People may have different limb lengths because of trauma or infection (acquired) or, because of hypoplasia or dysplasia of the femur or tibial (congenital). Unequal leg length can cause a limp, limit functional ability and have effect on other joints.
Lengthening of an abnormally short lower limb can be done after an osteotomy using an external fixation device. This exerts force along the long axis of the bone to induce new bone formation (distraction osteogenesis). The main problems with external fixation include infection of the pin tracts, and external frames that are impractical and aesthetically unacceptable. Once the external fixation is removed, in some people with underlying bone pathology, new bone is augmented by either an internal plate fixation or an intramedullary nail.
Once inserted and fixed, intramedullary distraction systems can be lengthened over time using different techniques. The aim is to lengthen the bone in a controlled manner.
With this procedure, under general anaesthesia, an osteotomy is done while avoiding damage to the periosteum and its blood supply. The adjustable intramedullary nail-like device is then implanted into the intramedullary space. Its proximal and distal sections are fixed to the relevant section of the bone with sterile locking screws. It then exerts a force along the long axis of the bone, which stimulates new bone formation (distraction osteogenesis) in the gap, causing bone lengthening. Over days, weeks or months, sequential distractions are used to produce the target limb length.
Different devices achieve distraction in different ways.
Soon after the procedure, with help from the physiotherapy team, people are able to partially weight bear. After clinical assessment, and when there is radiological evidence of adequate bone consolidation across the gap, full weight bearing is possible. The intramedullary device is usually removed after about 2 years using standard surgical techniques.