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Pedicle Screw Segmental Instrumentation


The term "fusion" means achieving a rigid bone union.  There was a time when all hip, knee and ankle problems were treated by fusion.  This paradigm changed when artificial joints were introduced.  This enlightenment has not occurred to some spine surgeons.

In spine surgery the classic bone fusion was  intended to create a rigid union between vertebral segments as a means of correcting segmental dysfunction or instability.  Although the term "arthrodesis" means "to bind joints" most spine surgeons have generally continued to think of arthrodesis as being the same as "fusion."  Due to this mind set the achieving of "rigid fixation" became the goal of most spine surgeons during the latter part of the 20th century.  When metallic internal fixation devices were first introduced in the 1950s it soon became evident that the stress factors directed to this instrumentation by the human body turned out to be much greater than anticipated leading to a quest for structurally stronger instrumentation rather than a quest for more functional and physiologic stabilizations.  In the process many of the basic physician goals of treatment in regard to patients were forgotten.

It is sad to reflect that many spine surgeons have completely lost sight of the real goal of surgery which is to achieve a functional patient rather than a "solid fusion" associated with a disabled patient.
The era of metallic spine instrumentation began with laminar hooks and rods as exemplified by the Knodt and Harrington fusion systems intended to produce "rigid fusion."  These were often found to be "non-rigid" and this finding was often the justification for additional surgery.  It was not recognized that the most common cause of the "failed back surgery syndrome" was failure to either correctly diagnose or failure to adequately treat lateral spinal stenosis

Devices such as the Luqué ring (shown above) allowed better fixation than its predecessors but the laminar wires needed to attach the ring to the lamina were unwieldy and, if the system was removed, at a late date, the fixating wires, (which had an unfortunate tendency to erode through the adjacent dura mater), could create serious cerebro-spinal fluid leakage problems.  Ring implants fell into disuse with spine surgeons when their attention became focused on pedicle screw fixation systems in the 1960s. Boucher, in 1959, has been credited as being the first to use pedicle screws but it was Roy-Camille, in the late 1970s, who was the first to use screws and hooks and connecting them with rods or plates.  In 1983 Arthur Steffee patented the VSP spinal fixation system.
The early pedicle screw fixation systems utilized rather thick rods to support the screws as shown to the left.  An internal bone growth stimulator is shown at the top of the image.  Not only were the rods difficult to bend at surgery but they tended to exert significant adverse stress on the screws and adjacent spinal segments.  Complications involving nerve compression or injury associated with the placement of pedicle screws still occur in approximately 8-15% of cases. 
With heavy rods and large screws these problems tended to be increased.  Initially, fractures of both pedicles and screws were fairly common.  In addition to this Zdeblick also described "post-fusion disease referring to the extensive paravertebral muscle damage often documented on post surgical MRI scans) in addition to the other potential problems.
As screw fixation systems continued to develop an important advance was the replacement of heavy plates with rods, particularly those with those allowing some degree of flexibility.  In this example a front and back (360o fusion) has been performed.  Anterior interbody femoral ring allografts have been placed at three levels.  The front and back approach was the first type of fusion capable of producing consistently solid and rigid spine stabilization, even among patients who were smokers when multi-level rigid stabilization was considered desirable. 
Unfortunately, because smokers have a 3-4x higher incidence of disc degeneration these patients have been more susceptible to stress related degeneration of adjacent segments.

The best application of rigid pedicle screw and rod fixation systems have been in cases of post-traumatic spine instability where the adjacent segments are basically normal.  For patients with advanced scoliosis or deformity where progressive pulmonary or neurologic impairment, or in the management of spinal trauma, pedicle screw systems can be life-saving.  The worst application of this technology has been in patients with multi-level degenerative disorders presenting with back pain alone.  In genomic disease such as juvenile discogenic disease, neurologic problems occur due to nerve compression.  Nerve decompression must be the first step.  Rigid fixation simply creates stress related problems at the adjacent abnormal segments causing greater harm than benefit for the patient.  In fact, the use of multi-level pedicle screw systems in treating patients with multi-level spinal degeneration can, at best, be considered to be investigational.


Rigid Stabilization

    Instrumented Metallic
    Instrumented Non-Metallic
    Non-instrumented

Flexible Stabilization

    Instrumented Metallic
    Instrumented Non-Metallic
    Non-instrumented


Liabilities of Rigid Fusion: Particular Reference
to Rigid Instrumented Spinal Stabilization

High Cost of Implanted Instrumentation
Added Cost of "Guidance Technology"
Surgical Revision Due to Screw Malplacement
Surgical Revision Due to Nerve Compression
Risk of Permanent Nerve Injury (see above)
Lengthy Operative Time
Increased Blood Loss
Increased Risk of Infection
Extensive Soft Tissue Dissection and Destruction
Possible Need for Surgery to Remove Painful Hardware
Inability to Remove Some Types of Painful Hardware
Liability of Metal Artifact on Future Imaging
Need for Invasive Myelography and CT Scanning
"Juxtaposition" Degeneration (the "Transitional" Syndrome")
Possible Stress Related Sacral and Pelvic Fractures
Additional Surgery Needed to Correct Stress-Related Problems

