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Complications in Adult Spine Deformity Correction Using a Computer-Assisted Rod Bending System

December 23, 2019

Rod contouring is a critical step in the correction of spinal deformity. However, manual rod contouring can be an arduous, time-consuming task at the late stage of surgery where blood loss from bony work is continuous. Bendini® (NuVasive; San Diego, Calif.) is a computer-assisted spinal rod bending system that expedites rod contouring. This tool can help reduce operation time and blood loss, in turn lowering the need for transfusion while following the principles of spine deformity correction. An in vitro study has shown that Bendini enhances screw pullout strength. However, because this system has yet to be studied in the clinical setting, its rate of complication is undescribed in the literature. 

We performed a retrospective review to compare the rate of complications in patients who underwent deformity spine surgery with the use of Bendini versus traditional manual rod contouring. One hundred forty-two patients from 2015 and 2016 were included in this study, 88 for whom the Bendini system was used. There was no significant difference in the age (58.6 ± 16.3 versus 61.6 ± 12.2), number of fused levels (10.6 ± 4.1 versus 11.3 ± 4.8, P=0.4), and length of follow up between the two cohorts (1.4 ± 0.6 versus 1.7 ± 0.4 years, P=0.6).

Intraoperative blood loss with the use of Bendini was 356 ml less (p=0.18) and the need to transfuse perioperatively was 2 units less (p=0.21). Length of surgery was on average 42 minutes faster (p=0.16). However, these differences were not statistically significant.

There were 30 complications necessitating revision surgery in the Bendini group compared to 13 complications in the other group, with the majority of complications being due to junctional kyphosis (60.0% vs. 53.8%), followed by rod/screw fracture (30.0% vs. 30.8%) and pseudarthrosis (10.0% vs. 15.4%). There was no statistically significant difference in the rate or distribution of overall complications between groups as revealed by a two-proportion z-test. 

In de novo operations, the rate of overall complications was statistically similar between groups. In patients with prior surgery, Bendini use was associated with a higher overall complication rate of 43.8% versus 25% for the manual rod contouring group, but not statistically significant (p=0.09). In those patients who underwent pedicle subtraction osteotomy and/or anterior column reconstruction, complications were more frequent in the Bendini group, with 36.4% of cases resulting in complications, versus 12% for the other group (p=0.06).

In summary, the use of Bendini was not statistically associated with a higher complication rate. However, in revision surgery, especially in severe deformities that required anterior column reconstruction or pedicle subtraction osteotomy, the use of Bendini showed a tendency toward a higher complication rate. Our case series did not demonstrate a statistically significant difference.

Note: Song Kim, BS; David Salvetti, MD; Nitin Agarwal, MD; Alp Ozpinar, MD; D. Kojo Hamilton, MD; Adam Kanter, MD; and David Okonkwo, MD, PhD, also contributed to this article.