The 12-year-old daughter of Prince Andrew is suffering from curvature of the spine.

She is expected to undergo surgery at the Royal National Orthopaedic Hospital in London later in October.

Princess Eugenie will be having a very minor routine operation

Buckingham Palace spokeswoman

Princess Eugenie is sixth in line to the throne.

Curvature of the spine is a relatively common condition, affecting approximately three in 1,000 children.

One in three of those with the condition usually require surgery to correct the defect.

It occurs when vertebrae - the bones that make up the spine - become twisted.

The twisted vertebrae can pull the ribs around them and form a bulge on the back and cause the shoulder blade to stick out.

Princess Eugenie is believed to suffer from a displacement of one of her vertebrae.

She is expected to have bolt inserted to straighten the spine.

Routine operation

A Buckingham Palace spokeswoman said the operation was routine.

"Princess Eugenie will be having a very minor routine operation," she told BBC News Online.

It is mainly a cosmetic issue but we know that if it is not treated it can get worse

Mr Philip Sell, consultant surgeon

Mr Philip Sell, a consultant orthopaedic surgeon at Queens Medical Centre in Nottingham and secretary of the British Association of Spine Surgeons, said operations are carried out to prevent the curvature from becoming worse.

"It is mainly a cosmetic issue but we know that if it is not treated it can get worse," he told BBC News Online.

"The surgery is aimed at preventing curvature of the spine from getting worse and reducing the incidence of back pain that may be associated with it."

He suggested that the princess would need rest after the operation.

"Generally speaking we allow children to return to school at about four to six weeks after the operation and to avoid contact sports for about a year."

A spokeswoman for the Scoliosis Association, a support and information group for people with curvature of the spine, said: "The condition generally affects adolescent girls."

Speaking to BBC News Online she added: "Girls go on to live a full and normal life after surgery."

The princess is the youngest daughter of Prince Andrew and his former wife the Duchess of York.