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

Summary

The purpose of this study was to study the effects of pin design and dynamic loading on the biological response of bone at the pin-bone interface (PBI). An electro-pneumatic pin-loading device was used to mimic the forces that would be experienced by external fixator pins, during patient ambulation following repair of a fracture with external skeletal fixation. The remodelling response was assessed histologically with fluorescence microscopy of plasticembedded undecalcified pin-bone sections, and surface-stained histomorphometry.

There were no significant differences between the AO Schanz and Howmedica Apex 5.0 mm diameter self-tapping pin designs when they were inserted in 4.5 mm diameter predrilled pilot holes. When pin type was controlled for, significant differences (p<0.05) existed between loaded and control groups as well as between entry (near) and exit (far) cortices. Less bone resorption was observed in the non-loaded group in comparison to the dynamically loaded group, and bone resorption in the near cortex consistently exceeded the amount of bone resorption in the far cortex for both treatment groups.

The purpose of this study was to examine the effects of pin design and dynamic pin loading on the remodelling response of cortical bone at the pin-bone interface (PBI) of intact sheep tibiae. No significant differences were demonstrated between pin designs; however, significant differences (p<0.05) existed between loaded versus control pins, as well as between entry and exit cortices.

Keywords

External fixator pin-bone interface - dynamic pin loading - bone remodelling

• REFERENCES

• 1 Aron DN, Toombs JP. Updated principles of external skeletal fixation. Comp Cont Educ 1984; 6 (09) 845-58.
• 2 Brinker WO, Flo Fl. Principles and application of external skeletal fixation. Vet Clin N Am Sm An Pract 1975; 2: 197-208.
• 3 Klip EJ, Bosma R. Investigations into the mechanical behaviour of bonepin connections. Eng Med 1978; 7 (01) 43-8.
• 4 Biliouris TL, Schneider E, Rahn BA, Gasser B, Perren SM. The effect of radial preload on the implantbone interface: A cadaveric study. J Orthop Trauma 1989; 3 (04) 323-32.
• 5 Finlay JB, Hurtig MH, Ng A. et al Study of the pinbone interface in fracture fixation: High techlow tech. In: Experimental Mechanics. Technology Transfer between High Tech Engineering and Biomechanics. Little EG. (ed) Amsterdam: Elsevier Science Publishers; 1992: 47-60.
• 6 Andrianne Y, Wagenknecht M, Donkerwolcke M. et al External fixation pin: An in vitro general investigation. Orthoped 1987; 10: 1507-16.
• 7 Hyldahl C, Pearson S, Tepic S, Perren SM. Induction and prevention of pin loosening in external fixators in sheep tibia. Proc 34th Ann Mtg Orthoped Res Soc 1988; 13: 304 Abstract
• 8 Perren SM. Physical and biological aspects of fracture healing with special reference to internal fixation. Clin Orthop Rel Res 1979; 138: 175-196.
• 9 Schatzker J, Home JG, Sumner-Smith G. The effect of movement on the holding power of screws in bone. Clin Orthop Rel Res 1975; 111: 257-62.
• 10 Uhthoff HK. Mechanical factors influencing the holding power of screws in compact bone. J Bone Jt Surg 1973; 55 B 633
• 11 Uhthoff HK, Germain JP. The reversal of tissue differentiation around screws. Clin Orthop Rel Res 1977; 123: 24-52.
• 12 Green SA. Introduction: History of external fixation. In: Complications of External Skeletal Fixation. Causes, Prevention and Treatment. Green SA. (ed) Springfield, Illinois: Charles C. Thomas; 1981: 3-11.
• 13 Green SA. Pin tract infection. In: Complications of External Skeletal Fixation. Causes, Prevention and Treatment. Green SA. (ed) Springfield, Illinois: Charles C. Thomas; 1981: 12-30.
• 14 Hurtig M, Rorabeck CH, Ng A, Finlay JB. Pilot hole size and radial compression affect pinbone interface quality in dynamicallyloaded external fixator pins. Proc 39th Ann Mtg Orthop Res Soc 1993; 18: 110 Abstract
• 15 Rubin CT, Lanyon LE. Osteoregulatory nature of mechanical stimuli: Function as a determinant for adaptive remodelling in bone. J Orthop Res 1987; 5: 300-10.
• 16 Goodship AE, Kelly DJ, Rigby HS. et al The effect of different regimens of axial micromovement on the healing of experimental tibial fractures. Proc 33rd Ann Mtg Orthop Res Soc 1988; 12: 98 Abstrct
• 17 Goodship AE, Kenwright J. The influence of induced micromovement upon the healing of experimental tibial fractures. J Bone Jt Surg 1985; 67 B 650-5.
• 18 Kenwright J, Goodship AE. Controlled mechanical stimulation in the treatment of tibial fractures. Clin Orthop Rel Res 1989; 241: 36-47.
• 19 Pettine KA, Chao EYS, Kelly PJ. Analysis of the external fixator pinbone interface. Clin Orthop Rel Res 1993; 293: 18-27.
• 20 Watkins PE, Kelly PJ, Righby HS. et al External fixation for fracture stabilization: What is the optimal mechanical environment? (Abstract). J Bone Jt Surg 1988; 70 B 154
• 21 Schenk RK, Olah AJ, Herrmann W. Preparation of calcified tissues for light microscopy. In: Methods of Calcified Tissue Preparation. Preparation. Dickson GR. (ed) Amsterdam: Elsevier; 1984: 1-54.
• 22 Hurtig MB, Finlay JB, Ng A. The Effect of Radial Compression on Dynamically Loaded External Fixator Pins in Sheep. 1992. (UnPub)
• 23 Ng A, Finlay JB. Photoelastic modelling of the pinbone interface. The Canadian Medical & Biological Engineering Society Conference May 7, 191 Banff Canada. 1991: 151-152. (Abstract)
• 24 Zaruby JF, Hurtig MB, Finlay JB, Valliant A. Studies on the external pinbone interface: The effect of pin design and pin cooling in an in vivo sheep tibia model. Submitted August. 1994. VCOT
• 25 Behrens F, Johnson WD. Unilateral external fixation: Methods to increase and reduce frame stiffness. Clin Orthop Rel Res 1989; 241: 48-56.
• 26 Finlay JB, Hurtig MB, Liggins AB, Batte SWP. Geometric properties of the ovine tibia: A suitable animal model for fracture fixation?. J Biomech 1994; submitted May. 1994
• 27 Bennet RA, Egger EL, Histand M, Ellis AB. Comparison of the strenght and holding power of 4 pin designs for use with half-pin (Type I) external skeletal fixation. Vet Surg 1987; 16 (03) 207-11.
• 28 Ramsey WS. Analysis of individual leukocyte behaviour during chemotaxis. Exp Cell Res 1972; 70: 129
• 29 Schatzker J, Sanderson R, Murnaghan JP. The holding power of orthopedic screws in vivo. Clin Orthop Rel Res 1975; 108: 115-26.
• 30 Vangsness CT, Carter DR, Frankel VH. In vitro evaluation of the loosening characteristics of self-tapped and non self-tapped cortical bone screws. Clin Orthop Rel Res 1981; 157: 279-285.