The original classification system was described by Ficat and Arlet in 1964 [2]. It consisted of Stages 1 through 4. Ficat proposed a modification in 1985 [1]. This latter Ficat classification recognized five different stages of bone necrosis from Stage 0 to Stage 4 [1]. We describe here the Ficat classification system presented in 1985 [1]. We shall correlate it with the original Ficat and Arlet classification system [2] and the modified Ficat classification system [17]. The system evolved before the advent of MRI and used a bone scan and “functional exploration of bone (FEB)” for diagnosis of the preradiographic stage [2]. Three stages of FEB were described [2].