Thank you Aditya, i ended up using a layer for my header, but your approach is more succint
\setupbackgrounds[page][background=mybg]
\setlayer[mybg] % name of the layer
[hoffset=2.5cm, voffset=0.2cm] % placement (from upper left corner of the layer)
{\framed[frame=off, background=color, backgroundcolor= , height=3cm]{
\starttabulate[|p|lrw(2cm)|pr|]
\NC \ss Clinique médico chirurgicale El Abrar\NC \externalfigure[logo.png][width=1cm, location=inline]\NC \ss Service de
cardiologie\NC \NR
\NC \ss\tfx Dr Yahyaoui .M.K \NC \NC \ss\tfx kaddourkardio(at)gmail.com \NC \NR \stoptabulate
}} % the actual contents of the layer
should i use the same layer for a sidebar, or better-off to define another layer ?