Then, using what doctors call a "bone biter," the 21st century medical equivalent of a ancient tool blacksmiths use to pull horseshoe nails, he "bit" off the two lamina, or dorsal ridges of the two vertebrae. This relieved a major part of the pressure on the spinal canal, which immediately began swelling back toward its normal diameter, like a tubular balloon released from a knot. But that was only part of the task.
Reaching into the cavity holding the membrane-encased nerve channel, Ludwig then shielded the nerves and their fluid-filled enclosure with dorsal retractors and began carefully scraping away the arthritic deposits and excess soft tissue that had been crowding them. The cyst that had shown up in the MRI burst harmlessly as it was being removed, but this had been expected. Biting off the two lamina and cleaning away the accumulated spinal debris took 40 minutes.
Surprisingly, at least to a layman, Ludwig did nothing direct or dramatic to correct the misalignment of the vertebrae.
"We've found that if we position the patient correctly on the operating table, the misalignment corrects itself with the pushing and pulling of the devices we install," he said. "The crux of the operation lies in stabilizing it in the correct position from then on."
To do that, he positioned two titanium rods on either side of her spine, each about 1½ inches long and roughly the diameter of a pencil. The rods spanned the disc between the fourth and fifth lumbar vertebrae. Each would be held in place by a titanium screw at either end.
"The process of stabilizing the spine like this is not particularly difficult," Ludwig said. "The art lies in selecting the right size screws and rods." People, he said, vary enormously in the thickness and density of their backbones. Some tiny people have hefty spines, he said; some very large people, quite small ones.
Roberta's spine, he said, is about average in size for her 5-foot-9 height and athletic build. But her bone quality, he said, is "really excellent"--far better than average in a female population where osteoporosis is close to epidemic.
For her he selected titanium screws about five millimeters in diameter and 55 millimeters--more than two inches--long. The task of setting them in place was not too different from that of a weekend do-it-yourselfer putting screws in a shelf, he said: "We both use power tools."
For each of the four screw holes, he used a high-speed electric burr to pierce the hard outer sheath of the vertebra, then inserted a probe into the softer marrow to create a pathway for the screw. The process was carefully monitored via a real-time X-ray, or fluoroscope, to route the channel away from any vulnerable nerve and to assure its positioning in bone large and dense enough to secure the screws.
Roberta's nerve function was also monitored during the operation, via small electrodes inserted in her hands and feet. These assured that the spinal nerves continued to carry the requisite tiny flow of electricity that triggers muscle movement. In addition, after each screw was driven in place, using the surgical equivalent of a Phillips screwdriver, a tiny amount of electrical current was sent through the screws themselves. When it wasn't picked up by the electrodes in her feet, the doctors were certain the screws were well insulated from the spinal cord.
Installing the screws and pins took about 20 minutes. During the final 20-minute part of the operation, Ludwig drilled from the spinal incision into Roberta's right hip bone -- the iliac crest of the pelvis -- just inches away. From there, using the surgical version of a miniature ice cream scoop, he removed a portion of bone marrow about the size of a large chickpea. This he packed alongside the titanium rods onto the two abraded vertebrae, into which it would grow and fuse them into one.
Then the surgeons removed the retractors that had spread Roberta's back muscles away from the spine, and closed the incision with 18 "staples," or knots of surgical thread.
