Journal of Pediatric Orthopaedics - 2026-08-19 - Journal Article
The Role of Caudal Screw Fixation in Outcomes of Posterior Dynamic Distracting Device for Adolescent Idiopathic Scoliosis.
Rogie GA, Braithwaite Iv H, Luhmann S
Topics
Key Takeaway
Convergent caudal screw sagittal angulation (OR 0.893 per degree, p=0.003) independently predicts mechanical failure in PDDD for AIS, with an overall mechanical failure rate of 27% and construct breakage in 17% at mean 2.3-year follow-up.
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Summary
This multicenter registry study evaluated whether caudal screw depth, trajectory, and diameter influence mechanical failure, revision, and curve correction in AIS patients treated with PDDD. Among 155 patients with mean initial Cobb of 46°, PDDD corrected curves to 21° but produced 27% mechanical failure, 17% construct breakage, and 14% revision for mechanical failure. Multivariable logistic regression identified convergent initial caudal sagittal screw angle (OR 0.893, p=0.003) and Lenke curve type (OR 0.446, p=0.049) as independent predictors of mechanical failure, with AUC=0.755; screw depth and diameter were not independent predictors.
Key Limitation
Mean follow-up of 2.3 years is insufficient to determine whether curve correction is durable or whether mechanical failure rates continue to rise beyond the early postoperative period.
Original Abstract
BACKGROUND
Nonfusion techniques, such as the posterior dynamic distracting device (PDDD), for adolescent idiopathic scoliosis (AIS), aim to correct deformity and preserve motion. PDDD relies on 2 pedicle screws cranially but only a single caudal screw, a design that may predispose to implant complications. This study evaluated the role of caudal screw parameters-depth, trajectory, and diameter-on mechanical failure, revision surgery, and curve correction.
METHODS
A review of AIS patients from a multicenter registry who underwent PDDD with ≥2 years of follow-up was performed. Radiographic measures included caudal screw depth, rod-to-caudal screw angle, and caudal screw-to-upper endplate angle postoperatively and at final follow-up or before revision.
RESULTS
A total of 155 patients (mean age 14.4 y, range 10 to 19 y) were included with a mean f/u of 2.3 years. Initial coronal deformity was 46 degrees, which improved to 21 degrees at final f/u. Construct breakage occurred in 17% and overall mechanical failure in 27%. Revisions for mechanical failure occurred in 14%. Revisions, breakage, and mechanical failure were all correlated with more convergent, negative, initial screw-toupper endplate angle (P=0.025, P=0.003, and P<0.001, respectively). Mechanical failure correlated with lower final caudal screw depth (P=0.025), lower initial actuator-to-caudal screw angle (P=0.010), and initial and final convergent screw-to-upper endplate angulation (P<0.001 and P=0.010, respectively). Multivariable logistic regression identified initial caudal sagittal angle (OR: 0.893; P=0.003) and Lenke curve type (OR: 0.446; P=0.049) as independent predictors of mechanical failure, with the final model demonstrating strong predictive capacity (AUC=0.755).
CONCLUSION
PDDD achieved meaningful curve correction, but with notable mechanical failure rates. Convergent caudal screw angulation, but not screw depth or diameter, was associated with construct breakage, mechanical failure, and revision surgery, emphasizing the importance of sagittal screw trajectory for optimal outcome. Furthermore, caution should be exercised with Lenke type 5 curves.
LEVELS OF EVIDENCE
Level III.