Iliac screw instrumentation to the pelvis in children with neuromuscular and syndromic scoliosis. No lateral connectors and respect sagittal balance


Study design

One-center retrospective cohort study.


Compared to the traditional iliac screw technique, the modified iliac screw technique has a lower rate of distal implant failure in the treatment of neuromuscular scoliosis patients with pelvic obliquity. However, the reasons for decreased failure with the modified iliac screw technique are controversial.


(1) Is distal implant failure, as evident by implant breakage or disconnection, more likely to occur in patients receiving the traditional iliac screw technique (PSIS) compared to the modified S2AI (MODS2) technique? (2) After controlling for relevant confounding variables, are there other identifiable risk factors for distal implant failure?


We identified patients who underwent pelvic screw fixation by three pediatric spine surgeons from January 2007 to July 2017. Based on the starting point of the iliac screws, patients were divided into two groups. Group 1 consisted of PSIS fixation with an offset connector. Group 2 consisted of modified S2AI fixation without an offset connector. Demographic, operative, and radiographic data were obtained.


Cobb angle, lumbar lordosis, and pelvic obliquity were not significantly different between the two groups. Overall distal implant failure was 40/100 (40%) and significant between Group 1 PSIS 29/53 (55%) and Group 2 MODS2 11/47 (23%) (p = 0.002). No other complications were significant. Three risk factors were identified with implant failure: high pelvic incidence (17-fold increase, 95% confidence interval [CI] = 5.5 to 53.1, p < 0.001), high angle rod contour (3.8-fold increase, 95% CI = 1.2 to 11.9, p = 0.023), and use of an offset connector (3.2-fold increase, 95% CI = 1.0 to 10.3, p = 0.049). Failure did not correlate with the use of a cross-link, iliac screw diameter, or screw density. Revision surgery related to distal implant failure did not significantly differ between the two groups.


Compared to the use of an offset connector with PSIS fixation, MODS2 fixation had a lower rate of implant failure. Sagittal balance parameters, namely pelvic incidence and angle of rod bend, were the major risk factors for implant failure.

Level of evidence


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Availability of data and materials

The datasets used and analyzed during the current study are available from the first author on reasonable request.


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Author information




ZW: Conceptualization, methodology, data collection, radiographic readings, formal analysis and investigation, writing original draft preparation, writing review and editing, preparation of poster for IMAST, approved the version to be published journal submission. RMS: Conceptualization, methodology, formal analysis and investigation, writing original draft preparation, writing review and editing, approved the version to be published journal submission, supervision as PI, IRB application and compliance. JTA: Conceptualization, methodology, formal analysis and investigation, review and editing, drafted the work or revised it critically for important intellectual content, approved the version to be published. JAMM: Methodology, acquisition, analysis and interpretation of data, radiographic reading, formal analysis and investigation, writing review and editing, drafted the work or revised it critically for important intellectual content, approved the version to be published. NJP: Methodology, acquisition, analysis and interpretation of data, radiographic reading, writing review and editing. We thank the Medical Writing Center at Children’s Mercy Kansas City for reviewing and editing this manuscript.

Corresponding author

Correspondence to Richard M. Schwend.

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Conflict of interest

The authors declare that they have no competing interests.

Ethics approval and consent to participate

This retrospective clinical study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The Human Investigation Committee (IRB) of Children’s Mercy Hospital approved this study, IRB # 000000387 on 11/9/18. This expedited study did not require signed informed patient consents.

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Wu, Z., Schwend, R.M., Anderson, J.T. et al. Iliac screw instrumentation to the pelvis in children with neuromuscular and syndromic scoliosis. No lateral connectors and respect sagittal balance. Spine Deform (2021).

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  • Neuromuscular scoliosis
  • Iliac screw fixation
  • Modified iliac screw fixation
  • Offset connector
  • Sagittal balance