Thailand's King Bhumibol Adulyadej will undergo surgery this week to treat a degenerative spinal disorder that he has suffered from for years, the palace said.

Thai King Bumibhol Adulyadej and Queen Sirikit. The king will undergo surgery this week to treat a degenerative spinal disorder that he has suffered from for years, the palace said. [AFP]

Doctors will perform the surgery on Thursday in Bangkok's Siriraj Hospital. The 78-year-old king will then require physical therapy as part of the recovery process, the Royal Household Bureau said in a statement.

The king, who last month celebrated his 60th year on the throne, fractured a rib when he fell while walking around the palace grounds on June 24.

The statement did not say if the surgery was related to that injury.

The king has suffered from spinal problems since 1995, which doctors said were caused by old age. The condition was diagnosed in 2003 as lumbar spinal stenosis, and the king has been receiving physical therapy as treatment since last year.

Symptoms of the disorder can include pain or numbness in the back or legs. The problem can be aggravated by standing or walking for long periods.

The surgery will try to relieve pressure on the nerves inside the king's spine, in hopes of easing the pain. Recovery from the procedure normally takes several weeks.

King Bhumibol is the world's longest-reigning monarch. Some one million Thais turned out to hear him speak last month to mark his 60th anniversary on the throne, and royalty from 25 nations came to Bangkok for the celebrations.