Do I have a case?

We can't say whether you do or don't; all we can say is that you might have a case, and if you do, it might be worth bringing. 
There are three compenents to a viable malpractice case: negligence; causation; and damages.
Negligence--it's not enough that the doctor was wrong; the law accepts that medicine and doctors are not perfect and sometimes mistakes are made or suboptimal treatment proscribed or situations misdiagosed. The issue is, was the doctor "negligent" or unreasonably careless at the time the diagonsis was made? That depends on whether a reasonable doctor in his or her circumstances, at that time, based on the symptoms you reported, would have diagnosed tendonitis without X-rays or whether a reasonable doctor, based on what you told them and their examination, either would have immediately realized it was a factured heel spur or else ordered X-rays to see what was going on in inside. If a reasonable doctor would have done what this doctor did, there is no negligence or malpractice; there only is if a reasonable doctor would have done something different. What is reasonable or not can only be determined by othe doctors, not laypersons. So do you have any other podaitrists saying that it was careless (negligent) for this doctor to not order X-rays or to diagnose the condition as tendenitis? If you do, you may well have a case; but if other doctors do not feel this one did anything wrong, you would not.
 Caustion: even if the diagnosis was negligent, you have have to prove it injured or harmed you or your life, and can only recover for the extent the misdiagnosis hurt you. The misdiagnosis did not cause the bone spur to fracture (so you can't recover compenation for having the facture), but it did cause you to suffer a year-plus of pain and possibly disability by delaying your treatment: you may be able to recover some compensation for that. And if it made the fracture worse by delaying treatment, so that you need more expensive or elaborate surgery or will have a worse outcome, you may be able to recover compensation for the extra costs or worse outcome. You have to be able to identify what the misdiagosis caused you, and can only seek compensation for that.
Damages: related to the above, what is the case worth? If you are getting the same surgery now that you would have then, with the same outcome, then all you'd be able to sue for is the year or year-and-half of pain, etc. and that is not likely enough to justify a lawsuit. (To bring a malpractice case, you need to hire one or more doctors to examine youl, write reports, and testify, and that can cost several thousand dollars.) On the other hand, if due to the delay in treatment, you now need expensive surgery or will likely suffer some amount of permanent pain or disability, that would result in much more compensation and a much more worthwhile case.