The effect of intramedullary pin size and monocortical screw configuration on locking compression plate-rod constructs in an in vitro fracture gap model

Summary

Objective: To investigate the effect of intramedullary pin size in combination with various monocortical screw configurations on locking compression plate-rod constructs.

Methods: A synthetic bone model with a 40 mm fracture gap was used. Locking compression plates with monocortical locking screws were tested with no pin (LCP-Mono) and intramedullary pins of 20% (LCPR-20), 30% (LCPR-30) and 40% (LCPR-40) of intramedullary diameter. Locking compression plates with bicortical screws (LCP-Bi) were also tested. Screw configurations with two or three screws per fragment modelled long (8-hole), intermediate (6-hole), and short (4-hole) plate working lengths. Responses to axial compression, biplanar four-point bending and axial load-to-failure were recorded.

Results: LCP-Bi were not significantly different from LCP-Mono control for any of the outcome variables. In bending, LCPR-20 were not significantly different from LCP-Bi and LCP-Mono. The LCPR-30 were stiffer than LCPR-20 and the controls. The LCPR-40 constructs were stiffer than all other constructs. The addition of an intramedullary pin of any size provided a significant increase in axial stiffness and load to failure. This effect was incremental with increasing intramedullary pin diameter. As plate working length decreased there was a significant increase in stiffness across all constructs.

Clinical significance: A pin of any size increases resistance to axial loads whereas a pin of at least 30% intramedullary diameter is required to increase bending stiffness. Short plate working lengths provide maximum stiffness. However, the overwhelming effect of intramedullary pin size obviates the effect of changing working length on construct stiffness.

Keywords

Plate-rod - intramedullary pin size - monocortical - screw configuration - working length

