Leg Length Inequality (LLI) is where one leg appears to be longer than the other. This is due to a load of reasons which can be separated in to two broad categories. Anatomical: when you’ve just grown legs like that or smashed them up in an accident (so, stay away from the motorcycle). And functional: typically caused by some pelvis rotation.
The biomechanical causes of functional LLI are simple to see if you have a model of a pelvis to hand. The lower edge of each sacroiliac joint (SI joint) has a slight bone promontory. This acts like ledge to help support the weight of the upper body across the SI joint. If one side of the pelvis moves forward it will ride up this ledge. Conversely, if it twists backwards it will fall off this ledge and become lower.
There are some suggestions that I’ve seen that the sacrum can only move up and down into the pelvis. This is called upslip. However, an Italian professor called Augusto Maganiello, who was a co-author on an old blog of ours and, far more importantly, a world expert on LLI said in a personal message to me that he didn’t think upslip occurred and that what was going on was the classic rotation.
Functional LLI is the most clinically important as it occurs in over 60% of the general population. For the majority of these people it is at such a low level to be insignificant. However, clinically, it is important because it can be present 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. Not-surprisingly, it is less prevalent in sports such as swimming, track and even football because of the even loading of the pelvis.
How common is LLI?
LLI has been researched over the years (see what Augusto Maganiello has written) because of it’s effect up the lower extremity and spine. The research suggests:
- Approximately 60% of the general population has a Functional LLI
- 79% of people who experience lateral patella femoral pain have a Functional LLI. 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.
Pleasingly it can be resolved pretty successfully by your chiropractor if treated correctly.