Murban,
21 CFR Part 820.180 covers the records retention requirements for medical devices.
"All records required by this part shall be retained for a period of time equivalent to the design and expected life of the device, but in no case less than 2 years from the date of release for commercial distribution by the manufacturer."
As Alf said, you need to know what the life of the device is and retain your records for at least that long. If you think about it, you are responsible for the proper performance of the device until it expires. If a device is used just prior to expiration and creates problems for a patient or practicioner, you will want to have all pertinent records available to show the FDA the due diligence that was performed in designing and manufacturing that device.
In our case, five years is a common lifetime for devices and we retain our records for seven years to cover its lifetime and any possible overlap in manufacturing, sales, and distribution.