Limb Length Inequality

Ashok Johari
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Management of Limb Length Discrepancy
Important considerations
- Below 2 cms of limb length discrepancy, no surgery is advisable. Beyond this discrepancy, surgery becomes a relative indication considering the total circumstances of the case.

- In growing children the decision to lengthen has to be made very carefully after considering the etiology of the limb length discrepancy and the projected shortening at maturity. It is feasible to recover 6 to 8 cms of discrepancy at one lengthening with a low incidence of problems.
Hence children whose projected shortening at maturity is within this range need only one surgery carried out at maturity. Others with much larger discrepancies may need 2 or 3 repeat lengthening and these could be phased out during the growth period. Beyond 6 to 8 cms of lengthening, even with modern techniques, there is likelihood of some problems or complications arising during the lengthening, hence it may be better to achieve the goal of limb length equality in two lengthenings.

- It is possible to achieve bone lengthening at any age but beyond maturity the incidence of complications with bone healing is higher and increases with age. Hence lengthening surgery is advisable around the maturity period rather then much beyond it.

- In neurologically affected or stiff lower limbs, it may be better to leave the extremity slightly short to allow for better clearance from the ground in walking.

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:
- The periosteum is important and should be minimally damaged at surgery so that its bone regeneration capabilities are preserved.
- The intramedullary blood supply is a large source of nourishment to the parent bone and needs to preserved. This is achieved by cutting the cortex in a circumferential manner (corticotomy) with minimal penetration into the medullary canal. New bone formation is better with this.
- The lengthening device should provide good stability to the bone so that healing is not disturbed.
- A delay of a few days before starting distraction is good as it allows a framework or lattice of tissue to form on which bone subsequently bridges.
- The distraction rate recommended is 1 mm in a day. In younger children and for larger lengthenings, it may be increased to 1.5 mm depending on the regeneration.
- The distraction frequency should, in practical terms, be 2 to 4 times daily i.e. 0.5 mm twice a day or 0.25 mm 4 times a day.
- The patient should as far as possible put weight on the operated extremity as this stimulates muscle action and blood supply of the bone and eliminates osteoporosis which would lead to pin loosening. Joint motion is to be maintained by physiotherapy.
- After a phase of lengthening, time has to be given for the new bone to consolidate. The lengthening device is removed once it is judged that consolidation is good. The approximate time to consolidation is 1 month per cm/ lengthening in children.

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.

Correction of bone and joint deformity:
Simultaneously with limb lengthening or even otherwise, fixation devices can be used for correction of bone and joint deformities. In such instances the bone is divided and fractionally distracted in the direction of correction. This corrects the deformity and preserves the length of the bone in comparison to open surgery, which in the usual form is closed wedge osteotomy, which shortens the bone. The lengthening device is used here to create an 'open wedge' of new bone. Further lengthening if required can be carried out either with or after the correction. Such correction would be useful in deformities due to rickets and allied situations, post traumatic malunions etc.

Joint deformities can be corrected by distracting the joint. This is especially useful where the muscles around the joint are weak. By open lengthening, this muscle power could be diminished and this may reduce a muscle which barely pulls against gravity to one which can not. Joint deformity correction would be helpful in cases of arthrogryposis, congenital problems and acquired conditions like poliomyelitis, joint sepsis etc.

Deformity near the epiphyseal ends can be corrected by distracting the epiphysis through the growth plate. Lengthening can be also be carried out in this way. At present this epiphyseal distraction is recommended only in the period near to skeletal maturity as it is possible that the physis can be damaged.

Bone transportation:
A bone fragment can be transported in any direction to fill in a bone gap. Bone continuity can still be maintained by the new bone regeneration-taking place in the area from which the bone fragment is being removed.

The applications of this technique are many. Unhealthy bone can now be radically resected e.g. in osteomyelitis, bone tumours and pseudarthrosis. In this situation or in bone loss following trauma or in gap non-unions the resulting gap can be filled in by bone transportation without resort to bone grafting.

Non- unions
Healing of recalcitrant non-unions is possible using the fixation devices by providing stability and vascular stimulus. Stability is provided by the fixator devices and this allows healing of many non-unions of the hypertrophic variety. Vascular stimulus can be provided by distraction, by repeated cycles of compression and distraction or by corticotomy which increases the vascularity of the bone segment.

Double lengthening:
To reduce the time spent in lengthening, a bone can be divided at two levels and lengthening carried out from each level. This saves time in long lengthenings. Also the muscles elongation is provided at two sites rather than at one site. This distributes the stresses more uniformly throughout the muscle.

Enhancement of stature:
An interesting offshoot of lengthening technology is the possibility of enhancement of stature in dwarfed patients. The process is lengthy and may involve different strategies like simultaneous ipsilateral lengthening of a femur and tibia followed by the same procedure on the opposite side. Lengthening of both legs can be carried out followed by the thighs or of one leg and opposite thigh followed by the other. Each has its own advantages and disadvantages.

Changes in lower limb length change the body proportions and this limits the length that can be gained. This situation is best where the extremities are short in relation to the trunk i.e. in achondroplasia. Another problem posed by the procedure is that after lengthening of the lower limbs, the upper limbs appear short and these may have to be lengthened too.

Because of the complexities of the procedure, this is not one to be lightly recommended to any patient. All the pros and cons have to be gone into and special consideration has to be given to the motivation of the patient and his psychological stability to withstand a long treatment which may be in the range of a year or so.


Limb Length Inequality


Limb Length Discrepancy



References
Limb Length Inequality Limb Length Inequality 02/20/2001
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