We had a similar problem with one of our hens a couple years ago (our hen came up lame, her legs were trying to pull up to her chest and she couldn't walk). When we took our hen to the vet he spent an hour reasearching the matter and found that she probably had a vitamin D3 deficiency causing the cartilage in her joints to break down. Our hen had spent most of the winter without sun, no fresh veggies, and when I reviewed the feed label it didn't contain vitamin D. In turn I changed her feed, started growing wheat grass for the winter months, gave her veggies, and a vitamin suppliment water solution that is sometimes purchased with new chicks... I also gave her physical therapy twice a day moving her legs back and forth and in bicycle motions. Within a couple weeks our hen was back to normal.
We were newbies in the chicken realm but what we did worked and we're more in tune with the needs of our birds now... Good Luck with your hens!