North American Spine Society Journal (NASSJ) 10 (2022) 100121

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North American Spine Society Journal (NASSJ)
journal homepage: www.elsevier.com/locate/xnsj

Clinical Studies

Accuracy and safety of percutaneous pedicle screw placement using theK-wireless minimally invasive spine percutaneous pedicle screw system inJapan: A randomized active controlled study
Kazuo Ohmori a,∗, Sei Terayama b, Koichiro Ono a, Miyuki Sakamoto c, Yukie Horikoshi cabcCenter for Spinal Surgery, Nippon Koukan Hospital, 1-2-1 Koukandori, Kawasaki-ku, Kawasaki, Kanagawa, Japan
Department of Orthopedic Surgery, Shunyokai Central Hospital, 485 Niitomi, Kimotuki-cho, Kimotuki-gun, Kagoshima, Japan
Johnson and Johnson K.K, Medical Company, 3-5-2 Nishikanda, Chiyoda-ku, Tokyo, Japana r t i c l e

i n f oKeywords:
Randomized controlled trial
K-wireless MIS PPS system
Accuracy of screw insertion
Percutaneous Pedicle Screw
Minimally Invasive Spine
PPS

a b s t r a c t
Background: Minimally invasive lumbar fusion has recently become a widely used technique worldwide. Thisrandomized active controlled study was conducted to demonstrate the non-inferiority of the K-wireless Minimally
Invasive Spine (MIS) Percutaneous Pedicle Screw (PPS) system compared with use of the six pedicle screw systems
currently used in our practices with respect to the accuracy of pedicle screw placement.Also to compare the screwinsertion time and number of ﬂuoroscopic observations during screw insertion between the groups.
Methods: A total of 80 patients with degenerative spinal diseases or vertebral fractures were assigned, including
41 patients in the K-wireless MIS PPS system group (K-wireless group) and 39 in the control group (K-wire group).
The accuracy of the screw insertion, screw-insertion time, number of ﬂuoroscopic observations during screw
insertion, and the incidence of adverse events were compared between the K-wireless group and the K-wire group.
The accuracy rate was calculated as the number of screws with no breach divided by the total number of screws.
Results: The accuracy rates of screw insertion were 85.7% and 75.0% in the K-wireless and K-wire groups,
respectively, with an intergroup diﬀerence of 10.7% (95% conﬁdence interval: 2.3–19.1%). The K-wireless groupdemonstrated non-inferiority compared with the K-wire group. The mean screw-insertion time was signiﬁcantly
shorter in the K-wireless group (2.62 and 2.97 min in the K-wireless and K-wire groups, respectively; P=0.005).
There were also signiﬁcantly fewer ﬂuoroscopies in the K-wireless group (10.7 and 17.4 in the K-wireless andK-wire groups, respectively; P<0.001). There were no device-related or study treatment-related adverse eventsin either group.
Conclusions: The accuracy of pedicle screw insertion using the K-wireless MIS PPS system was not inferior to thatof existing products. In terms of safety, no product-related or treatment-related adverse events were identiﬁed inthis study and no new safety concerns were noted.

Introduction
The percutaneous pedicle screw (PPS) technique was introduced inJapan in 2005, giving spine surgeons the opportunity to conduct minimally invasive spine (MIS) fusion surgery [1,2]. MIS fusion surgery is
becoming widely used in Japan because of its lower levels of complications, bleeding, and muscle injuries compared with conventional open
surgeries that require opening up the major paraspinal muscles [3–8].
Although several spinal-ﬁxation instruments have been developed for
MIS fusion surgery, MIS fusion surgery has a smaller surgical ﬁeld withlimited visualization compared to conventional procedures, and there
are learning curves for the operator’s experience and technical skills[9,10]. Furthermore, the procedure involves multiple steps, and a guidewire must be controlled with a limited view ﬁeld.
DePuy Synthes Spine obtained marketing approval for a K-wirelessMIS PPS system (VIPER PRIMETM System, DePuy Synthes Spine, Raynham, MA, USA; Fig. 1), from the US Food and Drug Administration in
December 2016. The K-wireless MIS PPS system was subsequently approved in Japan in December 2017. This system represents a rationalized approach to the procedures previously used for minimally invasive
pedicle screw placement and is designed to reduce the number of steps
required for the insertion of pedicle screws (no needles, guide wires,or taps required), and the number of devices delivered to the operation
room.

