Sagittal rebalancing of the pelvis and the thoracic spine after pedicle subtraction osteotomy at the lumbar level.

DESIGN

Retrospective study of radiologic records of patients who underwent lumbar pedicle subtraction osteotomy (PSO) procedures.

OBJECTIVE

To evaluate the restoration of spinal balance above and below the osteotomy site after PSO for various causes.

SUMMARY OF BACKGROUND DATA

The normal sagittal balance of the spine has been widely documented. Sagittal imbalance can be surgically treated with vertebral osteotomy. Reports have described its technical aspects and local radiologic results. Less is known about the spontaneous rebalancing of the spine cranially and caudally to the osteotomy site.

METHODS

The French Scoliosis Study Group conducted a multicenter retrospective study from the records of a combined cohort of 356 patients. Spinal balance after PSO was assessed radiologically. In this study, we focused specifically on measuring the reorientation of the pelvis and upper thoracic segments and investigated the influence of pelvic incidence, osteotomy level, and regional lordosis gain. The population was classified according to the indication for the procedure: posttraumatic deformity, degenerative kyphosis, scoliosis, or ankylosing spondylarthritis.

RESULTS

The average regional lordosis gain was 26.1 degrees. In the degenerative kyphosis and scoliosis groups, the level of osteotomy and the incidence angle tended to influence pelvic adaptation (better balance of the caudal portion was associated with low-level PSO and low-incidence angle). The posttraumatic deformity cases had a specific pattern: balance changes after PSO were limited to the local lordosis gain, with less pelvic and thoracic reorientation, probably due to spinal flexibility. On the contrary, the spondylarthritis cases showed less pelvic and more thoracic reorientation, probably due to hip and spinal stiffness.

CONCLUSIONS

Better knowledge from a large series of the overall spontaneous spinal balance after PSO and the pelvic/thoracic reorientation would be useful for preoperative planning of lumbar osteotomies and predicting pelvic and hip reorientation.

LEVEL OF EVIDENCE

Level II.