Deinonychus's pelvis had been modified so that the pubis was swung back and laid parallel to the ischium (McGowan, 1991). Although this has not been seen before in Theropods it is unusual because the pubis is usually inclined forward. Thus it looks more like a birds hip then a lizards hip.
The femur of Deinonychus was modified so that a large leg-retracting muscle could be attached. This was accompolished by having an extention of bone on the femurs trailing edge for the muscles attachment (McGowan, 1991).
Both of these features are adaptations for a powerful downward slashing motion of the foot (McGowan, 1991)