Petty “suffered from many serious ailments…most significantly a fractured hip”, the statement said.
Family members say they believe he was overusing prescription pain medication when he died in October aged 66.
Petty found fame as the lead singer of Tom Petty and The Heartbreakers, with hits like American Girl and Breakdown.
He was also a co-founder of the Traveling Wilburys group in the late 1980s, recording albums with Bob Dylan, Roy Orbison, Jeff Lynne and George Harrison.
Petty was found unconscious, not breathing and in full cardiac arrest at his Malibu home on 2 October.
He was taken to hospital, but could not be revived and died later that evening.
Petty’s family met with a medical examiner on Friday morning and updated his fans on Facebook.
“On the day he died he was informed his hip had graduated to a full on break and it is our feeling that the pain was simply unbearable and was the cause for his over use of medication”, the statement said.
“We knew before the report was shared with us that he was prescribed various pain medications for a multitude of issues including Fentanyl patches and we feel confident that this was, as the coroner found, an unfortunate accident.”
They added that his death “may spark a further discussion on the opioid crisis and we feel that is a necessary and healthy discussion”.
The Los Angeles coroner’s office attributed his death to “multisystem organ failure” due to a “mixed toxicity” of seven medications. They are fentanyl, oxycodone, emazepam, alprazolam, citalopram, acetyl fentanyl, and despropionyl fentanyl.
Years of over-prescription of opioid painkillers in the US has created a nationwide addiction crisis, with patients turning to heroin and other street drugs when their prescriptions stop.
In 2016, opioid-related overdoses increased by 28%, killing 42,249 people.