主論文

Accuracy of pedicle screw insertion in posterior scoliosis surgery: a comparison between
intraoperative navigation and preoperative navigation techniques(側彎症手術における椎弓根スクリュー挿入精度の検討：術中ナビゲーションと術前ナビゲーションの比較)【Introduction】
Pedicle screws are widely used for the treatment of adolescent idiopathic scoliosis (AIS) becauseof the excellent fixation achieved within a shorter fusion length and their three-dimensionalcorrection force. Accurate placement of pedicle screws in scoliosis patients is very important but
difficult because of the rotation of the corpus vertebrae as well as the difference in the radii of thepedicles, deviation of the spinal cord, and thinning of the pedicles, all of which increase the potential
risk of screw misplacement.
There are various navigation systems aimed at improving the accuracy of screw placement andavoiding neurovascular complications from screw misplacement. Clinical studies demonstrated
improved accuracy in pedicle screw insertion when using a preoperative CT-based navigation
system. The major limitation of this technique is associated with variable patient positioning. There
has been a technological evolution in the past year with the use of intraoperative navigation. With
this method of navigation, surgeons can avoid the position-variation problem and improve theefficacy of screw placement.
We conducted the current study to assess and compare the efficacy and accuracy of intraoperativenavigation (O-arm or Arcadis navigation) and preoperative CT based navigation in AIS surgery andto analyze misplacement patterns of pedicle screws.
【Materials and Methods】
Subjects
A retrospective study was conducted in patients with AIS who underwent surgical treatment at
our hospital between January 2009 and June 2015. Inclusion criteria were (1) an AIS patient whounderwent correction surgery, (2) single main thoracic or double thoracic curve patterns, and (3) anall pedicle screw-based posterior instrumentation. We excluded scoliosis patients who did not have
AIS, who were surgically treated by an anterior approach or who had other curve patterns. For eachpatient, we measured the number of pedicle screws, the number of pedicle screws per vertebra in
the apical region (apex ± 2 vertebrae), and the coronal Cobb angle of the main thoracic curve using
pre- and postoperative full-length standing radiographs and CT, respectively.
Accuracy assessment of the pedicle screws
Postoperative CT images (1.25- or 1-mm thickness) of the instrumented segments were used foranalyzing pedicle breaches in both groups. We classified pedicle perforations as either medial or1

lateral according to the Gertzbein classification.
【Results】
Demographic data
The study group included 27 patients who underwent intraoperative navigation-based insertionof 492 pedicle screws and 40 patients treated with preoperative navigation based insertion of 626
pedicle screws. The mean ages at the time of operation were 16.1 years (range 12–24 years) and16.2 years (range 13–25 years) for the intraoperative and preoperative groups, respectively. The
angles of the main curve before and after surgery were similar between the two groups. The Cobb
angle was corrected from 60.4 to 15.8 (correction ratio 74.6%) in the intraoperative group and from59.5 to 16.6 (correction ratio 72%) in the preoperative group. The difference between the two groups
was not statically significant (P = 0.410). The two groups were similar before surgery with respect
to apical vertebra rotation.
Accuracy rate of pedicle screw placement
In the two groups, a total of 433 pedicle screws were implanted in the apical regions of patients’
main curves. The accuracy of pedicle screw placement (grades 0, 1) was significantly higher in theintraoperative navigation group than in the preoperative navigation group (199/210, 94.8% vs
199/223, 89.2%, respectively; P = 0.035). Overall, there was a significantly higher frequency oflateral perforation (36/1118, 3.2%) than medial perforation (17/1118, 1.5%). Furthermore, using
intraoperative navigation significantly diminished the incidence of medial perforation (3/492, 0.6%
vs 14/626, 2.2%, P = 0.027).
Misplacement patterns of pedicle screws
The most common location of misplacement was around the apex vertebra (T7–9) of the curve.
Moreover, some misplaced pedicle screws were in the proximal thoracic spine at the apex of thethoracic curve (T3–T4) whether it was a structural curve or nonstructural curve.
【Discussion】
The mechanics of AIS increases the difficulty of inserting pedicle screws because of the deformityof the vertebral bodies, their relatively narrower pedicles, and the spinal cord shift to the concaveside resulting in a limited epidural safe zone, especially at the apical region.
The literature shows that preoperative CT navigation can achieve overall higher rates of accuracy
in scoliosis patients. In our study, the perforation rate were 10.8% in preoperative group and 5.2%
intraoperative group in apical region, because the major limitation of this technique is associatedwith the variable positioning of the patient. And the incidence of medial perforation was particularlyhigh in the preoperative group.
In this study, 45% (24/53) of misplaced pedicle screws were in pedicle channels of less than 3mm, which could be considered a planning error rather than a navigational error or technical error.
As to the misplacement pattern of the pedicle screws, the apical vertebra was at about T7–9, and we2

experienced a higher perforation rate at the apical region compared to the overall perforation rate inthis study. Since the apical region is the most rotated region in AIS, it is difficult to control theinclined angle when inserting pedicle screws without encroaching into the concave or convex sides.
Another major benefit of intraoperative navigation is the decreased pedicle insertion time. The
time required for the registration procedure and insertion of one pedicle screw was 11.3 ± 2.1 minin the preoperative group, but only 5.1 ± 1.1 min in the intraoperative group, because the surgeon
can avoid the time-consuming repetitive calibration for each vertebra.
【Conclusion】
Both preoperative CT-based and intraoperative navigation systems provide sufficient accuracy
and safety in pedicle screw insertion for AIS surgery. Intraoperative navigation systems facilitatepedicle screw insertion in the apical region and reduce registration time during AIS surgery which
improves the efficacy and accuracy of pedicle screw insertion.

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