Monday, 14 June 2010 23:39

Spinal Fixation

Spinal Fixation

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What is the Reason for Spinal Fixation?

Where your spine, for whatever reason, has too much movement or is not sufficiently stable by itself to support the necessary stresses and strains that tend to be put on it on a daily basis, then spinal fixation is often the answer. People who suffer considerable pain on movement, or when they experience tingling in an arm or a leg might be considered for spinal fixation if the cause is due to movement in the spine putting pressure on one of the nerves. Furthermore, if a person experiences numbness or weakness in an arm or leg this could be due to spinal compression, with the bones in the spine pressing on an adjacent nerve. Spinal fixation will fuse the bone in the area that is causing the problem, making a more rigid support that is also more stable.

How Did Spinal Fixation Develop?

Setting broken bones, in the past, involved the use of plaster casts made from plaster of Paris, to hold the bones in one place to enable healing. If bones move around too much when they need to heal, the cells involved in the process of healing will not be able to complete their job properly and the broken bones will heal badly, if at all. More recently, internal fixation has become the norm, using screws and plates to hold damaged bones together. The rigidity of the metal plates provides the necessary support that prevents movement as the bones knit together. There are many fractures that actually respond better to internal fixation, as well as being more comfortable for the patient.

Spinal support was largely reliant on external fixation and, in some cases, still is. However, internal metal plates, rods and screws are increasingly taking the place of what many people view as barbaric-looking external fixation devices. Support within the body has a number of advantages which are discussed in more detail later. Largely, however, a more rigid structure is achieved with internal fixation allowing for enhanced healing. Greater support is achieved enabling the patient to mobilize much more quickly after surgery, thereby reducing the chance of DVT and embolisms developing through sluggish blood flow. Patients are often able to return to their normal daily activities within 6 weeks of surgery, including a return to work in most cases, which has a far greater psychological and sociological outcome for all concerned.

Anatomy and Physiology of the Spine

The musculoskeletal system of the spinal area is quite complex so it is hardly surprising there are so many things that can go wrong with it. Two of the most common kinds of pain you can experience are from pain in the neck and pain in the lower back but, because of the sheer complexity of the anatomy and physiology of the spine any pain you experience in any areas of your spine could be caused by a range of conditions making these kinds of problems quite difficult for clinicians to diagnose, especially if the pain emanates from one of the facet joints. This condition causes chronic pain and, on the occasion it is diagnosed correctly, is known as Facet Syndrome, or Facet Joint pain.

Distinct Divisions of the Spine

The spine is made up of a series of very distinct areas, each containing a number of individual bones. Each section has a slightly different function although, overall, the spine is intended to provide support for your muscles and tendons and to provide protection for the spinal cord. The bones that make up the spine are each called vertebra, with 33 vertebrae making up the whole length of the vertebral column. The spine is divided up into:

  • Cervical vertebrae – 7 bones
  • Thoracic vertebrae – 12 bones
  • Lumbar vertebrae – 5 bones
  • Sacrum: these are fused vertebrae, consisting of 5 bones
  • Coccyx: this is the vestigial tailbones, consisting of 4 very small bones

Cervical Vertebrae

These tend to be labeled C1 – C7 and are responsible for the movement of the neck as well as providing protection for the top of the spinal cord together with other nerves and arteries that, in this area, are quite major as they extend into the skull and connect the brain with the rest of the body.

Thoracic Vertebrae

The 12 vertebrae making up the thoracic vertebrae are referred to as T1 – T12. These are the vertebrae that form the back of the rib cage.

Lumbar Vertebrae

The lumbar vertebrae are often referred to as the ‘small of the back’. They consist of 5 bones, referred to as L1 – L5. This is a very common area to experience back pain as the lumbar region takes considerable stress from the amount of weight placed on it.

Sacral Vertebrae and Coccyx

Together these consist of 9 bones, all of which are fused together in adulthood. The sacrum is generally referred to as S1 and consists of a single unit of bone.

Inter-vertebral Discs

These discs intersperse the above bones of the vertebral column.

Each one is a flexible cushion of tough, cartilaginous material that prevents friction between the bones and provides protection against potentially damaging jarring when moving. The shock absorbing qualities of each disc is achieved through the nucleus pulposus, a spongy liquid that absorbs any shocks, each of which is surrounded by a tough fibrous membrane. In cases where discs herniated through this outer membrane this interior jelly can press against nerves in the spinal cord, causing severe pain. The vertebral bones are put together and tend to be the cause of many of our spinal problems, as well as fulfilling a very essential function within the body.  Aside from protecting the spinal cord, the spine serves as a conduit through which all the major information from the brain reaches the network of muscles, nerves, bones, tendons and ligaments through which neural information is disseminated to every cell within the human body. In situations where illness or injury causes the spine’s function to be impaired, without active intervention the results could lead to chronic and debilitating pain as well as causing major disability.

