A Biomechanical Comparison of Headless Tapered Variable Pitch and AO Cortical Bone Screws for Fixation of a Simulated Slab Fracture in Equine Third Carpal Bones

Aloisio C D Bueno, Larry D Galuppo, Kenneth T. Taylor, David G. Jensen, Susan M Stover

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Objective - To compare the mechanical shear strengths and stiffnesses obtained from in vitro testing of a simulated complete third carpal bone (C3) frontal plane radial facet slab fracture (osteotomy) stabilized with either a 4/5 Acutrak (AT) compression screw or a 4.5-mm AO cortical bone (AO) screw inserted in lag fashion. Drilling, tapping, and screw insertion torques, forces, and times also were compared between AT and AO implants. Study Design - In vitro biomechanical assessment of site preparation, screw insertion, and shear failure test variables of bone screw stabilized simulated C3 slab fracture in paired cadaveric equine carpi. Sample Population - Eight pairs of cadaveric equine C3 without orthopedic abnormalities. Methods - Standardized simulated C3 slab fractures were repaired with either AO or AT screws (AO/C3 and AT/C3 groups, respectively). Drilling, tapping, and screw insertion torques, forces, and times were measured with a materials testing machine for each screw type. Repaired specimens were tested in axially oriented shear until failure. Paired Student's t-tests were used to assess differences between site preparation, screw insertion, and shear testing variables. Significance was set at P < .05. Results - There were no significant differences in bone fragment measurements of the standardized simulated C3 slab fractures created for AO or AT screws. There were no significant differences for mean and maximum drilling torques; however, the tapered AT drill had greater maximum drilling force compared with the 3.2-mm and 4.5-mm AO drill bits. Mean insertion torque and force measured from the self-tapping AT screw were not significantly different compared with the 4.5-mm AO tap. There were no significant differences in maximum screw torque among constructs. Total procedure time was significantly longer for the AT group (5.8 ± 1.6 minutes) compared with the AO group (2.9 ± 1.1 minutes; P = .001). AT stabilized specimens had significantly greater mean ± SD initial shear stiffness (3.64 ± 1.08 kN/mm) than AO specimens (1.64 ± 0.73 kN/mm; P = .005). All other shear mechanical testing variables were not statistically different among screw types. Conclusion-The 4/5 Acutrak insertion technique was accurate and safe, and the AT screw effectively stabilized simulated equine C3 frontal plane slab fractures. When tested in shear, this screw type was mechanically comparable to the 4.5-mm AO screw; however, AT constructs had greater initial shear stiffness. Initial shear stiffness was likely an indirect measure of interfragmentary compression, and thus may indicate that the AT screw provides a more rigid fixation for frontal plane C3 slab fractures in horses. Clinical Relevance - Considering the comparable mechanical behavior, greater initial shear stiffness for AT screw stabilized C3 slab fracture fragments, the ability to accurately insert the screw with the aid of a guide pin, and the potential for less persistent soft tissue irritation with the headless screw design, the 4/5 tapered AT screw is an attractive alternative for repair of C3 slab fractures in horses.

Original languageEnglish (US)
Pages (from-to)167-177
Number of pages11
JournalVeterinary Surgery
Volume32
Issue number2
DOIs
StatePublished - Mar 2003

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Bone Screws
Carpal Bones
slabs
Torque
screws
Horses
bones
horses
Mandrillus
shear stress
torque
Materials Testing
Shear Strength
drilling
Osteotomy
Orthopedics
Cortical Bone
Students
Bone and Bones
site preparation

ASJC Scopus subject areas

  • veterinary(all)

Cite this

A Biomechanical Comparison of Headless Tapered Variable Pitch and AO Cortical Bone Screws for Fixation of a Simulated Slab Fracture in Equine Third Carpal Bones. / Bueno, Aloisio C D; Galuppo, Larry D; Taylor, Kenneth T.; Jensen, David G.; Stover, Susan M.

In: Veterinary Surgery, Vol. 32, No. 2, 03.2003, p. 167-177.

