Spine. 2026;51(21):1538-1543
Reducing implant density in adult spinal deformity surgery should not be treated as a uniform strategy. Williams and colleagues found that higher fixation density was associated with fewer mechanical complications, particularly in constructs extending from the pelvis to T10-L2. Their findings support considering the upper instrumented vertebra when planning fixation, while stopping short of proving that fewer screws are safe in longer thoracic constructs.
Study and key findings
This retrospective single-center study included 170 adults undergoing deformity correction with pelvic fixation between 2008 and 2021. Mean age was 66.8 years and mean radiographic follow-up was 4.5 years. All constructs reached L2 or above, and inclusion required at least two years of radiographic follow-up.
Importantly, density counted fixation points, including screws or hooks, divided by instrumented levels; the sacrum and ilium were counted separately. High and low density were defined relative to cohort-specific medians, rather than a universal surgical threshold.
Across the entire cohort, higher density was associated with lower adjusted odds of the combined endpoint of rod fracture or pseudarthrosis (OR 0.40; 95% CI 0.18-0.86). For constructs with an upper instrumented vertebra at T10-L2, higher density was associated with lower odds of this endpoint (OR 0.18; 95% CI 0.05-0.52) and reoperation (OR 0.16; 95% CI 0.04-0.57). No significant associations were demonstrated in constructs reaching T9 or above. Density was not significantly associated with proximal junctional kyphosis.
Interpretation and limitations
These are associations, not evidence that adding screws prevents failure. Only 170 of 253 eligible patients had sufficient follow-up, creating potential selection bias. Surgeon preferences, anatomy and unmeasured confounding may influence both density and outcomes. Small subgroups limit precision, and nonsignificant findings in longer constructs do not establish equivalence or safety.
The analysis stratified whole constructs by their upper endpoint; it did not establish which individual levels can safely be skipped. Median-based categories should not become prescriptive density targets.
Clinical takeaway
Review fixation density alongside construct extent, bone quality and correction requirements. Be cautious about reducing fixation in T10-L2-to-pelvis constructs, but avoid interpreting this study as a mandate to instrument every level or permission to omit specific thoracic screws.
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