We've been seeing a spate of patients complaining of hip pain, sometimes with pain or abnormal sensations running down the legs and with hypertonic glut muscles all frustrated with their current care. The last patient we had in had been MRI'd twice for her pain and was eventually sent to a physio as the last gasp attempt to do something, anything. Yet, her leg length difference was signifcant and really obvious, and no one had thought to comment on this and wonder if leg length inequality (LLI) was a possible source of her problem.
I found this on the web by an Italian, AUGUSTO MANGANIELLO, MD, University Teacher in Radiology Via Savonarola 175. He said: "During growth, LLI, even of the order of just a few mm (Fig.1), can cause a tilt of the pelvis and consequently lateral deviation of the spine and head. The postural response, aimed at re-establishing equilibrium, is a compensatory counterdeviation of the spine." So it could just be that LLI caused by sacroiliac joint dysfunctyion may be part of the idiopathic scoliosis problem in school aged kids. I'll look into further but it'll be aggravating if so much pain could be avoided by a few sacroillac joint adjustments after falling off the swings.
C1CHC
Pro 
In my further searching I stumbled across this fascinating study:
Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance
Gary A Knutson
Knutson, who I know about and is no slouch concluded:
Using data on leg-length inequality obtained by accurate and reliable x-ray methods, the prevalence of anatomic inequality was found to be 90%, the mean magnitude of anatomic inequality was 5.2 mm (SD 4.1). The evidence suggests that, for most people, anatomic leg-length inequality does not appear to be clinically significant until the magnitude reaches ~ 20 mm (~3/4").
Conclusion
Anatomic leg-length inequality is near universal, but the average magnitude is small and not likely to be clinically significant.
90%! so that is every one in the world, you and I included in that. Now, no one told me that at University. But the key point it this it doesnt matter until it get too large. But then it really matters.