Orthoseek | Orthopedic Topics | Leg Length Discrepancy
What is it?
Leg length discrepancy (LLD) or Lower limb discrepancy is a conditionof unequal lengths of the lower limbs. The discrepancy may be in the femur,or tibia, or both. In some conditions, the whole side is affected, includingthe upper limbs. However, it is the discrepancy of the lower limbs thatcauses problems with ambulation, and the focus of this discussion willbe about lower limb discrepancy.
What causes it?
Some children are born with absence or underdeveloped bones in the lowerlimbs e.g., congenital hemimelia. Others have a condition called hemihypertrophythat causes one side of the body to grow faster than the other.
Sometimes, increased blood flow to one limb (as in a hemangioma or bloodvessel tumor) stimulates growth to the limb. In other cases, injury orinfection involving the epiphyseal plate (growth plate) of the femur ortibia inhibits or stops altogether the growth of the bone. Fractures healingin an overlapped position, even if the epiphyseal plate is not involved,can also cause limb length discrepancy.
Neuromuscular problems like polio can also cause profound discrepancies,but thankfully, uncommon.
Lastly, Wilms? tumor of the kidney in a child can cause hypertrophy ofthe lower limb on the same side. It is therefore important in a youngchild with hemihypertrophy to have an abdominal ultrasound exam done torule out Wilms? tumor.
It is important to distinguish true leg length discrepancy from apparentleg length discrepancy. Apparent discrepancy is due to an instabilityof the hip, that allows the proximal femur to migrate proximally, or dueto an adduction or abduction contracture of the hip that causes pelvicobliquity, so that one hip is higher than the other. When the patientstands, it gives the impression of leg length discrepancy, when the problemis actually in the hip.
What are the symptoms?
Many people walk around with LLD?s of up to 2 cm. and not even know it.
However, discrepancies above 2 cm. becomes more noticeable, and a slightlimp is present. But even up to 3 cm. a small lift compensates very well,and many patients are quite happy with this arrangement.
Beyond 3 cm. however, the limp is quite pronounced, and medical careis often sought at that point.
Walking with a short leg gait is not only unsightly, but increases energyexpenditure during ambulation. It could also put more stress on the longleg, and causes functional scoliosis.
Where the discrepancy is more severe, walking becomes grotesque or virtuallyimpossible.
What does your doctor do about it?
The key to treatment of LLD in a child is to predict what the discrepancyis at maturity. If it is predicted to be less than 2 cm., no treatmentis needed. Limb length discrepancies of up to 2 or 2.5 cm. can be compensatedvery well with a lift in the shoe. Beyond 2.5 cm., it becomes increasinglydifficult to compensate with a left in the insole. Building up the shoebecomes uncosmetic and cumbersome, and some other way of compensatingfor the discrepancy becomes necessary.
Surgical operations to equalize leg lengths include the following:
Shortening the longer leg. This is usually done if growth is alreadycomplete, and the patient is tall enough that losing an inch is nota problem.
Slowing or stopping the growth of the longer leg. Growth of the lowerlimbs take place mainly in the epiphyseal plates (growth plates) ofthe lower femur and upper tibia and fibula. Stapling the growth platesin a child for a few years theoretically will stop growth for the period,and when the staples were removed, growth was supposed to resume. Thisprocedure was quite popular till it was found that the amount of growthretarded was not certain, and when the staples where removed, the bonefailed to resume its growth. Hence epiphyseal stapling has now beenabandoned for the more reliable Epiphyseodesis.By use of modern fluoroscopic equipment, the surgeon can visualize thegrowth plate, and by making small incisions and using multiple drillings,the growth plate of the lower femur and/or upper tibia and fibula canbe ablated. Since growth is stopped permanently by this procedure, thetiming of the operation is crucial. This is probably the most commonlydone procedure for correcting leg length discrepancy. But there is onelimitation. The maximum amount of discrepancy that can be correctedby Epiphyseodesis is 5 cm.
Lengthening the short leg. Various procedures have been done overthe years to effect this result. External fixation devices are usuallyneeded to hold the bone that is being lengthened. In the past, the boneto be lengthened was cut, and using the external fixation device, theleg was stretched out gradually over weeks. A gap in the bone was thuscreated, and a second operation was needed to place a bone block inthe gap for stability and induce healing as a graft. More recently,a new technique called callotasis is being use.The bone to be lengthened is not cut completely, only partially andcalled a corticotomy. The bone is then distracted over an external device(usually an Ilizarov or Orthofix apparatus) veryslowly so that bone healing is proceeding as the lengthening is beingdone. This avoids the need for a second procedure to insert bone graft.The procedure involved in leg lengthening is complicated, and fraughtwith risks. Theoretically, there is no limit to how much lengtheningone can obtain, although the more ambitious one is, the higher the complicationrate.
There are several ways your doctor can predict the final LLD, and thusthe timing of the surgery. The easiest way is the so-called Australianmethod, popularised by Dr. Malcolm Menelaus, an Australian orthopedicsurgeon. According to this method, growth in girls is estimated to stopat age 14, and in boys at age 16 years. The femur grows at the rate of10 mm. a year, and the upper tibia at the rate of 6 mm. a year. Usingsimple arithmetic, one can get a fairly good prediction of future growth.This of course, is an average, and the patient may be an average. To cutdown the risk of this, the doctor usually measures leg length using specialX-ray technique (called a Scanogram) on threeoccasions over at least one year duration to estimate growth per year.He may also do an X-ray of the left hand to estimate the bone age (whichin some cases may differ from chronological age) by comparing it withan atlas of bone age. In most cases, however, the bone age and chronologicalage are quite close.
Another method of predicting final LLD is by using Anderson and Green?sremaining growth charts. This is a very cumbersome method, but was tillthe 1970?s, the only method of predicting remaining growth. More recently,however, a much more convenient method of predicting LLD was discoveredby Dr. Colin Moseley from Montreal. His technique of using straight linegraphs to plot growth of leg lengths is now the most widely used methodof predicting leg length discrepancy.
Whatever method your doctor uses, over a period of one or two years,once he has a good idea of the final LLD, he can then formulate a planto equalize leg lengths. Epiphyseodesis is usually done in the last 2to 3 years of growth, giving a maximum correction of about 5 cm. Leg lengtheningcan be done at any age, and can give corrections of 5 to10 cm., or more.
What can be expected after treatment?
The treatment of LLD is long-term treatment, and involves the physicianand patient?s family working together as a team. The family needs to weighthe various options available. If leg lengthening is decided on, the familyneeds to understand the commitment necessary to see it through. The treatmenttakes 6 months to a year for completion, and complications can happen.But when it works, the results are gratifying.