Recent Advances in Spine Surgery

The most dramatic advance in spine surgery over the past decade, says Dr. SK Rajan, Chief - Neuro Spine Surgery & Additional Director - Neurosurgery, Artemis Hospitals, Gurugram, India, is minimally invasive spine surgery (MISS) made reliable by 3D navigation: three-dimensional imaging in theatre linked to digital navigation. In his phrase, the field has moved from "first cut open and then see" to "first see and then cut".

For most of its history, spine surgery was practised the same way: a long incision, muscles stripped off the bone, a plain X-ray to confirm the level and coarse instruments to do the work. This guide sets out what changed, why it took the spine longer than other fields to get there, what the technology can and cannot do, and how surgeons should talk to patients about results.

How spine surgery evolved: safety first, then morbidity

Dr. Rajan describes the progress of spine surgery in two phases: the first made it safe, and the second has made it less punishing for the patient. The first was about safety. Operating microscopes, endoscopes and micro-instruments improved the surgeon's view of the nerves, and neuromonitoring (continuous electrical monitoring of nerve function during the operation) and modern bone drills joined them. Over the past two decades, and especially the past one, these advances have improved results dramatically, above all by making spine surgery safer.

Once safety was largely secured, the questions shifted to morbidity, the toll the operation itself takes on the patient. Will the operation be painful? What is the risk of infection? Most of medicine, in his view, has followed the same arc: first make a treatment safe, then make it less punishing. Minimally invasive spine surgery is the spine's answer to the second question, and it has taken its major leap in the past ten years.

The principle is that reaching a deep structure no longer requires collateral damage on the way. Instead of detaching the back muscles to expose the bone, the surgeon passes a narrow port through the muscle and works through it, carrying out the decompression (removing what presses on the nerves) and the fixation (screws and rods that hold the vertebrae) from inside. Side-by-side photographs of the same operation done both ways make the point: a long open wound on one side, a few short incisions on the other. The patient experiences less pain, less blood loss and a lower chance of infection. Operations that needed a large open exposure less than a decade ago, simply to place two screws, can now be done through a port.

Why 3D navigation came late to spine surgery

3D navigation reached spine surgery later than brain surgery because the spine moves once the patient is positioned, so images taken beforehand no longer match the anatomy. Surgical navigation works on the same logic as satellite navigation in a car: it shows where the instrument is in relation to a map of the patient. Neurosurgeons have used it for more than two decades to reach deep-seated brain tumours and in facial surgery.

The spine resisted, for a specific reason. Navigation depends on images taken before surgery, and the spine moves. Once the patient is positioned prone on the operating table, the vertebrae no longer sit where they did on the diagnostic scan, so the guidance drifts out of register with the real anatomy.

The solution was to take the images during surgery, after the patient is positioned, and feed that three-dimensional data set to the navigation system. The map then matches the anatomy as it actually lies on the table, and accuracy improves significantly. In theatre, the surgeon re-registers the navigation against a reference frame fixed to the patient at intervals during the operation to confirm that it is still accurate.

3D C-arm vs O-arm vs intraoperative CT

Dr. Rajan groups intraoperative imaging, meaning scans taken in theatre during the operation, into three broad categories: the 3D C-arm is the most basic and cheapest, intraoperative CT is the most accurate and most costly, and the O-arm sits between them. Each carries a different trade-off:

• 3D C-arm. The conventional C-arm gives two-dimensional X-ray images; the 3D version rotates around the patient to build a volume. It is the most basic of the three: image quality is limited, but it is cheaper and takes up little space in theatre.
• Intraoperative CT. The most accurate option, but also the one with the highest radiation exposure and the highest cost.
• O-arm. A mobile imaging system that rotates around the patient and reconstructs three-dimensional images, sitting between the other two: decent image quality, moderate radiation and a manageable cost. This is the system many centres around the world are now acquiring to enable minimally invasive and robotic spine surgery.

The O-arm's value extends beyond guidance. It shows the surgeon the size of the bone, confirms the accuracy of each screw, and provides a postoperative scan before the patient leaves theatre. That last point matters more than it might appear: a misplaced screw found on the table can be revised immediately, before the patient is woken and moved to the recovery area. In Dr. Rajan's experience, having this tool inside the theatre makes redo surgery very much less likely.

