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Spinal muscles and lumbar fusions: the quest to prevent destruction

Dr Didier, Dr Alexander Disch, Dr Denis Kaech and Mr Robert Lange
9 June, 2014  
A surgeon discovers forgotten anatomy can be used to navigate in surgery and creates a method to save them; teaching remains a challenge
 
Dr Didier Recoules-Arche
CH J. Monod Le Havre, Montivilliers, France 
Dr Alexander Disch 
Charité Hospital, Berlin, Germany
Dr Denis Kaech
Kantonsspital Graubünden, Chur, Switzerland 
Mr Robert Lange
Composite implant developer
Zurich, Switzerland
 
From a surgeon’s perspective, the spinal column lies deep within the body, its elements far to reach. Its anatomical neighbours can be vital and when inadvertently disturbed, unforgiving, at times life threatening. When spine fusion surgery is imagined for a patient’s treatment, this is always present in the surgeons’ minds. It leads them to ask the original question of all surgery: what to destroy or keep? What to pass through or avoid? All to make patients better after surgical intervention.
 
Medical literature brings some guidance, with its churning debate that presents best practice, probable outcomes and rates of complications that are considered acceptable misfortune for a specific problem. It tells how to mitigate risk for the most benefit to the patient, the cost to society. Still, each time a surgeon enters the operating room to perform a spinal fusion, questions nag: what will be enough? What too much? How can they do better for their patient? 
The questions do not go away.
 
Evolution to lumbar spinal disease
Some would argue that the human spine is an incomplete evolutionary solution for what it is asked to do. In addition to anchoring the limbs, connecting the brain, allowing movement while protecting nerves (something we share with the animal world), the human spine allows us to stand upright and walk long distance on just two legs while bearing compressive loads. Several million years of evolution has shifted the human spine’s musculature (lumbar erector spinae) still further posterior on the vertebra. They converge into a complex structure at the pelvis and sacrum upon which we depend for their role in primary stabilisation and movement. 
 
While this has enabled humans to develop their brains, to make tools and build all sorts of useful things, upright stance has put inordinate strains upon the intervertebral discs, the posterior joints called the facets and the posterior musculature.(1) With age, these can degenerate in cascade, closing the spinal canal, expanding the posterior facets to limit painful movement while squeezing nerves. Discs wear out to cause intervertebral bone grinding. 
 
Sometimes this condition is painful, sometimes not, and the surgeon seeks to determine if a vertebral level might benefit from fusion with others left alone. The first goal will be to reach and decompress nerves. The second is to stabilise vertebral motion segments with implants and a bone graft medium to allow bony fusion of one or several levels. The third goal is to leave the non-pathological structures alone, including the paraspinal muscles. The final part remains elusive in posterior lumbar spinal fusions.
 
Accepted destruction
When it comes to saving healthy anatomy, performing lumbar fusions from the posterior approach remains daunting in their subtleties. They are most often used to treat neurologic deficit with degenerative pain that originates from the spine’s posterior elements, together with the more anterior intervertebral discs. The surgeon’s challenge stems from the confluence of structures that converge at the pelvis and sacrum. These must be managed in posterior fusion surgery. 
 
Since the nineties, posterior lumbar interbody fusion (PLIF) with interbody cages and pedicle bone screw fixation has become a standard of care for the spine. From the posterior approach, surgeons resect posterior muscles and vertebral bone to enter the spinal canal and decompress the nerves. They continue into the intervertebral disc to make a void that is filled with intervertebral cages and bone fusion medium. Screws anchor to the vertebra at the posterior pedicles and connect to rods or plates to build a stable construct to allow two vertebral bones to fuse together. Because of its front and back construction, PLIFs and pedicle fixation are called a 360-degree fusion. 
 
Initially, achieving this from one posterior approach was the standard practice and many highly unstable conditions continue to be treated this way. But it came with an anatomical price. Bone, muscles and ligaments are destroyed in the wake of implant placement and access to the spinal canal. To prevent non-unions in highly unstable conditions, this was at first an acceptable collateral damage. It was also hoped that because vertebrae were fused, muscles at the same level would be less needed or at least compensated muscles near by.
 
Trans-muscular MIS
It was argued, why disrupt so much only for the approach? Muscle splitting techniques were developed to diminish the destruction of open surgery, first with open technique and later through special tubes or trocars. Now called minimally invasive surgery, or with some irony MIS, these techniques are designed to stab through the paraspinal muscles and bring the surgeon to the vertebra in order to decompress nerves and then to place stabilising implants. Fewer muscle fascicles are resected and some magnificent equipment has been developed.(2) But there are caveats. When a tool becomes more pathology specific, it may be less effective somewhere else. At times, gestures in tiny spaces are less complete. Finally, the extensive X-ray routine in MIS can expose patients and the operating team to more radiation.(3) 
 
This has led others to consider an open, while less destructive, way to perform posterior fusions of the lumbar spine. 
 
Surgeon obsession becomes ELIF
The premise was, why cut and cauterise what can be left intact? Some colleagues called it meticulously extreme, others obsessive, but one of the authors worked for several years to reduce posterior fusion blood loss considered routine in other theatres. Instead of the starting from standard midline, the surgeon used a lateral 45 degree approach, a more natural angle in relation to the converging pedicles and the disc. Plane by plane, blunt resection explored paths to the vertebra. The surgeon established soft tissue fibre orientation to identify safe passage between anatomically intact planes.
 
