HA Chairman Leung Che-hung said the authority had contacted about 1,500 patients who had recovered from the Severe Acute Respiratory Syndromeand found about 50 of the 500 who had undergone medical examinations were found to have avascular necrosis.

"We have carried out examinations on about 400 to 500 patients in about 12 post-SARS rehabilitation units and found that after X-rays were carried out, about 10 percent of them were shown to be suffering from bone degeneration," Leung said.

The disease results from the temporary or permanent loss of blood to the bones, causing tissue to die and sometimes bones to collapse. It commonly affects the ends of longer bones.

Medical experts have said the problem in some recovered SARS patients was possibly linked to the use of the controversial anti-viral drug ribavirin and steroids.

The disease was detected in the hip joints of 28 of the 50 patients, a HA spokeswoman said.

The amount of disability that results from avascular necrosis depends on which part of the bone is affected, the size of the affected area and how effectively the bone rebuilds itself.

Some patients recover naturally after a period of observation, others require a de-compression procedure on the hip joint, while a hip joint replacement operation is needed for the most serious cases.

The HA said it is continuing its investigation into whether the bone disease is linked to the treatment received by SARS patients or whether it is caused by SARS itself.

It conceded, however, that bone weakness was a known side-effect of steroid treatment.

The Hong Kong government was criticised by some in the medical sector for persisting with Ribavirin and steroids as a SARS treatment.

Studies by US health experts earlier found that Ribavirin was ineffective in combatting the virus while fears were raised over possible side-effects from the high steroid doses used in treatment.

Earlier this year, SARS infected more than 8,000 people worldwide, killing

Hong Kong was the second worst-affected region with 299 SARS-related deaths and nearly 1,800 infections.

TERRA.WIRE