Minimally Invasive Lumbar Spine Surgery

In medieval England a few hundred years ago before surgery was even considered part of medicine, and the only members of the Royal College were physicians. Almost all surgery consisted of looking after trauma to the limbs with the commonest surgery performed being amputations. The local barber was also the local surgeon and you would visit the same establishment to get your haircut as to get your leg amputated. That's is the reason why in the UK and some other parts of the world including some states in Australia surgeons, after gaining their fellowship to the Royal College of Surgeons, would make a considerable ceremony of losing the "Dr" prefix to their name and becoming a "Mr" once again - a kind of reverse snobbery to the physicians but also a remembrance of their roots. Walking down the high street you would see signs in the windows of barber shops advertising the 'average time to take off a limb' because, of course, anaesthesia as a speciality had not started, and describing techniques that minimised the trauma of surgery. Today surgery as a speciality has advanced tremendously, but still the onus is on developing newer and better techniques that enable us to get the desired result with as little collateral damage as possible.

Minimally Invasive Surgery (MIS) means different things depending on what speciality it is applied to. In general surgery for example many operations that decades ago required large incisions and 'direct vision' are now performed using tiny cameras and digital images. Whereas decades ago the pioneers of this technology were ridiculed, now the hangers-on to old techniques are held in ridicule. This is true laparoscopic surgery, or 'key-hole' surgery. A few decades ago in orthopaedic surgery, a broken bone had to be pieced anatomically together, piece-by-piece and a massive plate applied to the bone to hold it all together requiring a large incision, stripping of muscle and often devascularisation (killing the blood supply) of most of the bone fragments. Today small incisions are made away from the fracture site and the fracture stabilised with a nail which goes down the middle of the bone, or a plate which is slid up the side of the bone instead. Less attention is paid to getting the bone fragments anatomically perfect but instead preserving the tissues and stabilising the fracture. This type of surgery is called Lesser Invasive Surgery - it is not keyhole surgery, but is a far cry from traditional open surgery. Minimally Invasive Spine Surgery (MISS) is somewhere between these two in it's philosophy. Incisions have to be large enough to allow access to our instruments and implants (like a disc replacement for example) but a lot of the visualisation is performed with x-rays or computer navigation. I personally think that 'minimally invasive' is a poor choice of words to describe it's application to the spine - I prefer to describe it as 'minimally destructive'. This reflects the fact that sometimes our incisions can be quite large but they use tissue planes inside the body that cause very little damage - for example the anterior approach to the spine (i.e. going in from the front through the abdomen) uses an incision that gets to the spine by going between muscle (as opposed to splitting it) and simply moving structures out of the way - hardly any trauma is caused and very little blood is lost but the incision can still be upwards of 10cm especially if the patient is on the rotund side. Techniques and retractors now mean that even posterior surgery (through the back) which traditionally is the most traumatic in terms of muscle damage and blood loss, can be performed using muscle splits and, with radiographic guidance, sizeable implants can be inserted to reconstruct the spine. Pedicle screws and rods which are sometimes employed to augment reconstructive surgery used to have to be inserted through huge incisions with dissections that often devascularised levels away from the site of surgery can now be inserted through small stab incisions and x-ray guidance with far greater precision than ever before. The extreme lateral approach to the spine is the newest technique in the armamentarium of the modern spine surgeon and has revolutionised minimally destructive spinal reconstruction in that all of the advantages of anterior surgery can be utilised with very few of the risks. A great resource for patients wishing to understand more about the extreme lateral approach to the spine can be found at the NuVasive website or from the Society of Lateral Access Surgeons (SoLAS) website.

The trauma caused by surgery to perform the procedure has been called various things - "The Cost of Surgery" or "The Surgical Footprint" are two for example. In traditional, open spine surgery this is high and some patients quite frankly never recover from it. Modern minimally invasive techniques reduce the surgical footprint considerably and many studies in the scientific literature now attest to them being able to produce a much better outcome. One of the main reasons for this is that it is actually much easier to perform MISS (given the right training) than to perform traditional open spine surgery. If you have had a traditional approach taken to your spine and had a good result then you have been under the care of a tremendously skilled surgeon!

We will discuss on this page all of the techniques and approaches that are used in MISS because it is likely that a combination of them will be applied to your spine if you are contemplating surgery under my care. A quick lesson on terminology first though:

  • Anterior - this word simply means front. Anterior approach to the spine therefore means approaching the spine from the front, through the abdomen. Anterior reconstruction means addressing the front column of the spine - where the discs lie.
  • Posterior - this word simply means behind. Posterior approach to the spine therefore means approaching the spine from the back. Posterior fusion means fusing the spine down the posterior column - ie the back of the spine where the spinous processes, facet joints and lamina are.
  • Lateral - simply means from the side.
  • Fusion - stabilising the spine by fusing one vertebral body to the next with a bony bridge similar to how a fractured bone heals.
  • Arthroplasty - means joint replacement. If you have a total hip replacement, then you have had a total hip arthroplasty in medical speak. In the spine total disc arthroplasty (TDA) means you have had your disc removed and the spine stabilised with a moving prosthesis - see the page on Total Disc Replacement.

