Leg length discrepancy (Limb Length Discrepancy), also known as anisomelia, in which two limbs are of unequal lengths. Most people have some degree of leg length discrepancy, but larger differences can affect well-being and quality of life by keeping you from participating in the activities you like.
Leg length discrepancy is also referred to as leg length inequality or leg length asymmetry, as the name alludes to when there’s a difference in length between the right and left leg. Leg length asymmetries are much more prevalent than you think. About 90% of the population has been shown to have an anatomical leg length asymmetry, with the average being about five millimetres or half a centimetre.
Leg length differences of lower values (under 9 millimetres) are more prevalent in cases where differences more significant than 10 millimetres become less prevalent. it has been shown that only about 1 in 1,000 people have a 20-millimeter or 2-centimetre difference.
Leg Length Discrepancy Examination
The gold standard for measuring leg length discrepancy is doing an x-ray; by looking at the differences in the hip joint height. However, these are inaccessible and relatively expensive, so the clinical method of using a tape measure is more popular. If you’re someone that has ever had their leg length measured, this is the method you were pardoned most familiar with, so it is worth discussing in a 2019 systematic review. The validity and reliability of this method were examined, and a few key points were identified. Leg length can be measured by looking at the distances from different hip landmarks. In this case, the ASIS or AI is two various ankle landmarks, the medial or lateral malleolus; however, measuring from the ASIS to medial malleolus has shown to have the highest validity when compared to the gold standard of x-rays. This method is imperfect, and there tend to be more errors when measurements are smaller, so less than 5 millimetres. The skill level of the clinician also appears to affect results as you can probably guess the more skillful the
clinician, the more reliable the measurement and finally, the patient population can impact results. It is less accurate in obese individuals or those that present with more swelling muscle contractures or even muscle atrophy; in these cases, it can be a little bit more challenging to potentially find the bony landmarks, so while this method is not perfect compared to an x-ray it is still a viable clinical option.
What Causes Leg Length Discrepancy?
Leg length discrepancy has many causes, which can be divided into four main groups:
- Congenital – Congenital cases indicate a leg length discrepancy at birth. Generally, the length of the discrepancy is more significant and increases progressively over time.
- Acquired conditions which can lead to leg length discrepancy include:
- Severe leg trauma – E.g. from a car accident, fall or another high-impact injury.
- Bone infections (osteomyelitis) damaging the growth plate – From organisms such as Staphylococcus travelling through the bloodstream to infect the bone.
- Non-healing or non-union fractures
- Incorrectly healed fractures (malunion fracture)
- Bone tumours – Both bone and the treatments designed to eradicate them can affect bone growth. This is especially true if the illness happens in infancy.
Leg Length Discrepancy Causes and Treatments
Limb length discrepancy in children can be caused by many different reasons. Some of them are born with it, some acquire the condition because infection during childhood destroys the growth plates, or sometimes it can be caused by cancer.
However, there are various ways to sort out any limb length discrepancy depending on how much discrepancy one has to correct.
For example, if the discrepancy is minor, let’s say a centimetre. I will generally advise parents or the patient that nothing needs to be done because there is no proof that club foot can cause any long-term problems, and it is sorted out quickly by just adding a little insole into your shoes and then you will equalize the limb length.
However, if the limb length discrepancy is a lot bigger, let’s say three to four centimetres, if you know that this discrepancy is going to be a problem, we can predict from a younger age, after seeing the patient a few times, we can expect, once the patient reaches maturity, what the discrepancy is going to be.
Sometimes we can correct the discrepancy by stopping the long leg from growing at the correct time, so we can remove the growth plates. Hence the shorter leg will have time to catch up.
However, if the patient says: No, I do not want to be shorter than I am now. I want to grow to reach my potential.
So, if I’m born five feet six, I want to be five feet six.
If this is the case, the other option is to lengthen the shorter legs.
So, there are various ways. If there is no deformity associated with it, meaning that your bones are not bent, then obtaining those three or four centimetres is easily achievable by putting a little rod or nail into your thigh or tibia bone. And these days, we have what we call growing rods, which the computer can program to lengthen by one millimetre a day, It is all done internally, and this is one way of lengthening. However, if the discrepancy is quite significant it comes together with a deformity like a bent leg, then one of the methods we can use is an external fixator like a circular frame. So this will be attached to the bone using wires across it. And then all these little structures over here can be modified by feeding data into a computer program to establish what length you want and which deformities you wish to correct. And you can adjust it daily to slowly correct the deformity.
So there are many more straightforward ways these days we can use to correct limb length discrepancy and deformity.
Utilizing a heel lift can be a low-cost and relatively simple intervention to adjust for leg length differences. The amount of heel lift and use will vary from case to case.
As the evidence suggests, a leg length discrepancy of greater than 20 millimetres or 2 centimetres is rare, so if you’ve been told you have a leg length discrepancy, it’s probably not clinically significant. At the same time, lift still might help people generally benefit more from focusing on other lifestyle factors such as physical activity, sleep and load management as these have been proven to help reduce symptoms and help in recovery. You must see a physiotherapist help you correct your movements.