Development of a Novel Cervical Deformity Surgical Invasiveness Index

Peter G. Passias, MD; Samantha R. Horn, BA; Alexandra Soroceanu, MD; Cheongeun Oh, PD; Tamir Ailon, MD; Brian J. Neuman, MD; Virginie Lafage, PhD; Renaud Lafage, MS; Justin S. Smith, MD; Breton Line, BS; Cole A. Bortz, BA; Frank A. Segreto, BS; Avery Brown, BS; Haddy Alas, BS; Katherine E. Pierce, BS; Robert K. Eastlack, MD; Daniel M. Sciubba, MD; Themistocles S. Protopsaltis, MD; Eric O. Klineberg, MD; Douglas C. Burton, MD; Robert A. Hart, MD; Frank J. Schwab, MD; Shay Bess, MD; Christopher I. Shaffrey, MD; Christopher P. Ames, MD


Spine. 2020;45(2):116-123. 

In This Article


This study developed a novel CD surgical invasiveness index that accounts for a larger variation in EBL, operative time, and length of hospital stay than previously reported surgical invasiveness indices for spine surgery, in part because of the fact that none of the previous indices were CD-specific. We found that the CD-specific surgical invasiveness index presented in this study predicts operative time, blood loss, and LOS, making it a good first step in assessing surgical invasiveness for CD procedures by combining CD-specific surgical and radiographic factors.

This is not only the first study to develop a novel CD surgical invasiveness index, but it is the first study of invasiveness to assess the index in relation to hospital LOS in addition to operative time and EBL. The addition of using length of hospital stay to the previously used metrics of blood loss and operative time adds to the assessment of risk of these procedures and overall invasiveness.[13–15] Length of hospital stay has previously been shown to be reflective of the complexity of the procedure as well as can fluctuate based on complication occurrence.[16,17]

There are no studies that have applied a surgical invasiveness index to CD surgeries. Given the heterogeneous presentation of pathologies, the highly frail and comorbid patient cohort, and the challenging and complex procedures required for CD correction, metrics to assess surgical invasiveness are likely to be higher than for a general spine population or a thoracolumbar deformity population. In our study, we found that the ASD invasiveness index accounted for less of the variation in operative time and EBL than the current novel invasiveness index we developed specifically for a CD population.

The ASD invasiveness index set the groundwork for the development of this CD index, with modifications made to fit the procedures and sagittal alignment profiles of CD patients. There are certain variables that apply to both an ASD and CD population, and thus they remained unchanged in our index from the ASD index. Those included levels decompressed, implants, levels fused, posterior column osteotomy, three-column osteotomy, and revision status. However, a few of the components of the invasiveness index were changed to be specific for a CD cohort, including removing interbody fusions and fusion to S2 or iliac from the index and replacing those with corpectomy, ACDF, and fusion to the upper cervical spine. We included corpectomy procedures in our CD surgical invasiveness index given that these procedures are often associated with complications including dysphagia, hematoma, laryngeal nerve palsy, or graft migration.[18] ACDF procedures have previously been associated with adjacent segment disease at a rate of 13.6% at 5 years and 25.6% at 10 years after surgery.[19,20] Interestingly, there is evidence to suggest two-level ACDF and one-level corpectomy procedures have similar clinical outcomes.[20–22] CD surgeries that extend into the upper cervical spine are indicated for patients with severe malalignment that cannot be corrected solely by addressing the subaxial spine.[2,23]

Given that the ASD invasiveness index that included radiographic parameters performed better than the index that only included surgical factors, our CD invasiveness index was developed with relevant radiographic parameters for a CD cohort.[9] We kept the global SVA and T4-T12 TK measurements to assess the CD patients' overall alignment, given that many CD patients also have concurrent thoracolumbar deformity.[24] However, we replaced the PI-LL mismatch and PT with two cervical specific parameters, cervical SVA and TS-CL to better capture the sagittal malalignment of these CD patients, as these are commonly accepted radiographic measurements used to assess this relationship in CD patients that have been correlated with disability.[1,3]

The development of a surgical invasiveness index specific for a CD population is important to aid in preoperative risk assessment and surgical planning to help predict the invasiveness for a given procedure using baseline and planned surgical factors. Future studies could incorporate this CD invasiveness index for CD patients with the recently developed CD frailty index to take a holistic approach to assessing CD patients' risks and potential outcomes following corrective surgery.


We appreciate several limitations. First, the retrospective review of this study could potentially introduce bias into our study, even though the information in the database is collected prospectively. Additionally, our cohort is distinct from those of the Mirza et al's and Neuman et al's studies we have compared our results to, which might limit these comparisons; however it does highlight the need for an invasiveness index specific for CD surgery. The surgical invasiveness index developed in this study, and similarly for the previously developed ASD invasiveness indices, only explains a portion of the variation in EBL, operative time, and LOS. This could be because other factors beyond EBL, operative time and LOS can contribute to the invasiveness of a procedure.