Quit being a pusscake.
But in all seriousness, I mean, technically you can't straighten your Tibia out as it is your entire shin. I have no joints in my shin. If you're having difficulties straightening your leg, I would assume either you damaged a muscle in your quadriceps(since that isn't what hurts, it is unlikely) or your patellar tendon. The patellar tendon is going to connect your Tibia to the knee joint, and affect things around it. Could possibly explain the pain around your tibial area. It would be helpful if you can explain the type of pain, is it muscle strain, a sharp stabbing pain in a localized area. There are also numerous ligaments in that area that could get damaged, and I am not an expert, but the major cruciate and colateral ligaments dont really restrict those forms of motion, so I wouldn't expect them to be majorly damaged. However, certain things within those areas can irritate other things.
If it doesn't improve within a day or two, I would definitely say consult a physician again, and possibly ask to be referred to an orthopedics specialist if YOU think something may be really wrong. I had a doctor misread an Xray the first time I saw him once, turned out I had a hairline fracture that was very difficult to see. Could have caused some problems in a whole healing process thing.
Not a doctor by any means, majoring in human physiology and applying to medical school this summer though. I also volunteer and work with physical therapists.
AR6rider knows his shit with all the medical stuff, sooo maybe if he drops in here you'll get a better answer.