What are the major drivers of outcomes in cervical deformity surgery?
Authors: Passias Peter Gust , Pierce Katherine E. , Passano Brandon , Tariq Muhammad B. , Ahmad Salman , Singh Vivek , Owusu-Sarpong Stephane , Krol Oscar , Imbo Bailey , Passfall Lara , Tretiakov Peter , Williamson Tyler , Joujon-Roche Rachel , Ahmad Waleed , Naessig Sara , Diebo Bassel 
Published: December 2021

Background Context:
Cervical deformity (CD) correction is becoming more challenging and complex. Understanding the factors that drive optimal outcomes has been understudied in CD correction surgery.

Purpose:
The purpose of this study is to assess the factors associated with improved outcomes (IO) following CD surgery.

Study Design Setting:
Retrospective review of a single-center database.

Patient Sample:
Sixty-one patients with CD.

Outcome Measures:
The primary outcomes measured were radiographic and clinical “IO” or “poor outcome” (PO). Radiographic IO or PO was assessed utilizing Schwab pelvic tilt (PT)/sagittal vertical axis (SVA), and Ames cervical SVA (cSVA)/TS-CL. Clinical IO or PO was assessed using MCID EQ5D, Neck Disability Index (NDI), and/or improvement in Modified Japanese Orthopedic Association Scale (mJOA) modifier. The secondary outcomes assessed were complication and reoperation rates.

Materials and Methods:
CD patients with data available on baseline (BL) and 1-year (1Y) radiographic measures and health-related quality of life s were included in our study. Patients with reoperations for infection were excluded. Patients were categorized by IO, PO, or not. IO was defined as “nondeformed” radiographic measures as well as improved clinical outcomes. PO was defined as “moderate or severe deformed” radiographic measures as well as worsening clinical outcome measures. Random forest assessed ratios of predictors for IO and PO. The categorical regression models were utilized to predict BL regional deformity (Ames cSVA, TS-CL, horizontal gaze), BL global deformity (Schwab PI-LL, SVA, PT), regional/global change (BL to 1Y), BL disability (mJOA score), and BL pain/function impact outcomes.

Results:
Sixty-one patients met inclusion criteria for our study (mean age of 55.8 years with 54.1% female). The most common surgical approaches were as follows: 18.3% anterior, 51.7% posterior, and 30% combined. Average number of levels fused was 7.7. The mean operative time was 823 min and mean estimated blood loss was 1037 ml. At 1 year, 24.6% of patients were found to have an IO and 9.8% to have a PO. Random forest analysis showed the top 5 individual factors associated with an “IO” were: BL Maximum Kyphosis, Maximum Lordosis, C0-C2 Angle, L4-Pelvic Angle, and NSR Back Pain (80% radiographic, 20% clinical). Categorical IO regression model (R2 = 0.328, P = 0.007) found following factors to be significant: low BL regional deformity (β = [FIGURE DASH]0.082), low BL global deformity (β = [FIGURE DASH]0.099), global improve (β = 0.532), regional improve (β = 0.230), low BL disability (β = 0.100), and low BL NDI (β = 0.024). Random forest found the top 5 individual BL factors associated with “PO” (80% were radiographic): BL CL Apex, DJK angle, cervical lordosis, T1 slope, and NSR neck pain. Categorical PO regression model (R2 = 0.306, P = 0.012) found following factors to be significant: high BL regional deformity (β = [FIGURE DASH]0.108), high BL global deformity (β = [FIGURE DASH]0.255), global decline (β = 0.272), regional decline (β = 0.443), BL disability (β = [FIGURE DASH]0.164), and BL severe NDI (>69) (β = 0.181).

Conclusions:
The categorical weight demonstrated radiographic as the strongest predictor of both improved (global alignment) and PO (regional deformity/deterioration). Radiographic factors carry the most weight in determining an improved or PO and can be ultimately utilized in preoperative planning and surgical decision-making to optimize the outcomes.