Ms Garrihy was filming her RTÉ 2 TV sketch show, The Doireann Project, when the accident took place.
The 2FM presenter tweeted: “Home in my PJs after what can only be described as a weekend of f**** agony.
“Dislocated my knee Friday, hoped it would pop back in my sleep that night… then Sat night… Sun night…. Nope.
“So surgery today. Delighted it’s sorted - delighted tea and toast - on the mend.”
Ms Garrihy, 28, attended St James’s Hospital in Dublin on Saturday.
She told fans online she’d struggled with a problem with her knee long-term.
“Since I was 15, I have had an issue with my knees where they pop out of place,” she said.
“It can happen from exercise or sometimes just from crossing my legs while sitting down.”
The presenter told how she was filming final scenes for the TV show on Friday when she sat down on a chair, bent to the side to pick up a script and her knee “popped”.
“Most of the time I can pop it straight back in but this time it simply wouldn’t happen,” she added.
The star said she had been crying in pain with the injury and her boyfriend Paddy Wilson had carried her to his car.
She shared images of her injury online and told how the crew had to dismantle the set while she sat with her leg resting on a box.
The presenter had been filming upstairs in a house when the accident took place.
She explained she hadn’t let members of the crew carry her, feeling she “would never be able to look them in the eye professionally again."
“I really thought it would pop back into place when I relaxed in my sleep, with good pain killers but it didn’t, so off to James’s I went…”
The injury comes after the presenter thanked fans of her radio breakfast show for their support after a “manic” time presenting alone, after her co-presenter Eoghan McDermott, left the station.
She said “thank God” she had booked time off this week, although she was due back on the airwaves on St Patrick’s Day.
And she’s due back filming the TV show on Tuesday.
Ms Garrihy asked fans for prayers to help her get back to health to return to her job soon.
“If you’re someone who prays, will you pray for the pop and light a candle for me? Thank you, #prayforthepop.”