Liabilities of the Iliac Graft as a Site for Autologous Bone Grafts

Routine Post-Incisional Pain
Complex  Regional Pain Disorders due to Possible Neuroma Formation
Possible Infection
Possible Post-Operative Local Hematoma
Possible Injury to the Sacro-Iliac Joint
Possible Injury to Pelvic Ligaments
Possible Pelvic Soft Tissue Problems i.e. Tissue Hernia Through Inner    Table Defect
Gait Disturbances (Usually Seen in Older Patients)

  The Most Common Clinical Problems   

Limitation of Future Imaging Studies
Inability to perform future sophisticated imaging studies such as MRI without significant associated artifact . This problem is much greater with magnetic (i.e. magnetic stainless steel) metals than it is in non-magnetic materials such as titanium. Very often myelographically enhanced CT scans become necessary to obtain visualization.

Subsequent Need to Remove Instrumentation
Additional surgery may be required to remove the instrumentation (routine in some centers) if instrumentation itself becomes painful after time. 

Additional Future Surgery to Correct Stress-Related Problems
Additional surgery may also be required to deal with subsequent stress fractures and transitional syndromes.  The iatrogenic problems produced are referred to as "transitional changes" and often require additional surgery to correct the problems created.  This is particularly true when the surgeon has not recognized, prior to the first fusion, the existence of genomic spine problems.
 
  Case Presentations   
  The Best     
Gerald Souba is a 71 year old farmer (Identified with permission).  He became incapacitated by back and leg pain due to spinal instability and multi-level spinal stenosis.  The red dots above show the lateral listhesis (slip) in association with a severe scoliosis.  Corrective surgery required multi-level decompression in which two posterior titanium cages were placed to stabilize and to also act as spacers.  The listhesis was corrected and extensive pedicle screw and rod instrumentation was added to further stabilize the spine. 

Following surgery Mr. Souba did quite well.  He was able to return to work as a farmer and was proud that he could continue to operate a tractor.  At his 1½ year post-surgical follow-up he was essentially free of back or leg pain.
This case represents a good example of the sensible combination of  different spine surgical technologies in order to achieve a good result for the patient when accurate diagnosis is present to start with.
  The Worst   

On the other hand....in the case shown to the left, extensive pedicle screw instrumentation was placed to correct a lumbar claudication syndrome secondary to lateral spinal stenosis.  A spinal deformity was corrected but the actual reason for the patient's disability (lateral spinal stenosis) was not addressed and the patient continued to be disabled.  The surgical salvage of this patient required the following:

1. Removal of the multi-segmental instrumentation (see below).
2.  Partial take-down of fusion bone.
3.  Microsurgical removal of post-surgical scar tissue.
4.  Decompression of the nerves compressed by the lateral spinal stenosis.

5.  Restabilization of spine.  

The amount of surgical effort extended in this case was significant.  It is clearly better to address the problem effectively the first time and not provide the patient with the opportunity to reconstruct a $40,000 tinker-toy.

Summary
Pedicle screw fixation systems alone, or in combination with other surgical systems, may be beneficial in the care of any given patient.  They may also be contra-indicated in any given patient.  There may also be safer, more cost-effective, and more physiologic procedures indicated for use in any given patient.  Knowing this is often difficult for a patient to because pedicle screw fixation devices are in great vogue at the present time associated with poor informed consent.  Instrumented rigid pedicle screw fixation systems being used for stabilization in patients with multi-level degenerative disease have, however, probably reached their zenith of use as the future portends the more rational application of flexible stabilization systems.  The following observations, which do not reflect the patient's best interest are part of the problem:

There is a great deal of marketing and media hype surrounding rigid instrumented pedicle screw implant systems.
There is great profitability in selling these systems as reflected by their being almost three dozen manufacturers of such devices.
Spine-related medical meetings have now become a "feeding frenzy" for pedicle screw manufacturers (at the 2006 North American Spine Society Meeting in Seattle Burton Report counted 41 such manufacturer exhibits).
Surgeons can derive more personal income by using multi-level pedicle screw fixation devices on their patients.  This has led to their use a primary treatment for simple low back pain.
The spine device manufacturers spend effusive amounts of money to garner the allegiance and support of spinal surgeons.
The financial support, by hospitals, of high volume spine fusion surgeons is not unknown.
More appropriate "orphan" technologies typically receive less attention because of the lack of an "even playing field."
The overuse of pedicle screw and rod fusions has created a professional backlash which has led to the establishment of a American Association of Ethical Spine Surgeons.