Increased radiation but “no benefits” in pedicle screw accuracy with navigation

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Wiktor Urbanski

A recent study found no improvements in pedicle screw accuracy but increased radiation using intraoperative computed tomography (CT)-based navigation compared to a freehand technique in idiopathic scoliosis surgery. The study was carried out by Wiktor Urbanski (Wroclaw University, Wroclaw, Poland) and colleagues and recently published in the journal Clinical Orthopaedics and Related Research. The paper was presented by Urbanski at the 53rd annual meeting of the Scoliosis Research Society (SRS; 10–12 October, Bologna, Italy).

The investigators did not observe any benefits to pedicle screw placement with CT-based navigation in patients with moderate idiopathic scoliosis undergoing primary surgery, however the patients experienced “significantly greater” exposure to radiation. While navigation reduced significant screw misplacements, Urbanski suggested this was “potentially symptomatic” and there were no grade three pedicle screws in the navigated group. He noted that “caution is essential” to balance surgical safety and the adverse effects of increased radiation associated with CT-based navigation.

According to the authors, 96.3% of pedicle screws in the freehand group were properly positioned, compared to 95.8% in the navigation group. This included 315 (82.03%) described as grade zero and 55 (14.32%) as grade one in the freehand group, compared to 374 (82.92%) and 58 (12.86%), respectively, in the navigated group. Not all grade two screws were repositioned, however “most of them” were.

Only the freehand group contained grade three pedicle screws, all four of which were repositioned. Grade three screws occurred only in the upper and mid thoracic spine. Reduced accuracy was noticed in the upper thoracic spine (T1-T5), in both groups. No differences in accuracy between the navigated and freehand groups were noted (p=0.21) in the upper thoracic spine.

Urbanski noted how the navigation group usually has two times more O-arm 3D scans than the freehand group, which in this study was reflected in higher radiation levels. With 2D imaging, however, patients were exposed to higher radiation in the navigated group.

The investigators note that forty-nine patients were treated operatively for progressive idiopathic scoliosis in the Department of Orthopaedics at University Hospital Wroclaw (Wroclaw, Poland). Those included had idiopathic curves only, with a magnitude between 45 and 90 degrees, and had never undergone spinal surgery before. The two groups did not differ in age, sex, or magnitude of deformity.

In total, 835 pedicle screws were inserted by two surgeons. In 27 of the 49 patients, 451 screws were inserted with the aid of navigation based on 3D images obtained during surgery by an O-arm. In the other 22 patients, 384 screws were inserted using a freehand technique.

Two observers were not involved in the treatment and instead evaluated screw position. The pedicle breach was described on CT scans. Grade 0 was defined as no pedicle violation, grade 1 as a breach of 22m or less, grade 2 a breach of 2–4mm, and grade 3, a breach of more than 4mm. The comparison of the results was made between navigated screws and freehand.

The investigators aimed to compare the accuracy of two methods of pedicle screw placement in patients with idiopathic scoliosis; intraoperative 3D image navigation and a freehand technique. They also wanted to assess the radiation dose for the patients in both methods.

Pedicle screws are crucial in the surgical treatment of spinal deformity for a number of reasons. Urbanski noted a few: excellent mechanical conditions, improvement and maintaining of correction and a good long-term outcome, associated with solid fusion.

However, he pointed out that the technique of proper positioning of the screws is “demanding”, particularly in spinal deformities. He mentioned a number of complications related to screw malposition, including pain, reduced biomechanical strength, neurological injuries, and visceral and vascular injuries.

The navigation systems based on intraoperatively obtained 3D imaging were developed with the expectations of an increase in accuracy, however the authors mention a number of concerns regarding 3D-based navigation, such as radiation, insufficient data available confirming superiority of navigation above other techniques, costs of the necessary equipment and increased surgery time.

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