Anteroposterior instability of the knee: a sign of congenital limb deficiency.

A clinical sign of anteroposterior instability of the knee has been noted in patients with evidence of a congenital lower limb deficiency. This instability can be a reliable diagnostic sign during infancy when radiologic deficiency is barely evident. Furthermore this sign is evidence that apparent isolated deficiencies of femur, tibia, or fibula are actually deficiency in the development of the entire limb.