Anterior Cruciate Ligament Soft Tissue Graft Fixation in the Elderly: Is There a Reason to Use Interference Screws? A Human Cadaver Study

Abstract

To analyze the ultimate failure load, yield load, stiffness, and cyclic resistance of different anterior cruciate ligament (ACL) soft tissue graft fixation techniques in osteopenic bone. In this study, 24 fresh-frozen human cadaveric tibiae (mean age 82.6years; range 56-96; 6 male and 6 female donors) were used. Quantitative computed tomography was performed to match bone density. Looped porcine flexor tendon grafts were chosen as ACL graft substitutes for tibial graft fixation techniques (n= 8 each): (1) hybrid fixation with an interference screw and extracortical button fixation; (2) extracortical button fixation; and (3) interference screw fixation. In single cycle mode, constructs were loaded to failure to evaluate stiffness, yield load, and maximum load. In cyclic testing, 2,000 cycles (25-100N) were applied followed by loading to failure. A 1-way analysis of variance was performed with significance set at P= .05. Hybrid fixation resulted in significantly higher yield load (283.4 ± 86.19N; P= .0037) and maximum load (407.9 ± 102.3N; P= .0026) than interference screw fixation (yield load 176.4 ± 26.03, max load 231.8 ± 94.06N) in elderly bone. Yield load after extracortical button fixation (252.9 ± 41.97N; P= .0286) was also higher than that after interference screw fixation, but stiffness (18.98 ± 9.154N/mm; P= .0041) was less than that after hybrid fixation (37.28± 13.53N/mm). Of 8 specimens in the interference screw group, 7 did not survive 2,000 cycles and failed by graft slippage, whereas all other specimens in both other groups survived. Tibial hybrid fixation of ACL soft tissue grafts provides less vertical graft movement than extracortical button fixation and higher primary failure loads than interference screw fixation in elderly bone. In this elderly human joint invitro model, tibial hybrid fixation provides biomechanical advantages over other techniques. Graft fixation with only an interference screw should be avoided in osteopenic bone.