Remember that the company spent over 10 years on the work you are talking about. Also, they spent over a year in submitting the 510K to be granted approval for knee and foot in February, 2017. The only thing the FDA required for them to get full body approval for muscle and joint is the backpain clinical trial.
The device is exactly the same like the knee
The functionality and applications and instructions are exactly the same as the knee
The clinical trial for back pain was already analyzed and presented to the FDA similar to the Knee and foot.
If I am serious about the urgency of the submittal, I will submit Friday after May 9, and that is May 12 or worst case scenario, May 15.
This 510 is an expedited 510 or a special 510 that the FDA committed to reply to in 30 days. If they submitted on May 15, the approval is due on Thursday June 14.