We see leg length differences in patients quite frequently. Most commonly we see them occurring either after a surgery or injury to the leg. Depending on what kind of surgery or the mechanism of injury, it can result in either a shorter or a longer leg. We also see a lot of foot arch issues or older ankle sprains that will cause the arch to fall leading to shortening of the same leg. In my clinical experience, patients tend to have a dominant foot which is slightly shorter. The thought is this allows them to balance on the longer leg and freely swing their dominate leg for activities like soccer or kick ball. So, the difficulty then comes in determining if that leg length issue is significant enough to be causing other musculoskeletal changes leading to tightness or pain. There is an option of ordering a postural x-ray in which they will then look at how unlevel the sacrum (tailbone) is and measure how long the legs are anatomically. I have found a few issues with this method that have lead me more away from it. The first issue is that all the equipment used for that x-ray needs to be level and needs to be continually check to be level and that isn't always done. The other issue I run into is that the body is very dynamic and there are postural and gait patterns that a static picture of someone standing will not take in to account. So I rely more on the physical examination. This includes looking at how a patient wears out their shoes (Please bring lots of shoes with wear to your first visit!). A long leg will tend wear the heel out on the same side as it drags on the ground more than the shorter leg. Also, during the gait cycle as you put weight on your right leg you sacrum (tailbone) will rotate to the right as well. So, in theory, if while standing with your feet even your sacrum is rotated to the right you are likely putting more weight on your right leg and have a short left leg. An easy way to check is to put a lift (small piece of rubber) under the left leg, in this situation, and see if the sacrum levels out. It is very important that all of the lumbo-sacro-pelvic structures and surrounding muscles and tissues are free from restrictions before ever making a definitive diagnosis of a short leg and attempting a lift. It is also important to address any problems with the arches prior to trying a lift. I will rarely diagnose someone with a short leg after one visit, unless they show me a very convincing argument to do so.
After putting the biomechanics together, it is easy to see how a leg length issue can lead to any number of musculoskeletal issues. I have seen it lead to knee pain, hip pain, back pain, neck pain and even headaches. One word of caution, with lift treatment patients will tend to get more sore in new places at first as their body becomes used to being more level. If the body is free from restrictions, it's usually not as painful of a process.