The shorter leg: Do you have a leg length difference?
Author: By Doug James, intraining Physiotherapist, Podiatr
There are many causes of injury with overtraining being the most significant. In many cases there is an underlying biomechanical factor that contributes to the risk of an injury. These factors can lower the threshold of training that can be done before injury strikes.
One of these factors is a difference between the length of one leg and the other. When a runner comes in to see us at the clinic with an injury our goal is to identify the mechanism of action that could have led to that injury. It is not enough to diagnose the injury and the tissue affected. In order to choose the correct intervention, we must know the potential causes of the injury as well. While symptomatic treatment of the symptoms is important, if we do not change the risk factors then the injury will just continue to reoccur. A difference in leg length can be structural with an actual difference in the length of the long bones or it can be functional where asymmetry in the function of one side of the body affects the leg length.
Structural differences may just be developmental where one leg stopped growing sooner than the other. They can also be caused by trauma such as a fractured leg or osteoarthritis in a joint.
Functional differences are often caused by poor core stability on one side. They can also be caused by asymmetry in pronation between the feet, scoliosis or just a difference in foot strike and function.
It is critical to identify whether the leg length difference is structural or functional because a structural difference requires a lift in the short side while a functional difference requires treatment of the functional cause. If you put a lift in a leg with a functional leg length difference you will make it much harder to correct the functional cause which can lead to more significant problems down the track
The signs and symptoms we look for in the clinic is asymmetry either in gait or in our functional assessment. In stance there may be one shoulder and hip dropped to one side. During a heel raise
one heel will be higher off the ground than the other. While running there are many compensations to look out for:
- One leg may be more out toed
- One foot may pronate more; one foot heel strikes while the other forefoot strikes
- Limping or greater stride length on one side
- Early heel lift on one side
They may also be signs of a different wear pattern on one shoe compared to the other. Most significantly is whether there are more injuries on one side of the body. A measurement of the leg length difference can be done in the clinic, but it has a high margin of error. However, a small leg length difference can be found in a majority of runners. It normally only becomes significant when it is above or around 10mm. Less than this amount of difference can usually be compensated for by the runner. It is when the injury pattern suggests a leg length difference as a cause of the problems that we then need to address it. A CT scanogram can be done to more accurately identify the exact leg length difference and can differentiate between the structural and functional components.
Treatment of a structural leg length difference consists of putting a firm wedge in the short side. We do not put it on an orthotic but have it so it can be moved in and out of the shoe independently. Soft lifts are ineffective as they compress down on weight bearing and the correction is negated. Heel lifts are OK for standing and walking, but runners must have a full length lift so that the correction is also working during propulsion. In really significant cases we put an extra layer of EVA into the midsole of the shoe. Full correction of the difference will cause problems due to the fact that the runner has usually been compensating for the difference for many years. A 50% correction is usually the starting point and then it can be increased over time.
If you have been having ongoing injuries on one side of the body, run with an asymmetrical gait or suspect you may have a leg length difference then you should book in to be assessed by one of our running podiatrists.