My husband got shot in his upper thigh. femur got replaced with metal rod. why is his leg shorter than the other? will this affected his back?

Yes: The doctors who placed rod were perhaps not as skillful as they might have been, although placement of a metal rod to replace a shattered femur, to save a leg, and preserve function is no mean feat. In the old days it would have been simply off with the leg. A unilateral short leg can impose mechanical stress on sacroiliac joints of the pelvis and, over time with repetative stress, loosen them.