after surgical implantation by bone tissue ingrowth at regions 3a 5a and 7a respectively thus for example after implantation region 5a will lie adjacent to the bone of the resected tibia an expanded side view in section of a part of region 5a expanded side views of regions 3a and 7a are identical is shown in fig2 as shown in fig1 and 2 tibial component 5 comprises a metallic substrate 20 a plastic tibial bearing surface element 32 and a porous coating 30 bonded to substrate 20 over region 5a both substrate 20 and coating 30 are made of the same corrosion resistant surgical implant metal or metal alloy e g titanium or a cobalt chromium molybdenum alloy e g vitallium howmedica inc new york n y coaring 30 consists of a multiplicity of generally spherical particles bonded together at their points of contact these particles define between themselves a three dimensional network of interconnected interstitial pores such as the pore shown by the arrow in fig2 in more detail coating 30 consists of first and second monolayers 22 and 24 of particles the particles e g particle 16 in layer 22 are bonded to substrate 20 and layer 22 is bonded to layer 24 as stated earlier the average pore size in porous coating 30 as determined by the well known technique of mercury intrusion.