Influence of thread design on bioabsorbable interference screw insertion torque during retrograde fixation of a soft-tissue graft in synthetic bone.
OBJECTIVE
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.


METHODS
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/ft 3 (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/mm 2 v 66.4 +/- 14 N/mm 2 , 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.


CONCLUSIONS
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.
Wozniak
Tanya D
TD
Division of Sports Medicine, Department of Orthopaedic Surgery, University of Louisville, Louisville, Kentucky 40202, USA.
Kocabey
Yavuz
Y
Klein
Scott
S
Nyland
John
J
Caborn
David N M
DN
D020341:Absorbable Implants; D001696:Biomechanical Phenomena; D001863:Bone Screws; D016025:Bone Transplantation / Q000379:methods*; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D016268:Internal Fixators; D008422:Materials Testing; D019651:Plastic Surgery Procedures / Q000295:instrumentation / Q000379:methods; D013537:Sutures; D013977:Tibia / Q000601:surgery*; D019415:Torque; D014184:Transplantation, Homologous