Hospital sources said Kulsum was admitted on Sunday with severe pain in her knee. With her knee worn out, Kulsum had difficulty in walking, a doctor at the hospital (name withheld on request) said.

Post-surgery, doctors said Kulsum, 56, is “doing fine” and will be discharged as soon as she starts walking on her own. “Normally, a patient gets back on his or her feet within a day or two of the knee replacement surgery,” the doctor said. He added that the Sharif family has given doctors and the hospital authorities strict instructions to not disclose further about the surgery.

Kulsum is admitted in the heavily guarded presidential suite of the hospital. Doctors said her worn-out knee has been replaced with an artificial implant on the leg bone to accept metallic implants.

A plastic insert is then put between the two metallic implants to complete the assembly of knee replacement.

Dr Ashok Rajgopal, director of Orthopaedics at Fortis Hospital, led the team of surgeons. Practicing since 1986, Dr Rajgopal specialises in knee surgery — total knee replacement, arthroscopies and trauma around the knee. He has till now performed surgeries on many athletes, including former India cricketer Chetan Sharma, national football team captain Baichung Bhutia, former national badminton champion Madhumita Bisht, All-England winning shuttler Pullela Gopichand, and renowned actress Zohra Sehgal.