Purpose: Bioabsorbable interference screw design may influence biomechanical characteristics.
This study compared the insertion torque and load at failure characteristics of 2
types of screws during retrograde fixation of a soft-tissue graft. Type of Study: Biomechanical study. Methods: Eight matched pairs of doubled 100-mm long tibialis anterior allografts were prepared
and fixed in appropriately sized tunnels created in 10 lb/ft3 (0.16 g/cm3) dense synthetic bone blocks using screws of similar length and root and thread diameter
designed with either a large buttress thread with a smaller taper or small buttress
thread with a larger taper. Insertion torque was measured at one-third, two-thirds,
and full screw insertion. After the graft fixation constructs were mounted in a servohydraulic-testing
device with the loading axis aligned directly with the tunnel and preloaded to 25
N, they were cycled 3 times from 0 to 50 N, and then subjected to a 20 mm/minute traction
force to failure. Results: All constructs failed by graft slippage past the screw. Mean maximum load at failure
(360.5 ± 68 N v 341.6 ± 58 N, P = .2) and stiffness (63.6 ± 16 N/mm2 v 66.4 ± 14 N/mm2, P = .89) was similar between constructs fixed with a large buttress thread small-taper
screw and small buttress thread large-taper screw, respectively. The small buttress
thread screw with a large taper displayed greater mean insertion torque at one-third
insertion (4.1 ± 0.57 in-lb v 3.2 ± 0.49 in-lb, P = .03), whereas the large buttress thread screw with a small taper displayed greater
mean insertion torque at full insertion (11.1 ± 0.74 in-lb v 9.4 ± 1.3 in-lb, P = .012). Mean differences were not observed at two-thirds screw insertion (P = .12). Conclusions: Large buttress thread small-taper screws displayed biomechanical fixation characteristics
comparable to small buttress thread large-taper screws. Clinical Relevance: Given reports of superior screw-graft–bone tunnel contact area, these biomechanical
results suggest that use of a large buttress screw with a small taper may be preferable
for retrograde soft-tissue graft fixation.
Key Words
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Article info
Footnotes
Supported by the University of Louisville Summer Research Scholar’s Program.
Identification
Copyright
© 2005 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.
