Evaluation of a metal acrylic repair product as a clamp for an external fixator

Summary

Mechanical testing was performed to evaluate an acrylic steel repair paste when used in the construction of external fixators. Individual pin-bar-acrylic constructs were compared with those made from Kirschner-Ehmer (KE) clamps or polymethylmethacrylate. The constructs were subjected to cantilever bending forces, pin-pullout tests and cantilever bending after undergoing cyclical fatigue. Forty mm segments of acrylic were significantly stronger than medium ESF clamps. Twenty-five mm segments of acrylic were of equivalent strength to clamps. Ten mm segments failed under physiological loads expected from dogs greater than 20 kg and were less likely to provide adequate pin coverage to protect against pin pull-put. The placement of a wire loop to secure the pin-bar intersects made application of the acrylic easier but did not alter stiffness. There was not any significant variation between different operators in the strength of their constructs nor tolerance of their constructs to pin pullout. Cyclical loading forces were applied to acrylic-pinbar units without significant loss of strength, and acrylic and polymethylmethacrylate units did not show any difference in stiffness after being subjected to cyclical fatigue. The acrylic steel repair paste is a handkneadable, fast setting, inexpensive and readily available acrylic for use in the construction of external fixators. It allows more flexibility in frame design than a clamp and on the basis of mechanical testing offers a very stiff and secure substitute for KE clamps or polymethylmethacrylate.

Keywords

Acrylic - polymethylmethacrylate - fixator - clamp

• References

• 1 Armstrong GH. Use of car body fillers in external fixation. Vet Rec 1991; 129: 151.
• 2 Bennett RL, DeCamp CE, Flo GL, Hauptman JG, Stajich M. Kinematic gait analysis in dogs with hip dysplasia. AVJR 1996; 57: 966-70.
• 3 Budsberg SC. Long-term temporal evaluation of ground reaction forces during development of experimentally induced osteoarthritis in dogs. Am J Vet Res 2001; 62: 1207-11.
• 4 Brinker WO, Verstraea MC, Soutas-Little RW. Stiffness studies on various configurations and types of external fixators. J Am Anim Hosp Assoc 1985; 21: 801-8.
• 5 Davis M, Schulz KS, Fawcett A, Slater MR, Roths JB. Flexural and torsional analysis of five acrylics for use in external skeletal fixation. Vet Comp Orthop Traumatol 1998; 11: 53-8.
• 6 Gardner TN, Evans M, Kenwright J. A biomechanical study on five unilateral external fracture fixation devices. Clin Biomech 1997; 12: 88-95.
• 7 Goodship AE, Kenwright J. The influence of induced micromovement upon the healing of experimental tibial fractures. J Bone Joint Surg Br 1985; 67: 650-5.
• 8 Kirpensteun J, Van der Bos R, Van den Brom WE, Hazelwinkel HW. Ground reaction force analysis of large breed dogs when walking after the amputation of a limb. Vet Rec 2000; 146: 155-9.
• 9 Kraus KH, Wotton HM. Effect of clamp type on type 2 external fixator stiffness. Vet Comp Orthop Traumatol 1999; 12: 178-82.
• 10 Kraus KH, Wotton HM, Rand WM. Mechanical comparison of two external fixator clamp designs. Vet Surg 1998; 27: 224-30.
• 11 McCartney W. Use of a modified acrylic external fixator in 54 dogs and 28 cats. Vet Rec 1998; 143: 330-4.
• 12 Okransinski EB, Pardo AD, Graehler RA. Biomechanical evaluation of acrylic external fixation in dogs and cats. J Am Vet Med Assoc. 1991: 1590-3.
• 13 Roe SC, Keo T. Epoxy putty for free-form external skeletal fixators. Vet Surg 1997; 26: 472-7.
• 14 Shahar R. Relative stiffness and stress of type 1 and type 2 external fixators: acrylic versus stainless steel connecting barsa theoretical approach. Vet Surg 2000; 29: 59-69.
• 15 Tomlinson JL, Constantinescu GH. Acrylic external skeletal fixation of fractures. The Compendium 1991; 13: 235-41.
• 16 Willer 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: 541-8.