Monograph to the August 2002 issue

Minimally invasive technique for spine fusion

John H. Peloza, MDJohn H. Peloza, MD

  

… the increase in soft-tissue damage secondary to surgical exposure and operating time has had a negative impact on outcome.

  

Mechanical, discogenic low back pain that has failed conservative care has traditionally been treated by lumbar fusion. Fusion procedures have evolved over time. Fusions were initially performed through a posterior approach. This posterior procedure required the dissection of the paraspinal musculature off the bone elements. The dissection caused significant muscle injury and is informally known as “fusion disease.” The muscle damage is caused by direct compression of the muscle tissue by the retractors and is analogous to a tourniquet applied to the muscle of an extremity. This compression and damage causes decreased arterial inflow and decreased venous outflow to the muscle capillary beds with resultant microvascular and metabolic changes in muscle tissues. There is also devascularization of the feeder vessels to and denervation of the paraspinal muscles. Last, the exposure denervates and potentially injures the facet joints.1-9

The incidence of pseudarthrosis in noninstrumented posterior fusions is significant. Therefore, internal-fixation systems were developed to increase the fusion rate to make clinical outcomes more predictable.10 Rigid internal-fixation systems were successful in improving fusion rates.10-14 However, the increase in soft-tissue damage secondary to surgical exposure and operating time has had a negative impact on outcome.

Interbody-fusion techniques were developed in recognition that the disc is often the source of spine pain and that the disc space is a more favorable environment for bone healing.15-18 Several surgeons have reported successful results with anterior lumbar interbody fusion (ALIF) utilizing autograft or allograft bone blocks, dowels or femoral rings.15-18 Other surgeons have had success with the posterior lumbar interbody fusion (PLIF).19-25 However, the pseudarthrosis rate with stand-alone ALIF or PLIF techniques was unacceptably high, leading to unpredictable surgical outcomes and the need for improvement.

Developments in fusion procedures

A newer method emerged called the “360 fusion”, in which bone was placed in the interbody space through either an anterior or posterior approach. Posterior pedicle screws and rods then supplemented the interbody construct. Fusion rates approached 100% and the incidence of subsidence and flat back deformities was low.22,26 However, there was a significant complication rate and fusion disease remained.

Threaded fusion cages, implants made of titanium with space for packing autograft bone and the ingrowth of bone into the vertebral body, revived interest in anterior interbody fusion. The cages created a rigid construct that would act as a stand-alone device without the need for posterior fixation or the posterior surgical exposure, which often led to “fusion disease.” Fusion cages restored anatomic disc height, sagittal balance and could indirectly decompress the spinal canal without drastically altering the kinematics of adjacent disc segments. Several authors reported excellent fusion rates and clinical outcomes.27-29 However, after the initial clinical trials, problems with the cages became apparent. There was an increase pseudarthrosis rate, subsidence, loss of lumbar lordosis and difficulty determining bone healing through and around the cages.30 Most of the problems (e.g., misplaced/misdirected cages, osteoporosis, higher-grade spondylolisthesis or instability) were caused by poor surgical technique or judgment.

The most difficult challenge was surgery that appeared to be successful with excellent radiographs that resulted in a poor clinical outcome. In the first-generation cages, no imaging technique could reliably determine fusion healing. This problem has been overcome in second-generation cages but pseudarthrosis, subsidence and loss of lordosis may still occur with stand-alone cages.

Figure 1Figure 1
METRx dilators are held in place by a mechanical arm.

Figure 2Figure 2
Guidewires are placed in pedicles. Pedicles are tapped with cannulated tip.

Figure 3Figure 3
M10 pedicle screws are attached to Sextant extensions. Here, the Sextant alignment guide is shown with rod attachment to Sextant screw extensions.

Figure 4Figure 4
This figure is a fluoroscopic view of Sextant screws with rod advancing into top loading screw mechanism.

Figure 5Figure 5

The total length of the skin incision is 3 cm.

Figures 1-5 courtesy of John H. Peloza, MD.

The Sextant system innovates standard ALIF

The new procedure combines the rigidity of a “360” construct with minimally invasive technique. Specifically, posterior pedicle screw fixation is implanted without posterior exposure.31 The anterior exposure is performed with a mini retroperitoneal approach to implant the threaded fusion cages in the standard manner. The patient is then repositioned prone and posterior fixation is implanted with the Sextant Rod Insertion System (Medtronic Sofamor Danek, Memphis, Tenn.). Under fluoroscopic imaging, the pedicle entry sites are determined on the anterior posterior view of the spine and the skin is marked. A small skin incision (25 mm) is made and a Jamshiede needle is secured to the pedicle entry site under fluoroscopy. A wire is then placed through the Jamshiede needle and the needle is removed. Sequential dilation is then performed using the METRx dilator system (Medtronic Sofamor Danek) (Figure 1). Once the retractor tube is secured, the dilators are removed. The pedicle entry site (1 mm) is exposed at the wire/bone interface taking care to preserve the paraspinal muscle blood and nerve supply. The pedicle entry site is then decorticated with a Midas burr and the pedicle is entered with a gearshift awl.

A guide wire is placed into the pedicle and a cannulated tap threads the pedicle (Figure 2). This process is repeated for the second screw. Next, the cannulated M10 pedicle screws with their Sextant extensions are advanced into the pedicles over the guide wires. The extensions are then connected to the Sextant alignment guide (Figure 3). A small proximal stab wound is made in the skin to allow the rod to bluntly pass through the paraspinal muscles into the top loading mechanism of the screws (Figure 4). The top loading nuts are then secured through the pedicle screw extension tubes and the Sextant is disengaged. Figure 5 demonstrates the minimal incision that is used in performing ALIF. This procedure can be reliably, consistently and safely performed in 40 to 50 minutes with no posterior muscle “stripping” or blood loss.

Currently, I have performed 64 procedures and the patients are followed with validated outcome instruments that will be subjected to statistical analysis at a later time.

Early results are promising with rapid, significant decrease in pain, improvement in function and increased healing. It is important to note that only surgeons experienced in endoscopic pedicle screw fixation or those who are comfortable performing microendoscopic surgery should perform this procedure.

Treating an Olympian

John H. Peloza, MDA 25-year-old Olympic skier complained of lower back pain for five years and a marked increase in pain after training at the ski gates. Her pain became so unbearable that she could no longer ski, and her daily activities became uncomfortable and difficult. After undergoing one and a half years of aggressive conservative care including physical therapy, injections and a rhizotomy at the L5/S1 facet joints, she decided to undergo surgery.

Diagnostic workup revealed the following:

  • Lumbar spine radiographs: Decreased disc height with retrolistheses L5S1.
  • MRI scan lumbar: Decreased disc height and decreased disc signal with high intensity zone L5S1.
  • Discogram lumbar: Positive for concordant pain and morphology L5S1.

The patient underwent surgery in April 2001 with the Sextant technique (Figures A and B) as described in the article on page 5. She underwent rehabilitation protocol and began skiing again in October 2001. Since then, she has competed in World Cup skiing events in December 2001 and January 2002 and competed in the Salt Lake City Winter Olympics in February 2002 as a member of the United States Olympic Alpine Ski Team. Currently, she is training for the 2002/2003 World Cup season and reports no back pain.

Figure A.Figure B

Successful placement of the Sextant Rod Insertion System in an Olympic athlete.

Figures A and B courtesy of John H. Peloza, MD

References

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Copyright 2002, SLACK Incorporated. Revised 19 September 2002.