Defining a Surgical Invasiveness Threshold for Increased Risk of a Major Complication Following Adult Spinal Deformity Surgery

Brian J. Neuman, MD; Andrew B. Harris, BS; Eric O. Klineberg, MD; Richard A. Hostin, MD; Themistocles S. Protopsaltis, MD; Peter G. Passias, MD; Jeffrey L. Gum, MD; Robert A. Hart, MD; Michael P. Kelly, MD; Alan H. Daniels, MD; Christopher P. Ames, MD; Christopher I. Shaffrey, MD; Khaled M. Kebaish, MD


Spine. 2021;46(14):931-938. 

In This Article


Patients with ASD who undergo surgical procedures with an ASD-SR score ≥90 are almost twice as likely to experience a major complication as are patients below this threshold. Patients with scores substantially higher than 90 do not have significantly greater odds of developing a major complication. Our study is the first to use the ASD-SR score as a risk-stratification tool for major complications.

The ASD-SR invasiveness index affords a simple method to assess surgical invasiveness and can be calculated early in the postoperative period (by using the degree of radiographic correction) or in the preoperative period (by using the planned radiographic correction). Although we recognize that the invasiveness of a surgical procedure is not typically a modifiable factor, in some cases, a less invasive procedure may be considered in a high-risk patient. Our results show that the greatest increase in major complication risk is at an ASD-SR score of approximately 90. When this cutoff was used to divide the patient population in half, those in the highest invasiveness quartile did not have significantly more major complications than those in the second highest quartile. We believe this indicates a "plateau" in the prevalence of major complications above an ASD-SR invasiveness score of 90; after this point, increasing surgical invasiveness is not associated with substantially increased risk of major complications. This finding suggests that, for patients at high risk of complications and for whom the planned surgical procedure has an ASD-SR score of approximately 90, it may be beneficial to avoid aggressive deformity correction or additional factors that add to surgical invasiveness. However, patients for whom highly invasive surgical procedures are planned (ASD-SR score much higher than 90), may benefit less in terms of complication risk from slight reductions in surgical invasiveness.

Various strategies have been used to predict the risk of postoperative complications in ASD patients. Recently, Scheer et al[8] developed a model that predicted major postoperative complications in ASD patients with 87% accuracy. Similar predictive models for surgical complications in ASD patients have been developed with up to 92% accuracy.[25,26] In the model developed by Scheer et al,[8] the five variables most predictive of major complications were patient age, presence of leg pain, ODI value, number of decompression levels, and number of interbody fusion levels; two of these variables are accounted for in the ASD-SR invasiveness index. Given that the area under the receiver operating characteristic curve in our study showed 62% accuracy, the ASD-SR score should not serve as the sole metric for attempting to predict major postoperative complications. However, this study helps clarify the relationship between invasiveness and complications and suggests that there is an invasiveness threshold above which risk factors that have been identified in predictive models (eg, three-column osteotomy) may not contribute as much to complication risk in patients who are not already undergoing a highly invasive surgery.

The ASD-SR invasiveness score has not been well studied beyond its initial validation; however, studies of the Spine Surgical Invasiveness Index (SSII) developed by Mirza et al[27] serve as a useful comparison for our results. The SSII is not specific to deformity patients and thus does not account for radiographic changes. Cizik et al[28] showed that patients with higher SSII values are at higher risk of developing surgical site infection, and other studies reported that patients with higher SSII values are at higher risk of pulmonary complications,[29] cardiac complications,[30] and unintended durotomy.[31] The SSII has also been factored into predictive models and shown to be independently associated with a higher risk of major postoperative complications.[32] In the future, similar investigations should evaluate the extent to which the ASD-SR is associated with specific complications in ASD patients.

Our study should be viewed within the context of several limitations. Although the data were collected prospectively, our study question was proposed and analyzed in a retrospective manner. ASD-SR scores were calculated on the basis of the surgery that was performed, precluding modification of surgical invasiveness between groups to assess a causal relationship between invasiveness and complications. The patients we assigned to the "higher invasiveness" groups are likely to have more severe deformity and may have additional comorbidities. However, our analysis provides clinically important information regarding high- versus low-invasiveness procedures and how the ASD-SR score may be used to assess their associated risks. Our study is strengthened by the large sample size, 2-year follow-up, and enrollment from a diverse group of study centers with surgeons who have various surgical preferences and degrees of experience.