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5 Spinal Retractors
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a b
33
Fig. 5.5 Option for the lateral mini-open approach to the lumbar/thoracic spine: (a) table-anchored speculum-type retractor with counter-blade
(XLIF, NuVasive); (b) in situ (with permission from NuVasive Germany GmbH, Bremen, Germany)
abc d
Fig. 5.6 (a) Conventional lumbar monosegmental xation. (a) Two
Adson retractors (yellow arrows) provide the exposure by permanent
retraction. (b) Via a much smaller approach, the temporary retraction of
a part of the paravertebral muscles enables the insertion of the pedicle
awl. (c) The screw is inserted without any retraction device. (d) Slim
designed handheld muscle retractor
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L. Papavero
a
b
c
d
Fig. 5.7 (a) The uncommon design of the retractor aims to reduce the
skin incision and, at the same time, to maximize the retraction of the
muscle tissue in order to allow unobstructed introduction of pedicle
screws (SLR, Aesculap) (with permission from Aesculap AG,
Germany). (b) Following the percutaneous, transmuscular, uoroscopy-aided insertion of the pedicle screw, slim titanium blades are
docked into the screw head in order to retract the muscle and to allow
the insertion of the rod (Stryker, USA). (c) The Caspar-type retractor
has been developed in the 1970s and is still one of the most popular
retractors in spinal microsurgery (Aesculap AG, Germany). (d) The
miniaturized Caspar-type retractor (left) reduces the length of the skin
incision and the amount of muscle dissection and facilitates lateral uoroscopy because of the blades made of aluminum (Medicon eG,
Germany)
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References
1. Kobayashi Y, Kikuchi S, Konno S, et al. Increased intramuscular
pressure in lumbar paraspinal muscle and low back pain. Poster 101
at EuroSpine, 25–28 Oct 2007, Brussells; 2007.
2. Taylor H, McGregor A, Medhi-Zadeh S, etal. The impact of selfretaining retractors on the paraspinal muscles during posterior spinal surgery. Spine. 2002;27:2758–62.
3. Yokohama T. Release of the muscle retractors can reduce axial
symptoms after cervical laminoplasty. Poster presented at the 31st
annual meeting cervical spine research society, CSRS, 11–13 Dec
2003, Scottsdale; 2003.
4. Kotil K, Tunckale T, Tatar Z, etal. Serum creatine phosphokinase
activity and histological changes in the multidus muscle: a prospective randomized controlled comparative study of discectomy
with and without retraction. J Neurosurg Spine. 2007;6:121–5.
5. Datta G, Gnanalingham K, Peterson D, et al. Back pain and disability after lumbar laminectomy: is there a relationship to muscle
retraction? Neurosurgery. 2004;54:1413–20.
6. Stevens K, Spenciner D, Grifths K, etal. Comparison of minimally invasive and conventional open posterolateral lumbar fusion
using magnetic resonance imaging and retraction pressure studies.
J Spinal Disord Tech. 2006;19:77–86.
7. Brock M, Kunkel P, Papavero L. Lumbar microdiscectomy: subperiosteal vs. transmuscular approach and inuence on the early
postoperative analgesic consumption. Eur Spine J. 2008;17:518–22.
8. Hott JS, Henn JS, Sonntag VK. A new table-xed retractor for
anterior odontoid screw xation: technical note. J Neurosurg.
2003;98(Suppl 3):294–6.
9. Kieslich S. Anteriore cervikale Dekompression und Fusion: Der
Einuss von unterschiedlich kongurierten Retraktorvalven auf
die postoperative Dysphagie. Dissertation. Universitätsklinikum
Hamburg Eppendorf; 2015.
10. Fischer G, Saha S, Horwat J etal. Intra-operative ischemia sensing surgical instruments. Poster at complex medical engineering,
15–18 May 2005, Takamatsu; 2005.
Fluoroscopy andSpinal Navigation
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StefanKroppenstedt
6
6.1 Introduction and Core Messages
Standard uoroscopy is familiar to most spine surgeons because it provides real-time intraoperative
visualization of spinal anatomy. The major limitations
of uoroscopy are occupational radiation exposure and
the fact that the images can only be obtained in one
plane at a time. Image-guided spinal navigation has
evolved as a spinal surgical tool overcoming the limitations of standard uoroscopy. It has been proven to be
a versatile and effective tool for facilitating complex
surgical procedures. However, image guidance has its
limitations and does not replace the surgeon’s own
experience and judgment. There are several modalities
of spinal image guidance (such as CT-based,
uoroscopy- based, three-dimensional C-arm uoroscopy), and each has its own advantages and limitations. Pitfalls and errors are related to issues of the
accuracy, technique, and overall ease of use of the
technology during surgery. A thorough understanding
of these problems is required to ensure an effective use
of image-guided navigation for spinal surgery.