Spinal Cord

The spinal cord runs through the vertebrae, from the base of the brain to the lower end of L1, lumbar vertebra. The cord itself is protected, not just by the overarching bones of the vertebral bones, but by a particularly tough membrane known as dura mater. This completely encloses the spinal cord within a waterproof casing, within which is spinal fluid that helps to provide additional protection as a shock absorber for the spinal cord encased within. Each part of the body is joined to specific nerve roots that leave the spinal cord at certain points. The nerve roots in the cervical area of the spine provide neural support for a network of nerves over and around the arms and upper chest while the nerve root leaving the lumbar area supply nerve stimulus to the buttocks, hips and legs. If these nerves are damaged, or compressed, you will experience symptoms such as tingling, numbness, weakness or pain of varying degrees. This can be felt not just in the immediate vicinity of the injury, but as referred pain elsewhere in your body.

Muscles of the Spine

There are actually 7 layers of muscles that are responsible for moving the body and limbs around, each one of them surrounding the vertebral bones.  As you can see from the diagram, they are responsible for maintaining an upright posture and being able to carry loads and undertake normal day to day activities. Damage to the spine can interfere with the activity of these muscles, causing weakening or even preventing movement from occurring with any ease.

Normal Spinal Curvature

If you look at a normal spine you will note that, when viewed from the front or the back, the spine appears to be a straight line. Should the spine appear to curve to either side when looked at from this view, it is indicative of scoliosis. In a normal spine, when looked at from the side, there are three gentle curves, two inward and one outwards. The cervical spine and the lumbar spine both exhibit an inward curve. This is medically referred to as a lordotic curve. Meanwhile, the thoracic spine curves outwards. This is known as a kyphotic curve. The way the spine curves is adequate to support the weight of the upper body and the head as well as to maintain a suitably upright balance. If curvature is too extreme the spine could become too imbalanced, causing pain and disability.

  • Vertebrae. These consist of pedicle supports which are bony parts that provide an arch of bone across the spinal cord. The back of this bony arch consists of the laminae.
  • Intervertebral Disc.
  • Facet Joint. This joint connects the bony arches together. Each pair of vertebra has two associated facet joints, one above and one below. The facet joint is a synovial joint that enables each vertebra to pivot around, enabling rotating movement to occur.
  • Neural Foramen. This is an opening beneath each vertebral arch that enables the nerve roots to leave the spine to join up with other parts of the body. Each pair of vertebrae are associated with two neural foramen. The function of the neural foramen is to protect the junction of the nerves where they join the central nervous system.
  • The spinal cord runs the length of the vertebral column and is protected along its length by the interlinking vertebrae, the pedicle arch and their associated facet joints. The spinal cord runs from the base of the brain to the end of the 1st lumbar vertebra, where L1 meets L2 after which it frays out into a number of lesser nerves, each one major in their own right. The medical term for this is cauda equina as its appearance is that of a horse’s tail.

When Things Go Wrong

This very complex system of our musculoskeletal framework, with its interspersed network of nerves can be the cause of things going wrong, often something quite small can send quite major signals of pain to the recipient. The nerve roots that leave the spinal cord are extremely sensitive, not just to alterations in posture or movement but to pain.  Facet joints in the lumbar vertebrae are also particularly sensitive to pain so it is hardly surprising that so many people experience prolonged periods of incapacitation due to chronic pain in the lumbar region of the back.

When pain is experienced from subluxated facet joints or from impinged spinal nerves the muscles of the trunk are quick to respond. Muscles contract when the nerves supplying them are damaged in any way, resulting in muscular spasm which can be extremely painful. If any of the five sciatic nerves in the small of your back are impinged in any way you can experience a particularly painful condition known as sciatica. This often occurs if there is something pressing against any of these nerves. Apart from the pain, it can cause tingling and numbness in the gluteal muscle of the buttovcks and down both legs into feet and toes. If this continues, muscles can become weak and will eventually atrophy.

Imaging Tests

Accurate internal fixation has largely been achieved through the development of more accurate imaging techniques such as MRI scanning and bone scans using special dyes that show any boney defects in far greater detail than any X-ray could ever achieve by itself. There is still a place for X-rays, especially the various techniques associated with X-ray technology:  X-ray is a far cheaper imaging technique than MRI or CT scans, for example.  Diagnostic injections that insert a special dye into the body certainly produce far better results than what was available before these were sufficiently well developed to be of any use. Skilled clinicians trained in these new techniques have now come of age as well, with surgical training keeping pace with these new diagnostic tools. This ensures that surgeons are able to implement these technological advances while, at the same time, have the necessary skills to operate and use them to fix the spine more effectively.

