Fig. 8. Sextant device at moment of final rod engagement.
passage of the rod. The trocar is removed and a lordotic rod is attached to the arm of the Sextant. The rod is delivered through the same fixed arc into the side openings of the multiaxial screws. One additional real-time fluoroscopic image is recommended to ensure proper placement of the rod, though the fixed geometry of the screw extender Sextant system provides for consistent accurate placement. The rod is detached from the delivery arm, and the arm removed. The locking screws previously loaded into the screw extender chambers are tightened to the appropriate torque tension with a screwdriver. Then, the complete apparatus
is pulled out of the three (or if L5-S1, two) stab incisions. Subcuticular closure is then possible (fig. 9). The entire process can be repeated on the opposite side, though some surgeons may perform unilateral fixation when the biomechanical goal is to provide a posterior tension band following ALIF (fig. 10).
The preliminary results of this technique confirm that it is a safe, effective way to place lumbar pedicle screws and rods. Lefkowitz and Foley  presented their results for 10 patients with spondylolisthesis. Patients underwent ALIF followed by posterior percutaneous pedicle screw/rod fixation. There were no complications related to the percutaneous technique. The average total operating time for both the ALIF and the percutaneous screw placement in this initial series was 7.3 h. Blood loss was markedly decreased compared to open techniques. The average hospital stay was 2.9 days.
Nockels et al.  presented their experience in 15 patients with a wide range of pathology. A total of 64 screws with rods were placed. Two cases of a two-level instrumentation were done. Patients were evaluated postoperatively with plain radiography and CT scan. Most cases were performed in combination with an ALIF. The average time for the percutaneous placement of lumbar screws with rods was 65 min. No complications were reported due to the percutaneous technique. There were no cases of implant failure during the initial follow-up.
Lefkowitz et al.  also reported on their experience using percutaneous pedicle screw fixation following minimally invasive posterior lumbar interbody fusion (PLIF). This latter technique was performed through endoscopic tubular retractors but with the use of the operating microscope or surgical loupes. Six patients underwent this technique. The indications were spondylolisthesis or degenerative disc disease. One dural tear was reported but was not related to the screw technique (it occurred during the PLIF technique). The average operating time for the entire procedure was 6 h 45 min. The average blood loss was 183 ml. The average duration of hospitalization was 2.3 days.
Rodts  presented preliminary data of 5 patients who underwent unilateral posterior percutaneous pedicle screw fixation following ALIF. The indication for surgery was spondylolisthesis in 4 patients and recurrent disc herniation in a fifth. All patients received unilateral instrumentation alone. Follow-up ranged from 10 to 22 months. Solid arthrodesis has been achieved in all patients. Postoperative CT scans were performed showing satisfactory screw placement in all screws except one. One S1 screw had 3 mm of lateral cortical perforation of no clinical significance.
Lumbar instrumentation has proven to be a useful component of current lumbar fusion surgery. The advantages include higher rates of arthrodesis, provision of immediate spinal stability, and the ability to more effectively reduce or correct deformity [8-11]. For patients who require extensive posterior decompression with fusion, open placement of pedicle instrumentation remains a useful technique.
In some patients, however, the goals of arthrodesis may be achieved with an ALIF, a minimally invasive PLIF, or a minimally invasive posterolateral fusion technique. In cases of mobile spondylolisthesis, previous surgery (and suboptimal fusion bed, vascular supply), metabolic bone disease, or smoking, a surgeon may wish to supplement the ALIF or PLIF arthrodesis with instrumentation. In this setting, the percutaneous technique may offer an advantage over open techniques. Several very small stab incisions may be cosmetically superior to one longer midline or paramedian incision. The paraspinal musculature is spared the ill-effects of midline tendinous release and wide retraction causing ischemia and subsequent atrophy and scar formation. Blood loss is markedly less compared to open techniques. In their initial experience, surgeons using the percutaneous pedicle screw technique have found that their patients have substantially less back pain in the postoperative period.
The key component to safe, effective passage of percutaneous instrumentation is image guidance. Whether a surgeon chooses to use a single or biplane live fluoroscopy or computer-assisted virtual fluoroscopy, the proper radiographic identification of important landmarks is critical. Virtual fluoroscopy offers several advantages, including the ability to view four images at once (e.g. right and left oblique, AP, lateral), and the ability to virtually extend various instruments from the surface of the skin down to the spine on the radiographic images.
Further experience with percutaneous and minimally invasive techniques will not only lead to less postoperative pain, smaller incisions and soft tissue trauma, shorter operating time, and less blood loss, but it will also enable the surgeon to achieve the same desired result as in open procedures: successful arthrodesis. With the advent of new biological products such as bone morpho-genetic protein, and with the refinement of interbody fusion implants, the role of minimally invasive surgery may expand.
1 Wiesner L, Kothe R, Ruther W: Anatomic evaluation of two different techniques for the percutaneous insertion of pedicle screws in the lumbar spine. Spine 1999;24:1599-1603.
2 Lowery GL, Kulkarni SS: Posterior percutaneous spine instrumentation. Eur Spine J 2000;9: S126-S130.
3 Magerl F: External skeletal fixation of the lower thoracic and the lumbar spine; in Uhtoff HK, Stahl E (eds): Current Concepts of External Fixation of Fractures. Berlin, Springer, 1982, pp 353-366.
4 Lefkowitz M, Foley KT: Percutaneous pedicle fixation for spondylolisthesis. Annual Meeting of the AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves, Orlando, 2002.
5 Nockels R, et al: Percutaneous pedicle screw fixation. Annual Meeting of the AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves, Orlando, 2002.
6 Lefkowitz M, Palmer S, Foley KT: Percutaneous pedicle fixation following minimally-invasive PLIF. 2002 Annual Meeting of the AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves, Orlando, 2002.
7 Rodts GE: Unilateral percutaneous lumbar pedicle screw/rod fixation following ALIF. Global Spine Meeting, Mexico, 2002.
8 Tribus CB, Belanger TA, Zdeblick TA: The effect of operative position and short-segment fusion on maintenance of sagittal alignment of the lumbar spine. Spine 1999;24/1:58-61.
9 Zuckerman JF, Zdeblick TA, Bailey SA, et al: Instrumented laparoscopic spinal fusion: Preliminary results. Spine 1995;20:2029-2034.
10 Yuan HA, Garfin SG, Dickman CA, Mardjetko SM: A historical cohort study of pedicle screw fixation in thoracic, lumbar and sacral spine fusions. Spine 1999;19(suppl 20):2279S-2296S.
11 Foley KT, Gupta SK: Percutaneous pedicle screw fixation of the lumbar spine: Preliminary results. J Neurosurg 2002;97:7-12.
Department of Neurosurgery, Emory University
550 Peachtree St., NE, Suite 806, Atlanta, GA 30308 (USA)
Tel. +1 404 686 8101, Fax +1 404 686 4805, E-Mail [email protected]
Haid RW Jr, Subach BR, Rodts GE Jr (eds): Advances in Spinal Stabilization. Prog Neurol Surg. Basel, Karger, 2003, vol 16, pp 213-224
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