Minimally Invasive Spine Surgery: Indications and Limits

Minimally invasive spine surgery suits specific patients rather than every spine problem: a contained disc herniation, a painful osteoporotic compression fracture with no infection or retropulsed fragment, cervical disc disease where movement can be preserved, and some deep paravertebral tumours. Its gains are less blood loss, a shorter hospital stay, less pain and faster healing. Robots now guide screw placement, but nerve decompression is still done by the surgeon.

Dr. Anil Kumar Kansal, Vice Chairman & HOD - Neuro Surgery & Neuro Spine, BLK-Max Super Speciality Hospital, New Delhi, India, frames the case for minimally invasive spine surgery in those four outcomes. They are the reason his unit has adopted endoscopic, percutaneous and small-incision techniques across its neuro spine surgery work.

What follows is a procedure-by-procedure account of how that shift plays out in practice, from disc herniation and osteoporotic fractures to cervical disc replacement, deep paravertebral tumours, upper cervical instability and robot-guided screw placement. For each, the useful question for a referring doctor is the same: which patients are suitable, and where does the minimally invasive route stop being the right answer?

Endoscopic discectomy for a herniated disc

Needle-based percutaneous disc decompression suits only the contained disc, a bulge that is compressing the nerve but has not extruded into the spinal canal; endoscopic discectomy can also retrieve extruded fragments, provided they have not migrated far. Discectomy is the first tier of minimally invasive work. Dr. Kansal's unit removes disc material by percutaneous and endoscopic methods, working under direct vision to free the compressed nerve. That is the patient in whom a small working channel can reach the problem without the need for wider exposure.

In a case Dr. Kansal presented, an L5-S1 disc prolapse was compressing the nerve root on the right side, and the operation was done through a small retractor. Through it the team removed a limited amount of soft tissue and bone to reach the disc level, opened the annulus (the tough outer ring of the disc) while protecting the nerve root, took out the disc material and then retrieved the extruded fragment lying under the root. The entire operation proceeded through that small retractor.

The distinction matters when counselling patients. "Keyhole" is not a single procedure, and whether the disc is contained or extruded shapes which approach fits. Indicative costs for microdiscectomy and discectomy are listed separately.

Kyphoplasty for osteoporotic compression fractures

Kyphoplasty treats a painful osteoporotic compression fracture with an injection of bone cement into the collapsed vertebra, and the patient can be mobilised from the next day. It is the second procedure Dr. Kansal described, used for compression fractures of the spine. The typical patient is elderly with osteoporotic bone, and the fracture can follow trivial trauma such as a minor fall, a sudden movement, or even coughing or sneezing. The vertebral body collapses and the pain is considerable.

The conventional treatment was absolute bed rest for two to three months, with medication to let the bone heal. Dr. Kansal's objection is practical: most elderly patients cannot tolerate two or three months flat in bed, and they want to remain mobile.

Kyphoplasty replaces that approach: the cement is injected percutaneously, through the skin, and fills the vertebral body to stabilise it. Dr. Kansal puts the pain relief at more than 90% by the next day for a painful osteoporotic fracture.

Kyphoplasty contraindications

He named two contraindications:

• Infection. Kyphoplasty is not performed in an infected vertebra.
• A retropulsed fragment. If a fragment of bone has been pushed back and is compressing the nerve, kyphoplasty can worsen the compression, and cement can leak into the spinal canal, causing paraplegia or nerve damage.

The second contraindication is the one most worth checking on the imaging before referral, because it can turn a percutaneous case into one that needs decompression.

Cervical disc replacement vs fusion

Cervical disc replacement preserves movement at the treated level, which fusion gives up, and is associated with a lower rate of adjacent segment disease than fusion. Cervical disc disease most often affects the C5-C6 level, followed by C6-C7. For cervical disc disease, the established operation is anterior cervical discectomy and fusion: remove the disc, insert a graft and fuse the segment. Dr. Kansal's critique of fusion is that it trades one problem for another. The fused segment loses its movement, and over time the stress transfers to the levels above and below, which can degenerate and produce adjacent segment disease.

Disc replacement addresses this directly. It restores movement at the treated segment, and because mobility is maintained, the risk of adjacent segment disease is lower than after fusion.

The technique, as he demonstrated it, runs in a defined sequence:

1. Expose the cervical disc space from the front and remove the disc completely.
2. Place two pins and retract to open the disc space slightly.
3. Remove the posterior osteophytes as well as the disc.
4. Measure the disc space and select the implant size.
5. Insert the artificial disc, whose surface spikes hold it against the vertebrae.
6. Check movement on imaging: the disc space should be seen opening and closing as the neck moves.

The final check is the point of the operation. Fusion succeeds when nothing moves; replacement succeeds when the segment does. Dr. Kansal also notes a practical patient benefit: after disc replacement the patient does not need to wear a cervical collar for a long period.

Removing a paravertebral tumour through a 2 cm incision

A deep paravertebral tumour, one lying beside the spine, no longer automatically needs a large open operation. One case in the session was a neurogenic tumour in the paravertebral region. The conventional options for a tumour in this position are an approach through the spine itself or a retroperitoneal approach. Both need a large incision, and both make the tumour difficult to remove.

