Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 4, 2011, pp. 590-593

Neurology India, Vol. 59, No. 4, July-August, 2011, pp. 590-593

Brief Report

Use of O-arm for spinal surgery in academic institution in India: Experience from JPN apex trauma centre

Pankaj Ailawadhi, Deepak Agrawal, GD Satyarthee, D Gupta, S Sinha, AK Mahapatra

Department of Neurosurgery, JPN Apex Trauma Centre, All India Institute of Medical Sciences, New Delhi, India
Correspondence Address: Deepak Agrawal, Department of Neurosurgery, JPN Apex Trauma Centre, All India Institute of Medical Sciences, New Delhi, India, drdeepak@gmail.com

Date of Submission: 17-Aug-2010
Date of Decision: 22-Sep-2010
Date of Acceptance: 08-Oct-2010

Code Number: ni11176

PMID: 21891939

DOI: 10.4103/0028-3886.84343

Abstract
There is a relatively high incidence of screw misplacement during spinal instrumentation due to distortion of normal anatomy following spinal trauma. The O-arm^® is the next-generation spinal navigation tool that provides intraoperative 3-D imaging for complex spine surgeries. In this prospective study over 1-month period, 25 patients (mean age 29.16 years (range 7-58 years), 22 (88%) males) with spinal injury who underwent spinal instrumentation under O-arm^® guidance were included. Fall from height (64%) was the most common etiology seen in 16 patients. The majority (68%) had dorsolumbar fractures. Spinal canal compromise was seen in 21 patients (84%). Ten patients (40%) had American Spinal Injury Association (ASIA) grade A injuries, two patients (8%) had grade B, five patients (20%) had grade C, four patients (16%) each had grade D, and grade E injuries. A total of 140 screws were inserted under O-arm guidance. Of these, 113 (81%) were dorsolumbar pedicle screws, 2 were odontoid screws, 12 were anterior cervical screws, and 12 screws (48%) were lateral mass screws. Mean duration of surgery was 4.5 h with a mean blood loss of 674 mL. The mean postoperative stay was 6.3 days. None of the patients had screw malplacement ort canal breach. No patient deteriorated in ASIA grade postoperatively. The system was rated as excellent for ease of use by all faculty using the system. Accurate screw placement provides better patient safety and reduces the in hospital stay thereby leading early patient mobilization and may reduce the cost incurred in patient management.

Keywords: Instrumentation, O-arm, spine, trauma

Introduction

In the past decade, pedicle screw fixation of the spine has gained greater acceptance as a result of improved instrumentation and consequently better clinical outcome. Nevertheless, accuracy of screw placement remains a concern, especially in training institutes where expertise in screw placement may not be available with all surgeons. ^[1] C-arm fluoroscopy is commonly employed for intraoperative anatomical orientation of screw placement. ^[2] Intraoperative fluoroscopy and serial radiography only demonstrate the depth of screw penetration, but cannot be used to recognize screw malpositioning. Intraoperative radiographic observation of screw tips that have been placed too close or too far from each other might only suggest a possible misplaced screw. Unfortunately, these suspect screws can only be observed to be penetrating the medial or lateral cortex of the pedicle on postoperative CT scans. Complications of spinal instrumentation placement can be serious and include vascular, visceral, and neurological injury. ^[3],[4],[5] Image-guided spinal surgery was introduced in 1995 and has been designed to increase the accuracy of spinal instrumentation placement. The O-arm imaging system provides complete multidimensional surgical imaging and neuronavigation in a seamless manner and provides surgeons with real-time, 3-D images, as well as multiplane, 2-D, and fluoroscopic imaging. We describe our initial experience in patients who underwent spinal instrumentation using 3D O-arm with image guidance.

Material and Methods

The O-arm^® System with Stealthstation^® navigation (Medtronic^® , 826 Coal Creek Circle, Louisville, CO 80027, USA) was installed in our center in June 2010. In this prospective study over 1-month period, all patients with spinal injury who underwent spinal instrumentation under O-arm^® guidance were included [Figure - 1]. Patient demographic, clinical characteristics, and radiology were reviewed. Spinal injury was assessed using the American Spinal Injury Association (ASIA) grading. Briefly, the O-arm procedure consisted of acquiring a 3D data set of images with a reference frame attached to the spinous process one level higher or lower to the operative field. After acquisition of the images, navigation accuracy was confirmed by touching anatomical landmarks with the image-guided probe. The intraoperative planning function on the image-guided system, which places a phantom screw on the tip of the probe, was then used to ascertain the entry point and trajectory of the screw. The optimal length and diameter of the screw were also determined using this function, and it should be noted that in each case effort was made to place the maximum diameter screw that the anatomy could accommodate. After the pedicle was either probed or drilled under image guidance, a pedicle feeler was then used to confirm that there was no pedicle breach, and the hole was then tapped in the same trajectory and the screw placed. Navigation accuracy was briefly checked again prior to placement of the next screw by touching anatomical landmarks. Following surgery, 3D CT was performed using the O-arm inside the operating room in all patients to assess accuracy of screw placement and breach of the medial or lateral cortex of the pedicle.

