BOSTON (CNN) -- When surgeons built a new thumb joint Friday, it was a tiny step forward for reconstructive surgery -- about an inch. But according to researchers, that inch is an important first step in a new field of medicine.

The process is called tissue engineering: doctors harvest key cells from a patient's body, culture them, and shape them to create a new organ or body part.

Most of this work has been done on animals, but on Friday researchers at the University of Massachusetts Medical Center performed an operation to restore a man's thumb. Most of the last joint of his thumb had been lost in a car accident.

The surgeons built a scaffolding in the same shape as the bone in the last thumb joint.

That scaffolding was then encased in flaps of skin and fat at the end of his thumb, and stem cells destined to grow into bone were put into the scaffolding.

Bone cells grow to fill scaffolding

Capillaries were diverted to feed those immature bone cells, with the hope they will grow into the shape of the scaffolding, and provide the man with skeletal structure for a new thumb tip.

If this procedure works, they will perform a second operation to attach cartilage and tendons, so it can become a working appendage.

The key researcher, Dr. Charles Vacanti, said the operation appeared successful, but that it would take 12 to 16 weeks before they knew if the new bone was forming properly.

The patient was released from the medical center Saturday, according to the center's administrative manager, Steven Pease, but will return frequently for evaluations.

10 years of trials on animals

Vicanti said they had been working on these techniques in animals for about 10 years and had demonstrated their ability to build new ears and tracheas for animals.

Friday's operation was their first attempt at creating new bones for humans. The researchers said they were optimistic because of their success in the animal models.

Growing skin, bone, cartilage and tendons is quite practical, but they say the holy grail of tissue engineering -- nerves -- is still out of reach.

In order to create a whole new finger or limb, nerves would have to be grown, too, so that feeling and motor control could be conducted.

The technology for growing new nerves is still in it's earliest stages, even though some preliminary success has been reported in test trials with rats.