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In Vivo Analysis of Insertional Torque During Pedicle Screwing Using Cortical Bone Trajectory Technique

Matsukawa, Keitaro MD*; Yato, Yoshiyuki MD*; Kato, Takashi MD*; Imabayashi, Hideaki MD*; Asazuma, Takashi MD; Nemoto, Koichi MD*

doi: 10.1097/BRS.0000000000000116
Biomechanics
SLIDE

Study Design. The insertional torque of pedicle screws using the cortical bone trajectory (CBT) was measured in vivo.

Objective. To investigate the effectiveness of the CBT technique by measurement of the insertional torque.

Summary of Background Data. The CBT follows a mediolateral and caudocephalad directed path, engaging with cortical bone maximally from the pedicle to the vertebral body. Some biomechanical studies have demonstrated favorable characteristics of the CBT technique in cadaveric lumbar spine. However, no in vivo study has been reported on the mechanical behavior of this new trajectory.

Methods. The insertional torque of pedicle screws using CBT and traditional techniques were measured intraoperatively in 48 consecutive patients. A total of 162 screws using the CBT technique and 36 screws using the traditional technique were compared. In 8 of 48 patients, the side-by-side comparison of 2 different insertional techniques for each vertebra were performed, which formed the H group. In addition, the insertional torque was correlated with bone mineral density.

Results. The mean maximum insertional torque of CBT screws and traditional screws were 2.49 ± 0.99 Nm and 1.24 ± 0.54 Nm, respectively. The CBT screws showed 2.01 times higher torque and the difference was significant between the 2 techniques (P < 0.01). In the H group, the insertional torque were 2.71 ± 1.36 Nm in the CBT screws and 1.58 ± 0.44 Nm in the traditional screws. The CBT screws demonstrated 1.71 times higher torque and statistical significance was achieved (P < 0.01). Positive linear correlations between maximum insertional torque and bone mineral density were found in both technique, the correlation coefficient of traditional screws (r = 0.63, P < 0.01) was higher than that of the CBT screws (r = 0.59, P < 0.01).

Conclusion. The insertional torque using the CBT technique is about 1.7 times higher than the traditional technique.

Level of Evidence: 2

A cortical bone trajectory (CBT) is a novel lumbar pedicle screw trajectory that maximizes the thread contact with cortical bone. We measured the insertional torque of pedicle screws using the CBT in vivo. The mean insertional torque using the CBT technique is about 1.7 times higher than the traditional technique. Significantly fewer vascular structures in the prevertebral areas of C5–C6 and C6–C7 were found on the right side, whereas esophageal deviation was predominant to the left side. A right-sided percutaneous approach seems preferable because it poses less of a risk of encountering small vessels and causing esophageal injury.

*Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan; and

Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Tokyo, Japan.

Address correspondence and reprint requests to Keitaro Matsukawa, MD, Department of Orthopaedic Surgery, National Defense Medical College, 3–2 Namiki, Tokorozawa, Saitama 359–8513, Japan; E-mail: keitaro197897@hotmail.com

Acknowledgment date: April 24, 2013. First revision date: July 20, 2013. Second revision date: September 18, 2013. Acceptance date: October 28, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

© 2014 by Lippincott Williams & Wilkins