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10 Articles in Volume 10, Issue #1
An Overview of CRPS
Balancing Evidence, Efficacy and Stakeholder Values in Practical Pain Care
Biopsychosocial Approach to Management of Total Joint Arthroplasty Patients
Dextrose Prolotherapy Injections for Chronic Ankle Pain
Genetic Influences on Pain Perception and Treatment
Headache in Children and Adolescents
Hormone Replacements and Treatments in Chronic Pain: Update 2010
Opioid Treatment 10-year Longevity Survey Final Report
Therapeutic Laser in the Treatment of Herpes Zoster
Use and Effectiveness of Spinal Cord Stimulation

Use and Effectiveness of Spinal Cord Stimulation

Spinal cord stimulation has been one of the major advances in the efficacious and cost-effective treatment of chronic pain patients with multiple different pain processes—particularly of cervical and lumbar spinal origin.
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General Overview

It is important to identify all anatomical markers prior to attempting percutaneous implantation. Initially, the fluoroscope should be positioned to the planned point of implantation and the epidural space (EES). Also, we need to specifically identify the skin entry site (SES). This is the location on the patient’s skin where we intend to apply local anesthesia and advance the needle toward the EES. It is important to position the fluoroscope so that the EES is exactly squared on anterior-posterior (AP) and oblique views. Oblique positioning is important so that the entry site is anatomically correct when visualized on the fluoroscopy. The facets are the next most important anatomical marker for the skin entry site. You need to go down two facet levels below the EES and mark the midline inferior margin of the facet joint. A mark on the patient’s skin should be made there as well, and a line is then drawn between those two points. Of course, if bilateral implantation is anticipated, then the opposite side should be completed. A determination to enter right or left in a patient without any significant anatomical deformities is not relatively important. Another line is then drawn on the patient by marking down the spinous process and forming a cephalad-caudad line down the tips of the spinous process. You should then measure, or estimate, the angulation that you have formed between the line from the skin entry site to the point of entry and this angle should be less than 15 to 25 degrees. The angle of approach from the lateral view—in other words, the angle of the needle from the skin—should remain in the 15 to 25 degree range as well. Too sharp of an angulation on either of these entries can make it very difficult to advance the leads appropriately.

I have found it beneficial to use the stiffer stylets with curved tips which results in a curving of the lead as well. This is very effective in positioning and manipulating the lead wires. Figure 1 illustrates the line (identified as Line A in the figure) that would be drawn on the patient’s skin along the spinous process to demonstrate a cephalocaudad linear point of reference. Line B is drawn through Point 1, which is the EES and Point 2, which is the SES and at an angle to Line A. Please note that the angle formed using these reference points is less than 30 degrees.

Our normal point of entry for low back and lower extremity pain is the T12 spinous process. For cervical entry, it is normally at the T2 level. Patient positioning is very important and wedges and pillows should be positioned under the patient’s upper abdomen and lower chest to reduce the kyphosis as much as possible.

Obese Patients

The challenge of implanting spinal cord stimulation systems in obese patients is that the extra subcutaneous tissue often changes the angulation of the lateral AP approach. Therefore, this alters the skin entry site, making the AP angulation substantially steeper.

Figure 2a presents a lateral view that demonstrates the effect of excessive subcutaneous tissue. Point 1 identifies the skin entry site on this patient with a reasonable normal body habitus and a linear lateral line through Point 1 (SES) to Point 3 (EES). Line B demonstrates a similar line through where the SES point would be with additional subcutaneous tissue and a line is then drawn through Point 3 (EES). Note that the angulation of the angle of entry on Line B is increased to an acute level making it difficult to advance stimulator leads. In Figure 2b, we have extended the EES site caudally, forming a new Line A that is longer and maintains a more flat plane of entry to allow an easier implantation and advancement of spinal cord stimulator leads.

The remedy for dealing with the obese patient is relatively simple. The line that you have drawn between the anticipated EES and the SES should be extended beyond the normal SES. The practitioner at this point simply advances in a caudad manner along that line. The amount that you need to go caudally depends obviously on the amount of subcutaneous fat tissue and varies anywhere from 1 cm to 4 cm. This will change the angulation so that you maintain a shallow and appropriate AP angle of 15 to 30 degrees, and also makes the advancement of the spinal leads much easier. At the same time, you will be maintaining both your lateral angulations and oblique angulations discussed above. Companies that manufacture spinal cord stimulation systems make extended length needles and extended length lead wires with contacts, which are frequently necessary when you have to go back along that line a substantial amount in order to maintain the angulation. Outside of this relatively minor adjustment, the obese patient may obviously require some additional local anesthetic because of the depth of penetration of the stimulator needle. We frequently will use a longer Quincke needle to provide deeper subcutaneous local anesthetic in these patients. After trying this method on a few patients, you will find that it is an effective and easy way to overcome the additional challenge of implantation in the patient with additional subcutaneous fatty tissue.

Figure 1. Illustration of Line A that would be drawn on the patient’s skin along the spinous process to demonstrate a cephalocaudad linear point of reference and Line B drawn through Point 1 (EES) and Point 2 (SES). Please note that the angle formed using these reference points is less than 30 degrees. Figure 2A. Presents a lateral view that demonstrates the effect of excessive subcutaneous tissue. Point 1 identifies the skin entry site on this patient with a reasonable normal body habitus and a linear lateral line from Point 1 (SES) to Point 3 (EES). Line B demonstrates a similar line through where the SES point would be with additional subcutaneous tissue and a line is then drawn through Point 3 (EES).

Rotoscoliosis of the Spine

If you encounter a patient who has substantial rotoscoliosis, it is important to identify the side of convexity and concavity and the amount of spinal rotation. We emphasize the importance of identifying the EES and squaring the images at that location. Prior to implantation on all patients, it is also important to move the fluoroscope cephalad and preoperatively mark the anticipated final placement position (FPP) of the lead contacts. You will need to make some adjustments in the initial implantation angulation by recognizing the angle of curvature. The basic concept is to change the angulation of an oblique nature so as to reduce the acuity of advancement into the concave side of the scoliosis and to compensate for the convex side as well. This process is completed first by identifying the scoliosis and then identifying the severity and rotation. At this point, anticipate the variances in the EES and the FPP. Try to picture where the spinous process is when viewed on a direct AP view, which necessitates manipulating obliquely right and left to get an idea of the amount of rotation. By determining the amount of angulation right or left, you simply need to flatten out your approach angle and approach further to the left or right of the anticipated spinous process at the EES on the side of the concavity. What this will do is shorten the angulation and make it easier to manipulate the lead wire. On the side of the convexity, it is helpful to increase the angle just slightly in both cases, probably just 10 to 15 degrees.

Last updated on: January 5, 2012
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