Bone Lengthening

Limbs can be lengthened by creating new bone. An artificial break in the bone allows new tissue to form. If this new tissue is very slowly pulled apart, it stretches and allows lengthening of the bone. The new tissue gradually becomes solid over time. Typically this takes over 50 days for every centimetre of lengthening.

The bone is stretched 1mm each day. This can be achieved by one of two methods. One involves having a circular external fixator being applied to the leg. The other involves a telescopic metal rod being inserted within the bone.

Bones may need to be lengthened for a number of reasons. If the bone is short due to disease, injury or surgery, then this can have knock on effects such as back pain, hip pain, knee pain, ankle pain or wear and tear arthritis. The correction of a difference in the lengths in the bones can help reduce these problems, although it depends on how long they have been a problem whether the pain is completely resolved.


External Fixator Technique

The bone can be gradually pulled apart using an external fixator called a circular frame or Ilizarov frame. The metal rings in a fixator are connected to the bone underneath with wires and thicker metal pins. If the rings are pulled apart, then the bone they are connected to is pulled apart too. The bone has to be broken in order to allow the pulling apart. The mechanism to pull the rings apart can be through special rods that directly join the rings, or through a series of pistons which criss cross the space between the rings.

There are advantages and disadvantages to their use


Full weight bearing throughout the lengthening period

Working parts easy to adjust

Externally visible how much lengthening has been achieved

Less pain from application


Wires and pins lead to irritation of the skin or infection anywhere on the frame

Skin is dragged by the wires, and can lead to bunching up of skin which requires release

More pain from lengthening

Frame prevents normal clothes from being worn

Can be cumbersome and impractical


Expanding Nail Technique

The bone can be pulled apart from the inside with a metal rod within the bone. The metal rod is inserted within the bone, and is connected to the bone at both ends. A large magnetic device is applied over the top of the leg and this results in the motor in the metal rod extending the metal rod by a set amount. The bone has to be broken to allow the ends to be pulled apart. The number of times that the magnet is applied to the outside and for how long determines how much the metal rod expands. Xrays can show how much the bone has been pulled apart. Unless there are specific reasons, this is the method that we use nowadays to stretch the bone for correcting differences in leg length.


Completely within the bone

Can be worn with normal clothes

No dragging or bunching up of the skin

Less pain from lengthening


No weight bearing while the bone is lengthening and while it is calcifying

Can sometimes create an angulation of the bone

The motor can fail or the bone can fail to lengthen

More pain from application