TY - JOUR
T1 - Effect of off-axis screw insertion, insertion torque, and plate contouring on locked screw strength
AU - Gallagher, Bethany
AU - Silva, Matthew J.
AU - Ricci, William M.
PY - 2014/7
Y1 - 2014/7
N2 - Objectives: This study quantifies the effects of insertion torque, off-axis screw angulation, and plate contouring on the strength of locking plate constructs. Methods: Groups of locking screws (n = 6-11 screws) were inserted at 50%, 100%, 150%, and 200% of the manufacturer-recommended torque (3.2 Nm) into locking compression plates at various angles: orthogonal (control), 5-degree angle off-axis, and 10-degree angle off-axis. Screws were loaded to failure by a transverse force (parallel to the plate) either in the same ("+") or opposite direction ("-") of the initial screw angulation. Separately, locking plates were bent to 5 and 10-degree angles, with the bend apex at a screw hole. Locking screws inserted orthogonally into the apex hole at 100% torque were loaded to failure. Results: Orthogonal insertion resulted in the highest average load to failure, 2577 ± 141 N (range, 2413-2778 N), whereas any off-axis insertion significantly weakened constructs (165-1285 N, at 100% torque) (P < 0.05). For "+" loading, torque beyond 100% did not increase strength, but 50% torque reduced screw strength (P < 0.05). Loading in the "-" direction consistently resulted in higher strengths than "+" loading (P < 0.05). Plate contouring of 5-degree angle did not significantly change screw strength compared with straight plates but contouring of 10-degree angle significantly reduced load to failure (P < 0.05). Conclusions: To maximize the screw plate interface strength, locking screws should be inserted without cross-threading. The mechanical stability of locked screws is significantly compromised by loose insertion, off-axis insertion, or severe distortion of the locking mechanism.
AB - Objectives: This study quantifies the effects of insertion torque, off-axis screw angulation, and plate contouring on the strength of locking plate constructs. Methods: Groups of locking screws (n = 6-11 screws) were inserted at 50%, 100%, 150%, and 200% of the manufacturer-recommended torque (3.2 Nm) into locking compression plates at various angles: orthogonal (control), 5-degree angle off-axis, and 10-degree angle off-axis. Screws were loaded to failure by a transverse force (parallel to the plate) either in the same ("+") or opposite direction ("-") of the initial screw angulation. Separately, locking plates were bent to 5 and 10-degree angles, with the bend apex at a screw hole. Locking screws inserted orthogonally into the apex hole at 100% torque were loaded to failure. Results: Orthogonal insertion resulted in the highest average load to failure, 2577 ± 141 N (range, 2413-2778 N), whereas any off-axis insertion significantly weakened constructs (165-1285 N, at 100% torque) (P < 0.05). For "+" loading, torque beyond 100% did not increase strength, but 50% torque reduced screw strength (P < 0.05). Loading in the "-" direction consistently resulted in higher strengths than "+" loading (P < 0.05). Plate contouring of 5-degree angle did not significantly change screw strength compared with straight plates but contouring of 10-degree angle significantly reduced load to failure (P < 0.05). Conclusions: To maximize the screw plate interface strength, locking screws should be inserted without cross-threading. The mechanical stability of locked screws is significantly compromised by loose insertion, off-axis insertion, or severe distortion of the locking mechanism.
KW - biomechanics
KW - insertion torque
KW - locked screw
KW - off-axis
UR - http://www.scopus.com/inward/record.url?scp=84903304702&partnerID=8YFLogxK
U2 - 10.1097/BOT.0000000000000042
DO - 10.1097/BOT.0000000000000042
M3 - Article
C2 - 24343255
AN - SCOPUS:84903304702
SN - 0890-5339
VL - 28
SP - 427
EP - 432
JO - Journal of orthopaedic trauma
JF - Journal of orthopaedic trauma
IS - 7
ER -