Paired with digital navigation, the images are projected onto a screen as a three-dimensional view of the patient's internal anatomy. The surgeon can see the deeper structures before making an incision, plan the entry points and trajectories, and then make cuts sized to the job. Dr. Rajan describes keyhole spine surgery done this way as 99% safe, a figure he is careful to define.

What keyhole spine surgery means

Keyhole spine surgery is surgery through a small skin incision that opens into a much wider working space at depth. The term "keyhole surgery" is apt, Dr. Rajan argues, for a precise reason. A keyhole is small from the outside, but when you put your eye to it you can see a great deal of the room. The ports used in MISS are dilated and expanded once inside, so the working space at depth is much wider than the skin incision. Through a single port, by tilting it, he can decompress both sides of the canal, which once would have required an approach from the midline; in one demonstration, four nerve roots were visible through the same port.

The details of how a lumbar fusion is planned and performed this way, and why the technique has opened surgery to osteoporotic and very heavy patients, are set out in the companion article on minimally invasive lumbar fusion.

Robotic vs navigation-guided spine surgery

Robotic and navigation-guided spine surgery rest on the same imaging and the same plan; in Dr. Rajan's view, the robot's guidance is not fundamentally different from navigation, and its advantage lies in volume and repetition. In a navigated operation the surgeon sees a live three-dimensional rendering of the screw as it advances into the bone. In a robotic operation the robot holds the screwdriver and drives the screw along the planned trajectory, guided by the same imaging and the same planning.

Where robotics earns its place is volume and repetition: a scoliosis correction, for example, in which many screws must be placed. For most other operations the guidance is the same principle delivered by a different hand.

Which spine conditions can be treated minimally invasively

Dr. Rajan's neuro spine surgery unit applies navigated, three-dimensional MISS across degenerative, traumatic, inflammatory, congenital and neoplastic disease. In his assessment, the two problems patients face most often are that the technology is not available, so they are offered large open operations, or that the expertise is not available, so the surgery is unsafe and they end up worse. The combination of technology and accumulated experience is what now allows complex operations to be done safely through small incisions.

The range extends well beyond the lumbar spine: thoracic vertebral collapse, spinal tumours at one or several levels, tumours in the neck extending out through the foramen, ossification of the posterior longitudinal ligament treated by minimally invasive laminoplasty, atlantoaxial dislocation, fractures of the axis, small tumours inside the spinal cord and spinal arteriovenous fistulas. These are covered case by case in the companion article on minimally invasive complex spine surgery.

Spine surgery safety: why "99% safe" is not "99% successful"

When modern spine surgery is described as 99% safe, Dr. Rajan is precise about what that means, a point he took up in the masterclass live discussion. Safety and success are separate measures. Safety is about not making the patient worse: out of 100 patients, 99 will have no deterioration in their condition. Success is about making the patient better, and it is a different conversation.

No one should hear "99% safe" as "99% of patients will get up and walk". A patient who arrives paralysed, especially after trauma, is unlikely to be made to walk again by any technology anywhere in the world, he says. Safety comes first and success follows, and success depends on the patient's preoperative condition, how long the disease has been present and how advanced it is on MRI.

Success is also defined by the patient. Dr. Rajan contrasts two people. One is a go-getter who wants to run and return to the gym; relieving his pain without restoring that will not feel like success to him. The other is housebound and wants only the freedom to leave home, travel and feel independent; for that patient, the same degree of improvement is a clear success. The surgeon's job is to establish which patient is in the room and set the expectation accordingly, ideally in a one-to-one discussion. How he decides between surgery and medical management, and what recovery involves, is covered in spine surgery recovery and return to sport.

Why patients doubt keyhole spine surgery: the perception gap

Doctors who do not perform minimally invasive surgery themselves often face a battle of perception when patients ask about it, and Dr. Rajan's answer is that confidence comes most readily from seeing results. In his view, that confidence comes from seeing patients who have already been operated on and were up the next day, and that published patient testimonials now make that easier. As the technology spreads to more centres and results accumulate, he expects the outcomes to speak for themselves.

He sees the main limitation today as the availability of technology. Growing up in a small town, he heard that Delhi had very good hospitals and technology without being able to picture what that meant. The same gap exists today between India and countries where these facilities are not yet available, and he accepts that it can be hard to believe that keyhole spine surgery, with walking the next day and 99% safety, is now routine practice. His answer is simply that the field has reached that point, and the limiting factor for patients is whether the technology is within their reach.