The role of sagittal imbalance in adult spinal deformity patients has been extensively debated and studied over the past decade, and the spine community still has not completely come to terms with how to approach it. Prior studies have shown strong correlations between sagittal imbalance and worse patient reported outcomes, though most of these studies have included both post-operative and non-operative patients.1 In order to evaluate this topic further, Dr. Chapman and colleagues from multiple spinal deformity treatment centers analyzed the correlations between sagittal radiographic parameters and patient reported outcomes in 286 patients enrolled in a study comparing surgery to non-operative treatment for adult lumbar scoliosis. Approximately 90% of the patients were women, and the average age was 60. Most patients had a relatively pronounced coronal plane deformity, with the average lumbar Cobb angle 53 degrees. Average sagittal imbalance was much milder, with the average sagittal vertical axis (SVA) within the normal range at 3.1 cm. The only sagittal parameter that was more than mildly abnormal was the pelvic incidence-lumbar lordosis mismatch, which was an average of 17 degrees. The correlations between the sagittal parameters and baseline ODI and SRS-23 scores were non-existent or weak, with the correlation between SVA and ODI being the most consistent. When patients were stratified by SVA as < 4cm, 4-10 cm, and > 10 cm, there was a significant difference between patients with an SVA < 4 cm (ODI=32) compared to those > 4 cm (ODI=40). Interestingly, there was no difference between the 4-10 cm and > 10 cm groups. In a subgroup of patients with baseline ODI > 40, the correlations between sagittal parameters and baseline patient reported outcomes were more consistent though still in the weak range.
This paper does a nice job demonstrating that sagittal imbalance likely contributes to disability in the adult lumbar scoliosis population but is probably not the main driver of symptoms. Coronal deformity and spinal stenosis likely contribute at least as much. While prior studies have shown stronger correlations between sagittal imbalance and symptoms, these have tended to include a large number of post-fusion patients. As the authors point out, sagittal imbalance may have a more pronounced effect on the post-fusion patient than on the patient who has yet to have surgery. Major questions still remain unanswered in the sagittal balance realm. While it seems to have pronounced effects on some patients, many with poor sagittal imbalance, especially older patients, are unaffected by it. Assuming the surgeon can diagnose sagittal imbalance as a cause of symptoms, the next question is how to address it surgically. Finally, the spine community needs to decide what complication rate and costs are acceptable when performing these large magnitude, high morbidity procedures. We are all looking forward to the results of this study to determine how adult lumbar deformity patients do with surgery and non-operative treatment. There are sure to be many subgroup analyses looking at the role of sagittal imbalance, and hopefully those can provide surgeons with much needed guidance on the topic.
Please read Dr. Chapman's article on this topic in the November 15 issue. Does this change how you consider sagittal imbalance? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
1. Glassman SD, Bridwell K, Dimar JR, Horton W, Berven S, Schwab F. The impact of positive sagittal balance in adult spinal deformity. Spine 2005;30:2024-9.