Paprosky femur defect. Artwork of bone degradation in a type IIIA lateral femur cortex defect (Paprosky classification system). This system is used to assess revision (replacement or repair) of a hip implant. The ball and socket part of the implant is at top. The rest of the implant consists of a shaft inside the femur (thigh bone). The amount of degradation in the cortical (outer) bone layer determines the amount of bone grafting needed, and whether a cementless implant can replace a cemented one. Type IIIA indicates a large bone defect extending down to the shaft (see C016/6620). Named for US surgeon Wayne G. Paprosky, the classification was developed in the 1980s and 1990s.