Based on current military requirements, how unlikely is it one can get a medical waiver for hardware in the back to correct curvature?

Always start with the applicable Reg and go from there. Taking a quick cruise through, I don't see a match. So then the default becomes an assessment of "asymptomatic", durability of the fix, etc. So it's best to bone up (sorry pun) on the relevant stuff so intelligent questions can be asked later. You want to be proactive towards meeting the goal, not passive. Never ask while shaking your head side to side "You don't have a slot in the military for me with a back problem?" Be fully aware of the condition, the surgery, effectiveness, prognosis, etc. If the ortho deems it a permanent fix without limitations, get a letter that says it. If you get pushback from the recruiting side, then you ask "Show me where in the Reg it says that." If the condition is truly a nothingburger, then the rest is just salesmanship. BTW most MEPS docs are not qualified to assess unique issues. That's why the Ortho letter is important to have in the hip pocket. A side note, if he is looking at a ROTC scholarship later on, he will be assessed prior to granting it because the MIL doesn't toss money out for no return.


http://dtic.mil/whs/directives/corres/pdf/613003p.pdf

I think that the best answer to this that a non recruiter can give you is that you can look up the particular regulations for the service that he is wishing to join and see if he qualifies for the waivers. In addition, if he doesn't really well with his asvab and doesn't have a criminal background, basically if he is all around a good candidate besides the hardware, and he can prove that he can still physically endure basic he is more likely to receive a waiver. Of course the best way to get the answer to such a question can be given by your local recruiting offices.