Leg length difference
Many people have a leg length difference. If we were to measure everyone, we know that more than 90% of all people have a leg length difference. The average difference is about 0.5 cm. In about 20% of the population there is a leg length difference of more than 1 cm. And 1 in 1000 has a leg length difference of more than 2 cm. The exact difference must be measured by an X-ray photo which looks at the difference in height of both hips. This is a common and relatively expensive investigation. In practice, we often see that measurements are made from recognizable anatomical points in our body from the hip to the foot. This method is far from perfect but gives an indication of a possible leg length difference. But the most important question is: how important is a leg length difference in relation to pain symptoms?
More than 90% of the population has a leg length difference
Possible cause of pain
When a physiotherapist or doctor discovers a leg length discrepancy, it is easy to point to this as the cause of the pain. But can we really say this directly? Several studies have been carried out into the relationship between leg length difference and pain symptoms. A study in which people with a leg length difference and WITH BACKPLAIN were compared to people with a leg length difference WITHOUT BACKPLAIN showed the following. The average leg length difference in the group with pain was 5.1 mm and the average difference in the people without pain complaints was 5.2 mm. This small difference shows that the measured leg length difference does not contribute very much to the pain complaints. The average leg length difference of the people without pain complaints was even somewhat larger.
Another group where a leg length difference is often measured is people with a hip prosthesis or after a hip fracture. Both can result in a leg-length difference. Although there is an average difference of about 3 centimetres after an operation or fracture, we do not see that these people develop more or less back problems. We also see no change in the long term:
- development of hip osteoarthritis
- loss of function
- satisfaction after surgery
So does it really matter? Do we have to go to this much trouble to fix it?
When does it matter?
To answer this question we need to look at 2 different factors:
- The actual difference in length
- The individual load level
A leg length difference of less than 1 cm is highly unlikely to be a cause of complaints elsewhere in the body. A difference greater than 1 cm seems to be more relevant, certainly in combination with a high physical load. If there is no question of a higher physical load, we see that this makes little difference.
This means that for people with a leg length of more than 1 cm and a low daily physical load such as cycling or an office job, it is unlikely that the leg length difference is the reason for the symptoms.
What can we do about it?
When this is the case, an insole can be useful to reduce complaints. The height of the sole and the type of sole will differ per person. What is even more important than an orthotic is that other factors, such as physical activity, sleep and capacity, are taken into account. These can all contribute to the reduction of symptoms and the promotion of recovery.
A leg length discrepancy is normal up to a certain limit. When you first hear that you have a leg length discrepancy, it can be quite a shock. People often think that this MUST be repaired. So, please understand that in most cases this is not necessary and that a small difference in leg length is not the reason for possible complaints. It is also not the case that you can develop complaints sooner in the future. No back problems, no arthritis, this does not have to be the case. We are not symmetrical by a long shot. The evidence between deviations in position and pain is very minimal or often non-existent. Focus less on the leg length difference and more on what you can influence!
Knutson, G.A. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg length inequality: prevalence, magnitudes, effects and clinical significance. Chiropr Man Therap. 13,11(2005)
Paravizi et al,Surgical Treatment of Limb-Length Discrepancy Following Total Hip Arthroplasty. J Bone Joint Surg Am.2003 Dec;85(12):2310-7.