Minimally Invasive Complex Spine Surgery: Tumours and OPLL

Minimally invasive complex spine surgery applies the navigated, three-dimensional keyhole approach to problems that once demanded the largest open operations: tumours compressing the spinal cord, collapsed vertebrae, severe cervical compression, instability at the top of the neck, fractures of the axis and lesions inside the cord. Dr. SK Rajan, Chief - Neuro Spine Surgery & Additional Director - Neurosurgery, Artemis Hospitals, Gurugram, India, treats each through small ports.

Minimally invasive spine surgery is often associated with routine lumbar disc and fusion work, but the same logic extends to these harder cases. The common thread is a question he poses directly: when the problem lies deep, why punish the muscles on the way in?

The tools that make this possible are neuromonitoring, good endoscopes, specialised retractor systems and intraoperative three-dimensional imaging with navigation. What follows is a tour of the cases he presented, grouped by region and problem, from his neuro spine surgery practice. The lumbar work is covered separately in minimally invasive lumbar fusion.

Minimally invasive spinal tumour surgery and thoracic corpectomy

Dr. Rajan's unit removes spinal tumours at one or several levels, and treats collapsed thoracic vertebrae, through small ports rather than long open incisions. In one patient, a vertebra in the thoracic (dorsal) spine had collapsed; Dr. Rajan noted that the cause might be trauma, though he considered it a tumour case. The collapse was compressing the spinal cord significantly. The operation required removing the vertebral body (a corpectomy), placing a cage in the gap and fixing the segment with screws above and below. Conventionally this means a large open exposure. Here the screws were planned and placed with navigation, and the corpectomy and cage placement were carried out through a small port.

Epidural tumours are a second group. These are tumours that compress the spinal cord from outside rather than growing from within it. Through a small port that is expanded once inside, the surgeon removes the overlying bone and then works through that window to remove the tumour, or a collection such as pus. Dr. Rajan's unit now treats spinal tumours at one level or two, inside or outside the canal, through minimally invasive technique. In one case a tumour spanning three levels and compressing the cord was removed through a small port, through a short incision where the open operation needs a long one. He notes that the long open incision is still used in many countries. Large tumours lying outside the canal are also approached through the port.

Removing a cervical tumour near the vertebral artery

Even a tumour in the neck pressing on the vertebral artery was removed minimally invasively; in the case Dr. Rajan presented, a contrast MRI after surgery showed complete removal. One of the most demanding cases Dr. Rajan presented was a tumour in the neck growing out through the foramen, the opening through which a nerve root leaves the spine. It was compressing the spinal cord and the vertebral artery on that side, which was barely visible on imaging because of the compression. The patient had significant weakness, difficulty walking and bladder and bowel involvement, and had a short, thick neck, which would have made open surgery a very long incision with extensive dissection.

The team chose a minimally invasive approach instead. The bone was removed to reach the tumour, the tumour was excised, and the spine was stabilised. A contrast MRI after surgery showed complete removal. Dr. Rajan credits access to the technology and his experience from Cleveland Clinic for making the approach possible.

OPLL treatment: minimally invasive laminoplasty

Dr. Rajan treats severe cervical cord compression from OPLL with minimally invasive laminoplasty, an operation that widens the spinal canal from behind. Ossification of the posterior longitudinal ligament (OPLL) is a cause of degenerative cervical myelopathy in which the ligament running along the back of the vertebral bodies turns to bone, narrowing the canal and compressing the spinal cord. In the patient Dr. Rajan showed, the compression was very severe; after a fall he could not move his arms, and his leg movement was also poor.

The operation chosen was a minimally invasive laminoplasty under neuromonitoring. A small cut is made in the bone at the back of the canal, the space is opened up, and mini plates are fixed to hold the expansion. The canal widens dramatically and the cord is freed, which Dr. Rajan describes as allowing the spinal cord to breathe. The same approach has been used for stenosis extending over several levels.

Tethered cord release through a small port

A tethered cord in a child can be released through a small port and a scope rather than open surgery. A tethered cord is a congenital problem in children in which the spinal cord is pulled downwards by an abnormal attachment at its lower end, usually a thickened filum terminale. Treatment requires the tethering band to be divided. This is normally done by open surgery, and the open exposure is what causes much of the morbidity. Through a small port and a scope, Dr. Rajan's team locates the tethering tissue, clips it and divides it.

Atlantoaxial dislocation and hangman's fracture surgery

The craniovertebral junction, where the skull meets the top of the spine, is a risky area to operate on, and Dr. Rajan's unit treats its instability and fractures minimally invasively with navigation.

Minimally invasive surgery for atlantoaxial dislocation

Atlantoaxial dislocation is instability between the first and second cervical vertebrae, the atlas and the axis, which can damage the spinal cord at the top of the neck. It is conventionally treated by open surgery, the operations are very risky, and few centres in the country undertake them. Dr. Rajan's unit performs them in large numbers, and does so minimally invasively.

Navigation is the enabling factor. It shows, from outside the body, the trajectory each screw must take. A port is placed, a guide wire is advanced, and the first cervical vertebra is targeted step by step. The same technique is used for other cases of cord compression, dislocation and instability at this level.

Hangman's fracture fixation

A hangman's fracture is a fracture through both sides of the second cervical vertebra, which allows the front of the bone to slip forward on the vertebra below. In the case presented, the bone had displaced anteriorly. The aim of surgery is to realign the fragments, bring them together and fix them.

Because this area is risky to approach, Dr. Rajan has seen centres place screws at many points around it, because they lack the experience or exposure to approach it directly. Using techniques learned during his training in Mumbai and in the UK, his team places the screws through small cuts and aligns the fracture without open surgery. Several screws can be placed through the small port when the instability requires it.

Intramedullary spinal cord tumours and spinal AV fistulas

The newest application in Dr. Rajan's practice is small intramedullary tumours, those inside the spinal cord itself, which his unit now approaches through minimally invasive surgery. The problem lies within the cord, and the overlying muscle does not need to be sacrificed to reach it.

Spinal arteriovenous fistulas, abnormal direct connections between an artery and a vein around the cord, previously required open surgery. Angiography now tells the surgeon exactly which point to target, so there is no need to expose the whole region: a scope is placed at that point, a clip is applied and the problem is solved, all through a small cut.

Cervical and lumbar disc disease together: which to operate on first

Some patients have disc disease at both cervical and lumbar levels, a scenario Dr. Rajan addressed in the masterclass live discussion. Dr. Rajan's view is that multiple prolapses are not, in themselves, a reason for open surgery, and the question becomes one of sequence:

• Cervical myelopathy with weakness. If cervical myelopathy, meaning cord compression in the neck, is causing weakness, the cervical spine is operated on first, because the surgeon does not want the neck held in the wrong position during lumbar surgery.
• Arm pain without significant cord compression. If the neck problem is mainly pain radiating into the arm, the MRI shows little compression and most of the pain comes from the back, the lumbar spine is treated first, because that is the complaint the patient most wants resolved.
• Same sitting where feasible. When only a few levels are involved, both regions are usually treated in the same sitting where possible, and the order no longer matters. When separate operations are needed, the cervical spine usually comes first.

Across these cases, the decompression, removal or fixation the disease demands is unchanged; what has fallen sharply is the collateral damage required to reach it. How these gains should be explained to patients, and why "99% safe" must not be heard as "99% successful", is set out in the guide to recent advances in spine surgery.