Results

Twenty-five patients (mean age 29.16 years (range, 7-58 years), 22 (88%) males) with spine injuries were evaluated during the study period. Fall from height was the most common etiology seen in 16 patients (64%). Road traffic accidents were seen in nine patients (36%). Three patients (12%) had odontoid fracture, two patients (8%) had atlantoaxial dislocation, and three patients (12%) had subaxial cervical spine injuries. Another 17 patients (68%) had dorsolumbar fractures [Table - 1]. Ten patients (40%) had ASIA grade A injuries whereas two patients (8%) had grade B, five patients (20%) had grade C, four patients (16%) had grade D, and four patients (16%) had grade E injuries. Seven patients had other associated injuries. Spinal canal compromise was observed in 21 patients (84%). Patients injuries were graded as per ASIA grading system and five different subsets were formed [Table - 2].

Mean duration of surgery was 4.5 h with a mean blood loss of 674 mL. The mean postoperative stay was 6.3 days. A total of 140 screws were inserted under O-arm guidance. Out of these, 113 (81%) were dorsolumbar pedicle screws, 2 were odontoid screws, 12 were anterior cervical screws, and 12 screws (48%) were lateral mass screws [Table - 3]. None of the patients had screw malplacement or canal breach. No patient deteriorated in ASIA grade postoperatively. The system was rated as excellent for ease of use by all faculty using the system.

Discussion

Use of image-guidance techniques in spinal surgery procedures have been implemented in 1995 and the techniques have been designed to increase the accuracy of spinal instrumentation placement. ^[4],[5],[6] Standard techniques of pedicle screws insertion have included fluoroscopic guidance, as well as the freehand technique. The reported misplacement rate for pedicle screws using standard techniques has been 14-55%. ^[7],[8] Additionally, injury from pedicle screws placement has been reported to occur between1% and 8%. In a meta-analysis of the published literature on accuracy of pedicle screws placement, Kosmopoulos and Schizas ^[9] reported a median accuracy of 90.3% in 12,299 pedicle screws placed in vivo without navigation versus a median accuracy of 95.2% in 3059 pedicle screws placed in vivo with navigation. This meta-analysis did not include studies published after 2006 and also did not specify navigation techniques. Since this time, several studies have been published reporting accuracy of pedicle screws placement with the aid of 3D navigation. In a randomized clinical trial comparing thoracic pedicle screws placement using fluoroscopic assistance versus 3D fluoroscopy-based navigation in patients with spinal deformity, Rajasekaran et al. ^[10] found a 23% breach rate in the fluoroscopic group compared with a 2% breach rate in the navigation group. Nottmeier et al. ^[11] reviewed 220 consecutive patients undergoing posterior spinal fusion using 3D image guidance for instrumentation placement and noted a breach rate of 7.5%. No vascular or visceral complications occurred as a result of screw placement. Two nerve root injuries occurred in 1084 screws placed, resulting in a 0.2% per screw incidence and a 0.9% patient incidence of nerve root injury. Neither nerve root injury was associated with a motor deficit.

The image guidance systems used in our study use optical tracking of instruments, and a potential disadvantage of this is line-of-sight issues between the system camera and the image-guided instrument. Electromagnetic instrument tracking can decrease some of the line-of-sight issues that can arise with optical tracking of instruments and has been implemented successfully in otolaryngological surgery. ^[12] However, its use has been limited in image-guided spinal surgery because the metallic instruments and implants that are typically used in spinal fusion procedures can cause interference in the electromagnetic field, resulting in inaccurate navigation. Radiation exposure to the surgeon and operating room staff is a concern when placing instrumentation with the aid of active fluoroscopy. ^[13] Accordingly, the reported fluoroscopy time used to place a pedicle screws varies from 3.4 to 66 s per screw. ^[14],[15] When using 3D spinal image guidance in our practice, there is minimal to no radiation exposure to the surgeon or operating room staff. When registration is being accomplished with the aid of isocentric fluoroscopy, or when intraoperative radiographs are obtained to check instrumentation placement, the surgeon and operating room staff stand back from the radiation source and are protected by lead aprons or a lead shield, resulting in minimal to no radiation exposure.

Three-dimensional image guidance is an extremely useful adjunct for spinal surgery. The complication rate in this study was negligible. The O-arm imaging system provides complete multidimensional surgical imaging and neuronavigation in a seamless manner and provides surgeons with real-time, 3-D images, as well as multiplane, 2-D, and fluoroscopic imaging. Accurate screw placement provides better patient safety and reduces the in hospital stay thereby leading early patient mobilization and may reduce the cost incurred in patient management. Its use is especially beneficial in academic and teaching centers where novice surgeons can attain results equivalent to that of experts in spinal instrumentation.

References

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