Take a look at this video graphic of how the sacrum (base of the spine), inominates (wings of the pelvis) and spine move through the gait cycle.
https://vimeo.com/107191637
It's known that there's a set pattern to how all the parts of the spine and pelvis move in relation to each other during gait. Think of the sacrum (base of the spine) as being the foundation with everything moving in relation to that. When you step forwads with your right leg the sacrum tilts right and rotates right; as your sacrum tilts and rotates that way your lumber spine tilts and rotates the opposite way; your thoracic spine tilts and rotates the opposite way to lumber spine and cervical spine opposite to that. Scapular (shoulders) move in relation to thoracic spine. And as you can see from the diagram the wings of the pelvis move in relation to the sacrum too and this affects the whole leg.
When you get a movement impairment - so when your muscles stop firing in the correct sequence, your sacrum (and therefore the whole spine, pelvis and shoulders) will be held in the wrong position. With the boney structures of your body in the wrong place, the attatchement points of the muscles are also in the wrong place. Some muscles are in a compromised position and can't work as they should; other muscles try to take up the slack and do jobs they weren't designed to do. This will cause tension, pain and 'trigger points' in muscles. Because muscles designed to stabilise can't do their job, other muscles designed to move limbs have to act as stabilisers - this can prevent them from doing their job of moving limbs, further adding to joint restriction. Over time it will also cause joint wear.
Symptoms can be relieved with trigger point therapy / myofasial release. You can do this yourself and there is plenty of information online to guide you. In time you'll get a feel for where your tight muscles and trigger points are and you'll be able to relieve them with self-massage.
Loosening off those trigger points is part of the solution, but on it's own all it'll do is provide temporary symptomatic relief.
The 'cure' is to get all the muscles firing correctly - so to restore normal gait. That will restore correct posture, align joints correctly and take the pressure off of the soft tissue.
I've mentioned a few methodologies in this thread that can help, but as I said earlier, I really do think the most promising is Functional Patterns. They center everything around restoring correct gait - they are I believe unique in this respect and I think they're onto something special!! Their stuff is a bit hard to follow if you aren't used to exercising - it's aimed at athletes. But I think their gait training program is very doable. Ideally their entire 'human foundations' package. But if you were to get the gait program first (only a few pounds) and if you think you're likely to manage it then you can get the price of that taken off the full package.
I hope this makes sense.
Of course, other things can go wrong. But generally speaking, because of the way the entire spine, scapular and pelvis are tied into the position of the sacrum then anything that goes wrong in your body will typically upset the gait pattern. Fixing gait should bring everythign back into line.
If you're interested in the theory behind this I can give you links to some more info describing how being 'stuck' somewhere in the gait cycle causes an apparant leg length dyscrepency. Just let me know.
None of this is accepted or understood by mainstream medicine, but mainly I think because the 'cure' is complex and unlikely to be succesful with many people. Therefore there is little to be gained in teaching it to health professionals. That's essentially what one of my physios told me anyway! Chiropractors are very familiar with this theory, but their attempts at cure fail because they focus on 'clicking' the skeleton. What's needed in most cases is to retrain movement patterns so the muscles move the skeleton correctly during gait. VERY complex and difficult - but Functional Patterns seem to have cracked it. I recommended the videos, but perhaps their e-book on posture would be better for you? That will explain all you need to know to restore posture, gait and relieve pain. It's called "The Power of Posture" - not expensive and you can download it from their website.
The ideal would be to go see someone trained in Functional Patterns - I honestly think they could help. But you're out of luck if you're in the UK. Although they are planning on running a course here this summer (I'm hoping to go to it).