Fixed Sagittal Imbalance in a Very Young Adult Female Created by Settling of Cages at L4/L5 and L5/S1, Treated by Pedicle Subtraction Osteotomy

Figure 1

Standing lateral x-ray before this 16-year-old patient had any treatment. She has bilateral pars defect at L4. She has a component of spinal stenosis at L5/S1 with a "Wiltse congenital" spondylolisthesis at L5/S1.

For these pathologies, she is treated with decompression at L5/S1 and posterolateral spinal fusion without instrumentation from L4 to the sacrum. She is also treated with threaded cages at L4/L5 and L5/S1. Apparently posterior pedicle screw fixation was not used because of the patient's congenital anomalies at L5/S1, in particular the S1 pedicle on the right side.

Figure 2

These are standing long cassette AP and lateral x-rays on the same patient. She has been treated with decompressions at L5/S1 and posterolateral fusion L4 to the sacrum with autogenous iliac bone grafting. No implants posteriorly. Anteriorly she has had threaded cases placed at L4/L5 and L5/S1. She has a solid fusion at L5/S1, but a pseudarthrosis at L4/L5.

Figure 3
This is the appearance of the patient's spine when she lays prone.

Figure 4

These are supine AP and lateral x-rays demonstrating solid fusion at L5/S1, but pseudarthrosis at L4/L5. Subsequent to these surgeries, the patient gradually went from being able to stand perfectly erect to being able to stand only in a very pitched forward position. What transpired was that the cages settled into the L5 vertebral body and the patient lost approximately 30-degrees of lordosis from L4 to the sacrum.

If you look at her radiographs when she is supine and prone, the overall appearance of her spine from T12 to the sacrum is not terribly remarkable. But if you look closely, you will see that she does have substantially less lordosis from L4 to the sacrum postop than she did preop.

Therein she has relative kyphosis from L4 to the sacrum. Analysis of the sagittal imbalance in this circumstance is complex. She does not have frank kyphosis from L4 to the sacrum, but she does have a relative one. Often in this circumstance, surgeons are somewhat confused as to the etiology. Is there hip flexion contracture? Is there pathology in the hips? In this patient's case, she has full range of motion of her hips and totally normal hips.

The reason for her sagittal imbalance is the 30-degrees of lordosis from L4 to the sacrum.