• References

• 1 Reems MR, Beale BS, Hulse DA. Use of a plate-rod construct and principles of biological osteosynthesis for repair of diaphyseal fractures in dogs and cats: 47 cases (1994-2001). J Am Vet Med Assoc 2003; 223: 330-335.
• 2 Hulse D, Hyman W, Nori M. et al. Reduction in plate strain by addition of an intramedullary pin. Vet Surg 1997; 26: 451-459.
• 3 Hulse D, Ferry K, Fawcett A. et al. Effect of intramedullary pin size on reducing bone plate strain. Vet Comp Orthop Traumatol 2000; 13: 185-190.
• 4 Egol KA, Kubiak EN, Fulkerson E. et al. Biomechanics of locked plates and screws. J Orthop Trauma 2004; 18: 488-493.
• 5 Kubiak EN, Fulkerson E, Strauss E. et al. The evolution of locked plates. J Bone Joint Surg Am 2006; 88 Suppl (Suppl. 04) 189-200.
• 6 Chao P, Lewis DD, Kowaleski MP. et al. Biomechanical concepts applicable to minimally invasive fracture repair in small animals. Vet Clin North Am Small Anim Pract 2012; 42: 853-872.
• 7 Goh CS, Santoni BG, Puttlitz CM. et al. Comparison of the mechanical behaviors of semicontoured, locking plate-rod fixation and anatomically contoured, conventional plate-rod fixation applied to experimentally induced gap fractures in canine femora. Am J Vet Res 2009; 70: 23-29.
• 8 Gautier E, Sommer C. Guidelines for the clinical application of the LCP. Injury 2003; 34: 63-76.
• 9 Perren SM. The concept of biological plating using the limited contact - dynamic compression plate (LC-DCP). Injury 1991; 22 Supplement (Suppl. 01) 1-41.
• 10 Perren SM. Evolution of the internal fixation of long bone fractures. The scientific basis of biological internal fixation: choosing a new balance between stability and biology. J Bone Joint Surg Br 2002; 84: 1093-1110.
• 11 Korvick DL, Monville JD, Pijanowski GJ. et al. The effects of screw removal on bone strain in an idealized plated bone model. Vet Surg 1988; 17: 111-116.
• 12 Marti A, Fankhauser C, Frenk A. et al. Biomechanical evaluation of the less invasive stabilization system for the internal fixation of distal femur fractures. J Orthop Trauma 2001; 15: 482-487.
• 13 Fulkerson E, Egol KA, Kubiak EN. et al. Fixation of diaphyseal fractures with a segmental defect: a biomechanical comparison of locked and conventional plating techniques. J Trauma 2006; 60: 830-835.
• 14 Stoffel K, Dieter U, Stachowiak G. et al. Biomechanical testing of the LCP - how can stability in locked internal fixators be controlled?. Injury 2003; 34: 11-19.
• 15 Johnson AL, Houlton JEF, Vannini R. AO principles of fracture management in the dog and cat. Switzerland: AO Publishing; 2005
• 16 Silbernagel JT, Kennedy SC, Johnson AL. et al. Validation of canine cancellous and cortical polyurethane foam bone models. Vet Comp Orthop Traumatol 2002; 15: 200-204.
• 17 Glyde M, Day R, Hosgood G. The effect of screw number and plate stand-off distance on the biomechanical characteristics of 3.5mm locking compression plate (LCP) and 3.5mm string of pearls (SOP) plate constructs in a synthetic fracture gap model. Proceedings of the European College of Veterinary Surgery 20^th Annual Scientific Meeting; 2011 July 7-9. 2011. Ghent, Belgium:
• 18 Gautier E, Perren SM, Cordey J. Effect of plate position relative to bending direction on the rigidity of a plate osteosynthesis. A theoretical analysis. Injury 2000; 31 Suppl (Suppl. 03) C14-20.
• 19 Tomlinson JL. Fractures of the humerus. In Slatter D. editor Small Animal Surgery. 3rd ed. Philadelphia: Saunders; 2003: 1905-1918.
• 20 Langley-Hobbs SJ. Fractures of the humerus. In Tobias KM, Johnston SA. editors Veterinary Surgery Small Animal. St Louis, Missouri: Saunders; 2012: 709-723.
• 21 Chao PN, Conrad BP, Lewis DD. et al. Effect of plate working length on plate stiffness and cyclic fatigue life in a cadaveric femoral fracture gap model stabilized with a 12-hole 2.4 mm locking compression plate. BMC Vet Res 2013; 9: 125.
• 22 Maxwell M, Horstman CL, Crawford RL. et al. The effects of screw placement on plate strain in 3.5 mm dynamic compression plates and limited-contact dynamic compression plates. Vet Comp Orthop Traumatol 2009; 22: 125-131.
• 23 Field JR, Tornkvist H, Hearn TC. et al. The influence of screw omission on construction stiffness and bone surface strain in the application of bone plates to cadaveric bone. Injury 1999; 30: 591-598.
• 24 Hoffmeier KL, Hofmann GO, Muckley T. Choosing a proper working length can improve the lifespan of locked plates. A biomechanical study. Clin Biomech (Bristol, Avon) 2011; 26: 405-409.
• 25 Delisser PJ, McCombe GP, Trask RS. et al. Ex vivo evaluation of the biomechanical effect if varying monocortical screw numbers on a plate-rod canine femoral gap model. Vet Comp Orthop Traumatol 2013; 26: 177-185.
• 26 Ahmad M, Nanda R, Bajwa AS. et al. Biomechanical testing of the locking compression plate: when does the distance between bone and implant significantly reduce construct stability?. Injury 2007; 38: 358-364.
• 27 Zahn K, Frei R, Wunderle D. et al. Mechanical properties of 18 different AO bone plates and the clamp-rod internal fixation system tested on a gap model construct. Vet Comp Orthop Traumatol 2008; 21: 185-194.
• 28 DeTora M, Kraus K. Mechanical testing of 3.5 mm locking and non-locking bone plates. Vet Comp Orthop Traumatol 2008; 21: 318-322.
• 29 Cordey J. Introduction: basic concepts and definitions in mechanics. Injury 2000; 31 Suppl (Suppl. 02) S-B1-13.
• 30 von Pfeil DJ, Dejardin LM, DeCamp CE. et al. In vitro biomechanical comparison of a plate-rod combination-construct and an interlocking nail-construct for experimentally induced gap fractures in canine tibiae. Am J Vet Res 2005; 66: 1536-1543.
• 31 Riggs CM, DeCamp CE, Soutas-Little RW. et al. Effects of subject velocity on force plate-measured ground reaction forces in healthy Greyhounds at the trot. Am J Vet Res 1993; 54: 1523-1526.
• 32 Miller DL, Goswami T. A review of locking compression plate biomechanics and their advantages as internal fixators in fracture healing. Clin Biomech (Bristol, Avon) 2007; 22: 1049-1062.
• 33 ElMaraghy AW, ElMaraghy MW, Nousiainen M. et al. Influence of the number of cortices on the stiffness of plate fixation of diaphyseal fractures. J Orthop Trauma 2001; 15: 186-191.
• 34 Gordon S, Moens NM, Runciman J. et al. The effect of the combination of locking screws and non-locking screws on the torsional properties of a locking-plate construct. Vet Comp Orthop Traumatol 2010; 23: 7-13.
• 35 Demner D, Garcia TC, Serdy MG. et al. Biomechanical comparison of mono- and bicortical screws in an experimentally induced gap fracture. Vet Comp Orthop Traumatol 2014; 27: 422-429.