A procedure to refine joint kinematic assessments: Functional Alignment

Functional Alignment is a new method to determine the orientation of a joint's primary rotational axis and the associated movement. It employs three unique concepts. First, data analyses are based upon assessment of spatial positions and not upon movement in a time sequence. Second, analyses are conducted on derived joint rotation matrices instead of tracked markers. This permits reanalysis of published biomechanical results and, therefore, provides a basis for unifying perspectives among different research efforts. Finally, the independent perspectives of the move and base segments require the analysis to use two unique descriptors of the joint axis orientation. These two mathematically necessary descriptors are also shown to be obtainable without reference to the original marker data. The combination of these approaches provides opportunities for additional comparisons of kinematic joint features that have been heretofore underappreciated.