Important considerations

A number of procedures have been used to equalize limb lengths, but today the mainstay of treatment is lengthening.

In the past growth stimulation procedures were in vogue. These worked by causing a hyperemia around the growth plate but the results were unpredictable with a length gain of 1/2" - 3/4" in most cases and possibly a reduction in the ultimate shortening at maturity due to an increase in the growth velocity on the operated side. Such procedures may still have some role to play where the expected discrepancy at maturity is small.

Bone shortening procedures have never become popular as these need to carried out on the normal side. Inhibition of growth can also be caused by procedures, which staple the epiphysis. However in such cases precise calculations have to be made for timing the procedure. This would keep in mind the projected final length discrepancy and the rate of growth of the normal and abnormal limbs.

In cases where the magnitude of the final discrepancy is great and where that amount of lengthening may not be feasible for some reasons, amputation may be the treatment of choice. However the indications for such surgery are becoming less and less with the advent of modern methods of limb lengthening.

Biological principles

Ilizarov postulated the law of tension - stress, which, states that gradual traction on living tissues creates stresses that can stimulate and maintain the regeneration and active growth of certain tissue structures. This forms the basis of all limb lengthening surgery. His work has given us further insight into the role of different factors in the promotion of new bone formation when a bone is lengthened.

These factors are as follows:

Keeping these biological principles in mind, a good regenerate forms in the distracted gap and it is not necessary to graft the interval. The end point of this exercise is fixator removal. Repeat operation is usually unnecessary on this count.

Technical principles

Lengthening devices are of two types - a uniplanar system, which is fixed to one side of the extremity and a multiplanar system which grips the extremity in different directions e.g. the ring fixators. Each device has its own set of advantages and disadvantages.

Uniplanar lengtheners employ large threaded pins, which purchase the bone. These transfix tissues minimally but since they are located in one plane, are weak in resistance to bending in other planes. Ring fixators employ thin 'k' wires (1.2 to 1.5 mm diameter) which have good load bearing capacity on tensioning and can take loads as much as 130 kg. The resistance to bending is good because of their multidirectional placement but they transfix a lot of tissues.

The basic technique of lengthening comprises of sectioning the bone and distracting the two fragments of bone apart from each other at a defined rate. This distraction is done by the lengthening device, which is required to give stability to the bone fragments so that new bone can form in the gap and the fragment relationship to each other is maintained. By keeping the distraction rate at an optimum level, the regenerate always fills the gap created.