The arrested include Omana, the lady of the house where the rape and assault took place, her son, Manoj and Mohammed Shafi.
A police official on condition of anonymity told IANS that the charges include rape and brutal assault.
"The arrest has been made and shortly the three will be produced before a court, here," said the official.
According to police, the incident took place on Sunday afternoon, when the aged woman was at her friend's house, close to her home.
The Kerala Women's Commission has also suo moto registered a case.
The woman had been promised tobacco to chew and was brought to Omana's house, where the incident took place.
Omana told her neighbours that the elderly lady slipped and fell and injured herself.
After a while the bleeding woman was brought back to her home and was later taken to a nearby hospital.
From there she was moved to private medical college at Kolenchery and an emergency operation was performed and the doctors say that her condition is serious.
The lady's son said she had serious wounds inflicted by a sharp object and her private parts also have injuries.