I know it is painful and frustrating, but if you can, keep fighting the good fight. I am a worker's comp paralegal in California and the WC laws in Cali are almost identical to those in Texas and what they did was illegal on about a dozen levels. I can say that because I represent the insurance companies and normally I would be representing them if it had happened here. Having said that, it just means that I know when my clients screw up. $50K? That's a joke! Pre-existing condition or not, you had a major injury. The amount of force and impact it takes to break your tibia and fibula in the same fall is incredible and that makes it a major injury with major permanent disability attached.
Good luck! Please let me know if there is anything I can do, including be an ear to listen.
"If you think you can, you can. If you think you can't, you're right". - Mary Kay Ash