A tissue prosthesis insertion system (80) includes a first assembly (10) comprising a plurality of nested tubes (12), one of the tubes being a carrier tube (14) which, in use, receives a component (16) of a tissue prosthesis at a distal end of the carrier tube (14). A magnetic mount (44) is carried at a proximal end of the first assembly (10). A second assembly (82) is removably attachable to the first assembly (10). An attachment device (92) is carried at a distal end of the second assembly (92), the attachment device (92) being responsive to the magnetic mount (44) of the first assembly (10), the magnetic mount (44) and the attachment device (92) carrying complementary engaging formations to facilitate hermetic sealing between the magnetic mount (44) and the attachment device (92).