1. MIN-2009-09-0002
Percutaneous screw fixation for traumatic spondylolisthesis of the axis using three
dimensional fluoroscopy-assisted navigation (Case report)
Reviewer: 1
Comments to the Author
1) The number of seven! authors from four different departments writing a case
report about one single patient is hardly acceptable.
Answer:
Thank you for your comment. I agree with your opinion. I chose me and other 4
authors from one hospital.
2) “This is the first case report on percutaneous screw fixation using three
dimensional fluoroscopy-assisted navigation in a patient with polytrauma and a
hangman’s fracture.” In the discussion various examples of navigated C2-screw
placement in case of fracture are mentioned with only little variations compared to
the presented case: This phrase should be omitted.
Answer:
I agree with your suggestion. Similarly procedure had been published, so we
omitted this phrase.
3) Authors should explain Effendi-Grading shortly in the introduction section.
Answer:
I agree with your opinion. We added Effendi-Grading explanation in our article.
4) How was instability due to discoligamentous injury C2/3 excluded? According to
MRI or have supported flexion/extension x-ray images been performed
additionally? In case of hypermobility additional anterior plating would have been
necessary.
Answer:
Thank you for your message. This point is very important. We described “Although
disc injury at C2/3 was not detected by MRI, and Halo vest immobilization would typically

2. have been proper treatment for this type of fracture, external immobilization was difficult
due to her polytrauma.” at 5th sentence in first paragraph of Case Report. If you
recommend adding MRI, we can add MRI figure.
5) “A dynamic reference arc was attached to the spinous process of the axis
through a small incision.” In this case the reference star was attached to the
hypermobile arch of C2 without stable connection to the vertebral body, with which
the arch has to be fusioned. How did authors make sure that their screw trajectory
(generated on the navigation image, which is determined by the hypermobile star)
showed a direct and stable connection through both bony parts to connect during
the awling and screwing manipulation?
Answer:
Thank you for your comment. Hypermobility of C2 arch is very important point. We
carefully insert screws using navigation, and we should assess screw position using
intraoperative 3D fluoroscopy. We added bellow comment in Discussion.
“Limitation of our percutaneous screw insertion technique was that the reference
arc was attached to the mobile arch of C2 without stable connection to the vertebral
body. Bilateral screw position should be carefully assessed by intra-operative 3D
fluoroscopy imaging, if there were hypermobility of the C2 arch.”
6) “CT-based navigation requires anatomical registration, therefore, the posterior
surface of the axis would be totally exposed.“ This is completely wrong: CT-images,
generated for spinal navigation can be referenced by surface-based registration,
but also easily by 2-dimensional fluoro-images (e.g. BrainLab Navigation). This
wrong information should be omitted.
Answer:
Thank you for your comment. I agree with your opinion. This information is omitted.
7)References 3 and 4 can be hardly found by common readers and should be
omitted.
Answer:
I agree with your opinion. Reference 3 and 4 was changed to other English article.

3. Reviewer: 2
Comments to the Author
This is a nice paper of a well done case.
However, a couple of things need to be changed.
1) A stable fracture does not need surgery or any form of immobilization per
definition. An Effendy I type hangman´s fracture is not a stable fracture. It has just
no associated soft tissue injury (posterior ligaments and especially the disc) and
can therefore be treated by external immobilisation. One does not need a Halo for
that. A stiff neck is good enough in the opinion of most spine surgeons nowadays.
Thus, this would have been the feasible alternative in this case.
Answer:
This point is very important. We carefully discussed about alternative treatment
such as Halo fixation and neck collar. As mentioned in the article, we want to
choose Halo fixation for this patient, however external fixation is difficult for her
because of poly trauma.
2) Yet I am not opposing primary and direct screw fixation in a patient with multiple
injuries, because this is a more modern treatment concept. Direct and
percutaneous lag screws for C2 have been used and also described previously
irrespective of the mode of image-guidance. So I advise not to stress so much the
„first report of“ aspect. The discussion around this subtopic (navigation etc.) can be
omitted/reduced.
Answer:
Thank you very much. I agree with your opinion. We omit “first report”.
3) The authors found an elegant way to treat this (bilateral tubes) and used the
correct equipment. No less no more. However, it also took them 1.5 hours to place
2 screws. It is a rule that minimally invasive access takes longer than the regular
way in spinal procedures. So at least they should discuss the fact the part of the
advantages were outweighed by a longer OR time, which is relevant in patients with
multiple injuries.
Answer:

4. Thank you for your message. In discussion, we described “Minimally invasive
surgery and osteosynthesis using lag screws were extremely beneficial for this
patient allowing her to achieve early rehabilitation and reducing her need for
nursing care”. I agree with your opinion. We also added sentence of “In this case, it
took 1.5 hours to place two screws, however recently shorter time from 40 to 60
min”.
Comments Regarding Format from the Editorial Office:
Image quality is to low. Please upload high res jpg or tif files (300dpi)
Answer:
Thank you. I will send high res tif file.

5. Points/Contents of the Revision
1)The name of the authors
Two authors indicated below were deleted.
Masao Tomioka, MD, orthopaedic surgeon
Masato Tanaka, MD, orthopaedic surgeon
2) Introduction
First paragraph, last sentence
“C2 to C3 (4)” was changed to “C2 to C3”.
Last sentence
We deleted the word of “first”.
3) Case report
1st paragraph, in the middle
We added sentence of “In this type injury, there were isolated hairline fractures of the ring
of the axis with minimal displacement of the body of C2 without C2/3 disc injury.”
4) Discussion
First paragraphs, last sentence
We added sentence of “In this case, it took 1.5 hours to place two screws, however
recently shorter time from 40 to 60 min.”
Second paragraphs, last sentence
We deleted “however, CT-based navigation requires anatomical registration, therefore, the
posterior surface of the axis would be totally exposed.”
We added sentence of “Navigation system helps us to insert screw by minimally invasive
surgery.”
Last paragraphs, last sentence
We added “Limitation of our percutaneous screw insertion technique was that the
reference arc was attached to the mobile arch of C2 without stable connection to the
vertebral body. Bilateral screw position should be carefully assessed by intra-operative 3D
fluoroscopy imaging, if there were hypermobility of the C2 arch.”

6. 5) Reference
Article No.3 was changed to another article.
3. Hakało J, Wroński J. Operative treatment of hangman's fractures of C2. Posterior direct
pars screw repair or anterior plate-cage stabilization? Neurol Neurochir Pol 42:28-36,
2008.
3. Taller S, Suchomel P, Lukás R, Beran J. CT-guided internal fixation of a hangman's
fracture. Eur Spine J 9:393-397, 2000.
Article No4. was changed to another article.
4. Moon MS, Moon JL, Moon YW, Sun DH, Choi WT. Traumatic spondylolisthesis of the
axis: 42 cases. Bull Hosp Jt Dis 60:61-66, 2001-2002.
4. Blondel B, Metellus P, Fuentes S, Dutertre G, Dufour H. Single anterior procedure for
stabilization of a three-part fracture of the axis (odontoid dens and hangman fracture):
case report. Spine 34:E255-257, 2009.
5) Abstract
3rd sentence
We deleted the word of “first”.