ArticleJournal of orthopaedic surgery and research2026
C1 pedicle screw placement risks in patients with ponticulus posticus: a CTA retrospective simulation study.
Article in Journal of orthopaedic surgery and research, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundPonticulus posticus (POPO) may distort C1 surface landmarks for C1 pedicle screw (CPS) placement, raising concern for vertebral artery compromise (VAC). We aimed to establish a CTA-based workflow to identify POPO anatomies potentially suitable for CPS placement.
methodsThis single-center retrospective CTA simulation study included 141 subjects: 46 bilateral POPO, 65 unilateral POPO, and 30 pure non-POPO patients. CPS trajectories were primarily simulated using PedicleScrewSimulator. D1 and D2 were analyzed as supra-arch and infra-arch localization variables. Ten morphometric parameters were measured; key safety metrics included D3 and D5. Simulated CPS feasibility and VAC were evaluated for 2.5-, 3.0-, 3.5-, and 4.0-mm screws. A side was considered geometrically feasible when D5 ≥ screw radius (r), D6/2 ≥ r, and D7/2 ≥ r. Simulated VAC was defined as violation of D5 or D7/2 clearance. Outcomes were analyzed using patient-clustered generalized estimating equations.
resultsD1 and the D1-D2 shift differed markedly among groups (p < 0.001). D5 was smaller in bilateral POPO (2.93 ± 0.99 mm vs. 3.44 ± 1.14 mm vs. 3.81 ± 1.13 mm; p < 0.001). D3 did not differ significantly (p = 0.211). At 3.5 mm, overall simulated feasibility was 96.0%. Actual POPO sides showed 93.5% simulated feasibility and 6.5% simulated VAC, versus 99.2% and 0.8% in regular sides. In actual POPO sides, increasing diameter from 2.5 to 4.0 mm reduced simulated feasibility from 98.7% to 85.6% and increased VAC from 1.3% to 14.4%. The exploratory D3/D5 rule (D3 ≥ 3.4 mm and D5 ≥ 2.0 mm) achieved 88.4% sensitivity, 100% specificity, and 100% positive predictive value for avoiding simulated 3.5-mm VAC. Reliability for the four remeasured variables ranged from 0.702 to 0.799.
conclusionsCTA-based D3 and D5 thresholds can identify POPO anatomies potentially suitable for CPS placement, but simulation results reflect planning feasibility rather than validated operative safety. The D3 ≥ 3.4 mm and D5 ≥ 2.0 mm rule may serve as a conservative rule-in screening tool, pending clinical validation. POPO should not automatically preclude consideration of CPS but should trigger side-specific CTA analysis and conservative screw-diameter selection.
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