Investigation of Bioabsorbable Screw Usage for Long Bone Fracture Repair in the Horse: Interfragmentary Compression and Axial Load Response in Equine Cadaver Longbone Fractures

Summary

The purpose of the study was to compare biomechanical features of bioabsorbable, self-reinforced poly-L-lactic acid (SR-PLLA) and stainless steel (ASIF) 4.5 mm cortical screws. Tests were conducted in equine cadaver third metacarpal bones in which a simulated complete and displaced condylar fracture had been created by osteotomy.

An evaluation of the amount of interfragmental compression achieved with each screw type was performed using electrical resistance strain gauges placed in proximity to the osteotomy. This revealed a substantial increase in interfragmental compression when ASIF screws were used compared to the SR-PLLA screw. A hybrid of the two screw types did however achieve adequate interfragmental compression. Comparison of the strength of fracture fixation through response to axial loading revealed significant difference between use of three ASIF screws and a hybrid of one SR-PLLA and two ASIF screws (p = 0.04) or two ASIF (p = 0.01) screws alone. It appeared that the hybrid configuration did have a mechanical advantage over the two ASIF screw arrangement.

The results indicate that the SR-PLLA screw is inferior to the stainless steel screw as a means of primary fracture reduction in the horse. A less mechanically demanding role may yet enable usage of the bioabsorbable screws in equine fracture repair, although they proved inadequate in this testing environment.

This study examined the inter-fragmental compression and response to axial loading of bioabsorbable and stainless steel 4.5 mm cortical screws in simulated condylar fractures in equine cadaver longbones. The stainless steel screw was superior in both compression and response to axial loading. It was concluded that the bioabsorbable screw did not possess characteristics that would allow it to bring about adequate primary fracture repair.

Keywords

Bioabsorbable - interfragmental compression - fixation strength

• REFERENCES

• 1 Rick MC, O’Brien TR, Pool RR, Meagher DM. Condylar fractures of the third metacarpal bone and third metatarsal bone in 75 horses: Radiographic features, treatments and outcome. JAVMA 1983; 183 (03) 287-96.
• 2 Meagher DM. Lateral condylar fractures in the metacarpus and metatarsus in horses. Proc Am Assoc Equine Pract 1976; 22: 147-54.
• 3 Raiha JE, Parchman M, Krook L. et al Fixation of trochanteric osteotomies in laboratory beagles with absorbable screws of polylactic acid. V.C.O.T 1990; 3: 123-9.
• 4 Suuronen R, Pohjonen P, Taurio R. et al Strength and strength retention of self-reinforced poly-L-lactide screws and plates. In vivo and in vitro study. J Oral Maxillofac Surg 1991; 49: 989-95.
• 5 Field JR, Hearn TC, Arighi M. Investigation of bioabsorbable screw usage for longbone fracture repair in the horse: Biomechanical features. V.C.O.T 1993; 6: 42-6.
• 6 Field JR. Screw torque and interfragmentary compression in equine cadaver longbone fractures. V.C.O.T 1993; 6: 163-5.
• 7 Cordey J, Rahn BA, Perren SM. Human torque control in the use of bone screws. In: Current Concepts of Internal Fixation of Fractures. Uhthoff HK. ed Berlin: Springer; 1980: 235-43.
• 8 Cordey J, Florin P, Veihelmann D. et al The control of torque applied to screws and the compression achieved is self compressing plates. In Biomechanics V, Asmussen P, Joergensen L. eds Baltimore: University Park Press; 1978: 235-43.
• 9 Richardson D. Third metacarpal/metatarsal condylar fractures. In: Current Practice of Equine Surgery. White NA, Moore JN. eds Philadelphia: Lippincott; 1990: 617-22.
• 10 Schatzker J. Personal communication. 1995