Biomechanical testing of hamstring graft tibial tunnel fixation with bioabsorbable interference screws

This study evaluated the failure mode, maximum load at failure, displacement at failure, and stiffness differences of quadrupled hamstring graft-tibial tunnel fixation using 28-mm, tapered 35-mm, or bicortical 17- and 20-mm bioabsorbable interference screws (Arthrex, Naples, FL). Biomechanical study. Nine matched pairs (18 specimens) of young cadaver tibias (mean bone mineral density [BMD] = 0.847 g/cm 2, range, 0.689 to 1.11 g/cm 2) were divided into 3 groups of 6 specimens. Kruskal Wallis analysis of variance and Mann-Whitney U tests post hoc comparisons were used to assess group differences ( P < .05). Maximum load at failure for the 28-mm screw was 488.2 ± 197 N, with a displacement of 18.4 ± 7.5 mm and a stiffness modulus of 38.9 ± 7.0 N/mm. Maximum load at failure for the tapered 35-mm screw was 844.8 ± 121.4 N, with a displacement of 15.3 ± 1.6 mm and a stiffness modulus of 70.5 ± 21.1 N/mm. Maximum load at failure for bicortical screw fixation was 543.7 ± 266.5 N, with a displacement of 17.7 ± 6.6 mm and a stiffness modulus of 57.7 ± 14.9 N/mm. Fixation using the tapered 35-mm screw displayed greater maximum load at failure than either 28-mm screw fixation ( P = .015) or bicortical screw fixation ( P = .037). Significant differences were not evident for displacement. Both tapered 35-mm ( P = .016) and bicortical screw ( P = .026) fixation displayed greater stiffness than 28-mm screw fixation. All constructs failed by pullout. Fixation using a single tapered 35-mm screw displayed increased maximum load at failure compared with the 28-mm screw or bicortical fixation. Both the tapered 35-mm screw and bicortical fixation showed greater stiffness than fixation using a 28-mm screw. Use of a single 35-mm screw for quadrupled hamstring graft-tibial tunnel fixation may be preferred for patients with poor tibial BMD.