∗

Corresponding author.
E-mail addresses: kazuopsine@gmail.com (K. Ohmori), sei_tera@yahoo.co.jp (S. Terayama), koichirono@gmail.com (K. Ono), msakamo5@its.jnj.com (M.
Sakamoto), yhoriko2@its.jnj.com (Y. Horikoshi).
https://doi.org/10.1016/j.xnsj.2022.100121
Received 21 January 2022; Received in revised form 4 May 2022; Accepted 4 May 2022
Available online 8 May 2022
2666-5484/© 2022 The Author(s). Published by Elsevier Ltd on behalf of North American Spine Society. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

K. Ohmori, S. Terayama, K. Ono et al.

North American Spine Society Journal (NASSJ) 10 (2022) 100121

established to provide suﬃcient power for a successful non-inferiority
study. Based upon the results of previous clinical trials in Japan and theUnited States accuracy rate of approximately 93% was anticipated, andthe clinical non-inferiority (NI) margin for comparison with the existingproducts was assumed to be 10%. Under this anticipated success rateand NI margin, One hundred forty-four screws per group was estimatedto provide a power of >90% at a one-sided signiﬁcance level of 2.5%.
Assuming that a mean of 4 screws would be used for one patient, 36
patients per group was estimated. Considering that approximately 10%of patients could be excluded or drop out, a target sample size of 40 patients per group was adopted. The inclusion and exclusion criteria areshown in Table 1.

Fig. 1. Illustration of VIPER PRIMETM System. The system features a new screwtip design and a stylet that is fully controlled by the screwdriver. Using the stylet
control handle and the modular handle, surgeons can target pedicles and insert
screws in a single instrument pass.

The K-wireless MIS PPS system is expected to fulﬁll needs in clinical practice, including decreasing the time spent on each PPS surgery
and decreasing guide wire-related adverse events by the design featuresof the K-wireless MIS PPS system, although guide wire related complications are generally known in PPS surgery [11]. The decreasing thetime spent on each PPS surgery is also expected to decrease the number
and time of ﬂuoroscopic observations for surgery (C-arm). The existingproducts have been conﬁrmed to have suﬃcient screw-insertion accuracy based on clinical trials [12,13].
We conducted a randomized active controlled study in Japan todemonstrate the non-inferiority of the K-wireless MIS PPS system compared with existing standard-of-care PPS systems (K-wire PPS systems)
which has similar design and surgical steps as a technology alternative
group, with respect to the safety and accuracy of pedicle screw placement in patients with degenerative spinal diseases or vertebral fractures.

Site registration and subject enrollment and randomization
The registration center registered and randomized subjects using theelectronic data capture (EDC) system. The investigators at each studysite asked the registration center to register the site after approval by
the certiﬁed review board. The registration center registered the site andsent notiﬁcation of the completion of site registration to the investigator.
Subject enrollment and randomization were conducted as follows.
After providing written informed consent, each potential subject was
screened by the investigator or sub-investigator to judge their eligibility. Subjects were included in this study if the investigator or subinvestigator conﬁrmed that they met all the inclusion criteria and noneof the exclusion criteria.
The investigator or sub-investigator entered the required subject
information into the EDC system. At this time, an arbitrary subjectidentiﬁcation code was provided, which did not contain any informationthat could identify the individual.
If the EDC system determined that the patient was eligible, it automatically randomly allocated the subject to the trial treatment or control
group in a ratio of 1:1. Study site was used as a stratiﬁcation factor for
randomization to avoid signiﬁcant bias among the sites. The investigator and sub-investigator at each site were not notiﬁed of the detailed
randomization procedures.

Methods
Trial design
This was a conﬁrmatory, parallel-group, open-label, controlled, randomized study, with use of an approved spinal-ﬁxation instrument as
the control. The study was approved by the Institutional Review Boardof Nippon Medical School Foundation (trial ID: jRCTs032190039; approved May 13, 2019). The full study protocol is available on the jRCT
website.

