Comparison of knee joint orientation in clinically versus biomechanically aligned computed tomography coordinate system

This study aims to establish a relation between the knee-centred clinical coordinate system (CCS) and a biomechanical coordinate system (BCS) based on the Mikulicz line.MethodsCT data sets of 45 lower extremities were evaluated. Using VGStudio Max, a visualisation and measurement software program; each CT data set was aligned according to the CCS and BCS. After superimposing both the aligned data sets, the deviations of both coordinate systems in all three planes were measured with the centre of the knee defined as the origin.FindingsFor the coronal plane, the CCS was demonstrated to be 2.54° in adduction compared to the BCS [standard deviation (SD) = 1.8°]. In sagittal view, the CCS was demonstrated to be 0.3° retroversed (SD = 3.27°). Finally, the deviation in the axial plane showed an outward rotation of 3.39° (SD = 1.99°). The alignment as well as the measurements demonstrated high intraobserver and interobserver reproducibility.InterpretationBoth coordinate systems can be established in knee-centred CT data sets in a reproducible manner. Clearly, the CCS differs significantly from the BCS describing the biomechanical axis, but mathematical-based adaptations and corrections can be performed.The translational potential of this articleThe findings of this study allow a mathematical conversion of a knee CT to the biomechanical axis of the leg.

Source: Journal of Orthopaedic Translation - August 9, 2018 Category: Orthopaedics Source Type: research