Torsion

Torsion testingBiomechanical Testing of Fracture Fixation Devices

Torsional fractures

Torsional fractures usually initiated at smallest cross-sections: upper and lower 1/3 of humerus, femur, and fibula; upper 1/3 of radius; lower of ulna and tibia; and mid-clavicleCross-locking IM rods are used for torsional stabilityTargeting devices help place cross-locking screws using fluoroscopy (C-arm)For unstable fractures (location, comminution), bone plates are used (open surgery)2

Case Study: Biomechanical Testing of Clavicle Fracture Fixation DevicesTreatment for clavicle fractures:Conservative (sling and rest)Non-conservative (surgery w/plate or pin)When is surgery necessary?Shortening of more than 2 cmComminutedIf nonunion occurs Difficult for surgeons to determine appropriate fixation configuration

Objectives of StudyCompare the strength and stiffness of fracture fixation devices used to treat clavicle fracturesDetermine mode of failure of devices in torsion and bendingCalculate amount of elastic and plastic deformation in torsion and bendingProvide mechanical data to help clarify and inform clinical practice and experience

Synthes 2.7 mm DCDynamic Compression2.7 mm thickThinnest of all platesEasily bent into shape during surgery Low profile

Synthes 3.5 mm LCDC3.5 mm thickLimited Contact Dynamic Compression (LCDC)Bent into shape during surgery

Synthes 3.5 mm Locking LCDC3.5 mm thickLocking Limited Contact Dynamic CompressionLocks screw to plateBent in to shape during surgery

www.synthes-stratec.com

Locking compression plates allow better reduction of displaced fractures

Synthes 3.5mm Reconstruction and Curved Reconstruction PlatesReconstruction plate (left) is manufactured straight and bent into shape during surgeryCurved Reconstruction plate (right) is manufactured with a curve

DePuy Active Compression Plate (ACP) Dynamic compressionTitaniumVery biocompatibleMore difficult to bend into shape during surgery

www.jnjgateway.com

DePuy Rockwood Clavicle PinImproved blood supply to boneNo bulky hardwareEasier to removeSmaller incision required

Method of Testing: Torsion Record load (Nm) vs. position (deg)Elastic range (osteotomy and segmental defect): Rotate 10 degrees at 5 deg/secMeasure stiffness (Nm/deg)Test to failure (segmental defect):Rotate to failure, 5 deg/secMeasure load and displacement at yield and failure points

Sample Torsion Test Results

Torsional stiffness is the slope of the line (applied torque/angle of twist)Note angle at the limit of elastic behavior = about 9 degrees. Clinically, angular deformation beyond 9 degrees would be unacceptable.13

Boxes with the same color are not significantly differently (p