People may have different limb lengths caused by trauma or infection or, more rarely, hypoplasia or dysplasia (congenital conditions such as achondroplasia, Ollier's disease, and brachial plexus palsy). The condition can be unilateral or bilateral. Unequal limb lengths can lead to disability and limit functional ability.
Lengthening of a short upper limb can be attempted using external fixation devices, which exert force along the long axis of bone to induce new bone formation (called distraction osteogenesis). The main potential problems with external fixation include infection of the pin tracts, and external frames that are impractical and aesthetically unpleasant. In some people with an underlying bone pathology, once the external fixation is removed, the new bone is augmented by either an internal plate fixation or an intramedullary nail.
Intramedullary distraction systems are intramedullary devices that are similar to intramedullary nails used for managing fractures. Once inserted and fixed, they can be mechanically lengthened over time using different techniques, resulting in a controlled lengthening of the bone. The device can be inserted into the humerus from the top (antegrade), though this may cause damage to the shoulder muscles, or the lower end (retrograde).
Under general anaesthesia, a humeral osteotomy is done avoiding damage to the periosteum and its blood supply. The adjustable nail-like intramedullary device is then implanted into the intramedullary canal, and the proximal and distal sections of the device are fixed to the appropriate section of the humerus with sterile locking screws. Once implanted and fixed, the length of the device can be adjusted to provide an appropriate amount of compression and allow bony alignment at the osteotomy site. The device exerts a force along the long axis of the bone, which stimulates new bone formation (distraction osteogenesis) in the gap, causing bone lengthening. Over a period of days, weeks or months, sequential distractions are used to produce the target limb length.
Different devices achieve distraction in different ways. For example, some work mechanically by releasing a preloaded spring or using a motor. Others use an external electromagnetic device.
The intramedullary device remains implanted until bone consolidation is completed. When there is radiological evidence of adequate bone consolidation across the gap, full function and limb use (weight bearing) is permitted. The device can usually be removed using standard surgical techniques or may be left in place indefinitely.