Advances in Fixation Materials

Better rods and screws have certainly made a great difference to spinal fixation methods. A provisional patent was applied for in July 2008 for screws made from bio-absorbable material. This material combines the strength required for internal fixation with the advantages of not having metal encased within the body, especially relevant in terms of MRI testing, for one thing. One particular bio-absorbable screw for bone fixation has been awarded US patent number 5.470.334; others can be found under US patent number 4.968.317. Whether these bio-absorbable materials will completely replace the Kirschner apparatus that includes the various stainless steel pins and interconnecting rods used for internal fixation and the clamps, together with nuts, used for external fixation, remains to be seen.

 

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When is a Spinal Fixation Necessary?

Surgery to correct spondylolisthesis, which results in spinal bones becoming unstable and pressing on major nerve groups, is one condition which often makes spinal fixation necessary. This condition often results in patients developing bone spurs and protrusions of spinal discs. These are usually moved away from the spinal cord and any nerve roots at the time of surgery. In order to do this, it is often necessary to remove these: this causes further de-stabilization of the bones in the spine, necessitating the use of rods and screws to prevent the bones from slipping any further.

  • Scoliosis: Scoliosis, which is when the spine bends into abnormal positions, is another condition that can be successfully corrected with the use of rods and screws. When scoliosis results in the spine curving too much for the patient to be comfortable, it often becomes necessary to insert rods to correct the spine’s continued curving.
  • Infections: Infections and tumors also often result in bones becoming unstable, making spinal fixation necessary while the patient has the underlying cause treated. Removing tumors from the spinal region can reduce pain caused by the developing tumor, while spinal fixation can help the patient remain mobile, reducing the possibility of DVT and other blood clots from developing as well as improving the patient’s psychological outlook, enabling them to better cope with their illness.
  • Fractures: Fractures need to be dealt with on an individual basis depending where they occur in the spine. Statistics report that as much as 90% of all spinal injuries occur in the thoracolumbar region of the spine. Out of these between 10% - 20% are burst fractures. These are fractures that occur as the result of vertical compression when the spine is slightly flexed. Burst fractures can also occur as the result of a rotational injury. These burst fractures have been described in terms of different mechanisms of injury that can become intensely complex and detailed. Suffice to say that any injury to the spine that results in bone fragments being propelled towards the spinal canal, or where the vertebral pedicles are fractured, are considered to be major burst fractures and the source of severe injury that needs some form of spinal fixation to prevent further damage.

Burst fractures in the thoracolumbar region can result in neurological damage whereas an effective repair can result in an opportunity to heal with few problems. Spinal instability was adequately defined by Nicoll in 1949. This definition was based on the degree of subluxation or dislocation and the degree of disruption to interspinal ligaments, including if relevant, laminar fractures of lumbar vertebrae, L4 or L5. This definition is so respected in surgical circles that, even after more than 50 years, Nicoll’s definition continues to be used in decisions of how to treat these fractures. A decision to undertake spinal fixation needs to take into account the degree of mechanical and neurological instability caused by the injury and considers how appropriate the spinal fixation would be in terms of recovery. Basically, however, spinal fixation is appropriate to repair mechanical instability due to vertebral collapse; neurological instability where spinal fixation can prevent further neurological injury; and a combination of the two. This is referred to as the 3-column model. Instability has been interpreted as:

  • 50% of the vertebral height lost as the result of inter-disc compression
  • Widening of the interspinous process
  • Posterior ligamentous complex disruption involving more than 30 – 35 degrees of kyphosis

Furthermore, if a posterior longitudinal ligament injury was identified by MRI in conjunction with a burst fracture, this should be considered for spinal fixation. Another categorization of what is a stable or unstable spine is the AO/Magerl Classification that uses pathomorphological criteria together with three mechanisms of injury, the effect of which needs to be shown up on CT scans and radiographs. The results are categorized as being:

  • A:  compression
  • B:  distraction
  • C:  rotation type fractures

Where the Spinal Canal has been Compromised

When the CT scan reveals a spinal canal has been reduced by 40% - 50% by thorocolumbar burst fractures many surgeons will carry out spinal fixation. Nevertheless, there is no guarantee that, by the time spinal fixation has been carried out, paralysis wouldn’t have occurred. Imaging appears to indicate that the worst spinal occlusion occurs at the place where the most pressure compresses the spinal cord. Despite the prospect of catastrophic injury occurring from burst fractures in the spinal region evidence shows that the spinal canal has the capability to reabsorb intracanal bony fragments in order to help clear the spinal canal. It would appear that this occurs regardless of whether spinal fixation is attempted or not.

