In vitro biomechanical testing of a micro external skeletal fixator

Summary

Objective: To biomechanically test the properties of three different Universal Micro External Fixator (UMEX™) configurations with regard to their use in very small animals (<5kg) and compare the UMEX system to the widely used IMEX External Skeletal Fixation (SK™) system in terms of stiffness, space needed for pin placement and weight.

Methods: Three different UMEX configurations (type Ia, type Ib, and type II modified) and one SK configuration type Ia were used to stabilize Delrin plastic rods in a 1 cm fracture gap model. These constructs were tested in axial compression, craniocaudal bending, mediolateral bending, and torsion. Testing was conducted within the elastic range and mean stiffness in each mode was determined from the slope of the linear portion of the load-deformation curve. A Kruskal Wallis one-way analysis of variance on ranks test was utilized to assess differences between constructs (p <0.05).

Results: The UMEX type II modified configuration was significantly stiffer than the other UMEX configurations and the SK type Ia, except in craniocaudal bending, where the SK type Ia configuration was stiffer than all UMEX constructs. The UMEX type Ia configuration was significantly the weakest of those frames. The UMEX constructs were lighter and smaller than the SK, thus facilitating closer pin placement.

Conclusions: Results supported previous reports concerning the superiority of more complex constructs regarding stiffness. The UMEX system appears to be a valid alternative for the treatment of long-bone fractures in very small animals.

Keywords

External skeletal fixation - frame configuration - close pin placement - miniature dogs - cats

