Cervical sagittal alignment as a predictor of adjacent-level ossification development

Abstract

Purpose: To explore the role of cervical sagittal alignment in the occurrence of adjacent-level ossification development (ALOD) in patients who underwent anterior cervical discectomy fusion with self-locking stand-alone polyetheretherketone cage, and the relationship between cervical sagittal alignment and clinical outcomes.

Background: Because of its advantages, anterior cervical plating systems have been used as the classic surgical method in the treatment of patients with cervical disc herniation. However, the proximity (<5 mm) of the plate to the adjacent disc space has proven to be a critical risk factor for ALOD. How cervical sagittal alignment influences the development of ALOD is unknown and its role in ALOD needs clarification.

Patients and methods: One hundred and eighteen adults who underwent anterior cervical discectomy fusion with self-locking stand-alone polyetheretherketone cage for cervical radiculopathy or myelopathy between December 2013 and December 2015 were retrospectively recruited. Of these, 15 patients developed ALOD and 103 patients did not, representing two groups for comparison. The cervical sagittal parameters were measured, including C2-C7 Cobb angle (Cobb), fused segment angle, cervical tilt (CT), T1 slope (T1S) and C2-C7 sagittal vertical axis. Clinical outcomes and efficacy were evaluated using a visual analog scale, Japanese Orthopedic Association (JOA) score and neck disability index (NDI) score before and after surgery.

Results: There were no significant differences in patient demographics between the two groups. Cobb value (P<0.05), CT (P<0.05) and T1S (P<0.05) were significantly different between the two groups, while fused segment angle (P>0.05) and C2-C7 sagittal vertical axis (P>0.05) showed no difference. Compared with preoperative scores, improvement was seen in postoperative visual analog scale, JOA and NDI scores at each time point (P<0.05). However, the postoperative scores at 24 months in the NO-ALOD group indicated greater improvements compared with the ALOD group (P<0.05). There were significant correlations between Cobb and CT (r=0.607, P<0.05) and CT and T1S (r=0.681, P<0.05). Also, T1S was significantly correlated with clinical outcomes (JOA: r=0.689, P<0.05; NDI: r=-0.710, P<0.05).

Conclusion: Maintaining a lordotic cervical sagittal alignment was related to a lower risk of ALOD and improved clinical outcomes.

Keywords: adjacent-level ossification development; cervical sagittal alignment; clinical outcomes; stand-alone anchored cage.

Figure 1

Cervical sagittal alignment measurements. Note: a: C2–C7 Cobb angle (Cobb); b: the FSA; c: CT; d: T1S and e: C2–C7 SVA. Abbreviations: C2–C7 SVA, C2–C7 sagittal vertical axis; CT, cervical tilt; FSA, fused segment angle; T1S, T1 slope.

Figure 2

Representative images of NO-ALOD and ALOD at the final follow-up. Abbreviation:ALOD, adjacent-level ossification development.

Figure 3

VAS, JOA and NDI scores before and after surgery. Note: *P<0.05 between NO-ALOD and ALOD groups. Abbreviations: ALOD, adjacent-level ossification development; JOA, Japanese Orthopedic Association; NDI, neck disability index; VAS, visual analog scale.

Figure 4

Linear regression analysis of cervical sagittal parameters and clinical outcomes. Note: (A–D) Linear regression analysis comparing T1S and CT, CT and Cobb, T1S and JOA, and T1S and NDI, respectively. Abbreviations: CT, cervical tilt; JOA, Japanese Orthopedic Association; NDI, neck disability index; T1S, T1 slope.