f the thigh model ('R' for right side or 'L' for left side)
   - Mass: mass of the solids
   - AttachmentPoint: name of the attachment point of the model on the
   already existing model (character string)
   OUTPUT
   - Human_model: new osteo-articular model (see the Documentation
   for the structure) 
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 Licence
 Toolbox distributed under GPL 3.0 Licence
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 Authors : Antoine Muller, Charles Pon