Study patients
Participants
Eighty patients were randomized by the EDC system, 41 patients to
the K-wireless MIS PPS system group (K-wireless group) or 39 to thecontrol device group (K-wire group). Subjects in both groups had to undergo lumbosacral surgery within 60 days after enrollment, and patients
who did not undergo surgery within this period were asked to re-sign
the informed consent form if they wished to participate in the study.

This study included patients in two study sites who were diagnosed
with a spinal degenerative disease (e.g., degenerative disc disease, lumbar spinal stenosis, spondylolisthesis, or scoliosis) or vertebral fractures,and who required pedicle screw placement and were considered suitable for PPS. The overall target sample size was 80 patients which was
Table 1
Inclusion and exclusion criteria.
Inclusion criteria

Exclusion criteria• Individual aged ≥20 years at the time of surgery.
• Diagnosis of a spinal degenerative disease (e.g.,• Pregnant or breastfeeding woman• Revision surgery of the lumbar spine

degenerative disc disease, lumbar spinal stenosis,
spondylolisthesis, or scoliosis), spinal tumor, or vertebral
fracture• First instrumentation lumbosacral surgery withpercutaneous pedicle screw and undergoing an
instrumentation lumbosacral surgery involving at least one
intervertebral segment• Voluntarily participated in this study and signed theinformed consent form stating that patient information• Understanding the purpose of the clinical trial in theopinion of the investigator or sub-investigator, and iswilling and able to follow the surgical and study
procedures• Able to read and understand the Japanese informed
consent form

• Prior pedicle screw placement in the lumbar spine• Severe osteoporosis• Severe spinal deformity due to scoliosis• Extremely narrow or severe osteosclerotic change in thetarget pedicle• Drug or alcohol abuse (in the past 5 years) or psychiatricdisorder and considered in the opinion of the investigatoror sub-investigator to be unable to comply with the study
requirements deﬁned in the protocol

2

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North American Spine Society Journal (NASSJ) 10 (2022) 100121

Table 2
Percutaneous pedicle screw systems used in this study.
K-wireless group
TM

VIPER PRIME System
K-wire group
PathFinder NXT® Minimally Invasive Pedicle Screw System
RELINE® System
M.U.S.T. Pedicle Screw System
CD HORIZON® SOLERA® VOYAGERTM 5.5/6.0 mm Spinal System
CREO® MIS Stabilization System
Associa spinal system

Number of patients

Number of screws

39

187

4
9
6
3
11
1

25
44
34
12
56
6

Table 3
Surgical procedures for the K-wireless and K-wire groups.
K-wireless groupK-wire group• Make a skin incision• Insert the screw-loaded inserter through the incision and• Make a skin incision• Insert the needle or probe through the incision anddock the stylet tip on an entry point at an appropriate
position• Extend the stylet into the pedicle• Advance the screw into the pedicle• Remove the inserter and stylet

advance it to the pedicle• If the needle or probe enters into the centrum, remove theinner needle, and then insert the guidewire into thecentrum• Remove the needle or probe• Insert the tap along the guidewire• Remove the tap• Insert the screw• Remove the guidewire• Remove the driver from the screw

Seventy three patients (39 in the K-wireless group and 34 in the Kwire group), a total of 364 screws (187 in the K-wireless group and
177 in the K-wire group) were included in the ﬁnal analysis. Excluding
25 screws that were used to intentionally perforate the anterior wallto undergo bi-cortical ﬁxation at S1 (12 screws in K-wireless group, 13
screws in K-wire group), 339 screws were evaluated for screw insertion
accuracy (175 screws in K-wireless group, 164 screws in K-wire group).
Details of the screws used in this study are shown in Table 2.

each screw relative to the pedicle was assessed and graded according toa previous report [14] as follows: grade A: no breach; grade B; breach<2 mm; grade C: breach 2–4 mm; grade D: breach >4 mm.
The time required for each screw insertion and the number of ﬂuoroscopic observations for all patients were summarized and compared
between the K-wireless and K-wire groups. Adverse events associatedwith screw insertion were also investigated.
Statistical analysis

Treatment planEﬀectiveness analyses were performed using the full analysis population who underwent surgery with the randomized device withoutmajor protocol deviations. Safety analyses were performed using thesafety analysis population who underwent surgery with the randomized
device.
The accuracy rate was calculated according to the formula below.
Diﬀerences in accuracy rates between the K-wireless and K-wire groups,
and 95% conﬁdence intervals (CIs) were calculated and compared. Noninferiority of the K-wireless group compared with the K-wire group wasconcluded if the lower limit of the CI of the intergroup diﬀerence was
not below −10%. The non-inferiority one-sided test was performed using
the Wald test with a 10% non-inferiority margin.

