Sorry to hear about your bought your back, I too have had back problems with unaligned and twisted vertebrae in my upper back. Flexibility doesn't come easy especially if you have had injuries in the past, it took me close to three months to touch my toes on a hamstring stretch. That was stretching twice a day! Kicks are an important part of sparring and while their application may be limited with your lack of flexibility they can still be used for feints/fakes. Using punching techniques alone will limit the scope of your sparring and allow your opponent a great advantage. Just keep stretching and with time you will definately improve.