Dr. Kansal's team instead used a minimally invasive approach through an incision of about 2 cm in the paravertebral region. The steps were:

• Dilators were placed to create a working corridor.
• Soft tissue and bone were cleared until the tumour came into view.
• The tumour, which was highly vascular, lay between two transverse processes, so part of the transverse process was nibbled away to create space.
• Bleeding was controlled with coagulation as the dissection progressed.
• Because the tumour would not deliver in one piece, it was removed piecemeal, with its attachments coagulated and cut before the final portion was delivered.

At the end, the nerve root was visible and intact. The tumour had been removed completely through the 2 cm incision with the nerve preserved, an operation Dr. Kansal describes as very difficult by conventional means. For a referring doctor, the lesson is that a deep paravertebral tumour is no longer automatically a large open operation.

Upper cervical instability: odontoid fracture and atlantoaxial dislocation

An odontoid fracture can now be fixed with a single screw from the front, while atlantoaxial dislocation with compressive tissue needs two operations.

Odontoid fracture screw fixation

A fracture of the odontoid process, the peg of the second cervical vertebra, can look nearly aligned on a static image. With movement, however, the odontoid fragment shifts forward while the rest of the vertebra stays in place, which is the instability that has to be fixed.

Fixation from behind is possible but requires extensive opening. Dr. Kansal's unit now uses a percutaneous or minimally invasive anterior approach, passing a single screw across the fracture to achieve internal fixation of the two fragments.

Atlantoaxial dislocation: two-stage surgery

Atlantoaxial dislocation, abnormal movement between the first and second cervical vertebrae (C1 and C2), is a more complex problem. In the case Dr. Kansal showed, abnormal tissue at the craniovertebral junction was causing compression and the arch of C1 was moving forward. This requires two operations:

• First stage, through the mouth (transoral decompression). The abnormal compressive tissue is removed to free the cord.
• Second stage, from behind. The segment is then fixed posteriorly.

The staging reflects two separate problems: the compression lies in front and must be removed from the front, while stability is restored by a separate posterior fixation.

When does a vertebral haemangioma need surgery?

Small haemangiomas are benign vertebral tumours and need no treatment unless there is a fracture of the vertebra. A referring doctor from Nigeria raised a case of a haemangioma found on MRI in the cervical vertebrae in the Live Discussion, and Dr. Kansal's answer sets out a clear threshold.

Intervention becomes necessary in three situations:

• The haemangioma is large and involves the pedicle, the bony bridge joining the vertebral body to the back of the vertebra.
• It has caused a fracture.
• It has weakened the bone enough to threaten stability.

In those cases the spine needs decompression and fixation. Where a larger haemangioma is destroying the vertebra, it must be removed. These are very vascular tumours, and after removal the vertebra is reconstructed with a cage and bone, and the spine is fixed. Size and the integrity of the vertebra, not the presence of the lesion, decide the management.

Robotic spine surgery: benefits and limitations

Robotic spine surgery places screws accurately, with less radiation and in less time, but the current robot cannot decompress nerves. Dr. Kansal's assessment of robotic spine surgery is precise about both its value and its limits.

What the robot does

Planning happens before the first incision. The surgeon plans on the robot's system which screw size is needed and which trajectory each screw should follow. Once the plan is set, the robotic arm guides the drill along the planned path, and the surgeon watches the screw's progress on screen. The screw goes where it was planned to go.

He identifies three advantages:

• Accurate placement. Screws are placed at the planned position without failure, avoiding the complications of malplaced screws and the nerve damage they can cause.
• Less radiation. Radiation exposure is lower.
• Time saved. The bulk of the work is done in the planning stage, so the operation itself moves faster.

In a case he presented, the post-operative images showed near-identical, well-placed screws with the listhesis (slippage of one vertebra over another) reduced.

What it does not do yet

The current robot cannot decompress nerves. The robotic arm places screws; it does not remove the bone or disc compressing a nerve root. That part of the operation is still done by the surgeon under the microscope or endoscope. Dr. Kansal therefore describes current robotic spine surgery as partial robotic surgery: robot-guided instrumentation combined with conventional decompression.

Companies are working on a robotic arm for decompression, and only when that arrives will fully robotic spine surgery become possible. Until then, the value of the robot lies in instrumentation accuracy and radiation reduction, not in replacing the surgeon's hand for the neural work.

Choosing the right minimally invasive spine surgery

The common thread is that each technique narrows the gap between the size of the problem and the size of the operation. A contained disc no longer requires open exposure; an osteoporotic fracture no longer requires months in bed; a cervical disc can be treated without sacrificing motion; a deep tumour can come out through 2 cm. The robot adds accuracy to the part of spine surgery that is most mechanical.

Each procedure also carries a clear selection rule, and those rules are where the referring doctor adds most value: a contained versus extruded disc, a retropulsed fragment on the fracture imaging, the size and pedicle involvement of a haemangioma. The realistic outcomes and complication rates of spine surgery, which shape how these options should be presented to patients, are covered in recent advances in spine and neurosurgery: a complete guide. The same planning-first precision in cranial surgery, from stereotaxy to neuronavigation, is described in endoscopic brain surgery, from ventriculostomy to colloid cysts.