S. Kroppenstedt (*)
Department of Spinal Surgery, Center of Orthopedic Surgery, Sana
Hospital Sommerfeld, Kremmen, Germany
e-mail: s.kroppenstedt@sana-hu.de
6.2 Fluoroscopy
Fluoroscopy is an X-ray procedure that produces real-time
moving images of internal structures through the use of a
uoroscope. Standard uoroscopy is familiar to most spine
surgeons because it provides immediate intraoperative visualization of spinal anatomy. A modern surgical image intensier (also called C-arm because of its shape) consists of a
generator (radiation source), an image receiver (intensier
with camera), and a monitor unit (containing an image memory and processing unit) (Fig.6.1). Today, two monitors are
mandatory for surgical machines. The C-arm is xed on a
mobile stand in such a way that it can be moved and turned
to all sides (transverse and longitudinal to the patient, orbital
movement around the patient, rotation and adjustment of
height).
6.2.1 Radiation Protection
Besides the fact that the images can only be obtained in one
plane at a time, a further major limitation of uoroscopy is
occupational radiation exposure. Thus, radiation protection
is a very important issue. When using X-rays on a patient,
a differentiation is made between effective radiation and
scattered radiation. Part of the effective radiation is scattered by the patient’s body and leaves the body as lowerenergy scatter radiation in all directions. In order to protect
the user and the parts of the patient’s body not being
© Springer-Verlag GmbH Germany 2023
U. Vieweg, F. Grochulla (eds.), Manual of Spine Surgery, https://doi.org/10.1007/978-3-662-64062-3_6
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Fig. 6.1 Surgical image
intensier (C-arm) consisting
of a generator (a), an image
receiver (b), and a monitor
unit (c) (with permission of
Siemens)
S. Kroppenstedt
examined from this scattered radiation, the following rules
should be observed:
(a) Prevention of scattered radiation:
• Keep the radiation times as short as possible.
• Do not start radiation until the emitter and image
receiver system are correctly positioned. A laser light
visor makes it easier to position the machine without
radiation.
• Use pulse techniques for procedures with
movement.
• As far as possible, always work with the lowest dose
(half-dose program).
• Use the slot or iris diaphragm for gating because
the amount of scattered radiation is directly related
to the patient volume through which radiation has
passed.
(b) Protection from scattered radiation:
• Distance is the best radiation protection because radiation decreases by the square of the distance.
• Use radiation protection clothing.
• Cover those parts of the patient’s body which are not
being examined.
In addition, positioning the image receiver system as
close as possible to the patient’s body (Focal spot/skin distance is thereby enlarged.) does not only improve the physical image quality but also considerably reduce radiation
exposure for the patient [1].
6.3 Tips andTricks
• Check before every operation that the machine is fully
functional.
• After the patient has been positioned (before washing and
covering), ensure that a trouble-free use of the C-arm dur-
ing the operation will be possible.
• Everyone in the room must wear protective clothing.
• Prevent of and protect from scattered radiation.
• Store images with important interim results so that they
are available later on for documentation.
• Whenever an image has to be compared with another one,
transfer one image to the auxiliary monitor.
• After the operation, save/document the necessary
images.
6 Fluoroscopy andSpinal Navigation
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Fig. 6.2 Spinal navigational
system with camera (a) and
workstation monitor (b) (with
permission of Brainlab)
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6.4 Spinal Navigation
Using spinal navigation technology, a three-dimensional
model of the patient’s spine appears on a computer screen
with virtual representations of real surgical instruments
that the surgeons have in their hand. A variety of spinal
navigational systems are available on the market using different imaging modalities for navigation. The common
components of most of these systems include an imageprocessing computer workstation interfaced with two-camera optical localizer (Fig. 6.2); a dynamic reference base
(DRB), which is xed at the patient; and navigated instruments. The camera transmits and tracks infrared light,
which is continuously reected back to the camera by passive reectors attached to the DRB and the navigated
instruments (Fig. 6.3). Alternatively, the infrared light is
emitted by a series of LEDs mounted on the DRB and navigated instruments. The tracked infrared light is relayed to
the computer workstation. After registration process, the
computer workstation provides simultaneous, multiplanar
visualization of the spinal anatomy and allows virtually any
dedicated or manual calibrated surgical instrument to be
tracked in relation to the displayed anatomy in real time
(Fig. 6.4) [2]. At present, the various different imaging
modalities in use for spinal navigation include CT, uoroscopy, the combination of both (CT-uoro matching), and
three-dimensional uoroscopy [3, 4].
6.4.1 Preoperative CT-Based Image Guidance
CT-based navigation systems use a preoperatively acquired
CT data set, which has to be transferred to the computer
workstation. The computer reconstructs the data into
different views. Thus, preoperative surgical planning is possible. Intraoperatively, after surgical exposure, the image-
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Fig. 6.3 Reference frame
(a) attached to a spinous
process C2 and navigated drill
bit (b)
S. Kroppenstedt
guided procedure begins with the patient registration. The
DRB is attached rmly to the spine. The electrooptical camera tracks the spatial position of the patient by way of signals
from DRB.The surface of the vertebral level of interest is
touched/scanned with a registration probe (matching
Fig.6.5). This information allows the computer to create a
contour map of the vertebra, which is then automatically
mapped to CT data. Finally, the accuracy of the system needs
to be veried. The probe tip is placed on several anatomic
landmarks within the operative eld, and the computer workstation monitor displays the virtual probe. The positions of
the real and virtual probes had to correspond.