Research output: Contribution to journalArticle

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abstract = "Objective - To compare the mechanical shear strengths and stiffnesses obtained from in vitro testing of a simulated complete third carpal bone (C3) frontal plane radial facet slab fracture (osteotomy) stabilized with either a 4/5 Acutrak (AT) compression screw or a 4.5-mm AO cortical bone (AO) screw inserted in lag fashion. Drilling, tapping, and screw insertion torques, forces, and times also were compared between AT and AO implants. Study Design - In vitro biomechanical assessment of site preparation, screw insertion, and shear failure test variables of bone screw stabilized simulated C3 slab fracture in paired cadaveric equine carpi. Sample Population - Eight pairs of cadaveric equine C3 without orthopedic abnormalities. Methods - Standardized simulated C3 slab fractures were repaired with either AO or AT screws (AO/C3 and AT/C3 groups, respectively). Drilling, tapping, and screw insertion torques, forces, and times were measured with a materials testing machine for each screw type. Repaired specimens were tested in axially oriented shear until failure. Paired Student's t-tests were used to assess differences between site preparation, screw insertion, and shear testing variables. Significance was set at P < .05. Results - There were no significant differences in bone fragment measurements of the standardized simulated C3 slab fractures created for AO or AT screws. There were no significant differences for mean and maximum drilling torques; however, the tapered AT drill had greater maximum drilling force compared with the 3.2-mm and 4.5-mm AO drill bits. Mean insertion torque and force measured from the self-tapping AT screw were not significantly different compared with the 4.5-mm AO tap. There were no significant differences in maximum screw torque among constructs. Total procedure time was significantly longer for the AT group (5.8 ± 1.6 minutes) compared with the AO group (2.9 ± 1.1 minutes; P = .001). AT stabilized specimens had significantly greater mean ± SD initial shear stiffness (3.64 ± 1.08 kN/mm) than AO specimens (1.64 ± 0.73 kN/mm; P = .005). All other shear mechanical testing variables were not statistically different among screw types. Conclusion-The 4/5 Acutrak insertion technique was accurate and safe, and the AT screw effectively stabilized simulated equine C3 frontal plane slab fractures. When tested in shear, this screw type was mechanically comparable to the 4.5-mm AO screw; however, AT constructs had greater initial shear stiffness. Initial shear stiffness was likely an indirect measure of interfragmentary compression, and thus may indicate that the AT screw provides a more rigid fixation for frontal plane C3 slab fractures in horses. Clinical Relevance - Considering the comparable mechanical behavior, greater initial shear stiffness for AT screw stabilized C3 slab fracture fragments, the ability to accurately insert the screw with the aid of a guide pin, and the potential for less persistent soft tissue irritation with the headless screw design, the 4/5 tapered AT screw is an attractive alternative for repair of C3 slab fractures in horses.",
author = "Bueno, {Aloisio C D} and Galuppo, {Larry D} and Taylor, {Kenneth T.} and Jensen, {David G.} and Stover, {Susan M}",
year = "2003",
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AU - Galuppo, Larry D

AU - Taylor, Kenneth T.

AU - Jensen, David G.

