The bum knee was cited by Kilpatrick's attorney, Harold Gurewitz, as the reason his client should be granted bail while he awaits sentencing, The Detroit News reported Thursday.
Gurewitz said Thursday the surgery had taken place and that Kilpatrick was recuperating, the Detroit Free Press reported.
The attorney said he had not received any updates.
Gurewitz described the knee's condition before the surgery as "pretty bad," adding that "the delay that occurred until the surgery took place may have had some effect on it."
Kilpatrick has been in federal prison since he was convicted in March on 24 counts including racketeering, conspiracy and tax evasion.
The attorney said Kilpatrick was in the custody of the U.S. Marshal's Service without bail.
In a court filing Sunday, Gurewitz argued Kilpatrick should be released on bail because his bad knee prevented him from being a flight risk.
Sentencing for Kilpatrick is not expected until fall.
Wisconsin business offering 'therapeutic cuddling' forced to close
Trader Joe's: Car crashes into Long Island store, injuring 11