The surgeon chose the appropriate screw size preoperatively basedon computed tomography (CT) images of each subject. Intraoperative
ﬂuoroscopy (antero-posterior and lateral) without navigation was used
to guide insertion of all screws. PPS insertion was performed in the prone
position, and the C-arm positioning was adjusted for the target vertebra
before skin incision for screw insertion. The pre-speciﬁed steps for eachgroup were followed sequentially for each screw insertion. Notably, thisstudy did not impose any restrictions on the surgical procedure, ﬁxationlevel, or target vertebrae, which were determined by the surgeon. The
time spent on each screw insertion and the number of ﬂuoroscopic observations required per screw insertion were measured and recorded
intraoperatively by a site member.
The surgical procedure in the K-wireless group was performed according to the VIPER PRIMETM System operation manual. Surgeries in
the K-wire group were performed according to the operation manual forthe respective spinal-ﬁxation system. The procedures in both groups areshown in Table 3.

accur acy r ate(%) =number of screws, grade A
number of screws, grades A + B + C + D

The screw-insertion time and number of ﬂuoroscopic observations
per screw during screw insertion were summarized using descriptive
statistics for each treatment group. Group comparisons were made using
Student’s t-test.

Assessment of outcome
Results
The following variables were assessed: (1) accuracy of PPS, (2) timespent on each screw insertion, and (3) number of ﬂuoroscopic observations required per screw insertion. All patients underwent ﬁne-cut(1.5 mm) CT within 2 weeks postoperatively, and the accuracy of screw
placement, speciﬁcally axial, coronal, and sagittal CT images of eachpedicle screw, was evaluated by an independent spine surgeon or radiologist other than a co-investigator, based on CT data. The position of

The enrollment period was from June 2019 to May 2020, and thefollow up period for each subject was from the informed consent to
the discharge date or day 14 post-surgery, whichever came ﬁrst. Eighty
patients, which was the overall target sample size were enrolled.
Fig. 2 shows a ﬂow chart of the study. Eighty patients were randomized by the EDC system into the K-wireless group (n=41) and the K-wire3

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North American Spine Society Journal (NASSJ) 10 (2022) 100121

Fig. 2. CONSORT ﬂow diagram.

Table 4
Basic data for randomized groups.

Table 5
Basic surgical data.
Randomized group

Randomized groupGroup

K-wirelessK-wireGroup

K-wirelessK-wireNumber of patients
Sex
Male
FemaleMean age (range), years
Primary
Lumbar spinal canal stenosis
Spondylolisthesis
diseaseVertebral fracture
Degenerative scoliosis
Lumbar disc herniation39
18 (46.2%)
21 (53.8%)
67.2 (50–84)
19
15
4
0
1

34
19 (55.9%)
15 (44.1%)
67.6 (40–88)
19
9
4
1
1

Number of patients
Mean operating time (range), min
Mean amount of bleeding (range), ml
SurgicalTLIF
LLIF or XLIF(R)methodOLIF/ATPHA insertion
XLIF+TLIF
OLIF+TLIF

