The effect of different torque wrenches on rotational stiffness in compressive femoral nails: a biomechanical study.

Abstract

Rotation instability and locking screws failure are common problems. We aimed to determine optimal torque wrench offering maximum rotational stiffness without locking screw failure. We used 10 conventional compression nails, 10 novel compression nails and 10 interlocking nails with 30 composite femurs. We examined rotation stiffness and fracture site compression value by load cell with 3, 6 and 8Nm torque wrenches using torsion apparatus with a maximum torque moment of 5Nm in both directions. Rotational stiffness of composite femur-nail constructs was calculated. Rotational stiffness of composite femur-compression nail constructs compressed by 6Nm torque wrench was 3.27±1.81Nm/angle (fracture site compression: 1588N) and 60% more than that compressed with 3Nm torque wrench (advised previously) with 2.04±0.81Nm/angle (inter fragmentary compression: 818N) (P=0.000). Rotational stiffness of composite-femur-compression nail constructs compressed by 3Nm torque wrench was 2.04±0.81Nm/angle (fracture site compression: 818N) and 277% more than that of interlocking nail with 0.54±0.08Nm/angle (fracture site compression: 0N) (P=0.000). Rotational stiffness and fracture site compression value produced by 3Nm torque wrench was not satisfactory. To obtain maximum rotational stiffness and fracture site compression value without locking screw failure, 6Nm torque wrench in compression nails and 8Nm torque wrench in novel compression nails should be used.