Accuracy of Screw Placement and Fusion Rate after Transforaminal Lumbar Interbody Fusion with O-arm Navigation: A Review of 475 Patients


 Purpose

To evaluate the accuracy of screw placement and fusion rate after the minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) technique under O-arm navigation.
Methods

In 475 consecutive patients at a single-center, the accuracy of screw placement was evaluated on intraoperative O-arm imaging. Misplaced screws were investigated to identify the direction of deviation and associated clinical outcomes. The fusion rate was evaluated on postoperative computed tomography scan at 1 and 2 year(s). The assessment of screw placement and fusion level was analyzed for inter-rater reliability and reported as a kappa value. Accuracy of screw placement (Gertzbein-Robbins Classification), extent of fusion (Bridwell Interbody Fusion Grading System), and complications were considered as outcome measures.
Results

A retrospective data analysis from 2,098 pedicle screws in 475 patients. The mean age of participants was 56.61 ± 12.30 years, and 45.26% were female. Their ethnicities were as follows: Asian (58.74%), Caucasian (20.21%), Middle-eastern (14.32%), and African (6.74%). The final fusion levels were single (80.63%), two (18.11%), three (1.05%), and four (0.21%). There were L4/L5 as the most prevalent placement (55.35%), followed by L5/S1 (36.29%), L3/L4 (5.22%), L2/L3 (2.35%), L1/L2 (0.52%), and S1/S2 (0.26%). Seven out of 2,098 screws were breaches. None of screw needed immediate revision. In total, 99.66% of the screws were grade A (no breach), 0.19% were grade B (breach < 2 mm) and 0.14% were grade C (breach < 4mm).
Conclusion

The accuracy of pedicle screw insertion was 99.66%, with a fusion rate of 95.45% after MIS-TLIF under O-arm navigation. Breaches were not associated with poor clinical outcomes or fusion rates.


Conclusion
The accuracy of pedicle screw insertion was 99.66%, with a fusion rate of 95.45% after MIS-TLIF under Oarm navigation. Breaches were not associated with poor clinical outcomes or fusion rates.

Background
Since 2000, interbody fusion has become more popular as the technique for lumbar spine fusion [1]. This minimally invasive transforaminal lumbar interbody fusion procedure was rst reported by Foley et al. [2] and has been used for a variety of spinal diseases [3,4] because of the advantages of less operative blood loss, less soft tissue damage, and faster recovery compared to an open technique [5].
Like pedicle screw placement, interbody fusion procedures vary across contexts. Our surgical technique for minimally invasive surgical transforaminal lumbar interbody fusion (MIS-TLIF) using pedicle screw placement without K-wire and navigated by a surgical imaging system has been modi ed from the Wiltse approach [18]. More information regarding the accuracy of screw placement and fusion rate associated with this technique will help clarify the advantage of O-arm navigation.

Patients
The study was approved by the Bumrungrad International Institutional Review Board (approval number 278-01-20 CDEK-H Exp).
We retrospectively reviewed data from 2,098 pedicle screw procedures and the fusion rate in 475 consecutive patients who underwent MIS-TLIF with surgical imaging (O-arm Navigation System, Medtronic Inc., Dublin, Ireland) and computerized navigation (StealthStation Surgical Navigation System, Medtronic Inc.) systems at Bumrungrad International Hospital between October 2013 to December 2017 by the same surgical team. Patients were included if they were diagnosed with spondylolisthesis, disc herniation, recurrent disc herniation, foraminal stenosis, or recurrent facet cyst. The exclusion criteria were incomplete patient data or missing O-arm scan images.

