Abrasion of artificial ligaments: a simulative study.
Abrasion failure of artificial ligaments possibly occurs in the early postoperative stages prior to the lining of bone tunnels with protective tissue. The effect of abrasion on the strength and stiffness of a polyester ligament was studied by implanting it in cadaveric knees, which were cyclically flexed through a physiologically relevant range, while subjecting the implant to tension of 300 N. The test was performed using ten cadaveric knees: (a) applying 49 000 load cycles to simulate the postoperative period after which the protective tissue fills the bony tunnel; (b) with the mouth of the bone tunnel radiused or left as after drilling the tunnel, and (c) for each of the two above conditions, with and without a protective sleeve surrounding the implant where it emerges from the tunnel. Following the tests, the implant strength was reduced by 33% when the mouth of the tunnel was not radiused, and by 28% when it was radiused, by 14% when the implant was protected without radiusing the tunnel exit, and by 13% when the tunnel was radiused. The stiffness was reduced by between 39% and 47% for the four conditions tested. It appears that the effect of abrasion is ameliorated by using a protective sleeve and by radiusing the mouth of the bone tunnels through which the implant is placed. The effect of the protective sleeve appears to be greater than that of just radiusing the tunnels, but it is appropriate to benefit from the combined effect of both measures.