Spine. 2026;51(20):1427–1434
Zero-profile implants offer different approaches to fixation after anterior cervical discectomy and fusion (ACDF).
This randomized trial compares a two-screw variable-angle device with a four-screw fixed-angle device.
The two-screw group had more radiographic fusion at six months, while the difference was no longer significant at one year.
The study helps distinguish an early imaging advantage from a demonstrated improvement in patient recovery.
Objective
Compare six-month fusion rates, clinical outcomes and complications after single-level ACDF using two zero-profile implant designs.
Methods
Eighty adults were randomized, with allocation concealed until surgery. Seventy-seven were analyzed: 39 received Zero-P VA with two variable-angle screws and 38 received Zero-P with four fixed-angle screws.
Fusion required both dynamic radiographic criteria and CT evidence of bridging bone. Both groups received artificial bone graft and were advised to wear a rigid collar for three months.
Main results
At six months, fusion rates were 69.2% versus 42.1%, favoring the two-screw device (reported P=0.022): an absolute difference of 27.1 percentage points.
At 12 months, reported rates were 91.9% versus 88.9% (P=0.711). JOA, Neck Disability Index and neck/arm pain scores improved in both groups, without significant between-group differences.
Complications occurred in 9/39 (23.1%) versus 8/38 (21.1%). Subsidence or displacement occurred in 6/39 (15.4%) versus 3/38 (7.9%), respectively; this difference was not statistically significant.
Interpretation
The trial supports an advantage in the prespecified six-month radiographic endpoint. It does not demonstrate better pain relief, function or safety.
The comparison changes screw number, angulation and implant mechanics together. Consequently, the result cannot be attributed to screw count alone. Micromotion and load sharing provide a possible explanation, but were not directly tested as mechanisms.
Limitations
This single-center study analyzed completers, without imputation for three patients lost to follow-up. Patients older than 65 years, those with severe osteoporosis and multilevel cases were excluded.
Secondary outcomes were exploratory. The sample cannot establish equivalent safety or exclude meaningful differences in subsidence, while twelve-month follow-up limits conclusions about durability.
Clinical takeaway
Two-screw variable-angle fixation is an option to consider for selected single-level ACDF patients. Earlier radiographic fusion alone does not justify changing collar protocols or return-to-activity advice; these benefits were not tested.