earm model contains one solid (forearm), exhibits 2 dof for the
   elbow

   INPUT
   - OsteoArticularModel: osteo-articular model of an already existing
   model (see the Documentation for the structure)
   - k: homothety coefficient for the geometrical parameters (defined as
   the subject size in cm divided by 180)
   - Signe: side of the forearm 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 