Short communicationO 002- Is it the right moment to change how we report kinetics?
Introduction
During gait analysis, inverse dynamics calculations output the net forces and moments at the joints of the lower limbs. To facilitate clinical interpretation, the net moment 3D vector may be decomposed onto the joint’s proximal or distal segment coordinate system, or projected onto the joint coordinate system (JCS) [1]. Although no standard choice exists, several authors have advocated the use of projection onto the joint coordinate system. However, most clinical software still uses the decomposition onto the distal segment’s coordinate system.
Children with femoral torsional deformities present large differences in the medio-lateral orientation of the proximal part of the femur, modelled with the neck axis, and the distal part, modelled with the condylar axis. These children often walk with large internal rotation of the condylar axis compared to the pelvis.
Section snippets
Research question
Would clinical interpretation change if hip moments were expressed in the joint coordinate system instead of the distal femoral coordinate system?
Methods
We used two datasets collected as part of previous projects [2,3]. DatasetA consisted of our laboratory normative dataset and originated from 35 typically developing children who underwent 3D gait analysis (3DGA). DatasetB consisted of 12 children with idiopathic increased femoral neck anteversion who underwent 3DGA and low-dose biplanar radiography, which allowed us to specify personalised joint centres and axes registered to the skin markers in a standing position [2]. In both datasets,
Results
Fig. 1 presents graphically the hip moment expressed in the distal and JCS. Fig. 2 presents graphically the number of limbs that had a change in test outcome depending on if the moment was expressed in either the distal or JCS. On average, over stance phase, there was a 20% change in test outcome for both the sagittal and coronal hip moment.
Discussion
The choice of expressing the hip moment in either the distal or JCS had a significant effect on the clinical interpretation. We advocate the use of the JCS because of the interpretation of the moment components as individual motor torques and the link with the calculation of power
References (3)
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