Despite this natural clearance technique the body is equipped with, patients who clearly have neurological complications have been shown to be significantly better off following spinal fixation. This has been shown to assist them with earlier mobilization, improved pulmonary function and much greater relief from pain. The prime reason for spinal fixation is to reduce compression on the nerve roots and spinal canal, as well as realign the spine. Surgery is also effective in reducing the incidence of kyphotic deformity as well as increasing the stability, in the long term, for vertebral segments that has suffered trauma.

Certain surgery will be performed in injuries that reveal progressive neurological deterioration, as well as spinal canal compromise in excess of 50%, anterior vertebral body height loss in excess of 50%; incomplete neurological injury; kyphotic deformity of more than 25o – 35o angle; as well as an assortment of contiguous vertebral injury and trauma.

Proposed Treatment Algorithm

A new classification has been proposed by the Spine Trauma Study Group as a treatment algorithm for patients who have experienced thorocolumbar fractures. This algorithm is known as the Thoracolumbar Injury Classification and Severity Score, or TLICSS. It refers to the importance of three types of criteria that need to be considered to establish stability and decide on whether to resort to surgery or rely on conservative treatment. The TLICSS criteria are:

  • Morphology of the fracture:

1 point – compression

3 points – translational/rotational

4 points – distraction

  • Neurological Injury:

0 points – intact

2 points – nerve root injury

2 points – cord or conus medularis incomplete injury

3 points – cord or conus medularis complete injury

3 points – cauda equina syndrome

  • Integrity Status of Posterior Ligamentous Complex:

0 points – intact

2 points – injury suspected/indeterminate

3 points – injured

Total Score:  this score measures from 1 – 10 points

For surgery to be considered necessary the criteria needs to exhibit 5 points or less

Non-surgical treatment will be provided when the criteria measures at 3 points or more.

Who is Unsuitable for Spinal Fixation?

Clinicians are far more selective about who undergoes spinal fixation nowadays. Too often in the past spinal fixation was carried out as a remedy for generic lower back pain. Without suitably advanced imaging techniques to prove otherwise, patients were operated on in an attempt to eradicate severe back pain for which no cure could be established. Nowadays, full imaging results are acquired to establish the need for spinal fixation, without which spinal fixation is not carried out. Patients with degenerative disc disease are not considered suitable candidates for spinal fixation and only very rarely is lower back pain treated with spinal fixation.

Devices Used for Spinal Fixation

So many unwarranted misconceptions abound when it comes to spinal fixation that people are understandably concerned about the prospect of having to face such surgery. Obviously, the best way to dispel such concerns is to discuss the various procedures in detail and to investigate who would best benefit from such procedures as well as what patients, having had spinal fixation carried out, can expect from it, as well as how this surgery is likely to affect their lives. Devices to enhance spinal stabilization are used in all areas of the spine, including the cervical, thoracic and lumbar regions.

Basically, a device used for spinal fixation needs to stabilize the posterior spine while limiting compression and enabling the maximum amount of movement. Generically, a spinal fixation device offers a permanent support that is either rigid or semi-rigid. The prosthesis itself is usually made from titanium. They include plates, rods, and screws, any of which could be incorporated into a device to fix an unstable spine. Another fixation device that is used in some instances is the resorbable fixation device made from a bio-resorbable substance such as one of the polymer products. If this is used there needs to be a device to prevent any acid damage occurring that might damage bone near the fixation device.There are various stabilizing techniques that are currently used, all of which are intended to provide additional stability for the posterior aspect of the spine. Most often, nowadays, spinal fixation is the preferred route although in a worst case scenario, spinal fusion is still an option. Spinal fixation is preferred as it tends not to limit range of movement.

The Generic Surgical Procedure for Spinal Fixation

There are all sorts of techniques that are used to undertake surgery for the fixation of the spine. Nowadays, any good surgeon will operate using the least invasive route possible. However, the ultimate outcome has to be the welfare of the patient and the success of the operation. The surgeon is trained to make these decisions on your behalf.  First and foremost, minimally invasive surgery really relates to the amount of retraction needed by the surgeon to access the site of the operation to be able to carry out the repair that needs doing. If, during this time, he is able to use some of the newest tools available such as laser techniques then that is what the surgeon will do.  However, the surgeon will advise you beforehand what he intends to do. What the surgeon actually does is totally dependent upon what he sees once you are under anesthetic and the surgeon can see the damaged area. The surgeon will then make a decision based on his knowledge, skills and experience, on the best way to complete the surgery successfully.

Expectations from Spinal Fixation

Invariably, patients will be able to resume their normal daily activities within a couple of months following spinal fixation surgery. Patients will notice that, following this surgery, they are largely free of pain, encouraging them to resume their lives where they left off prior to spinal problems preventing them living their lives to the fullest.

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