• References

• 1 Chao YSE, Aro HT, Lewallen DG. et al. The effect of rigidity on fracture healing in external fixation. Clin Orthop Relat Res 1989; 143: 25-35.
• 2 Lappin MR, Aron DN, Herron HL. et al. Fractures of the radius and ulna in the dog. J Am Anim Hosp Assoc 1982; 19: 643-650.
• 3 Egger EL, Histand MB, Norrdin RW. et al. Canine osteotomy healing when stabilized with decreasingly rigid fixation compared to constantly rigid fixation. Vet Comp Orthop Traumatol 1993; 6: 182-187.
• 4 Toombs JP, Bronson DG, Ross D. et al. The SK TM external fixation system: description of components, instrumentation, and application techniques. Vet Comp Orthop Traumatol 2003; 16: 76-81.
• 5 Muir P. Distal Antebrachial fractures in toy-breed dogs. The Compendium 1997; 19: 137-145.
• 6 Larsen LJ, Roush JK, McLaughlin RM. Bone plate fixation of distal radius and ulna fractures in small- and miniature-breed dogs. J Am Anim Hosp Assoc 1999; 35: 243-250.
• 7 Waters DJ, Breur GJ, Toombs JP. Treatment of common forelimb fractures in miniature- and toy breed dogs. J Am Anim Hosp Assoc 1993; 29: 442-448.
• 8 Lincoln JD. Treatment of open, delayed union, and nonunion fractures with external skeletal fixation. Vet Clin N Am Small 1995; 22: 195-207.
• 9 Laverty PH, Johnson AL, Toombs JP. et al. Simple and multiple fractures of the radius treated with an external fixator. Vet Comp Orthop Traumatol 2002; 15: 97-103.
• 10 Welch JA, Boudriaeu RJ, DeJardin LM. et al. The intraosseous blood supply of the canine radius: implications for healing of distal fractures in small dogs. Vet Surg 1997; 26: 57-61.
• 11 Wilson JW. Vascular supply to normal bone and healing fractures. Semin Vet Med Surg (Small Animal) 1991; 6: 26-38.
• 12 Dugat D, Rochat M, Ritchey J. et al. Quantitative analysis of the intramedullary arterial blood supply of the feline tibia. Vet Comp Orthop Traumatol 2011; 24: 313-319.
• 13 Langley-Hobbs SJ, Carmicheal S, McCartney WT. External skeletal fixation for stabilisation of comminuted humeral fractures in cats. J Small Anim Pract 1997; 38: 280-285.
• 14 Dudley M, Johnson AL, Olmstead M. et al. Open reduction and bone plate stabilization, compared with closed reduction and external fixation, for treatment of comminuted tibial fractures: 47 cases (1980-1995) in dogs. J Am Vet Med Ass 1997; 211: 1008-1012.
• 15 Haas B. Use of the tubular external fixator in the treatment of distal radial and ulnar fractures in small dogs and cats. Vet Comp Orthop Traumatol 2003; 16: 132-137.
• 16 Piras L, Cappellari F, Peirone B. et al. Treatment of fractures of the distal radius and ulna in toy breed dogs with circular external skeletal fixation: a retrospective study. Vet Comp Orthop Traumatol 2011; 3: 228-235.
• 17 Eger CE. A technique for the management of radial and ulnar fractures in miniature dogs using transfixation pins. J Small Anim Pract 1990; 31: 377-387.
• 18 Voss K, Kull MA, Heassig M. et al. Repair of long-bone fractures in cats and small dogs with the unilock mandible locking plate system. Vet Comp Orthop Traumatol 2009; 22: 398-405.
• 19 Johnson AL, Kneller AK, Weigel RM. Radial and tibial fracture repair with external skeletal fixation. Vet Surg 1989; 18: 367-372.
• 20 Hamilton MH, Langley Hobbs SJ. Use of the AO veterinary mini ‘T’-plate for stabilisation of distal radius and ulna fractures in toy breed dogs. Vet Comp Orthop Traumatol 2005; 18: 18-25.
• 21 Diaz-Bertrana MC, Durall I, Puchol JL. et al. Interlocking nail treatment for long-bone fractures in cats: 33 cases (1995-2004). Vet Comp Orthop Traumatol 2005; 18: 119-126.
• 22 Altunatmaz K, Ozsoy S, Mutlu Z. et al. Use of intramedullary fully-threaded pins in the fixation of feline and canine humeral, femoral and tibial fractures. Vet Comp Orthop Traumatol 2012; 25: 321-325.
• 23 Shahar R. Relative stiffness and stress of type I and type II external fixators: acrylic versus stainless-steel connecting bars-a theoretical approach. Vet Surg 2000; 29: 59-69.
• 24 Kenwright J, Goodship AE. Controlled mechanical stimulation in the treatment of tibial fractures. Clin Orthop Relat R 1989; 241: 36-47.
• 25 Claes LE, Wilke HJ, Augat P. et al. Effect of dynamization on gap healing of diaphyseal fractures under external fixation. Clin Biomech 1995; 10: 227-234.
• 26 Kawoosa AA, Dhar SA, Mir MR. et al. Distraction osteogenesis for ulnar lengthening in Kienbock`s disease. Int Orthop 2007; 31: 339-344.
• 27 Rumph PF, Kincaid SA, Visco DM. et al. Redistribution of vertical ground reaction force in dogs with experimentally induced chronic hindlimb lameness. Vet Surg 1995; 24: 384-389.
• 28 Rumph PF, Lander JE, Kincaid SA. et al. Ground reaction force profiles from force platform gait analyses of clinically normal mesomorphic dogs at the trot. Am J Vet Res 1994; 55: 756-761.
• 29 Bronson DG, Ross JD, Toombs JP. et al. Influence of the connecting rod on the biomechanical properties of five external skeletal fixation configurations. Vet Comp Orthop Traumatol 2003; 16: 82-87.
• 30 White DT. A mechanical comparison of veterinary linear external fixation systems. Vet Surg 2003; 32: 507-514.
• 31 Bouvy BM, Markel MD, Chelikani S. et al. Ex vivo biomechanics of Kirschner-Ehmer external skeletal fixation applied to canine tibiae. Vet Surg 1993; 22: 194-207.
• 32 Reaugh HF, Rochat MC, Bruce CW. et al. Stiffness of modified Type 1a linear external skeletal fixators. Vet Comp Orthop Traumatol 2007; 20: 264-268.
• 33 Muir P, Johnson KA, Markel MD. Area moment of inertia for comparison of implant cross-sectional geometry and bending stiffness. Vet Comp Orthop Traumatol 1995; 8: 146-152.
• 34 O´Doherty DM. Stress protection due to external fixation. J Biomech 1995; 28: 575-586.
• 35 DeAngelis MP, Old RB, Stoll SG. et al. Repair of fractures of the radius and ulna in small Dogs. J Am Anim Hos Assoc 1973; 9: 436-441.
• 36 Silva HR, Clements DN, Yeadon R. et al. Linear-circular external skeletal fixation of intra-condylar humeral fractures with supracondylar comminution in four cats. Vet Comp Orthop Traumatol 2012; 25: 61-66.
• 37 Worth AJ. Management of fractures of the long bones of eight cats using external skeletal fixation and a tied-in intra-medullary pin with a resin-acrylic bar. N Z Vet J 2007; 55: 191-197.
• 38 Ross JT, Matthiesen DT. The use of multiple pin and methylmethacrylate external skeletal fixation for the treatment of orthopaedic injuries in the dog and cat. Vet Comp Orthop Traumatol 1993; 6: 115-121.
• 39 Yu J, DeCamp CE, Rooks R. Improving surgical reduction in radial fractures using a ‘dowel’ pinning technique in miniature and toy breed dogs. Vet Comp Orthop Traumatol 2011; 24: 45-49.
• 40 Shani J, Shahar R. The unilateral external fixator and acrylic connecting bar, combined with I.M pin, for the treatment of tibial fractures. Vet Comp Orthop Traumatol 2002; 15: 104-110.
• 41 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: 541-548.
• 42 Staudte KL, Gibson NR, Read RA. Evaluation of a metal acrylic repair product as a clamp for an external fixator. Vet Comp Orthop Traumatol 2004; 17: 97-103.
• 43 Bennett RA, Egger EL, Histand M. et al. Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation. Vet Surg 1987; 16: 207-211.
• 44 Anderson MA, Mann FA, Wagner-Mann C. et al. A Comparison of nonthreaded, enhanced threaded, and Ellis fixation pins used in type 1 external skeletal fixators in dogs. Vet Surg 1987; 16: 207-211.