Reset bones, regain form
Whatever the technique or equipment, no doctor can deny that the final beneficiary should be the patient whose disability should be corrected, writes GOUTAM GHOSH.
THE afternoon before her surgery, Deepa, a teenager from Kerala, was in high spirits, though her back had an imperceptible bend like an inverted S a typical case of scoliosis. She had complained of laboured breathing. Her mother noticed the deformity and brought her to hospital.
Early next morning, an inert Deepa lay prone on pillows that raised her back. Her skin wore a yellow tint because of the self-adhesive disposable sterilised drape. She was then covered with cloth drape, exposing only her vertebral column. After a quick incision down the curve of her spine, the surgeon reflected (rolled back) her muscles to expose the milky white vertebral column.
"It is difficult to drive a screw correctly into the pedicle," said Dr. S. Rajasekaran, director, Ganga Hospital, Coimbatore. A pedicle is a narrow bone bridging the front and back sections of a vertebra. "Like fingerprints, the pedicle's shape and size vary greatly. At its widest it is seven to eight millimetres, requiring screws to a maximum six millimetre diameter. In scoliosis, the anatomy is deranged not only at each vertebral level but also between the convex and concave sides of the curve in the spine. Higher up the vertebral column the pedicle becomes smaller and angles more acute," said Dr. Rajasekaran.
"The aim is to correct the deformity. To grip the bone, the screws have to be driven in the right direction. A little deviation, and you will hit the spinal cord or the nerve root or damage the pedicle that supports the screw. Traditionally surgeons have depended on fluoroscopic images. While such images may suffice for normal people with well-shaped pedicles, these are inadequate in scoliosis patients where the pedicle's size, shape and tilt change not only between levels but also between the concave and convex sides. The anatomy changes as the severity of curve progresses," said Dr. Rajasekaran.
Even though the surgeon begins by pushing a sharp probe to form the path for the screw and moves away the moment he hits the hard outer edge of the pedicle, there could be errors of judgement.
"Suppose the screw is misaligned, there may not be a second chance as reorientation will reduce the hold of the screws. This will fracture the pedicle or pull out the screw when the curve correction is tried by aligning the screws to suitably contoured rods. It is the rod that corrects the scoliosis or kyphosis, not the screws. I decided to invest in the 3D navigation system to rule out errors," said Dr. Rajasekaran.
The computer-aided spine surgery depends on two sophisticated machines: the one, the iso-C 3D C-arm (isocentric three-dimensional C-shaped arm) that rotates 360 degrees and produces 240 slices similar to a computerised tomographic (CT) scan of every 12 cm of the surgical section; the other, a computer-aided navigation system that uses the slices to generate a 3D view of the surgical field. Without these, a surgeon can see only the surface and must rely on his experience, knowledge of anatomy, ability to generate 3D images in his mind's eye, and translate all these into corrective action. At the end of the three-hour operation, Deepa's vertebral column looked straight. The implanted alloy rod had corrected her deformity.
"Error in placing the screws to correct kyphosis (vertical warping of the vertebral column) or scoliosis (lateral warping of the vertebral column) has been five to seven per cent, according to data available worldwide. It is theoretically possible to reduce the error with a sophisticated guidance system," said Dr. R.H. Govardhan, professor of orthopaedic surgery, Children's Hospital, Egmore, Chennai.
The navigation system is installed only in a handful of hospitals because of its price nearly Rs.1.4 crores. Unless there is a huge demand for surgical procedures where the system can be used, the investment may be unjustified.
"We have been replacing hips and knees without the navigation aid. The surgical jigs are enough to rule out errors. The re-do case load to correct our errors is low. The navigation system can reduce the margin of error, but not very significantly, especially in knee replacement where the outcome of the surgery depends on soft tissue balance. To my knowledge, there is no navigation system for soft tissue balance in knee replacement," insisted Dr. C. Rajasekhara Reddy, orthopaedic surgeon, Vijaya Institute of Trauma and Orthopaedics, Vijaya Hospital, Chennai. The probable reality is a patient may opt for re-do surgery at another hospital.
Surgeons innovating surgical techniques or using state-of-the-art equipment are loners, the majority being happy with time-tested norms. Whatever the technique or equipment, no doctor can deny that the final beneficiary should be the patient whose disability should be corrected. There is little any doctor can do about the quality of a patient's existence the effects of stress, malnutrition, and injurious habits.
Names of patients changed to protect their identity.
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