Mariam Kolo, the Director-General of the state Child Rights Protection Agency said the surgery was done at the Federal Medical Centre (FMC), Bida, Niger.
It is the first in a series of operation Buhari will need.
“He was operated upon by four neurologists and he is responding to treatment.
“Several other tests will still be conducted to prepare him for the next operation,’’ Kolo said.
Muhammad’s genital was cut off by his 17-year-old step mother, Bara’atu Muhammad, when he was barely a month old.
The incident occurred in Dafe community in Shiroro Local Government Area of Niger in June 2016.
The step-mother had confessed that she took the action because she was jealous and that she also wanted to get back at the victim’s mother, whom, she claimed was always insulting her.
Muhammad was subsequently remanded in Minna prison.
The Police Public Relations Officer, DSP Bala Elkana, said the suspect was still in Minna Prison, pending the conclusion of investigations.