A Comparison of the Mechanical Properties of Two External Fixator Designs for Transarticular Stabilization of the Canine Hock

Summary

Biomechanical testing was performed on 20 canine tibiotarsal joints. The conventional transarticular external skeletal fixator (ESF) was applied to one rear limb while the alternative design using acrylic was applied to the contralateral rear limb. The mode of failure for all models was fracture of the phalanges at the point of fixation in the distal grip device.

The mean stiffness for the acrylic design was 58.5 N/mm and for the conventional ESF 44.8 N/mm. The mean maximum load to failure for the acrylic design was 490.7 N, compared to 405.1 N for the conventional ESF. The angle of deformation at maximum for the acrylic apparatus was 0.45 degrees compared to 2.36 degrees for the standard ESF. The mean energy absorbed to maximum load was 1.92 N-m for the acrylic design and for the conventional ESF 2.69 N-m. This study indicated that the acrylic design was superior in maintaining immobilization across the tibiotarsal joint, indicated by the angle of deformation (p = 0.002) and was structurally comparable in stiffness (p = 0.295), maximum strength (p = 0.438), and total energy absorbed to failure (p = 0.276).

The properties of an acrylic and a stainless steel external transarticular skeletal fixator were biomechanically evaluated. Biomechanical parameters evaluated included: maximum load to failure, stiffness, angle of deformation across the tibiotarsal joint, and energy absorbed to failure. The angle of deformation was less (p = 0.002) for the acrylic device. Based on this study, we conclude that the new acrylic design is structurally comparable to the conventional transarticular ESF and warrants clinical trials.

Keywords

External fixation - methylmethacrylate - transarticular

• REFERENCES

• 1 Brinker WO, Flo GL. Principles and application of external skeletal fixation. Vet Clin North Am Small Anim Pract 1975; 5: 197-208.
• 2 Pettit GD. History of external skeletal fixation. Vet Clin North Am Small Anim Pract 1992; 22: 1-10.
• 3 Toombs JP. Transarticular application of external skeletal fixation. Vet Clin North Am Small Anim Pract 1992; 22: 181-94.
• 4 Bjorling DE, Toombs JP. Transarticular application of the kirschner-ehmer splint. Vet Surg 1982; 11: 34-8.
• 5 Reneger WR. Leeds EB, Olds RB. The use of the Kirschner-Ehmer splint in clinical orthopedics part I. long bone and mandibular fractures. Comp Contin Educ Small Anim Pract 1982; 4: 381-92.
• 6 Toombs JP, Aron DN, Basinger RR. et al. Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 1989; 25: 213-6.
• 7 Morshead D. Leeds EB. Kirschner-Ehmer apparatus immobilization following achilles tendon repair in six dogs. Vet Surg 1984; 13: 11-4.
• 8 Okrasinski EB, Pardo AD, Graehler RA. Biomechanical evaluation of acrylic external skeletal fixation in dogs and cats. J Am Vet Med Assoc 1991; 11: 1590-3.
• 9 Wilier RL, Egger EL, Histand MB. Comparison of stainless steel versus acrylic for the connecting bar of external skeletal fixators. J Am Anim Hosp Assoc 1991; 27: 541-58.
• 10 Rumph PF, Lander JE, Kincaid SA. et al. Ground reaction force profiles from force plate gait analyses of clinically normal mesomorphic dogs at the trot. Am J Vet Res 1994; 55: 756-61.
• 11 Bennett RA, Egger EL, Histand M. Ellis AB. Comparison of the strength and holding power of 4 pin designs for use with the half pin (type I) external skeletal fixation. Vet Surg 1987; 16: 207-11.