My injury in the military was misdiagnosed, do I have any grounds to file a disability claim with the VA?

Yes you do have grounds for a claim. Having just been through a medical board, I will tell you with 100% certainty it is the loss of range of motion that will be the compensating factor. Also documentation. There are other miscellaneous diagnosis that can be awarded with that as well. Remember, with extremities it is mostly loss of range of motion, painful scars that is the compensating factor.

As long as there is decreased range of motion, artheritis neuropathy or any other permanent diagnosis then yes. Just make sure it is documented in your medical record and focus on what happened and how it has progressively gotten worse over the years.

You should file the claim, ensure you have ALL your medical records, and be prepared to help them connect the docs in terms of relating your current medical status to your initial injury. Going to your doctor now and asking directly if your current condition could be a result of, or have been made more likely to occur, or be more severe now, because of the initial injury could get you more supporting documentation (unless the answer is no - although if it is a civilian doctor this would not likely be in the VA claim file unless you put it there.) If the initial injury occurred while you were on active duty and not AWOL or committing a crime (basically) it is presumed to be in the line of duty. If you were a National Guard or Reservist, they will look for a Line of Duty determination, but if you were in the Regular Army, it is presumed. Even if you were in a reserve component, if you were in Title 10 status, it will probably be presumed (there are ways to correct the lack of an LOD determination if you have military medical records.)

Any disability resulting from an injury which occurred while on active duty is rateable and compensable by the VA. Your issue may be in showing that your current condition is a result of the initial injury. You stated that you were diagnosed with a sprain while on active duty, but that you believe it to have been a torn meniscus. I presume, by your reply to a later comment that is based on what the results of your surgery following your discharge. Even though your surgeon suggested that you had suffered an injury prior to the surgery, based on the scar tissue found during the surgery, there is no way of knowing if that was from the 'sprain' or if it existed prior to service, or if it happened after your service, I would imagine (absent previous scopes). So there is no way of knowing that the diagnosis of a sprain was incorrect. And as for linking your current condition to that event, it is highly unlikely. You state that you tore your ACL in 2015. Your current condition is almost undoubtedly linked to that condition, and that could viewed as totally unrelated to a sprain that was at least eight years previously, with at least one surgery in the interim, but post-service. People tear ACLs all the time - linking it to a sprain years previously is a long stretch. Linking your current condition to your service injury rather than the much more severe ACL tear which occurred post-service is highly unlikely.

However, there is nothing to lose from trying. If they do decide that your knee injury was service related and that any portion of your current condition is related to that injury, even if it is rated at 0% you would still be eligible for treatment at a VA facility, and could apply for upgrades if the condition worsens. See a Veteran's Service Organization (such as the VFW or American Legion) for assistance with filing your VA claim, or you can do it online.

Best of luck.