Firstly, what are we calling it: leg-length discrepancy or leg-length inequality?
Well, there is no real clear answer. However, the last research document we read used the term leg-length inequality (LLI), so we will.
Secondly, what is leg-length inequality?
This is where one leg appears to be longer than the other. There are numerous reasons why this happens. However, pleasingly, leg-length inequality can be separated in to two broad categories:
- Structural leg-length inequality or anatomical leg-length inequality. This is when you’ve just grown one leg longer than the other or more significantly smashed one up in an accident (so, stay away from motorcycles) or:
- Functional leg-length inequality. This is caused not by an actual change in your bones but by a change in how they are arranged. This is the one we see most often and are most interested in.
A reminder: there are 3 main bones of your pelvis. These are the Sacrum, sitting in the centre, and the two Iliac bones either side. These Iliac bones join with the Sacrum at the Sacroiliac Joints (SIJ) at the back and with each other at the front. Now your SIJ are important as the biomechanical causes of functional leg-length inequality are all about them. The base of each SIJ, the two main joints of the pelvis, has a slight bone promontory that acts like ledge to take the weight of the body across the joint.
It has been suggested that the sacrum can just move directly up (up-slip) into the pelvis. Augusto Maganiellio, a co-author on this blog, and a world expert on LLI, said in a personal message to me that he didn’t think up-slip actually occurred. He thinks that if the Iliac bone moves forward on one side it tends to ride up on the ledge and, if it moves back, tends to fall off it. This is what causes the functional leg-length inequality we are interested in.
Functional leg-length inequality:
This is the most clinically important LLI as it occurs in over 60% of the general population. For the majority of us this is at such a low amount to be insignificant. However, clinically, we would expect to see LLI in over 90%+ of an athletic team depending upon what sport they are doing and level of activity of the team. For example, a basketball team tends to have a large number of LLI cases because of the repetitive nature of jumping and landing on one foot. This is the same in, say, fast bowlers in cricket and squash players. Surprisingly, it is less prevalent in sports such as swimming, track and even football because of the even loading of the pelvis.
Problems caused by Leg length-Inequality
- Approximately 60% of the general population has a functional LLI;
- 79% of people who experience lateral patella femoral pain (knee pain on the side) have a functional LLI;
- This is almost always in the longer leg because the body will increase the Q angle of a longer leg in an effort to try and shorten the leg. This increased Q angle will cause a lateral tracking of the patella and knee pain.
Links have been established between functional LLI and biomechanical abnormalities including increased lateral lumbar flexion, altered running mechanics and shoulder leveling.
The 5 key problems we see every day are as follows:
- Trigger points in the Gluteal Medius and Minimus muscles. These are the muscles that keep the pelvis level when you stand on one leg – so every time you take a step. In a patient with LLI we would always expect to see some very unhappy gluteal muscles. They may even be why the patient has come in to see us. These trigger points can cause referred pain across the back or down the leg that is often mistaken by last practitioners for sciatica.
- Similarly, the big muscles that flex your hip, so the ones you use to step up something, your Iliopsoas muscle will be affected. They attach onto the Iliac crest and so one will be longer than the other which can cause groin and thigh pain.
- The classic is the hamstrings. The origin of the hamstrings is on the base of the pelvis. If this is twisted out of position the muscle will not work well. We often see patients with leg-length inequality complaining that they are unable to touch their toes. This is because their hamstrings are elongated and have no spare stretch capacity.
- Hot sacroiliac joints. This will present as an inflammatory pain over the bony lump of the Iliac bone sitting over the SIJ.
- The LLI will nearly always lad to a the pelvis being slanted. This means the lumbar spine sits on a slanted base and is loaded unevenly as as result. This means you are far more likely to get episodes of low-back pain.
What else can happen?
There is one other weird thing that can also happen. For example: your high hip can sometimes touch or overlap your bottom rib. If you are sitting down have a feel for how close your rib comes to your Iliac crest by prodding your side just above you belt and you should be able to feel both the crest and the rib. In most people these should be just a few cm apart.
What else happens? See part 2!