Comparison of Subsidence Rates of Large and Small Footprint Cages in Anterior Cervical Interbody Fusion

Abstract

Introduction Subsidence rates after ACDF have been reported widely in literature and range from 0 to 57%. Polyetheretherketone (PEEK) cages are one of the most commonly used interbody spacers. Although subsidence rates of different types of cages have been described, there are still no data on the effect of cage footprint size on subsidence. The primary aim of this study was to compare the subsidence rate between small and large footprint polyetheretherketone (PEEK) cages. The secondary aim was to determine if a correlation exists between subsidence and health outcome scores. Methods We performed a retrospective medical chart and radiographic review. Two fellowship-trained spine surgeons performed the surgeries from November 2008 to January 2013. Immediate postoperative and 6-month lateral cervical radiographs were evaluated for subsidence. Anterior and posterior disc heights at each operative level were measured. Subsidence was defined as a decrease in anterior or posterior disc height of > 1 mm. Cases were then designated to either the subsidence group (SG) or nonsubsidence group (NSG). Small footprint cage group (SF) consisted of PEEK cages measuring 14 × 11, 14 × 12, or 12.5 × 11.5 mm. Large footprint cage group (LF) consisted of cages measuring 15 × 13, 16 × 14, or 18 × 16 mm. Subsidence rates of the SF and LF groups were compared using chi-square test (α = 0.05). Preoperative and final (minimum 6 months) postoperative Neck Disability Index (NDI) scores of the SG and NSG were compared using t-test (α = 0.05). Results We reviewed 140 levels (71 cases*) of ACDF using small and large footprint PEEK cages. The small footprint group had 45 cases* (79 levels) and the small footprint group had 27 cases* (61 levels) with large footprint cages (* one case had both large and small footprint cages implanted on different levels) . There was a statistically significant difference between the subsidence rates of SF (54%; 43/79) and LF (30%; 18/61) ( p = 0.003). Fig. 1 breaks down the subsidence rate by cage size. Overall mean subsidence (SG) was 1.6 ± 1.1 mm anteriorly and 1.9 ± 1.1 mm posteriorly. Mean NDI improvement was 8.8 ± 23.2 mm (average follow-up: 13 months) for the SG and 22.9 ± 18.8 (average follow-up: 13 months) for the NSG ( p = 0.01). Conclusion Use of large footprint cages seems to have a protective effect against subsidence. Furthermore, cage subsidence > 1 mm results in less clinical improvement. [Figure: see text]