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

PURPOSE: 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). TYPE OF STUDY: Biomechanical study.
METHODS: Nine matched pairs (18 specimens) of young cadaver tibias (mean bone mineral density [BMD] = 0.847 g/cm2, range, 0.689 to 1.11 g/cm2) 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).
RESULTS: 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.
CONCLUSIONS: 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.