Limb Length Inequality
Ashok Johari
Consulting Pediatric Orthopedic, Bombay Hospital, B.J.Wadia Children's Hospital, Children's Orthopedic Centre, Mumbai, India
First Created: 02/20/2001 

Introduction

A limb length discrepancy in a child is a source of concern and anxiety for the parents and the attending pediatrician. This discrepancy may have a number of causes that also influence its natural history. A thorough clinical examination for the cause, magnitude of a discrepancy, and the associated problem is important. This discrepancy has to be measured accurately and projection made of the expected discrepancy at skeletal maturity. Finally, on this background, management decisions have to be taken.

In the past, limb-lengthening surgery acquired a poor reputation because of a lack of understanding of the biological principles involved and the poor technique and technology associated with it. In recent years many advances have taken place in these areas and utilizing these advances we can now achieve lengthening never possible before. Whereas formerly the recommended lengthening ranged up to 20% of the original length of the bone, currently 100% or more lengthening is possible. It is practical today to lengthen any long bone, even the phalanges, and metacarpals. Besides this, diverse applications of lengthening devices have been found which can solve a number of complicated orthopedic problems in children e.g. correction of deformities of bones and joints with or without lengthening, simultaneous lengthening of different bones, double lengthening in a single bone, bone transportation, healing of recalcitrant non-unions and enhancement of the stature to name a few. The possibilities are immense and the field is poised at a very exciting stage with promise and potential for the future.

Causes of Limb Length Inequality

Table 1 lists the common causes of limb length inequality encountered in pediatric practice

Table 1: Causes of limb length discrepancy

  • Congenital

  • Infection

  • Post traumatic

  • Neoplasms

  • Irradiation

  • Skeletal Dysplasias

  • Miscellaneous

Congenital causes are the best-known reasons for a limb length discrepancy. They are the most difficult to treat also. Examples are the congenital short femur and the spectrum of proximal focal femoral deficiencies which may exhibit a shortening in the range of 6% to 90% of the femoral length, the partial or total absence of the tibia and fibula, etc. Other congenital causes of discrepancy would be conditions like hemihypertrophy giving rise to lengthening and the constriction band syndrome.

Infection can cause shortening in a variety of ways e.g. by causing joint dislocation or by damaging the growth plate. By asymmetric damage to the growth plate, angular and complex deformities can be produced along with shortening. Depending on the growth contribution of a growth plate, the age of the patient at the time of physeal damage and the extent of the growth plate damage whether partial or total, minimal or large amount of shortening can be produced. An example is a complete damage to the lower femoral epiphysis inhibiting 70% of the femoral growth or 40% of the total lower limb length. Roughly an inhibition of 1 cm would take place per year of remaining growth. However, this is true only for the latter years of growth. A third way by which infection can cause limb length discrepancy is by causing a pathological fracture which mal-unites.

Posttraumatic malunions would cause an immediate discrepancy in limb length. However, damage to growth following trauma would cause an insidious increase in the discrepancy. Interestingly, accurate reduction of fractures e.g. of the femur or tibia may give rise to a lengthening because of growth stimulation.

Neoplasms and irradiation also act by causing growth plate damage. Some skeletal dysplasias e.g. Ollier's or hereditary multiple exostosis cause shortening of a limb by affecting the growth plate.

Miscellaneous causes of limb shortening would include paralytic causes e.g. poliomyelitis which causes an inhibition of growth. Reduced mass and activity coupled with an abnormal vasomotor control may be responsible for this. Perthes disease and slipped capital femoral epiphysis cause shortening by early fusion across the growth plate and by causing varus of the upper femur. Rarely shortening can be iatrogenic following surgery in the vicinity of a growth plate or following varus osteotomies of the upper femur which shortens the limb.

Patterns of Increase in Limb Length Discrepancy

This is an important factor to consider when planning treatment. If lengthening is carried out in a condition that is progressive e.g. Ollier's diseases, a repeat lengthening would be required at skeletal maturity. On the other hand, posttraumatic malunions may give rise to a static limb length discrepancy.

Shapiro has studied the growth patterns in lower extremity length discrepancies and classified them into 5 patterns. Important in this is type 1 or an upward slope pattern in which the length discrepancy increases with time at the same proportional rate. This happens for example in the proximal focal femoral deficiencies in Ollier's disease and with physical damage.

Other patterns show varying responses with time, e.g. Type V which shows a gradual reversal of the limb discrepancy with time. This underlines the importance of a repeated and regular evaluation and charting of the discrepancy to enable conclusions to be formed about the projected final limb length discrepancy.

