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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.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare the mechanical characteristics of polymerized caprolactam and monofilament nylon loops with those of the cranial cruciate ligament (CCL) in cattle.

Sample—6 femorotibial joints harvested from 3 cows and suture constructs made from No. 8 polymerized caprolactam, 80-lb test monofilament nylon fishing line, and 450-lb test monofilament nylon fishing line.

Procedures—Joints were cleared of soft tissue structures except the CCL, connected to a load frame, and loaded to failure while measuring force and elongation. Synthetic constructs tested in a similar manner included single-stranded and 3-stranded No. 8 polymerized caprolactam, 3- and 6-stranded 80-lb test monofilament nylon fishing line, and 3- and 6-stranded 450-lb test monofilament nylon fishing line.

Results—The CCL ruptured at a mean ± SD force of 4,541 ± 1,417 N with an elongation of 2.0 ± 0.3 cm. The tensile strength of 3-stranded 450-lb test monofilament nylon fishing line was similar to that of the CCL, rupturing at loads of 5,310 ± 369 N (braided strands) and 6,260 ± 239 N (parallel strands). Elongation was greater for braided constructs.

Conclusions and Clinical Relevance—The 3-stranded cords of 450-lb test monofilament nylon fishing line most closely approximated the strength of the CCL. Marked increases in elongation occur when large-sized materials are constructed in braided configurations, and this elongation would likely not provide stability in CCL-deficient stifle joints. Additional studies are needed to determine whether any of these materials are suitable CCL replacements in cattle.

Full access
in American Journal of Veterinary Research