Surgical and Radiographic Outcomes in Cervical Deformity Patients with High T1 Slope and High C2 Slope (HTHC) Versus Low T1 Slope and High C2 Slope (LTHC)

STUDY DESIGN: Retrospective analysis of a prospective multicenter operative cervical deformity (CD) database. OBJECTIVE: To determine whether T1 slope (T1S) and C2 slope (C2S) together identify distinct CD phenotypes: cervical-only versus global sagittal deformity, and to compare surgical invasiveness, radiographic correction, and patient-reported outcomes. SUMMARY OF BACKGROUND DATA: T1S and C2S mark cervical malalignment, and elevated T1S has been linked to global sagittal malalignment. Combining them may distinguish CD-only from global deformity on cervical imaging alone. METHODS: Operative CD patients with ≥2 years follow-up and preoperative C2S >30° were stratified by T1S into low T1S-high C2S (LTHC; ≤30°) and high T1S-high C2S (HTHC; >30°). Multivariable regression assessed group effect on 2-year NDI change, adjusted for age, sex, baseline NDI, and posterior levels fused. NDI MCID was set a priori at ≥7 points per the ISSG threshold. RESULTS: Ninety-two patients met criteria (31 LTHC, 61 HTHC). HTHC patients were older (64.7 vs. 60.0 years; P=0.035) with higher Charlson index (P=0.022). Preoperatively, HTHC had greater thoracic kyphosis, TPA, cSVA, PI-LL mismatch, and C7 SVA (all P≤0.010). HTHC underwent more extensive surgery: more posterior levels fused (10.3 vs. 6.7), more circumferential fusions (66.7% vs. 38.7%), and more caudal LIV (T7 vs. T3) (all P<0.05). At 2 years, HTHC retained higher TK and cSVA despite greater absolute correction. Baseline NDI was similar (P=0.906), but 2-year NDI improvement was smaller in HTHC (-6.2 vs. -14.6 points; P=0.013), and fewer achieved MCID (45.9% vs. 71.0%; P=0.022). HTHC remained an independent predictor of smaller improvement (β=+7.4; P=0.020). Reoperation, DJK, and complication rates did not differ. CONCLUSIONS: Among CD patients with elevated C2S, additional elevated T1S identifies a global-deformity phenotype requiring more invasive correction and showing smaller 2-year patient-reported improvement despite comparable complications. T1S and C2S, measurable on cervical imaging alone, screen for which CD patients warrant full-spine imaging. LEVEL OF EVIDENCE: III (retrospective analysis of prospectively collected multicenter data).