39
125.8 (30–253)
67.9 (5–250)
22
7
3
4
3
0

34
128.1 (27–269)
86.2(6–450)
16
7
2
4
4
1

TLIF: Transforaminal Lumbar Interbody Fusion; LLIF: Lateral Lumbar Interbody
Fusion; XLIF: Extreme Lateral Interbody Fusion; OLIF: Oblique Lateral Interbody
Fusion; ATP: Anterior to Psoas; HA: hydroxyapatitegroup (n=39). Seven patients who did not undergo surgery were excluded, and a total of 73 patients (39 in the K-wireless group, 34 in the
K-wire group) were therefore included in the ﬁnal analysis. The reasonsfor discontinuation were withdrawal of patient consent (n=1), failure tomeet selection/exclusion criteria (n=3), and other reasons (n=3). The
characteristics of each group, including sex, age, and primary disease,are shown in Table 4 and the surgical data are shown in Table 5.
The accuracy of the screw-insertion position is shown in Table 6.
The accuracy rates were 85.7% and 75.0% in the K-wireless and K-wiregroups, respectively, with an intergroup diﬀerence of 10.7% (95% CI:
2.3–19.1%). The lower limit of the 95% CI of the intergroup diﬀerence
exceeded the pre-speciﬁed −10%, which veriﬁed the non-inferiority ofK-wireless group compared with the K-wire group (P<0.001).
The accuracy of screw placement by vertebral level is indicated inTable 7. The accuracy rates were 79.7% in the K-wireless group and68.5% in the K-wire group for L4, and 87.9% in the K-wireless groupand 80.4% in the K-wire group for L5. The accuracy was approximately

10% higher in the K-wireless group in all categories. There was no screw
misplacement in the S1 vertebra in either group.
Table 8 shows the number of screws in the direction of the pedicle
crossing according to the adjudicated grading. The proportion of lateralbreaches was >50% at Grade B and C in both groups. One screw in the
K-wire group was judged as grade D, however, none in the K-wirelessgroup. None of the patients with grade B, C and D required any further
treatment and caused any symptoms in both groups in this study during
the study follow up period.
The insertion time and number of ﬂuoroscopic observations requiredfor insertion of each screw are shown in Table 9. The mean insertion
time was signiﬁcantly shorter in the K-wireless group (2.62 min in the
K-wireless group and 2.97 min in the K-wire group; P=0.005). Similarly,
the mean number of ﬂuoroscopic observations was signiﬁcantly lower
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North American Spine Society Journal (NASSJ) 10 (2022) 100121

Table 6
Accuracy of screw placement.

Table 8
Direction of pedicle breach.
Randomized group

Number of screws
Accuracy ofscrew
placement

Grade A
Grade B
Grade C
Grade D

Accuracy rate (%)
P-value∗

Randomized groupK-wirelessK-wire175
150 (85.7%)
22 (12.6%)
3 (1.7%)0 (0.0%)85.7
P<0.001164
123 (75.0%)
33 (20.1%)
7 (4.3%)1 (0.6%)75.0

Number of screws
Direction of
pedicle breach

Grade BMedialLateralCranialCaudalGrade CMedialLateralCranialCaudalGrade A: no breach; Grade B: breach <2 mm; Grade C: breach 2–4 mm; Grade
D: breach >4 mm
Table 7
Accuracy of screw placement by vertebral level.

Grade DMedialLateralCranialCaudalRandomized group
Vertebral level of allocated screw insertion
L1

L2

L3

L4

L5

S1

Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)
Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)
Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)
Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)
Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)
Number of allocated screws
Accuracy ofGrade Ascrew placement Grade B
Grade C
Grade D
Accuracy rate (%)

K-wirelessK-wire66 (100.0%)
0 (0.0%)0 (0.0%)0 (0.0%)100
44 (100.0%)
0 (0.0%)0 (0.0%)0 (0.0%)1002419 (79.2%)
3 (12.5%)
2 (8.3%)0 (0.0%)79.2
59
47 (79.7%)
12 (20.3%)
0 (0.0%)0 (0.0%)79.7
66
58 (87.9%)
7 (10.6%)
1 (1.5%)0 (0.0%)87.9
16
16 (100.0%)
0 (0.0%)0 (0.0%)0 (0.0%)100

64 (66.7%)
2 (33.3%)
0 (0.0%)0 (0.0%)66.7
148 (57.1%)
5 (35.7%)
1 (7.1%)0 (0.0%)57.1
30
25 (83.3%)
5 (16.7%)
0 (0.0%)0 (0.0%)83.3
54
37 (68.5%)
12 (22.2%)
4 (7.4%)
1 (1.9%)68.5
56
45 (80.4%)
9 (16.1%)
2 (3.6%)0 (0.0%)80.4
44 (100.0%)
0 (0.0%)0 (0.0%)0 (0.0%)100

