Lumbar Pedicle Subtraction Osteotomy

John M. Rhee

Mathew Cyriac

Tyler Jenkins

Illustrative Case

A 52-year-old woman underwent rod-sublaminar wire stabilization for L2 fracture 20 years ago. Subsequently, she underwent decompression and instrumentation from L4 to the sacrum for subjacent stenosis by an outside surgeon. She then presented to the senior author with difficulty standing upright and incapacitating low back pain. X-rays demonstrated severe sagittal imbalance (sagittal vertical axis [SVA] 22 cm), compensatory thoracic lordosis, and a retroverted pelvis. CT myelogram demonstrates solid fusion from T12 to L5 in kyphosis (˜45° from L1 to L4), with nonunion at L5-S1 (Figure 29-1).

Figure 29-1 ▪ Anteroposterior (A) and lateral (B) x-rays. There is a very mild coronal trunk shift. The lateral x-ray demonstrates a sagittal vertical axis of 22 cm, lumbar kyphosis, distal thoracic lordosis, and retroverted pelvis. (C) Sagittal CT myelogram shows focal kyphosis at L1-L2. Other CT images (not shown) demonstrate solid fusion T12-L5 with nonunion at L5-S1.

Radiographic Assessment

On pre-op anteroposterior x-ray, look for coronal imbalance, which may need an asymmetric pedicle subtraction osteotomy (PSO).
On lateral x-ray, determine C7 SVA, lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope. These measurements can be used as a rough guide to the amount of correction needed.³
Lordosis is measured on sagittal supine MRI and CT scans. These measurements provide an assessment of the sagittal alignment that can be passively obtained by “eliminating gravity” and placing the patient prone on the operating room table for surgery. In that sense, they may be more realistic measurements of the amount of correction that actually needs to be obtained through the osteotomy.
Typical levels of PSO include L2, L3, L4, or L5. Choice will be determined by a number of factors, including levels of prior surgery, bone quality, and size/height of the vertebra.

Positioning

Refer to the chapter on posterior lumbar laminectomy and fusion for overview.
Use Jackson Spinal Table with pads. Keep hip pads distal to the anterior superior iliac spine and extend hips to maximize lumbar lordosis. Keep chest pad relatively more proximal to induce as much “sag” as possible in the lumbar spine and increase lordosis.
Slight reverse Trendelenburg to decrease venous congestion of eyes/head