Surgical procedure
Patients were positioned prone on the operating table with a Jackson frame. A reference pin was xed securely to the posterior superior iliac spine. Intraoperative 3D images were made after the O-arm scan. The skin incision for screw placement was made according to the optimal entry point for pedicle screw placement indicated by a probe. The Wiltse approach was performed. The size and trajectory of the screw were selected during the tapping procedure by sagittal, axial, and coronal images on the StealthStation [ Fig. 1]. The preparation of screw placement was completed before all decompression. However, only pedicle screws on the non-decompression side (non-TLIF approach side) were rst manually inserted without K-wire under navigation control before the decompression procedure started.
For decompression, an incision was made according to the intraoperative imaging. The microscopic decompression started from the facet removal on the side of the symptoms to identify the traversing and exiting nerve roots. After decompression, the polyetheretherketone cage with the autogenous bone graft and the bone substitute was packed into the disc space. Cross decompression, if needed, was performed.
The pedicle screw on the decompression side, prepared and selected according to size, was then inserted under navigation control. The O-arm scan was redone to check the accuracy of all screw placements. The positions of the screws were evaluated based on the O-arm scan images in the sagittal, axial, and coronal planes. Any unacceptable pedicle breach; >4mm breach lateral direction or > 2 mm breach medial direction detected was revised immediately and another O-arm scan, which was performed to con rm the nal pedicle screw position. Once the positions of the screws were accepted by the surgical team, rods were inserted. All wounds were closed in layers [ Fig. 2].

Complications
Pedicle screw perforations may lead to serious complications, such as neurovascular injury and neurologic complications. In the present study, 1.68% of patients(7cases) had a pedicle breach. However, there was no effect on the neurological status or ODI score in these patients.

Discussion
This study aimed to evaluate the accuracy of screw placement and fusion rate after MIS-TLIF under Oarm navigation. Results show that accuracy of pedicle screw insertion was 99.66% with a 95.45% fusion rate. Of the breach cases, none were associated with complications.
Pedicle screw xation has been widely used due to the three-column control of the vertebral body in spinal surgeries. The malposition of a screw may violate the nearby vital structures and lead to neurovascular injury. Intraoperative assistance, such as O-arm navigation, has the potential to improve the accuracy of screw placement [7][8][9][10]20]. Therefore, we used O-arm navigation to optimize the pedicle screw placement in MIS-TLIF procedures.  [22]. Higher than in previous reports, the present study showed 99.66% accuracy.
Since the surgeries included in the present study were mainly single-level surgeries, the high rate of accuracy could be because the distance between the reference frame and surgical site was short. In addition, not using K-wire for the surgeries in this study eliminated the risk of K-wire di culty and complications. Furthermore, we started using O-arm navigation in 2013, thus, the learning curve may not be a factor in more recent results. For the misplacement recorded in the present study, they occurred similarly in both sides and among the ethnic groups.
Obtaining the O-arm scan after pedicle screw insertion could reduce reoperation rates. A previous study showed a 3.6% intraoperative revision rate [12] and Van et al. reported a 1.0% intraoperative revision rate [15]. In this study, there was no intraoperative revision (0%). The indication for immediate screw revision was the detection of a > 4-mm breach lateral direction or > 2-mm breach medial direction on the O-arm images. None of the 2,098 screws needed intraoperative revision, and the reoperation rate for screw revision was also 0%.

Fusion rate
In a systematic review and meta-analysis, lumbar fusion rates were reported at 95.7% at 24-months when recombinant human bone morphogenetic protein-2 was used for TLIF/posterior lumbar fusion (PLF) [23]. According to another systematic review, the 93-93.3% fusion rate associated with MIS-TLIF seemed to be higher compared to lateral lumbar interbody fusion, anterior lumbar interbody fusion, and PLF [24]. Khan

Limitations
There are limitations to this study to consider. First is the retrospective and single-center design that limits the generalizability of the results. To reduce these limitations, the evaluators were blinded to the clinical results and the O-arm images were independently reviewed. Second, some O-arm images were not clear because of the material of the inserted pedicle screws. In cases where the breach was questionable, the poorer grade was selected for data analysis.  A caption was not provided with this version Figure 4 A caption was not provided with this version