This is what Lotus F1 Team said yesterday on a Press Release:
As planned, Kimi Räikkönen underwent back surgery yesterday at The University Hospital of Strasbourg. Lotus F1 Team is happy to report that the operation was totally successful, according to Professor Afshin Gangi.
Kimi will now rest for a few days and he will start his recovery process as early as next week. Everyone at the track and at Enstone wishes him a quick recovery.