Lengthening is appropriate to consider in children 8 to 12 years of age who have a predicted leg-length discrepancy at maturity of 5 cm or more. The discrepancy in a skeletally immature child should be greater than can be corrected with epiphysiodesis of the long limb, which by convention has been considered to be approximately 5 cm. Muscle strength should be sufficient so that little power is lost by lengthening. However, even gradual lengthening may cause several systemic complications, including transient hypertension, anorexia and weight loss, and emotional lability. Lengthening the bone by more than 15% increases the complication rate.

The technique of limb lengthening known as distraction osteogenesis was introduced by Ilizarov in 1951 (see Plate 4-36). After subperiosteal division of the bone at the diaphysis or metaphysis (corticotomy) without disturbing the medullary canal, the bone fragments are fixed above and below with an external fixation device. The Ilizarov device incorporates metal rings that encircle the limb and attach to the bone with thin metal wires or half pins. Telescoping rods connect the rings and provide the distraction capability. The De Bastiani device, called a dynamic axial fixator, is a rigid telescoping bar that attaches to one side of the limb with screws (see Plate 4-36).