What are the major drivers of outcomes in cervical deformity surgery?
Authors: Passias Peter Gust , Pierce Katherine E. , Imbo Bailey , Krol Oscar , Passfall Lara , Tretiakov Peter , Moattari Kevin , Williamson Tyler , Joujon-Roche Rachel , Passano Brandon , 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 corrective surgery.

Purpose:
The purpose of the study was to weight baseline (BL) factors on impact upon outcomes following CD surgery.

Study Design Setting:
This was a retrospective review of a single-center database.

Patient Sample:
The sample size of the study was 61 cervical patients.

Outcome Measures:
Two outcomes were measured: “Improved outcome (IO)”: (1) radiographic improvement: “nondeformed” Schwab pelvic tilt (PT)/sagittal vertical axis (SVA) and Ames cervical sagittal vertical axis (cSVA)/T1 Slope – cervical lordosis (TSCL); (2) clinical: MCID Euro-QOL 5 Dimension (EQ5D), Neck Disability Index (NDI), or improvement in modified Japanese Orthopedic Association (mJOA) scale modifier; and (3) complications/reoperation: no reoperation or major complications and “poor outcome” (PO): (1) radiographic deterioration: “moderate” or “severely” deformed Schwab SVA/PT and Ames cSVA/TS-CL; (2) clinical: not meeting MCID EQ5D and NDI worsening in mJOA modifier; and (3) complications/reoperation: reoperation or complications.

Materials and Methods:
CD patients included full BL and 1-year (1Y) radiographic measures and Health related quality of life (HRQLs) questionnaires. Patients who underwent a reoperation for infection were excluded. Patients were categorized by IO, PO, or not. Random forest assessed ratios of predictors for IO and PO. Categorical regression models predicted how BL regional deformity (Ames cSVA, TS-CL, and horizontal gaze), BL global deformity (Schwab PI-LL, SVA, and PT), regional/global change (BL to 1Y), BL disability (mJOA score), and BL pain/function impact outcomes.

Results:
Sixty-one patients were included in the study (55.8 years, 54.1% of females). Surgical approach included 18.3% anterior, 51.7% posterior, and 30% combined. The average number of levels fused for the cohort was 7.7. Mean operative time was 823 min, and estimated blood loss (EBL): 1037ccs. At 1Y, 24.6% had an IO and 9.8% had PO. Random forest analysis showed the top five individual factors associated with an IO: BL maximum kyphosis, maximum lordosis, C0–C2, L4 pelvic angle, and NSR back pain (80% radiographic, 20% clinical). Categorical IO regression model (R2 = 0.328, P = 0.007) showed low BL regional deformity (β = [FIGURE DASH]0.082), low BL global deformity (β = [FIGURE DASH]0.099), global improvement (β = [FIGURE DASH]0.532), regional improvement (β = [FIGURE DASH]0.230), low BL disability (β = [FIGURE DASH]0.100), and low BL NDI (β = [FIGURE DASH]0.024). Random forest demonstrated the top five 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) showed high BL regional deformity (β = [FIGURE DASH]0.108), high BL global deformity (β = [FIGURE DASH]0.255), global decline (β = [FIGURE DASH]0.272), regional decline (β = 0.443), BL disability (β = −[FIGURE DASH]0.164), BL and severe NDI (>69) (β = [FIGURE DASH]0.181).

Conclusions:
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 outcomes.