A Prospective Study of Clinical and Radiological Outcomes of Zero-Profile Cage Screw Implants for Single-Level Anterior Cervical Discectomy and Fusion: Is Segmental Lordosis Maintained at 2 Years?

STUDY DESIGN Prospective cohort study. PURPOSE To study clinicoradiological parameters of zero-profile cage screw used for anterior cervical discectomy and fusion (ACDF). OVERVIEW OF LITERATURE Radiological parameters of various implants used for ACDF are available, but those for zero-profile cage are sparse. METHODS Patients with unilateral intractable brachialgia due to single-level cervical disc prolapse between April 1, 2011 and March 31, 2014 were included. Clinical assessment included arm and neck pain using visual analogue score (VAS) and neck disability index (NDI) scores. Radiological assessment included motion segment height, adjacent disc height (upper and lower), segmental and cervical lordosis, implant subsidence, and pseudoarthrosis. Follow-ups were scheduled at 1, 3, 6, 12, and 24 months. RESULTS Thirty-four patients (26 males, 8 females) aged 30-50 years (mean, 42.2) showed excellent clinical improvement based on VAS scores (7.4-0 for arm and 2.0-0.6 for neck pains). Postoperative disc height improved by 11.33% (p<0.001), but at 2 years, the score deteriorated by 7.03% (p<0.001). Difference in the adjacent segment disc height at 2 years was 0.08% (p=0.8) in upper and 0.16% (p<0.001) in lower disc spaces. Average segmental lordosis achieved was 5.59° (p<0.001) from a preoperative kyphosis of 0.88°; at 2 years, an average loss of 7.05° (p<0.001) occurred, resulting in an average segmental kyphosis of 1.38°. Cervical lordosis improved from 11.59° to 14.88° (p=0.164), and at 2 years, it progressively improved to 22.59° (p<0.001). Three patients showed bone formation and two mild protrusion of the implant at 2 years without pseudoarthrosis/implant failure. CONCLUSIONS The zero-profile cage screw device provides good fusion and cervical lordosis but is incapable of maintaining the segmental lordosis achieved up to a 2-year follow-up. We also recommend caution when using it in patients with small vertebrae.