6.4.1.1 Advantages
• Preoperative surgical planning is possible.
• No occupational radiation exposure.
• Radiolucent table is not a must.
6.4.1.2 Disadvantages
• It requires a special CT protocol preoperatively.
• Registration process can be difcult and time-consuming.
• Because the CT images are acquired preoperatively with
the patient in a different position than at the time of sur-
gery, the preoperative data set may not reect the intraoperative anatomy on others and then the registered
level.
6.4.2 Fluoroscopy-Based Image Guidance
Fluoroscopy-based image guidance uses intraoperative
uoroscopic images gained with a C-arm on which a calibration target is attached or temporarily hold into the
beam. The images (at least one projection) are automatically transferred to the computer workstation for processing. The computer shows the saved uoroscopic images
that allow for the superimposition of the tracked surgical
instruments. In contrast to CT-based navigation, no manual registration (matching) is necessary. Software programs exist that can match a preoperative CT scan with
intraoperatively acquired uoroscopic data (CT-uoro
matching).
6.4.2.1 Advantages
• It provides real-time intraoperative visualization of the
spinal anatomy.
• It is suited for minimal access applications.
6 Fluoroscopy andSpinal Navigation
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Fig. 6.4 Workstation screen
demonstrating a trajectory for
the insertion of a C1–C2
transarticular screw (upper
screen) and a C5 facet screw
(lower screen)
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Fig. 6.5 Navigational
workstation screen
demonstrating a region
matching for C2 vertebra
S. Kroppenstedt
Fig. 6.6 Three-dimensional
C-arm uoroscopy. The
isocentric C-arm rotates
automatically 190deg around
the patient (with permission
of Siemens)
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6.4.2.2 Disadvantages
• It does not offer the axial images that are helpful during
CT-based navigation.
• Impaired image quality in certain areas of the spine like
the lower cervical or upper thoracic spine and under certain conditions like in patients who are obese and osteopenic or have spinal deformity.
6.4.3 Preoperative CT-Based Image
Guidance, Registered withFluoroscopy
(CT-Fluoro Matching)
The minimally invasive CT-uoro matching method uses two
intraoperatively acquired uoroscopy images to register a preoperatively acquired CT data set. For this registration, the level
of interest in the uoroscopy image and in the CT is fused by
the system after a manual prepositioning workow.
6.4.3.1 Advantages
• Minimally invasive registration
• Full CT image quality, three-dimensional reconstructions,
and axial views
• The three-dimensional C-arm provides three-dimensional
reconstructed views of the patient as currently positioned
on the operating room table.
• The surgeon-dependent registration step is eliminated.
• As many as three adjacent lumbar levels can be imaged
and navigated during each cycle.
• It offers the ability to obtain a postoperative scan while
still in the operating room.
6.4.4.2 Disadvantages
• High radiation exposure to the patient
• High initial costs
6.5 Indications
• The following spinal xation procedures are especially
useful:
– Upper cervical and cervicothoracic junction
– Deformities
– Less invasive/percutaneous approaches
• En bloc tumor resection
• Biopsy
6.6 Contraindications
6.4.3.2 Disadvantages
• Extra time for pre-positioning steps
• Final verication of the registration accuracy demanding
for minimally invasive cases
6.4.4 Three-Dimensional C-Arm Fluoroscopy-
Based Image Guidance
Three-dimensional C-arm uoroscopy uses a rotating
C-arm uoroscope tted with a calibration target. An isocentric C-arm is capable of obtaining multiple successive
images during an automated partial rotation around the
patient while maintaining the relevant spinal anatomy in
the center of the eld (Fig. 6.6). Specialized software
allows the uoroscopic images to be reconstructed into
axial, sagittal, and coronal views, and the unit can effectively function as a CT scanner.
6.4.4.1 Advantages
• It reduces X-ray exposure to surgical team.
• It is well suited for minimal access applications.
• Insufcient image quality.
• Verication of the system accuracy fails.
• Lack of experience in spinal navigation.
• Surgeon is not able to perform the surgical procedure
without navigation.
6.7 Technical Prerequisites
• Complete spinal navigation system
• Carbon table and carbon head clamp/xation (exception:
CT-based navigation)
6.8 Tips andTricks
• Put the monitor of the C-arm in an ergonomic position
directly next to the monitor of the workstation. The surgeon must be allowed to look at the monitors easily during the operation.
• Using (three-dimensional) C-arm: Before the operation,
check if images can be gained without artifacts, and position the camera to allow for unimpaired line of sight for
registration during scan.
• Using CT-based navigation: Check if preoperatively
acquired CT data can be used for navigation (e.g., no arti-
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