An approach that first was used for posterior–lateral disc herniations, was explored for specialised posterior cage insertion and later pedicle screws with ostaPek carbon composite plates to make a 360 degree stabilisation that was comparable to the PLIF. But the blood loss that used to be measured in hundreds of millilitres, now was only a few stains on several compresses. Suction was almost eliminated. The method was called Erriva ELIF (extra-foraminal interbody fusion).(4)
 
It was good to muscles. The procedure was open, with better view than through a tube, but without the associated trauma of normal posterior technique, fewer X-rays. 
 
Triumph? Not quite. First it had to be understood by another and for this it had to be described.
 
Seeing and believing is not understanding
“At 45 degrees, he’s performing a lateral muscle splitting approach. Its been around for years,” said a surgical anatomy professor consulted for the purpose of writing the surgical technique.
 
“But it does not bleed. If you split a muscle from lateral approach, why doesn’t it bleed?”
Further studies were counselled.
 
Several spine fusion specialists, all teachers, worked with the inventor to replicate the Erriva ELIF 360 degree stabilisation. They learned to perform the fusion from a 45 degrees approach, without loss of blood, but could not completely describe what they did or saw. It made them uncomfortable.
 
Three were asked to describe the approach on paper. All texts were different. Did they retract or pass through such and such a muscle? Why could they separate a fascia from its muscle to prepare the approach when this is not physiologically possible?
 
With the goal to build a usable description, the team was invited to an Erriva ELIF intervention. One surgeon assisted the inventor in the sterile field and was asked to precisely describe each structure and gesture. Two other surgeons sat with anaesthesia, behind the drape out of view. Their job was to write what was being performed. The implant design team would referee.
 
After 30 minutes, four surgeons, otherwise friends, did not quite come to blows, but nearly. 
“That can’t be such and such a tendon? Were you sleeping in school?” was one remark.
“Orthopaedists don’t bother with soft tissues! That’s why you got chisels…”
“I’m telling you that trabecula is connected to that tendon!”
“That’s not possible!”
“Really? I’m looking at it now.”
 
Anatomy forgotten, and ignored
How could teaching specialists, performing each several hundred spinal fusions a year, not agree on what should be routinely seen? 
 
As hard as it was for the implant design team to believe, some areas of human topography are as disputed as the territorial waters around coastal Japan. Conflicting descriptions find their way into different traditions of teaching. Furthermore, from midline posterior spine surgery, muscles are resected, split or worked around, but almost never described with precision. Such information is just not used. Posterior lumbar spinal surgeons navigate with bone and nerve, not muscle, fascia or tendon to reach the vertebra, spinal canal and disc. 
 
It transpires that award-winning erector spinae anatomical studies were published in 1987.(5) Authors demonstrated that erector spinae, previously described as one confluent structure, was in fact two independent ones, that converged indiscernibly at the sacrum, one originating in the thoracic spine, the other at the sacrum and pelvis. 
 
Nobody seemed to care, until the Erriva ELIF. It explained how the muscles could be separated without trauma or blood to create a new approach to vertebral bone, the spinal canal, the disc. This was validated in dissection. A muscle map with accurate paths was drawn. 
But it did not help surgeon acceptance. 
 
Easy to teach? Not really
“It’s not intuitive,” said the late Dr Christian Pere, who prided himself in learning and teaching new methods. “I’m not used to orienting my self with soft tissue. I can’t see the bone. It’s not dangerous, but sure feels like it.”
 
Dr Alicja Baranowska, who taught many other approaches, described it differently. “It is not difficult. We do not know how to do it. That is not the same thing.”
 
“There is no evidence,” said others. “You have not proven that saving muscles improves clinical outcome.”
 
This is true. Not yet proven. But the question becomes: is this because there is no difference between keeping or destroying a viable muscle structure in surgery? Or is the difference not yet detected? After all, most will agree if the structure is viable it is probably doing something of use. Recent studies have compared the muscle destruction of PLIF and ELIF using biopsies and magnetic resonance imaging to show viable tissue.(6) There was less destruction with the Erriva ELIF than PLIF. The clinical value of this still must be validated. 
 
Partially blind
In their ability to stand upright, humans are dependent on the posterior muscles. Classic PLIF fusions destroy a part of the spine. Until recently spine fusions have been mostly concerned with disc, nerves and bone, only recently the muscle. The Erriva ELIF approach with specialised carbon composite implants, rather than remove or pass through the paraspinal muscles, uses fascia, tendons and the muscles themselves for navigation. This preserves the muscular system. But when an angle of approach moves lateral 45 degrees, just one width of a hand, surgeons can feel like the fabled blind men stroking the elephant. They argue. The first blind man holds the truck and declares the elephant is like a snake. The second holding the leg, insists that an elephant is like a robust tree. The third, holding the ear, says it is like an enormous leaf. All truths must be assembled into a usable form.
 
This takes time, persistence, a change of equipment and mind. But more structures can be saved and perhaps spinal fusion treatment improved as treatment.
 
References
  1. Lovejoy C. The natural history of human gait and posture Part 1. Spine and pelvis. Gait Posture 2005;21:95–112.
  2. Kim C. Scientific basis of minimally invasive spine surgery.Prevention of multifidus muscle injury during posterior lumbar surgery. Spine 2010; 35(26S):S281–S286.
  3. Mariscalco M et al. Radiation exposure to the surgeon during open lumbar microdiscectomy and minimally invasive microdiscectomy: A prospective, controlled trial, Spine 2011;36(3):255–60. 
  4. Recoules D. Extra-foraminal lumbar interbody fusion (ELIF) 30 dislocations lombaires degeneratives. Rachis 2004;16(3):197–204.
  5. Macintosh M et al. The morphology of the lumbar erector spine. Spine 1987;12(7):658–68. 
  6. Recoules D. In press.