Quantifying the importance of upper cervical extension reserve in adult cervical deformity surgery and its impact on baseline presentation and outcomes

Abstract

BACKGROUND CONTEXT: Hyperextension of the upper cervical spine is a prominent compensatory mechanism to maintain horizontal gaze and balance in adult cervical deformity (ACD) patients, akin to pelvic tilt in spinal deformity. The relaxation of ER and its impact on postoperative outcomes is not well understood. PURPOSE: To evaluate upper cervical ER impact on postoperative disability and outcomes. STUDY DESIGN/SETTING: Retrospective cohort study. PATIENT SAMPLE: Adult cervical deformity. OUTCOME MEASURES: ER, HRQLs. METHODS: ACD patients undergoing subaxial cervical fusion with 2Y data were included. Upper cervical extension reserve (ER) was defined as: C0-C2 sagittal Cobb angle between neutral and extension. Relaxation of ER was defined as the ER normative mean in those that met the ideal in all Passias ACD modifiers. Outcomes were defined as "good" if meeting ≥2 of the three: (1) NDI <20 or meeting MCID, (2) mild myelopathy (mJOA≥14), and (3) NRS-Neck ≤5 or improved by ≥2 points from baseline. Controlled analysis was conducted with ANCOVA and multivariable logistic regressions. Conditional inference tree (CIT) analysis determined thresholds. RESULTS: A total of 108 ACD patients met inclusion. (Age 61.4 ± 12.3, 61% F, BMI 29.4 ± 7.5 kg/m2, mCD-FI .24 ±.12, CCI 0.97 ± 1.30). Radiographic alignment is depicted in Table 1. Preoperative C0-C2 ER was 8.7 ±9.0 ±, and at the last follow-up was 10.3 ± 11.1. ER in those meeting all ideal CD modifiers at 2Y was 12.9 ± 9.0. Preoperatively 29% had adequate ER, while 59.7% had improvement in ER postoperatively, with 50% of patients achieving adequate ER at 2Y. Higher ER significantly correlated with lower cervical deformity (p<.05). Preoperatively, greater ER was predictive of lower preoperative disability, with worse baseline mobility, pain, and anxiety (EQ5D) (B = -6.1, -2.9, -2.9 respectively; R2 =0.212, p<.001). Improvement of ER depicted a higher rate of MCID for NDI (64% vs 39%, p=.008), and meeting good clinical outcomes (72% vs 54%, p=.04). Controlling for baseline deformity and demographic factors found resolution of inadequate ER to have 7x higher likelihood of meeting MCID for NDI (6.941 [1.378-34.961], p=.019) and 4x higher odds of achieving good outcomes (4.022 [1.017-15.900], p=.047). Isolating those with inadequate preoperative ER, found postoperative resolution having 5x odds of good outcomes (p<.05). In those with inadequate ER at baseline, the preoperative C2-C7 of <-18 and TS-CL of >59 for TS-CL was predictive of ER resolution (p<.05). In those with preoperative C2-C7 >-18, a T1PA of >13 was predictive of postoperative return of ER (p<.05). Independently TS-CL of >59, was significant for predicting ER return postoperatively, highlighting its compensatory role for proximal spinal deformities (all p<.05). Surgical correction of C2-C7 by >16 from baseline was found to be predictive of ER return. CONCLUSIONS: Increased preoperative utilization of the extension reserve in the upper cervical spine in cervical deformity was associated with worse baseline regional and global alignment while impacting health-related measures. The majority of patients had relaxation of extension reserve postoperatively, however, in those who didn't, there was a decreased likelihood of achieving good outcomes. FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.