title: Fixation strength of tapered versus bicylindrical hydroxyapatite-coated external fixation pins: an animal study.
abstract: The purpose of this study was to comparatively measure the bone-pin interface strength in two types of hydroxyapatite-coated pins that differed in shape, diameter, and implantation technique. Both pin types are commonly used for tibia fixation. Thirty bicylindrical 5/4-mm stainless-steel pins (Group A) and 30 tapered 6/5-mm stainless-steel pins (Group B) were implanted in the left tibiae of 10 adult sheep. A monolateral fixator was mounted on the pins after implantation. A 5-mm-long bone segment was removed from the tibial mid-diaphysis to ensure high load at the bone-pin interface. Pin insertion torque was 830 +/- 446 N/mm in Group A and 3415 +/- 743 N/mm in Group B (p<0.0001, one-way ANOVA). Six weeks after surgery, the sheep were euthanized and pin extraction torque measured. Pin extraction torque was 1237 +/- 499 N/mm in Group A and 3367 +/- 1512 N/mm in Group B (p<0.0001, Mann-Whitney test). Morphological analysis performed at 60x magnification showed a direct bone-pin contact in both groups. Despite challenging biomechanical conditions, this study showed both pin types to be well-fixed and osteointegrated. Therefore, both pin types are recommended for tibial fixation. However, the tapered pins showed higher extraction torque, an important result for external fixation treatments.
authors.affiliation: Division of Orthopaedic Surgery, Rizzoli Orthopaedic Institute, Bologna University, Via G. C. Pupilli, 1, Bologna, 40136, Italy. a.moroni@ior.it
authors.forename: Antonio
authors.initials: A
authors.lastname: Moroni
authors.forename: Cesare
authors.initials: C
authors.lastname: Faldini
authors.forename: Francesco
authors.initials: F
authors.lastname: Pegreffi
authors.forename: Sandro
authors.initials: S
authors.lastname: Giannini
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D004867:Equipment Design; D016267:External Fixators; D005260:Female; D008422:Materials Testing; D016348:Osseointegration; D012756:Sheep; D013314:Stress, Mechanical; D013977:Tibia / Q000601:surgery; D019415:Torque
chemical_list: D020099:Coated Materials, Biocompatible; D017886:Durapatite