Question about car seats with Spica cast

Hi everyone. My name is Jen and my son, Luke, has PFFD class 1b(Dr. Paley classification) in his left leg. He is 17 months right now and although this is my first time actually writing on this wonderful site, I have to say THANK YOU to all who have shared their stories b/c it has helped me out tremendously!!! I absolutely crushed when he was born and we found out about his leg. I cried for 2 weeks straight and then I realized that this was not the end of the world. I have been reading entries from this site for the past year and all of these children are such inspirations!!! Luke will have an estimated 28cm. difference at maturity so our doctors here in Pittsburgh recommended amputation, but Dr. Paley said that it will be a long road but he will lengthen him! Luke is scheduled for the super hip/knee surgery this Feb. and I was wondering if anyone had any advice as to what car seat to buy that will accommodate the spica cast. Luke is actually still in his carrier as he is really small(he was 16#9oz. at 16 months). I was hoping to buy a forward facing car seat anyway so I might as well get one that will work with his cast. I appreciate any suggestions!! Thank You, Jen W.