His Majesty the King will undergo minor surgery on Thursday at Siriraj Hospital to correct a condition that is making it difficult for him to walk, the Bureau of the Royal Household announced yesterday.

His Majesty is suffering from lumbar spinal stenosis, a narrowing of the spinal canal that compresses the nerves travelling through the lower back to the legs.

He has been receiving medication to deal with the condition since it was detected in 2004 when His Majesty first noticed that during long walks he was having difficulty controlling the movement of his right leg.

The symptom stood out during a 200-metre stroll that year.

Later, magnetic resonance imaging and tomography tests found that his spinal canal had narrowed between two vertebrae in his lower back and pinched a nerve. The condition is common with age.

Doctors at Siriraj Hospital and other medical institutes decided on surgery at a May meeting but decided to wait until after last month's celebrations to mark his 60 years on the throne.

His Majesty will undergo

a microscopic decompressive laminectomy, which will create more space for the nerves.

The King suffered minor injuries to his back and shoulder while exercising at Chitralada Palace on June 24, a Royal Household Bureau statement released last Saturday said.

His Majesty accidentally stumbled and fell.

Later, an X-ray found a small fracture on the fourth rib on his right side. Following treatment, his condition has gradually improved.

Doctors have recommended he refrain from official duties and rest.

According to the Royal Household Bureau, the recovery period following the surgery is likely to be drawn out.

The King has suffered from spinal problems since 1995.

Meanwhile, the Army yesterday distributed 50,000 pictures of His Majesty through its secretariat.

Army spokesman Colonel Akra Tiproj said the Army's Tsunami and Disaster Centre wanted to publicise the King's speech to the general population and the infantry.

It printed 50,000 copies of the famous picture featuring the King waving from the main balcony of the Ananta Samakhom Throne Hall to a large crowd at the nearby Royal Plaza on June 9.