Evaluation of Limb Length Discrepancy

The clinical examination

A thorough clinical examination is a must and this would demand a degree of expertise in evaluating the true lower limb lengths, in evaluating the role of other concomitant deformities like flexion/abduction deformity at the hip or pelvic obliquity due to other causes.

True lower limb lengths are obtained by squaring the pelvis if possible and keeping the lower limbs in an identical position. Measurement of the length is taken from the anterior superior iliac spine to the knee joint line and the second from the knee to the medial malleolus indicating the tibial length.

Apparent limb lengths are measured by keeping both lower limbs parallel to each other and in the long axis of the body. It does not take any note of the position of the pelvis which will not be square if there are hip deformities of abduction or adduction or suprapelvic contractures giving a pelvic obliquity. If these deformities are not all correctable or not to be corrected, the apparent limb length will form the basis for all calculations of the discrepancy.

In the clinical examination, it would be important to assess the status of all joints for the presence of deformity, the joint range of motion & stability, the local neurovascular status, and the gait of the patient. A thorough general examination is mandatory. Wooden blocks are used to level the pelvis on standing to assess the discrepancy and the raise, which may be required. An easy method of knowing what the patient will be like functionally after lengthening - temporary shoe lifts can be given and the patient assessed.

When considering the enhancement of stature, it is important to measure the ratio of the upper segment to that of the lower segment, the sitting height, and sub-ischial limb length as well as the upper limb lengths and their level relative to the lower limbs on standing.

Radiographic Measurement of Limb Length Discrepancy

Because clinical measurement of limb lengths has some fallacies and inter-observer errors, x-rays are utilized for limb length measurements. Two commonly employed methods of x-ray measurement are the teleoroentgenogram and the scanogram. Both techniques use a radio-opaque ruler kept alongside the extremity during the exposure.

The teleoroentgenogram is used for small children below the age of 5 to 6 years. In this, a single exposure is made from the hip to the ankles and the length read on the ruler markings. The scanogram is used for larger children and it utilizes sequential exposures of the hips, knees, and ankles and reads their level on the ruler. This technique requires that the child be still so that the lower limb position in relation to the ruler is not altered during different exposures. These techniques provide a reliable method of storing data for future reference and for calculating the final growth discrepancy.

Limb lengths can also be measured utilizing CT scans but at present this is costly. Ultrasound has also been employed for this but is subject to inter-observer errors.

Projection of limb length discrepancy

It is important to know what the final discrepancy of limb length at skeletal maturity will be. A rough idea can be gained by repeated measurements and calculation of the percentage inhibition in relation to the normal limb. The growth of the normal limb in terms of percentile is charted and on this basis, the length of the normal limb at maturity is calculated. Applying the percentage inhibition the length of the affected limb can be calculated.

There are a number of fallacies involved in these methods. Firstly growth does not proceed linearly. It is age-dependent and in the case of the affected lower limb, it is dependent on the etiology of limb shortening. Secondly, normal limb length data is not available for the Indian population. The available charts are those of the Green - Anderson growth prediction chart and the Moseley straight line graph. Thirdly, the skeletal age according to the Greulich and Pyle's atlas itself is an approximation.

Menelaus predicts growth by a simple method of calculating the growth of the distal femur at 3/8 inch per year and that of the proximal tibia at 1/4 inch per year in adolescents over 9 years of old age. Growth ceases at age 14 years in girls and in age 16 years in boys.

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 a 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 than 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.

Surgery for Equalization of Limb Lengths

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 hyperemia around the growth plate but the results were unpredictable with a long 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 be 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 reason, 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 the 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 be 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, the 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 endpoint 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 that 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 place, 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 fragmented relationship to each other is maintained. By keeping the distraction rate at an optimum level, the regenerate always fills the gap created.

Other Applications of Limb Lengthening Devices

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 that 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 tumors, and pseudarthrosis. In this situation or bone loss following trauma or 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. The 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 muscle 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 - Images


Limb Length Inequality


Limb Length Discrepancy

Complications

In spite of all recent advances, limb-lengthening surgery is fraught with complications relating to the bone and joints, muscles, vessels, and nerves. The commonest problems are:

  • Pin tract infection, which is prevented by proper pin track care. If this is not controlled pin loosening is inevitable.

  • joint deformities and loss of range of motion because of the pull on the muscles during lengthening. This requires sustained physiotherapy.

  • Malpositioning of the bone fragments and consequent deformity because of selective muscle pull, the stronger muscles pulling the bone in their direction. This requires correction during lengthening or after it but before the bone consolidates.

  • Vessel and nerve damage by improperly placed 'k' wires - a complication peculiar to the ring devices, which employ 'k' wires. These can be prevented by proper study of limb cross-sectional anatomy.


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