Microdamage at the pin-bone interface of external skeletal fixation pins after short-term cyclical loading ex-vivo

Summary

This study determined microdamage associated with external fixation pin insertion and short-term cyclical loading, using an ex vivo ovine tibial model. Orthofix tapered blunt-tipped 3.5/4.5 mm fixation pins and Apex® self-drilling self-tapping fixation pins, 4 mm in diameter, were used. After insertion, the constructs were either loaded in cantilever bending or not loaded. Constructs were then bulk-stained in basic fuchsin, and calcified sections were made. The sections were reviewed qualitatively and the microcrack surface density (Cr.S.Dn, μm/mm²) was quantified at the pin-bone interface. The pattern and quantity of microdamage induced was significantly influenced by fixation pin design and cortical region within the cisor transcortex, but not short-term cyclical loading. Overall, Cr.S.Dn was significantly increased with use of the Orthofix fixation pin (P < 0.01). Cr.S.Dn was also increased in the medial cis-cortex, compared with the lateral transcortex (P < 0.05). Diffuse damage within the medial cis-cortex was higher with the Orthofix pin. In contrast, the Howmedica Apex® fixation pin caused fracture of the periosteal region of the lateral transcortex, but relatively little microdamage within the medial cis-cortex. In this model as a consequence of pin insertion, fixation pin design had significant specific damage effects on both the medial cis-cortex and the lateral trans-cortex

Keywords

Microdamage - external fixation pin - cyclical loading

• References

• 1 Aro HT, Markel MD, Chao EYS. Cortical bone reactions at the interface of external fixation half-pins under different loading conditions. J Trauma 1993; 35: 776-85.
• 2 Bentolila V, Boyce TM, Fyhrie DP. et al. Intracortical remodeling in adult rat long bones after fatigue loading. Bone 1998; 23: 275-81.
• 3 Burr DB, Hooser M. Alterations to the en bloc basic fuchsin staining protocol for the demonstration of microdamage produced in vivo. Bone 1995; 17: 431-3.
• 4 Draper ERC, Wallace AL, Strachen RK. et al. The design and performance of an experimental external fixation device with load trans-ducers. Med Eng Phys 1995; 17: 618-24.
• 5 Finlay JB, Hurtig MB, Hardie WR, Liggins AB, Batte SWP. Geometrical propreties of the ovine tibia: a suitable animal model to study the pin-bone interface in fracture fixation?. Proc Inst Mech Eng [H] 1995; 209: 37-50.
• 6 Green SA. Complications of external skeletal fixation. Clin Orthop Rel Res 1983; 180: 109-16.
• 7 Halsey D, Fleming B, Pope MH. et al. External fixation pin design. Clin Orthop Rel Res 1992; 278: 305-12.
• 8 Huja SS, Katona TR, Burr DB. et al. Microdamage adjacent to endosseus implants. Bone 1999; 25: 217-22.
• 9 Hyldahl C, Pearson S, Tepic S, Perren SM. Induction and prevention of pin loosening in external fixation:An in vivo study on sheep tibiae. J Orthop Trauma 1991; 05: 485-92.
• 10 Moroni A, Toksvig-Larsen S, Maltarello MC. et al. A comparison of hydroxyapatite-coated, titanium-coated, and uncoated tapered external-fixation pins. J Bone Joint Surg [Am] 1998; 80: 547-54.
• 11 Wikenheiser MA, Markel MD, Lewallen DG, Chao EYS. Thermal response and torque resistance of five cortical half-pins under stimulated insertion technique. J Orthop Res 1995; 13: 615-9.
• 12 Zaruby JF, Hurtig MB, Finlay JB, Valliant AE. The effect of external fixator pin geometry and dynamic loading on bone remodelling at the pin-bone interface (PBI), in an in vivo sheep tibia model. Vet Com Orthop Traumat 1995; 08: 9-19.
• 13 Zaruby JF, Hurtig MB, Finlay JB, Valliant AE. Studies on the external fixator pin-bone interface: The effect of pin design and pin cooling in an in vivo sheep tibia model. Vet Com Orthop Traumat 1995; 08: 20-31.