K-wirelessK-wire17522
7 (31.8%)
12 (54.5%)
3 (13.6%)
0 (0.0%)3
1 (33.3%)
2 (66.7%)
0 (0.0%)0 (0.0%)
0
0
0
0
0

164
33
14 (42.4%)
15 (45.5%)
3 (9.1%)1 (3.0%)7
1 (14.3%)
6 (85.7%)
0 (0.0%)0 (0.0%)1
0 (0.0%)1 (100.0%)
0 (0.0%)0 (0.0%)

Grade A: no breach; Grade B: breach <2 mm; Grade C: breach 2–4 mm; Grade
D: breach >4 mm
Table 9Insertion time and number of ﬂuoroscopic observations per screw insertion.
Randomized group

Number of screws
Mean time (range), min
P-value∗
Mean number of ﬂuoroscopic observations(range)P-value∗∗

K-wirelessK-wire175
2.62 (1.3–9.3)
0.005
10.7 (4–43)

164
2.97 (1.3–6.2)
17.4 (5–57)<0.001Student’s t-test

ﬂuoroscopy is therefore considered the mainstream method of PPS insertion.
The current study was conducted to verify the accuracy and safety ofpedicle screw insertion using the K-wireless MIS PPS system in Japan,
in comparison to the existing standard PPS systems. A recent retrospective study reported that the K-wireless MIS PPS system shortened thescrew-insertion time approximately 0.4-fold, with equivalent insertion
accuracy [22], however, no prospective, randomized studies have investigated the accuracy of screw insertion, insertion time, and ﬂuoroscopy
frequency between the K-wireless MIS PPS system and control systems.
In this study, the accuracy rate of screw placement was 85.7%(150/175 screws: 95% CI: 79.6−90.5%) in the K-wireless group and
75.0% (123/164 screws: 95% CI: 67.7−81.4%) in the K-wire group, withan intergroup diﬀerence of 10.7% (95% CI: 2.3−19.1%), which indicates non-inferiority of the K-wireless compared with the K-wire group.
In addition, the lower conﬁdence interval limit exceeded 0.0%, whichsuggests superiority of the K-wireless group over the K-wire devices regarding the accuracy rate of screw placement. We conﬁrmed that the accuracy of screw insertion by the K-wireless MIS PPS system was not inferior to that of the existing products, and that the insertion accuracy wasmaintained. The screw is inserted along the stylet in the VIPER PRIMETM
System procedure and it is easy to be aligned, and would therefore theaccuracy rate in the K-wireless group was higher than the K-wire group.
The reason why the accuracy rate of this study was slightly lower than
the target accuracy rate of 93% is considered that the small number ofpatients and diﬀerent ﬂuoroscopic techniques in the clinical studies byciting to this study.
In the assessment of insertion accuracy, the directions of perforated
pedicle screws (Grade B, C, or D) were similar in both groups, withthe most common breach being lateral (K-wireless group 56.0%, K-wiregroup 53.7%), followed by medial breach (K-wireless group 32.0%, K-

Grade A: no breach; Grade B: breach <2 mm; Grade C: breach 2–4 mm; Grade
D: breach >4 mmin the K-wireless group (10.7 in the K-wireless group and 17.4 in the
K-wire group; P<0.001).
Adverse events were observed in 12.8% and 20.6% of subjects in
the K-wireless and K-wire groups, respectively (Table 10). There were
no device-related or study treatment-related adverse events in eithergroup. Moreover, there were no adverse events attributable to device
malfunction, and no new safety concerns were noted.
Discussion
The usefulness of PPS insertion by robot-assisted [15–18] and O-arm
navigation [19–21] has recently been reported. Both systems are expensive technologies and thus are frequently impractical. Conventional
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North American Spine Society Journal (NASSJ) 10 (2022) 100121

Table 10Adverse events.
Randomized groupK-wireless (N=39)

Any adverse event
Skin and subcutaneous tissue disorders
Gastrointestinal disorders
Respiratory, thoracic, and mediastinal disorders
Injury, poisoning, and procedural complications

K-wire (N=34)

