Anterior cruciate ligament fixation: is radial force a predictor of the pullout strength of soft-tissue interference...

In anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.

The objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.

Controlled laboratory study.

A resultant force (F(R)) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F(R) was measured while each device was inserted into synthetic bone mounted on a test machine (n=5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50mm/min. The pullout strength was measured as the ultimate load before failure (n=10 for each device).

The F(R) values generated during insertion into synthetic bone were 777 ± 86N, 865 ± 140N, 1313 ± 198N, and 1780 ± 255N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125N, 716 ± 249N, 1147 ± 142N, and 1233 ± 190N, respectively.

These results suggest that the F(R) generated during interference fixation affects the pullout strength with sheath-based devices providing superior F(R) compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.

These results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.