wholly of metal and the intercondylar guide may have a plastics surface suitable plastics materials for the sheath of the guide post and the meniscal component may be ultra high molecular weight polyethylene fig1 to 18 show a second embodiment in which the femoral component has a lower surface which is continuous the femoral component 110 is usually a metal casting or forging and includes a pair of condylar portions 112 having curved bearing surfaces 113 shaped to cooperate with corresponding bearing surfaces 121 of a plastics meniscal component 130 pegs 120 serve to fix the femoral component into the resected femur recesses 124 are provided to receive bone cement a patella track is provided on the anterior portion 118 between the condylar portions 112 is located a box like structure 134 having a downwardly open mouth for receiving an abutment or peg 119 see fig1 18 peg 119 is fixed to a metal tibial base plate 201 having an anterior rim stop 202 the peg 119 comprises a metal core 204 having a plastic sheath 205 projecting through a slot 206 in the meniscal component 130 as can be seen in fig1 and 18 the peg 119 has a sloping posterior face 127 which engages on a rounded face 126 in the interior of the box structure 134 when the prosthesis is in its extended position the tip of the peg 119 is located within a recess 128 in the box like structure in this condition the joint is stabilised in an a p direction by interaction of the anterior face of the peg and the anterior wall 140 of the box like structure also the prosthesis is stabilised laterally by the interaction between.