Intraoperative torsion control with radiological cortical thickness parameters in distal tibial shaft fractures: a cadaveric study

Intramedullary nailing is a common and safe procedure in the treatment of distal tibial shaft fractures. It is often accompanied with maltorsion of the tibia due to insufficient intraoperatively available and objective diagnostic tools. Therefore there´s high need for reliable tools for intraoperative torsional control. Radiographic parameters such as the Cortical Step Sign (CSS) and the Diameter Difference Sign (DSS) may serve for diagnosing relevant maltorsion intraoperatively. The aim of this study was to investigate the effect of maltorsion on CSS and DSS parameters in a distal tibial fracture model and to construct a prognostic model to detect maltorsion. A distal tibial shaft fracture (AO/OTA type “A”) was set on 19 human tibias. Torsion was gradually adjusted from 0° to 30° in external and internal torsion. Images were acquired with a C-arm in two planes and transferred to a PC for measurement of medial cortical thickness (MCT), lateral cortical thickness (LCT), tibial diameter (TD) in a.p., and anterior cortical thickness (ACT), posterior cortical thickness (PCT), and transverse diameter (TD lat.) in lateral view of the proximal and distal fragment. For the various levels of torsion significant differences for each of the values of the examined variables could be shown. Highest visibility was found for ACT, TD a.p. and TD lat. Highest correlation of radiographic difference and maltorsion was found in internal torsion (TD lat./ TD a.p.). A threshold of less than 2 mm led to a probability to detect maltorsion of 0.7. ROC for the lateral model was better than for the a.p. model (0.866 vs. 0.829). TD lat. performed best regarding ROC in single parameter evaluation (0.778). Best prediction for relevant maltorsion was obtained with TD a.p. and TD lat. CSS and DSS are useful tools for detection of maltorsion in distal tibial shaft fractures. The parameters can be easily collected and therefore represent promising parameters for intraoperative torsional control.