Number of patients%

Number of cases

Number of patients%

Number of cases

5
4
2
1
0

12.8%
10.3%
5.1%
2.6%
0.0%

7
4
2
1
0

7
5
1
0
1

20.6%
14.7%
2.9%
0.0%
2.9%

7
5
1
0
1

wire group 36.6%). This suggests that the risk of neurological complications caused by screw perforation could be reduced by paying attention
to medial perforation.
The highest radiation exposures in patients during spinal surgery
have been reported in the surgical ﬁeld, gonad area, and thoracic region, while the surgeon was exposed to signiﬁcantly higher radiation
than other operating room personnel, with the surgeons’ dominant hand,which is mainly used to ﬁx the screw in the surgery ﬁeld, receiving thehighest radiation dose. Furthermore, the surgeon’s eye-lens region was
exposed to signiﬁcantly higher radiation doses compared with the assisting surgeon [23]. Spinal surgeons and other operating room personnel
who are routinely exposed to occupational radiation should thus takecare not to exceed the dose equivalent limit (eye lens: 20 mSv averaged
over 5 years with no more than 50 mSv in any single year; skin andextremities: 500 mSv per year) [24][25].
In this study, the mean screw-insertion time was signiﬁcantly shorter(K-wireless group 2.62 min, K-wire group 2.97 min; P=0.005) andthe number of ﬂuoroscopy observations was signiﬁcantly smaller (Kwireless group 10.7; K-wire group 17.4; P<0.001) in the K-wirelessgroup than in the K-wire group. In this study, the average number of
ﬂuoroscopies was reduced by approximately 40% in the K-wireless compared with the K-wire group. The reason of this result is considered that
the K-wireless MIS PPS system have fewer operative steps than K-wiregroup as shown in Table 3. Although there was a statistically signiﬁcantdiﬀerence in the screw-insertion time, it may not be of great clinicalsigniﬁcance. On the other hands, it is considered that a decrease in thenumber of ﬂuoroscopy observations is of great clinical signiﬁcance.
Although no measured data on actual radiation exposure were obtained in this study, we showed that the new procedure could reduce
the number of ﬂuoroscopic imaging required per surgery compared withthe use of conventional products, which suggests that it would also contribute to reduce the hazards associated with radiation exposure among
patients, surgeons, and surgical staﬀ. In addition, this advantage of theK-wireless MIS PPS system could potentially provide additional surgicalopportunities for more patients with excellent spine surgeons.
The K-wireless MIS PPS system reduced screw-insertion time, whichmight in turn contribute to a shorter operation time and reduce the burdens on patients (in terms of duration of anesthesia, amount of bleeding,infection risk, etc.) and on spinal surgeons and medical staﬀ (in termsof physical and mental workloads, distribution of resources or operating
room eﬃciency, etc.).
Complications associated with MIS fusion generally include large
vessel and intestinal tract injuries caused by guide wire perforation. A
study of 781 patients who underwent percutaneous pedicle screw insertion showed guide wire breakages in three patients (0.4%) and aortic
guide wire-related injury in one patient (0.13%) [11]. The K-wirelessMIS PPS system does not require guide wires in its procedure, and would
therefore reduce the incidence of these complications, although it could
not be evaluated in this study because no adverse events related to theguidewires occurred. Accordingly, no guide wire-related complications
were observed in the current study.
The limitations of this study include the use of various diﬀerent systems in control group, relatively small number of sites (total two sites),

and the learning curve of PPS. The results of this trial are not generalizable to all surgeon because the accuracy of PPS depends upon thesurgeon’s experience. In addition, there is a limitation that the radiation dose was not evaluated in this study, although the number of ﬂuoroscopy was evaluated.
Conclusion
Our study results conﬁrmed that the accuracy rate of pedicle screw
placement using the K-wireless MIS PPS system is non-inferior to thatof existing products and can indirectly reduce radiation exposure to patients and surgical staﬀ.
Declarations of Competing Interests
None.
Funding
This study was funded by Johnson and Johnson K.K, Medical Company.
Acknowledgments
Funding from Johnson and Johnson K.K, Medical Company is gratefully acknowledged.
Supplementary materials
Supplementary material associated with this article can be found, inthe online version, at doi:10.1016/j.xnsj.2022.100121.
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