Depending on your spine and pathology, a combination of approaches and a combination of fusion and arthroplasty is usually employed to reconstruct and stabilise the degenerate segment. TDA will be discussed on it's own page.

Anterior Spine Surgery

The lower two discs in your spine (L4/5 and L5/S1) are especially amenable to reconstruction via the anterior approach. This technique means an incision about 6-10cm on the front of the abdomen below the belly button. Whilst sounding like the most ludicrous way to get to the spine it is actually the least destructive, quickest and least painful. Another big advantage of the anterior approach is that the nerves of the cauda equina do not have to be touched - in fact they are not even seen - meaning far less chance of scar tissue forming around them. The front of the your spine, where the disc lies, is actually closer to the skin on the front of your abdomen than the skin on your back - depending on how big you are. It is the front of your spine that needs to be reconstructed so it makes sense to approach it from the front. You will have understood from the page on spine anatomy and mechanics, and the page on the causes of back pain, how important restoring disc height and lordosis is to the normal functioning of the spine and the nerves? The anterior approach to the spine allows for greater restoration of both these attributes than any other approach. Given that 60-70% of the lordosis of the lumbar spine comes from L4/5 and L5/S1 and given that the L5 and S1 nerve roots are the most commonly affected nerves in spinal pathology, it makes sense that these two levels get addressed via the anterior approach in my opinion. Provided you are not too rotund, and provided you have not had extensive abdominal surgery there are very few reasons not to address these levels anteriorly. The diagram to the right shows a minimally invasive tool replacing an L4/5 disc with a carbon-fibre reinforced cage. The Anterior Longitudinal Ligament is removed during this approach - if a fusion is being performed this is not an issue but if a total disc replacement with a moving prosthesis is being inserted, this ligament is usually reconstructed once the operation is over, as this is an extremely important stabilising structure and important for overall kinematics.

The two images to the far left show a patient who has 2 level degenerative disc disease (DDD). The disc at L4/5 is black and lost its hydration - it was proven on discography to be responsible for pain. The disc at L5/S1 is completely collapsed with bone-on-bone. On the CT (middle image) you can see where the disc has herniated through the endplate of L5 and into the vertebral body (red arrow - an inter-osseous disc herniation). As a result of the collapse there is instability between L5 and S1 - the green arrow points to the mal-alignment of L5 on S1 and the vertebral bodies don't even line up. You can see that the spine has straightened up at L5/S1 and there is loss of lordosis here.

Using the anterior approach the patient had a very successful Total Disc Arthroplasty at L4/5 and fusion at L5/S1. The disc height has been restored at L5/S1 and lordosis has been normalised. This kind of reconstruction is not possible using anything other than the anterior approach to the spine.

Lateral Spine Surgery

Whereas by far the best approach to L4/5 and L5/S1 is the anterior approach, the best approach to any other level in the spine is the lateral approach, also called the Extreme Lateral Approach, or the Trans-Psoas Approach. Using this technique a whole motion segment can be reconstructed through a 3-4cm incision on the side of the abdomen without any of the risks of anterior surgery and any of the trauma of posterior surgery. In the past this approach has been abandoned due to excessive numbers of patients who had damage to the nerves of the lumbar plexus. In the last few years nerve monitors have allowed surgeons to safely navigate the lumbar plexus and so this approach has become very popular. It is imperative the nerve monitors are directional however - not all are! What this means is that nerve monitors that simply tell you when you're close to a nerve with your instruments are not good enough - it has to tell you exactly where the nerve is in relation to your instrument. It s also now possible to perform a total disc arthroplasty through this approach meaning that the high levels in the lumbar spine are now amenable to being reconstructed using motion preserving technology as apposed to fusions.

On the right is a schematic illustrating a spine lying on it's side. The large black arrow represents how the disc is accessed and removed. Once removed, height and lordosis can be restored and a cage or moving prosthesis (total disc arthroplasty) inserted. This approach has some advantages over the anterior approach:

  1. The anterior longitudinal ligament is preserved, which is a big stabilising structure, which resists rotational and extension forces.
  2. Levels from as high as T6/7 in the thoracic spine right down to L4/5 in the lumbar can be reconstructed without having to move to a significant degree any important organs or blood vessels out of the way.
  3. Whatever implant is used to reconstruct the motion segment (cage or arthroplasty) it sits over the hardest bone in the spine (shaded green on the schematic on the right - called the apophyseal rim) making it the approach of choice if the bone is a bit soft (osteopaenia).

It also has significant advantages over posterior approaches - the main one being that, like the anterior approach, the nerves of the cauda equina are not moved.

