ± 180, (P = 0.043). There were no significant differences observed in the PFIAs. The failure criterion of 5° BA was reached after a mean of 7929 cycles ± 2004 in the augmented group and 4129 cycles ± 2178 in the non-augmented group, corresponding to loads of 893 N ± 200 vs. 513 N ± 218, (P = 0,090). The mean load-to-failure of the four specimens in the augmented group that completed the cyclic loading was 1969 N over a 1742-2483 N range., Conclusion: Screw tip augmentation significantly improved the mechanical stability of the calcanei after osteosynthesis in terms of decreased tuber fragment tilts and less changes in Böhler's angle.

Abstract Background C ement augmentation of pedicle screws to prevent screw loosening is associated with significant complications, such as cement leakage or bone necrosis. Therefore, an alternative strategy to improve pedicle screw anchorage has been recently developed: Polymer reinforcement of pedicle screws uses an in situ melted polymer sleeve in order to enhance screw anchorage. This biomechanical study evaluated the effect of polymer-reinforcement by comparing polymer-reinforced pedicle screws to non-augmented as well as cement-augmented screws under cyclic loading. Methods For each of the two comparisons (polymer-reinforced vs. non-augmented screws and polymer-reinforced vs. cement-augmented screws), polymer-reinforced screws and control screws were placed into the left and right pedicle of seven vertebrae (mean age: 74.0 (SD 9.3) years) to allow for pairwise left–right comparisons. Each screw was subjected to cyclic cranio-caudal loading with an initial load ranging from −50 N to +50 N and with stepwise increasing compressive loads (5 N every 100 cycles) until screw loosening. Findings Polymer-reinforced pedicle screws resisted a higher number of load cycles until loosening than the contralateral non-augmented control screws (4300 SD 2018 vs. 2457 SD 1116 load cycles, p = 0.015). Screw anchorage of polymer-reinforced pedicle screws was comparable to that of cement augmented control screws (3857 (SD2085) vs. 4300 (SD1257) load cycles until failure, p = 0.64). Interpretation Our findings indicate that polymer-reinforcement significantly enhances pedicle screw anchorage in low quality bone and that its effect is similar in size than that of cement augmentation. Highlights • Cyclic loading in cranio-caudal direction to investigate pedicle screw anchorage was applied. • Reinforcement with a polymer sleeve improved pedicle screws anchorage compared to control. • Compared to cement-augmentation reinforcement with a polymer sleeve showed no difference. [ABSTRACT FROM AUTHOR]