The thing is, if you can do 50 pushups in a row, you're due for some added resistance. The key to progress is overloading, and that can be done either with
volume (doing more reps/sets), which you've accomplished
intensity (using more weight), which is the second piece of this puzzle you're trying to complete
Also, you're right to be concerned, not just about lesions and tendonitis, but also about the effect on your body from doing ONLY pushups. What do you think is going to happen when you have a big chest? That the rest of your body is going to look equally good? No! It's going to look weird, and you're going to develop imbalances which, around your core, means chronic neck/back problems.
If you push, you also need to pull. And if you're working your upper body, you need to work your lower body too.
Don't neglect anything! If you have the time to do 200 pushups, try instead to do a total of 100 pushups with more weight instead, and spend the rest of the time doing pullups and squats. Then you have something that's starting to look like a more well-rounded routine!