Winnie Madikizela-Mandela still recovering in hospital
The foundation has released a statement at the request of the Mandela family saying Madikizela-Mandela underwent an initial procedure on March 8.
This was to relieve the pain that a compressed spinal nerve was causing.
A follow-up surgery took place on April 14.
The Mandela family has thanked South Africans for respecting its privacy and for the messages of support it's receiving.
President Zuma also urged the nation to keep her and the Mandela family in their thoughts and prayers during this time.
The 79-year-old former anti-apartheid campaigner who has been having problems with her health recently, suffered a blow last week after the High Court in Mthatha dismissed, with costs, her claim to Mandela's ancestral home in Qunu in the Eastern Cape.