Biologic fixation of ligament prostheses and augmentations

Abstract

The biologic fixation (bone ingrowth) of three prosthetic ligament devices (bovine xenograft Xenotech Labora tories, Inc., Irvine, CA; Gore-Tex, W. L. Gore and As sociates, Flagstaff, AZ; and knitted dacron, Stryker, Kalamazoo, MI) and one ligament augmentation device (LAD, braided polypropylene, 3M, St. Paul, MN) were evaluated in vivo. The devices were placed unstressed, in an extraarticular location in the cortical-cancellous bone of the proximal femur and humerus of dogs. Six months following implantation tissue ingrowth was eval uated using high resolution radiography, routine histol ogy, scanning electron microscopy, and biomechanical tensile tests to measure the ultimate (maximum) pull- out strength of the devices.

The knitted dacron and Gore-Tex prosthesis showed marked ingrowth of trabecular bone into the interstices of the device with evidence of bone growth around individual fibers of the prosthesis. The bovine xenograft demonstrated bone immediately adjacent to the mate rial with evidence of spicular ingrowth of bone into the natural clefts of the prosthesis. The LAD showed no evidence of bone ingrowth and demonstrated a fibrous tissue interface between the prosthesis and surround ing trabecular bone.

Six months following implantation the pull-out strengths of the devices were as follows: knitted dac ron, 445.7 ± 151.ON; Gore-Tex, 438.1 ± 131.94N; bovine xenograft, 332.8 ± 64.2N; and LAD, 78.4 ± 47.9N. Statistical analysis revealed no significant differ ence between the pull-out strengths of the knitted dacron, Gore-Tex, and bovine xenograft. While the pull- out strength of the LAD was significantly lower (P < 0.01) than the other devices it should be noted that this device was designed as a temporary augmentation for biological grafts and as such permanent biological fix ation through bone ingrowth is neither required nor desired. The Gore-Tex, LAD, and bovine xenograft devices all failed by pulling out of the bone tunnel, while all the dacron grafts failed by separation of the dacron outer sleeve of the prosthesis from its inner dacron reinforcement. This rupture occurred at the entrance of the graft into the bone tunnel.