The x-rays shown on the right are of a patient who had 4 level disc disease from L2/3 down to L5/S1. All levels reproduced pain on discography. The L5 nerve was compressed in the neuroforamen at L5/S1 (bottom red arrow on the x-ray far left) - compare how small this neuroforamen is with the one at L2/3 (top red arrow). The overall lordosis is not too bad but there is instability at L3/4 and L4/5 (on the x-ray you can see gas in the disc space which can only be there with severe degeneration and instability) and so in order to get on top of the back pain and radicular pain 4 levels had to be reconstructed. Not many years ago this patient would have been sent to a chronic pain clinic, as no surgical solution was available. 4 levels can be reconstructed using traditional methods but most surgeons today would view this as destruction, not reconstruction. The x-rays on the right show how using minimally invasive techniques the anterior approach was used to reconstruct the lower two levels and the lateral approach used to reconstruct L3/4 and L2/3. L2/3 has been replaced with a moving prosthesis (red arrow), and L3/4 with a cage and plate applied from the side (green marker). All of the neuroforamen have been opened up indirectly decompressing the nerves. No surgery was performed through the back of the spine at all and no nerves were even seen during this operation.

The anterior and lateral approach both have the ability to decompress the nerves in the posterior column by restoring height and lordosis. This is called indirect decompression - in other words decompressing the nerves without having to actually see them. Direct decompression, if deemed necessary, requires removal of the posterior elements and visually determining if the nerves are free of compression - this involves quite a destructive approach to the spine with considerable muscle stripping and removal of the spinous processes, lamina and facet joints. In severe cases this may have to be combined with anterior and lateral surgery. On the page regarding lumbar reconstructive surgery I talk about performing surgery in two stages sometimes spaced a few days apart. In severe cases when you can't be sure of the ability of anterior or lateral surgery to indirectly decompress the nerve roots, delaying posterior surgery by a day or two allows this question to be answered - if direct decompression is required (rare) then we can perform this at stage two.

Posterior Spine Surgery

Most modern spine surgeons today perform minimally invasive posterior spine surgery. Traditional, open posterior spine surgery does not feature heavily in my own practice. My personal philosophy is to offer reconstructive surgery using minimally invasive anterior and lateral approaches only performing posterior surgery if the anterior reconstruction needs some kind of reinforcement (extra scaffolding) because of soft bone or long constructs. This extra scaffolding means pedicle screws and rods but placed through minimally invasive stab incisions (1cm or so) on the back, or sometimes minimally destructive muscle splitting incisions (called Wiltze incisions) - at all times trying to preserve the bones and muscles in the middle of the back. These structures are often referred to as the 'tension-band' structures because they form an extremely important lever arm to counter the weight of the body at the front of the spine thus preserving balance. Why is it so important to preserve these structures? Ask any nurse, heavy labourer or orthopaedic surgeon, and they will tell you how important those structures are for balance, upright posture and efficient work.

If the actual entire reconstruction itself is being performed posteriorly, then the commonest technique is called minimally invasive TLIF. This involves a small incision on the back, made with the patient prone - or facing down - and a tubular retractor docking on the facet joint. The facet joint is removed and the cauda equina and nerves underneath are directly visualised. Usually very little retraction of the nerves is required and the disc is removed and a cage inserted to reconstruct the motion segment.

The images above show how small this incision actually is and very little collateral damage is made on the patient. One very big advantage of this technique is that pedicle screws can be inserted at the same time without having to make any extra incisions. The main disadvantage in my opinion is that of all the techniques of reconstructing the spine it has the least ability to restore height and lordosis. It is also technically more difficult to perform than anterior or lateral surgery and takes longer.

Percutaneously (i.e. through small stab incisions in the skin) placed pedicle screws are now standard practice in modern spine surgery.

On the left is a CT scan through a vertebra which has two pedicle screws inserted into it. On the right is a lateral x-ray showing what a pedicle screw / rod system looks like over 1 motion segment.

You can see from the x-ray on the right how this might be useful if you have soft bone in supporting the anterior reconstruction while the fusion matures. Up until a few years ago placing pedicle screws required a big operation which often devascularised (stripped the blood supply) the spine level above and below the area of interest. It is this devascularisation which has led to the syndrome of adjacent segment degeneration (ASD) which refers to the rapid deterioration of the level of the spine next to the one operated on. In an attempt to mitigate against this disastrous syndrome techniques were developed to place these screws and rods yet preserving the blood supply to the rest of the spine. This is now possible and can be performed over long spinal reconstructions. It is also much quicker to place them in this fashion compared with traditional exposures.

On the right are nine wires in a patient's back on each side. A screw can be fed over each wire and into the pedicle with very little blood loss, preservation of all the important posterior 'tension-band' structures and is a very relaxed operation compared with traditional placement methods.

Whether you want to call it Minimally Invasive, Minimally Destructive, Maximal Access or Percutaneous Surgery the philosophy is the same - to perform a better job than traditional surgery with a smaller surgical footprint. This is very achievable. 95% of my own practice utilises techniques described above, and I am a big advocate of the extreme lateral approach to the spine which has revolutionised minimally invasive deformity surgery for complex scoliosis.

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