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Assessment of two augmentation techniques on the mechanical properties of titanium cannulated bone screws

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  • 1 1Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996.
  • | 2 2Center of Renewable Carbon, University of Tennessee, Knoxville, TN 37996.

Abstract

OBJECTIVE

To determine the effects of 2 augmentation techniques on the mechanical properties of titanium cannulated bone screws.

SAMPLE

33 titanium cannulated bone screws (outer diameter, 6.5 mm; guide channel diameter, 3.6 mm).

PROCEDURES

11 screws were allocated to each of 3 groups. The guide channel of each screw was filled with polymethyl methacrylate bone cement alone (OCS group) or in combination with a 3.2-mm-diameter orthopedic pin (PCS group) or remained unmodified (control group) before mechanical testing. Each screw underwent a single-cycle 3-point bending test to failure with a monotonic loading rate of 2.5 mm/min. Failure was defined as an acute decrease in resistance to load of ≥ 20% or a bending deformation of 15 mm. Mechanical properties were determined for each screw and compared among the 3 groups.

RESULTS

All screws in the control and OCS groups and 1 screw in the PCS group broke during testing; a 15-mm bending deformation was achieved for the remaining 10 screws in the PCS group. Maximum load and load at failure differed significantly among the 3 groups. Stiffness and load at yield for the PCS group were significantly greater than those for the control and OCS groups but did not differ between the control and OCS groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of bone cement and an orthopedic pin to fill the guide channel of cannulated screws significantly increased the strength of the construct, but ex vivo and in vivo studies are necessary before this augmentation technique can be recommended for clinical patients.

Abstract

OBJECTIVE

To determine the effects of 2 augmentation techniques on the mechanical properties of titanium cannulated bone screws.

SAMPLE

33 titanium cannulated bone screws (outer diameter, 6.5 mm; guide channel diameter, 3.6 mm).

PROCEDURES

11 screws were allocated to each of 3 groups. The guide channel of each screw was filled with polymethyl methacrylate bone cement alone (OCS group) or in combination with a 3.2-mm-diameter orthopedic pin (PCS group) or remained unmodified (control group) before mechanical testing. Each screw underwent a single-cycle 3-point bending test to failure with a monotonic loading rate of 2.5 mm/min. Failure was defined as an acute decrease in resistance to load of ≥ 20% or a bending deformation of 15 mm. Mechanical properties were determined for each screw and compared among the 3 groups.

RESULTS

All screws in the control and OCS groups and 1 screw in the PCS group broke during testing; a 15-mm bending deformation was achieved for the remaining 10 screws in the PCS group. Maximum load and load at failure differed significantly among the 3 groups. Stiffness and load at yield for the PCS group were significantly greater than those for the control and OCS groups but did not differ between the control and OCS groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of bone cement and an orthopedic pin to fill the guide channel of cannulated screws significantly increased the strength of the construct, but ex vivo and in vivo studies are necessary before this augmentation technique can be recommended for clinical patients.

Contributor Notes

Dr. Zarzosa's present address is Austin Veterinary Animal Clinic, 1550 Lennoxville Rd, Beaufort, NC 28516.

Address correspondence to Dr. Mulon (pmulon@utk.edu).