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Katherine G. Holste, Mark M. Zaki, Clare M. Wieland, Yamaan S. Saadeh, and Paul Park


Image guidance requires placement of a dynamic reference frame (DRF), often either onto local spinous process or by freehand intraosseous DRF placement into the ilium via the posterior superior iliac spine (PSIS). There is a paucity of studies in the literature that describe the complications of intraosseous DRF placement. The aim of this study was to describe the radiographic location, prevalence and nature of complications, and long-term clinical outcomes of attempted DRF placement into the PSIS.


All lumbosacral spine surgical procedures performed between August 2019 and February 2021 at a single institution were queried, and operations in which a DRF was targeted to the PSIS were included. Patient demographic characteristics, indications for surgery, surgical outcomes, and complications were extracted. Intraoperative CT scans were reviewed by 2 independent researchers to determine the accuracy of DRF placement into the PSIS and to assess for DRF malposition.


Of 497 lumbar spine operations performed between August 2019 and February 2021 by 4 surgeons, 85 utilized intraoperative navigation with a PSIS pin. Thirteen operations were excluded due to an inability to visualize the entirety of the pin on intraoperative CT. Of 72 DRFs evaluated, 77.8% had been correctly placed in the PSIS. Of the 22.2% of DRFs not placed into the PSIS, 11 entered the sacrum, 6 crossed the sacroiliac joint, and 2 were deep enough to enter the pelvis. Pain at the pin site was present in 4 patients, of whom 3 had resolution of pain at the last follow-up evaluation. There were no significant complications due to DRF placement: no sacral fractures, significant navigation errors, retroperitoneal hematomas, or neurological deficits. Over a mean ± SD follow-up period of 9 ± 5.2 months, there were no incidences of pin site infection. Interrater reliability between the reviewers was 95.8%.


This was the first study to examine radiological and clinical outcomes after DRF placement in the PSIS. In this study, a majority of pins were correctly placed within the PSIS, although 22.2% of pins were malpositioned. There were no serious complications, and a majority of those patients with persistent pin site pain had resolution at last follow-up.