I've been seeing a physio to try to address this problem. He has isolated a number of possible causes. After a thorough examination, he identified some muscle imbalances. I have weak glutes, and extremely tight muscles in the front of my hips (hip flexors,sartorius). Over the past few weeks, I have been doing squats and leg abductor exercises to strengthen the weak muscles and getting my physio guy to release the tight muscles. After a few months of getting nowhere with my splits, I am finally starting to make some progress (3 inches lower in about month). It might be worthwhile to go to a physio guy. Be careful though, while my current guy is really good, the first guy I went to was a joke. I'll keep you guys posted on any new progress.