AU - Stover, Susan M

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N2 - Objective - To compare the mechanical shear strengths and stiffnesses obtained from in vitro testing of a simulated complete third carpal bone (C3) frontal plane radial facet slab fracture (osteotomy) stabilized with either a 4/5 Acutrak (AT) compression screw or a 4.5-mm AO cortical bone (AO) screw inserted in lag fashion. Drilling, tapping, and screw insertion torques, forces, and times also were compared between AT and AO implants. Study Design - In vitro biomechanical assessment of site preparation, screw insertion, and shear failure test variables of bone screw stabilized simulated C3 slab fracture in paired cadaveric equine carpi. Sample Population - Eight pairs of cadaveric equine C3 without orthopedic abnormalities. Methods - Standardized simulated C3 slab fractures were repaired with either AO or AT screws (AO/C3 and AT/C3 groups, respectively). Drilling, tapping, and screw insertion torques, forces, and times were measured with a materials testing machine for each screw type. Repaired specimens were tested in axially oriented shear until failure. Paired Student's t-tests were used to assess differences between site preparation, screw insertion, and shear testing variables. Significance was set at P < .05. Results - There were no significant differences in bone fragment measurements of the standardized simulated C3 slab fractures created for AO or AT screws. There were no significant differences for mean and maximum drilling torques; however, the tapered AT drill had greater maximum drilling force compared with the 3.2-mm and 4.5-mm AO drill bits. Mean insertion torque and force measured from the self-tapping AT screw were not significantly different compared with the 4.5-mm AO tap. There were no significant differences in maximum screw torque among constructs. Total procedure time was significantly longer for the AT group (5.8 ± 1.6 minutes) compared with the AO group (2.9 ± 1.1 minutes; P = .001). AT stabilized specimens had significantly greater mean ± SD initial shear stiffness (3.64 ± 1.08 kN/mm) than AO specimens (1.64 ± 0.73 kN/mm; P = .005). All other shear mechanical testing variables were not statistically different among screw types. Conclusion-The 4/5 Acutrak insertion technique was accurate and safe, and the AT screw effectively stabilized simulated equine C3 frontal plane slab fractures. When tested in shear, this screw type was mechanically comparable to the 4.5-mm AO screw; however, AT constructs had greater initial shear stiffness. Initial shear stiffness was likely an indirect measure of interfragmentary compression, and thus may indicate that the AT screw provides a more rigid fixation for frontal plane C3 slab fractures in horses. Clinical Relevance - Considering the comparable mechanical behavior, greater initial shear stiffness for AT screw stabilized C3 slab fracture fragments, the ability to accurately insert the screw with the aid of a guide pin, and the potential for less persistent soft tissue irritation with the headless screw design, the 4/5 tapered AT screw is an attractive alternative for repair of C3 slab fractures in horses.

AB - Objective - To compare the mechanical shear strengths and stiffnesses obtained from in vitro testing of a simulated complete third carpal bone (C3) frontal plane radial facet slab fracture (osteotomy) stabilized with either a 4/5 Acutrak (AT) compression screw or a 4.5-mm AO cortical bone (AO) screw inserted in lag fashion. Drilling, tapping, and screw insertion torques, forces, and times also were compared between AT and AO implants. Study Design - In vitro biomechanical assessment of site preparation, screw insertion, and shear failure test variables of bone screw stabilized simulated C3 slab fracture in paired cadaveric equine carpi. Sample Population - Eight pairs of cadaveric equine C3 without orthopedic abnormalities. Methods - Standardized simulated C3 slab fractures were repaired with either AO or AT screws (AO/C3 and AT/C3 groups, respectively). Drilling, tapping, and screw insertion torques, forces, and times were measured with a materials testing machine for each screw type. Repaired specimens were tested in axially oriented shear until failure. Paired Student's t-tests were used to assess differences between site preparation, screw insertion, and shear testing variables. Significance was set at P < .05. Results - There were no significant differences in bone fragment measurements of the standardized simulated C3 slab fractures created for AO or AT screws. There were no significant differences for mean and maximum drilling torques; however, the tapered AT drill had greater maximum drilling force compared with the 3.2-mm and 4.5-mm AO drill bits. Mean insertion torque and force measured from the self-tapping AT screw were not significantly different compared with the 4.5-mm AO tap. There were no significant differences in maximum screw torque among constructs. Total procedure time was significantly longer for the AT group (5.8 ± 1.6 minutes) compared with the AO group (2.9 ± 1.1 minutes; P = .001). AT stabilized specimens had significantly greater mean ± SD initial shear stiffness (3.64 ± 1.08 kN/mm) than AO specimens (1.64 ± 0.73 kN/mm; P = .005). All other shear mechanical testing variables were not statistically different among screw types. Conclusion-The 4/5 Acutrak insertion technique was accurate and safe, and the AT screw effectively stabilized simulated equine C3 frontal plane slab fractures. When tested in shear, this screw type was mechanically comparable to the 4.5-mm AO screw; however, AT constructs had greater initial shear stiffness. Initial shear stiffness was likely an indirect measure of interfragmentary compression, and thus may indicate that the AT screw provides a more rigid fixation for frontal plane C3 slab fractures in horses. Clinical Relevance - Considering the comparable mechanical behavior, greater initial shear stiffness for AT screw stabilized C3 slab fracture fragments, the ability to accurately insert the screw with the aid of a guide pin, and the potential for less persistent soft tissue irritation with the headless screw design, the 4/5 tapered AT screw is an attractive alternative for repair of C3 slab fractures in horses.

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