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Stripping torque as a predictor of successful internal fracture fixation
Author(s) -
Edwards Thomas R.,
Tevelen Greg,
English Hugh,
Crawford Ross
Publication year - 2005
Publication title -
anz journal of surgery
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.426
H-Index - 70
eISSN - 1445-2197
pISSN - 1445-1433
DOI - 10.1111/j.1445-2197.2005.03497.x
Subject(s) - washer , torque , fixation (population genetics) , internal fixation , medicine , load cell , stripping (fiber) , femoral shaft , external fixation , biomedical engineering , composite material , femur , materials science , orthodontics , surgery , structural engineering , mechanical engineering , external fixator , population , physics , environmental health , engineering , thermodynamics
Background: Internal fixation of fractures using plates and screws is a common method of treatment. Occasionally the internal fixation fails prior to fracture healing. This often requires revision surgery. Determining the force that internal fixation needs to withstand postoperatively would enable this force to be applied intraoperatively as a test to predict successful fixation. The purpose of the present paper was to determine the minimum stripping torque needed to predict successful internal fixation strength. Methods: The pull‐out strength and stripping torque relationships of 4.5‐mm cortical bone screws in Sawbones polyurethane foam were determined. Screw forces were directly measured using an LCM load cell washer on a model intertrochanteric neck of femur fracture fixed with 135° 4‐hole pin and plate loaded to single leg stance conditions. Additionally a 135° 4‐hole pin and plate was mounted on foam blocks and loaded until failure of the shaft screws from the foam occurred. Predicted stripping torque/yield load was determined. Results: Pull‐out strength and stripping torque of 4.5‐mm cortical bone screws in polyurethane foam have a high degree of linear correlation R 2 = 0.95. Direct measurement of shaft screw forces at single leg stance conditions were 585−686 N. This correlated with a stripping torque of 0.9 Nm. Load to yield testing at single leg stance conditions corresponded to a stripping torque of 1.8 Nm. Conclusion: Withstanding 0.9−1.8 Nm of torque during insertion of the femoral shaft screws of a 135° 4‐hole pin and plate predicts that the construct will successfully withstand single leg stance.