Can anyone explain this to me?

I know I have some really smart people reading my blog, and I wonder if any of you might be lawyers. I'm a little confused about something.

A 2000 ruling by the Tennessee Supreme Court ruled that requiring all second trimester abortions be performed in hospitals as unconstitutional. This ruling came from the case Planned Parenthood of Middle Tennessee vs. Sundquist. So, we have this unconstitutional law that is still on the books and is still being enforced. I want to know how this is possible.

When we got home from Atlanta, I called several clinics in Tennessee (there are only actually five or six in this state at all; 94 percent of all Tennessee counties have no abortion provider), and none of them perform abortion after 14 weeks. When I asked why, they stated that it was the law in Tennessee that abortions after 16 weeks have to be done in a hospital, and their doctors and nurses could get into trouble if they did so.

I did a little more research later on, and of the ones I didn't call, only one provided abortion after 14 weeks and that was up to 16 weeks. It's all because of the law.

So, can anyone answer this? If a law has been deemed unconstitutional, how can it been still on the books and enforceable? This isn't a rhetorical question; I'm really curious how the law works.