Endoscopic/Percutaneous Lumbar Pedicle Screw Fixation Technique

21 Endoscopic/Percutaneous Lumbar Pedicle Screw Fixation Technique

Faheem A. Sandhu, Josh Ryan, and R. Tushar Jha

21.1 Introduction

The desire to minimize the surgical morbidity caused by excessive muscle dissection and retraction, which is typical of traditional open procedures, has been a major impetus in the development of minimally invasive spine procedures. The first description of a paraspinal muscle-splitting approach between the multifidus and longissimus muscles for insertion of pedicle screws was done by Wiltse and Spencer in 1988.1 This procedure served as a gateway through which surgeons have continued to advance minimally invasive lumbar spine techniques. Percutaneous pedicle screw insertion was first described in 1982 by Magerl, but it was intended to be used as part of an external fixation construct.² In 2001, Foley et al described the insertion of a longitudinal connector rod between the percutaneous pedicle screws via a minimally invasive approach, which heralded the use of percutaneous pedicle screws for internal fixation.³ Other systems for percutaneous pedicle screw fixation (PPSF) have since emerged, and the endoscope can be employed with these systems in various ways. The traditional percutaneous method and the endoscopic method of pedicle screw insertion are both be described here.

21.2 Choice of Patient

21.2.1 Indications

Indications for lumbar pedicle screw fixation include:

• Symptomatic grade I or II spondylolisthesis, including postlaminectomy spondylolisthesis and spondylolisthesis caused by spondylolysis

• Augmentation of anterior element fusion procedures, such as anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), minimally invasive transforaminal lumbar interbody fusion (MI-TLIF), or minimally invasive posterior lumbar interbody fusion (MI-PLIF)

• Recurrent lumbar disk herniation leading to radiculopathy that is not responsive to conservative management

• Fractures of the lumbar vertebral body, pedicle,⁴ or facet causing instability in a neurologically intact patient. Pedicle screw fixation has also been described as an option for lumbar Chance fractures to avoid long periods of external casting and to facilitate early mobilization of the patient.⁵

• Degenerative scoliosis

• Stabilization of osteotomies

21.2.2 Relative Contraindications

Relative contraindications are:

• Morbid obesity, as retractor tubes may not be long enough and radiographic anatomy may be obscured

• Patients with osteoporosis, as K-wires can advance easily through the bone

• Patients with prior posterior surgery at the same level in whom an open procedure may be safer because of the risk of encountering abnormal anatomy

• Patients with multiplanar deformity

• Active systemic or spinal infection

• Allergy to metals

21.3 Percutaneous Technique

21.3.1 Position and Anesthesia

• General anesthesia is used and the patient is placed in the prone position, with the hips and knees in flexion and the abdomen supported, on a Jackson table (Fig. 21.1).

• If PPSF is being used as an augmentation to ALIF or LLIF, the patient may need to be repositioned to prone after the prior procedure before the procedures can be staged.

• Percutaneous transfacet screw insertion has been described with the patient in the lateral decubitus position after LLIF, and this position could also be used for percutaneous pedicle screw insertion, but description of this technique is outside the scope of this chapter.⁶

• Either intraoperative 3D imaging or C-arm fluoroscopy may be used. Two C-arm machines may be utilized simultaneously in the AP and lateral planes to avoid moving a single C-arm between planes (Fig. 21.1).

• If the C-arm is used, true AP and lateral views must be obtained. A true AP view is indicated by a flat superior end plate with spinous processes centered between pedicles. A true lateral view is indicated by a flat superior end plate with pedicles superimposed.

• Prep and drape the patient in the same fashion as for an open procedure.

Fig. 21.1 Patient is placed in the prone position with the hips and knees flexed. Two C-arms are used in the AP and lateral positions to expedite the procedure.

Fig. 21.2 A vertical incision is made with a scalpel and is extended through the lumbodorsal fascia.

Fig. 21.3 Jamshidi needle is placed through the skin and fascial incision down to the base of the transverse process and facet junction.

21.3.2 Marking and Skin Incision

• Two vertical incisions are made for each level of interest, each 1.5 cm in length and ~ 4 cm from the midline on either side, centered at the level of the pedicles (Fig. 21.2).

• Patients with larger or smaller body habitus may require incisions farther from or closer to the midline, respectively, to account for the amount of soft tissue traversed.

• Extend the incision through the lumbodorsal fascia using either sharp dissection or monopolar electrocautery.

21.3.3 Needle Insertion and Dilation

• Use the index finger to extend through the fascial incision and palpate the base of the transverse process.

• Alternatively, just insert a Jamshidi needle through the skin and fascial incisions down to the junction of the base of the transverse process and the facet (Fig. 21.3).

• The Jamshidi needle should be docked on the lateral border of the pedicle in the AP fluoroscopic views.

• Tap the Jamshidi needle gently with a mallet (Fig. 21.4) until it has advanced through the pedicle and to the border of the pedicle and vertebral body. Intermittently check both AP and lateral fluoroscopic views as the needle is advanced. The Jamshidi should be ~ 20 mm deep from the docking point as it passes from the pedicle into the vertebral body. The final AP view should show that the tip of the Jamshidi needle has not advanced past the medial border of the pedicle.

21.3.4 Screw Insertion

• With the Jamshidi needle in place, remove the inner cannula (Fig. 21.5) and then pass the K-wire through the Jamshidi needle (Fig. 21.6). With gentle pressure, advance the K-wire into the vertebral body.

• Remove the Jamshidi needle over the K-wire, ensuring not to inadvertently pull the K-wire out (Fig. 21.7).

• All previous steps up to this point are repeated for each pedicle until K-wires have been placed in all pedicles of interest. Fluoroscopic AP and lateral confirmation of adequate position of all K-wires is now obtained (Fig. 21.8).

Fig. 21.4 Mallet is used to advance the Jamshidi needle through the pedicle to the junction of the pedicle and vertebral body. The distance is ~ 20 mm deep from the docking point.

Fig. 21.5 Inner cannula of Jamshidi needle is removed.

Fig. 21.6 K-wire is inserted and gently advanced to the vertebral body.

Fig. 21.7 Jamshidi needle is removed over the K-wire.

• Advance a cannulated tap (if desired) over the K-wire and tap the pedicle down to its base. Electromyography (EMG) stimulation of the tap can be used to detect medial or inferior wall breaches.

• Remove the tap over the K-wire. Advance the pedicle screw over the K-wire, through the pedicle, and into the vertebral body (Fig. 21.9a). The K-wire is removed as the screw enters the vertebral body (Fig. 21.9b). Align the screw heads in the rostral-caudal direction to facilitate passage of the rod. Each screw has removable extenders attached to the head to create a small working channel through which the screw head can be visualized and a rod may be passed.