A radially expandable stent-graft endoprosthesis is provided. The graft included in the stent-graft is a knitted tubular structure circumferentially disposed and securably attached to the stent. The knitted tubular structure has a warp knit pattern of interlacing yarns with at least a two-needle underlap to provide greater than 150 percent longitudinal stretchability while substantially inhibiting dilation. A knitted tubular graft and a knitted medical fabric with greater than 150 percent longitudinal stretchability are also provided.