Pietersen, 33, picked up the injury to his right knee during March's tour of New Zealand and only returned in June, just a few weeks before the start of the series opener at Trent Bridge.
"I didn't have surgery because I didn't want to miss the Ashes," he told reporters.
"I could have done but it's proved to be the right decision from the surgeon's perspective and mine."
Pietersen went on to reveal that he will "be in rehab for the rest of my career, unfortunately".
The batsman made 113 runs to take England to 294-7 at the close of play on day three of the third Test.
In doing so, Pietersen became England's leading run scorer of all time.