Percutaneous Lumbar Fusion and Pedicle Screw Instrumentation

Illustrative Case

A 65-year-old with neurogenic claudicating low back pain/buttock pain and left leg radiating pain. Patient underwent anterior lumbar interbody fusion L4-S1 for indirect central and foraminal decompression followed by L4-S1 percutaneous pedicle screws and facet fusion.

Radiologic Assessment

Evaluate anteroposterior (AP) and lateral x-rays (Figure 21-1) to evaluate for vertebral rotation in anticipation of appropriate C-arm rotation intra-op.
Look at axial MRI (Figure 21-2C) to measure screw length and width.

Figure 21-1 ▪ A, B Anteroposterior and lateral x-ray showing L4-5 anterolisthesis and significant disk degeneration at L5-S1.

Figure 21-2 ▪ A, Sagittal T2 MRI showing L4-5 spondylolisthesis with central stenosis. B, Parasagittal MRI showing foraminal stenosis bilaterally at L5-S1. C, Axial T2 showing adequate width and length for L4 pedicle screws.

Positioning

Prone on spine Jackson table per usual for posterior lumbar fusion protocol.

Anesthesia/Neuromonitoring Concerns

Typically free running and triggered electromyography monitoring is used to test for screw malposition. Avoid intermediate or long-acting neuromuscular blockade agents such as rocuronium.

Localization of Incision

Obtain perfect C-arm AP view (Figure 21-3A) to mark levels of each pedicle. Adjust C-arm tilt until a true AP view showing parallel endplates for the level being instrumented.
- Adjust C-arm rotation until spinous process is perfectly centered between the two pedicles.

Before marking, swing C-arm around to make sure perfect lateral (Figure 21-3B) is obtainable.

Figure 21-3 ▪ A, True anteroposterior x-ray showing a single superior endplate shadow. The pedicle shadow should be just inferior to the superior endplate shadow and the spinous process should be in the middle of the pedicles. B, Lateral x-ray showing parallel endplates.

After true AP view, place K-wire longitudinally over the lateral border of the pedicles on either side of the spine. Draw a longitudinal line to mark the lateral border of the pedicle (Figure 21-4A).

The actual incision will be slightly lateral to this line because of medial angulation of screw trajectory (Figure 21-4B).

An even more lateral incision may be needed for large patients.

Figure 21-4 ▪ A, Instrument placed lateral to L4 and L5 pedicle to mark the lateral aspect of the pedicle. The actual incision will be 1 to 3 cm lateral to the skin depending on how obese the patient is. B, Diagram showing that the actual skin incision will be 1 to 3 cm lateral to skin mark placed on the lateral aspect of the pedicle depending on patient obesity.

Place K-wire transversely across the midpedicle for each targeted vertebrae (Figure 21-5A). Where the transverse line intersects the longitudinal line will be skin marking (Figure 21-5B).

Figure 21-5 ▪ A, Anteroposterior x-ray showing K-wire intersecting the middle of the pedicle shadow to localize cranial/caudal location of incision. B, The actual incision will be 1 to 3 cm lateral where the transverse line intersects the longitudinal line depending on patient obesity.

Approach

Skin incision with No. 10 blade

Cautery for hemostasis, continue with cautery through subcutaneous tissue to fascia.

Need to medialize as one proceeds deeper because skin incision was lateral and screw start point is medial to incision (Figure 21-6).

Figure 21-6 ▪ A, Jamshidi at right pedicle screw start point at the 3 o’clock position. B, Sawbones model showing start point where the transverse process meets lateral aspect of the facet.

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