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Holding Power of Bioabsorbable Self-reinforced Poly-L/LD-lactide 70/30 Tacks and Miniscrews in Human Cadaver Metatarsal Bone

Leinonen S (1), Tiainen J (1), Kellomäki M (2), Törmälä P (3), Waris T (1), Ashammakhi N (1).

1. Department of Surgery, Oulu University Hospital, P.O. Box 22, FIN-90221 Oulu, Finland.
2. Institute of Biomaterials, Tampere University of Technology, P.O. Box 589, FIN-33101 Tampere, Finland.

Background: Several bioabsorbable internal fixation systems are currently in use in the field of bone surgery.

Aims: To test the mechanical properties of recently developed self-reinforced poly-L/DL-lactide [SR-P(L/DL)LA] 70/30 tacks in comparison with commercially available SR-P(L/DL)LA 70/30 (BioSorbFXä ) miniscrews.

Material and methods: SR-P(L/DL)LA miniscrews (length = 6.0 mm, core diameter = 1.5 mm, thread diameter = 2.0 mm) and tacks (length = 5.4 mm, core diameter = 1.5 mm, thread diameter = 2.0 mm) were applied to human cadaveric metatarsal (MT) bones (six pairs of 4th and six pairs of 5th MT bones from donors who were from 29 to 56 years of age at the time of death). Pullout force was measured using a mechanical testing machine. Forty-eight pullout tests were carried out for each implant type. Studentīs t-test, the Mann-Whitney U test and Spearman’s coefficient were used for statistical evaluation.

Results: The pullout force of tacks was 135.0 ± 26.1 N and that of the miniscrews was 119.3 ± 26.1 N (p = 0.04, statistically significant difference).

Conclusions: SR-P(L/DL)LA 70/30 tacks have a statistically better pullout strength than the SR-P(L/DL)LA 70/30 miniscrews when tested in cadaver MT bones.

Key words: Biosorb; Bioabsorbable; Polylactide; Miniscrew; Tack.