CT Classification System of Intervertebral Disc Features for PCO Surgeries

Introduction: Posterior column osteotomy (PCO) is a common procedure for treating spinal curvature deformities that increases lordosis at affected levels. Existing literature discusses the importance of measuring sagittal balance and disc flexibility in surgical planning. However, there is no literature describing how intervertebral disc features affect surgical outcome. The objective of this project is to formulate a grading chart that correlates disc characteristics to degrees of correction achieved through PCOs.

Methods: This retrospective study includes adult spinal deformity patients who received long segment (5+ levels) fusions and PCOs. Preoperative supine CT and standing X-rays were analyzed, along with early and last postoperative radiographs. Data was analyzed at each level (T10-S1) individually and holistically.

Results: 62 patients were included (average age 63.6, BMI 31.71). Analysis of lordotic change (in degrees) in early postoperative x-rays revealed the following:
T10-11 was 2.73, T11-12 was 1.97, T12-L1 was 2.69, L1-2 was 3.96, L2-3 was 3.65, L3-4 was 3.76, L4-5 was 2.81, and L5-S1 was 2.15. Average disc heights were as follows with each increasing lower in the spine: anterior was 6.142mm, middle was 5.778mm, and posterior was 4.041mm. Additionally, there was a significant negative correlation between preoperative segmental lordosis and change in lordosis.

Conclusion : In our study, all vertebral levels had lower lordosis added than existing literature suggests is common to obtain (8-10 degrees per level). Disc heights were also shorter compared to other literature. It is known that obese patients experience higher incidences of disc degeneration due to increased mechanical load, diminished blood supply, and chronic inflammation. These factors may account for the observed reduction in lordotic change and disc heights. Finally, it’s reasonable that greater preoperative segmental lordosis resulted in less lordotic change because the vertebral level was already correctly angled.
This work is important for determining an accurate level of degree correction in PCOs based on preoperative disc features and will help surgeons determine how many and which levels to operate on for maximal results with least invasion. Future work will evaluate the influence of other features, such as vacuum disc, on lordotic change and will include more patients within normal BMI range.