The chief of orthopedic surgery at Children's Hospital has invented and successfully used a device designed to straighten the severely curved spines of younf children suffering from a condition known as kyphosis.

Dr. Doughlas McKay said at a press conference yesterday that his procedure does not eliminate the paralysis from which these children suffer, but it does eliminate the hump back with which they have previously had to live.

The operation, which takes eight hours and has been performed 13 times, also extends the life of the children, by straightening them up, McKay said. This relieves pressure on their lungs and intestines caused by their bent-over posture.

"This has been an answer to a prayer," said David Mannes of Norfolk, who was attending the press conference with his wife, Irene, and 10-year-old daughter Laura, one of McKay's patients.

"We've been looking for years for a doctor with the skill and knowledge to do this," said Mannes. "We've gone from hospital to hospital."

McKay showed slides of Laura before and after the operation. In one photo she was bent over and had a large hump in her back. In the other she sat as straight as any child is willing to sit, hump free and smiling.

McKay's procedure involves using U-shaped stainless stell bolts to pull the spine, which curves outward, in to its natural position where it is held fast to a narrow stainless steel plate.

Some of the material between the vertebrae is removed, and the space thus created is packed with some chips. The goal, explained McKay, is to fuse the spine in the proper position. The plate and bolts are left in, but only as a precaution.

Kyphosis is caused by a number of conditions, McKay said. Some children are born with it, some develop it as a result of paralysis, some because of a tumor, while in others it develops after a serious accident.

According to McKay, one in every 10,000 children is born with the problem. At that rate, about 350 such children would be born in the United States every year. An additional group develops the condition after birth. Thus far McKay has tried his procedure only on those children who developed the condition after birth as a result of paralysis.

He said he has not yet tried it on those born with kyphosis because the are generally not paralyzed. he said he has been wary of attempting to use the device on a child whose spinal cord has been functioning, because of the possibility of damaging the cord.

Describing the effect of the operation on the children, McKay said, "The greatest improvement we've seen has been in social problems," he young patients - who have ranged in age from 6 to 10 - had dropped out of school because of her deformity, "and now does well in school."

Carol Holden, who attended the press conference with her paralyzed 7-year-old son, David, the first child on whom McKay used his device, said David used to suffer from constant problems with open sores on his back. "I don't have to worry about his back now," said Holden.