Influence of bolt tightening torque, wire size, and component reuse on wire fixation in circular external fixation.
OBJECTIVE
To evaluate the effects of bolt torque, wire size, and component reuse on the ability to maintain wire tension in 3 external skeletal fixation systems.


METHODS
Biomechanical study.


METHODS
Yield strength in tension of 1.0-, 1.2-, 1.5-, and 1.6-mm-diameter wires, and yield strength in torque of Hofmann Small Bone Fixation (SBF) cannulated and slotted bolts and IMEX regular and miniature bolts were determined on a testing machine. The minimum bolt tightening torque needed to prevent wire slippage at clinically recommended wire tensions was determined. Components were tested 10 times, and loads at slippage were recorded.


RESULTS
The IMEX system required a mean of 8 Nm of bolt tightening torque to maintain 900 N (1.6-mm wires). The SBF system required a mean of 3 Nm bolt torque to maintain 300 N (1.0-mm wires) and 5 Nm to maintain 600 N (1.2-mm wires). The SBF cannulated bolt required 9 Nm of torque to maintain 900 N (1.5-mm wires). The SBF slotted bolts could only maintain 800 N before yield. The IMEX miniature system required a mean bolt torque of 1.1 Nm to maintain 300 N. The cannulated and slotted bolts from both manufacturers failed to maintain 70% of initial wire tension after 7 and 4 uses, respectively.


CONCLUSIONS
The IMEX systems and the SBF system using 1.0- and 1.2-mm wires could maintain clinically recommended wire tension safely. Only the IMEX system could maintain clinically recommended wire tension safely using 1.5- or 1.6-mm wires.


CONCLUSIONS
The SBF system using 1.0- and 1.2-mm wires and the IMEX system using all wire sizes can maintain clinically relevant wire tension. The SBF system using 1.5-mm wires could not. Cannulated and slotted bolts should not be used more than 6 and 3 times, respectively. Nuts should not be reused.
Wosar
Marc A
MA
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA.
Marcellin-Little
Denis J
DJ
Roe
Simon C
SC
D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000662:veterinary; D001864:Bone Wires / Q000662:veterinary; D004868:Equipment Failure; D005592:Fracture Fixation / Q000379:methods / Q000662:veterinary*; D009984:Orthopedic Fixation Devices / Q000662:veterinary*; D019415:Torque