Keywords fluoroscopy - surgical diagnostic techniques - percutaneous discectomy - spine - diagnostic
imaging
Palavras-chave fluoroscopia - técnicas de diagnóstico por cirurgia - discotomia percutânea - coluna
vertebral - diagnóstico por imagem
Introduction
The Scottish Terrier, also called the "Scottie" or "Scotty", is a small breed of dog
known for its distinct shape, which is similar in format to vertebrae when visualized
via x-ray at an oblique incidence ([Fig. 1 ]). At 45 degrees, it is possible to clearly see the dog's body parts corresponding
to the pars interarticularis (neck), the transverse process (the Scotty dog's nose), the pedicle (eye), the superior
(ear) and lower facet joint (leg).[1 ]
[2 ] The oblique incidence is used to achieve an image resembling the Scotty Dog in interventional
treatments for back pain, such as radio and transforaminal blocks[2 ]
[3 ], since needle insertion is safer when viewing the pedicle completely. This type
of visualization is also commonly used only for non-surgical procedures.
Fig. 1 Classic profile of the Scotty Dog outlined on an oblique view radiograph.
Minimally invasive surgery is increasingly replacing open surgery in all the medical
specialties. The same holds true for spinal surgery, where percutaneous trans-pedicular
fixation has been increasingly used in cases of degenerative diseases, fractures,
or deformities.[4 ]
[5 ]
[6 ]
[7 ] Traditional methods (fluoroscopic images in anterior-posterior and profile incidences),
on the other hand, hinder the visualization of the pedicle in all its extension, which
makes medialized insertion of screws difficult.[8 ]
[9 ] Fluoroscopy in anterior-posterior (AP) view promotes a two-dimensional image, in
which the medial part of the pedicle overlaps with part of the spinal canal. This
is called the lateral recess ([Fig. 2 ]). Thus, it is difficult to verify that the screw has reached beyond the confines
of the pedicle, invading the spinal canal, and placing structures at risk, such as
the dural sac medially, nerve roots above and below, as well as vascular structures
in the anterolateral area.
Fig. 2 Lumbar spine in surgical view (left), with no precision of pedicle borders. Lumbar
spine in oblique surgical view (right), with precision of pedicle borders for screw
insertion. Red curves show medial and foraminal borders of the pedicle.
When performing minimally invasive surgery, surgeons need to compensate for the lack
of direct visualization of the structures; thus, they deal with the problem using
resources such as neuronavigation[8 ], electromyography[10 ], or intraoperative neurophysiological monitoring[4 ], whereby a neurologist supervises the procedure and alerts as to whether nerve structures
have been affected (nerve roots). It important to note, however, that costs of minimally
invasive surgery become higher once these resources are added.
The visualization of the pedicle in blocking or radiofrequency procedures is usually
made easier with oblique positioning of the fluoroscope. Starting in 2011, we began
using the so-called Scotty Dog technique to better view the pedicle in its full extent and insert screws percutaneously
in surgical arthrodesis with greater ease. With experience, this treatment allowed
the application of the imaging monitoring method in percutaneous surgery as well,
favoring the onset of this study.
The aim of this study is to describe a series of cases in which percutaneous pedicle
screws were placed using the fluoroscopic monitoring technique known as Scotty Dog , and to verify the safety of this technique, by the ratio of canal and foramen invasion
by screws.
Materials and Methods
The present study is an analysis of a case series of all patients consecutively operated
on in the Hospital Especializado de Ribeirão Preto, between August 2011 and August
2012, by the same surgeon (ASG). The surgeries were indicated for spondylolisthesis,
lumbar canal stenosis, disc herniation, and fractures. All the patients underwent
surgery using the Scotty Dog fluoroscopic monitoring technique, as described below.
All patients were treated under private payment or medical insurance. They were informed
about the surgical method and were verbally informed that surgery would be accompanied
by fluoroscopy using an incidence that was different from the usual to facilitate
visualization of the pedicle and for a safer screw insertion. All agreed to the procedure.
All patients underwent postoperative computed tomography (CT) with bone window and
three-dimensional reconstruction. We only included patients who were consecutively
operated on in the same hospital by the same surgeon using a standard technique, as
described below, with no age limit for inclusion in the study. We excluded patients
without CT examination postoperatively.
We investigated and recorded patientś age at surgery, gender, duration of surgery,
incidence of bleeding, need for blood transfusion, and hospitalization in the intensive
care unit (ICU), as well as complications, such as infections and injuries to nervous
structures.
The Scotty Dog Monitoring Technique
The Scotty Dog Monitoring Technique
The patient is in the prone position. However, unlike the percutaneous surgical procedure
commonly performed, instead of positioning the fluoroscope for anterior-posterior
incidences, the Scotty Dog image technique is obtained on oblique incidence until adequate visualization of
the figure of the Scotty Dog, delimiting the expected structures (transverse process,
pedicle, upper and lower articular facets, foramen, and lateral recess), as shown
in [Fig. 3 ].
Fig. 3 Fluoroscope C-arm positioned in the traditional anterior-posterior incidence (above)
and in oblique incidence, as in the new technique (below), schematic illustration
of the visualization and the obtained images with each.
In the case of pedicular instrumentation following a discectomy or decompression of
the spinal canal, in other words, any intervention in the surgical act that requires
prior incision, percutaneous placement of the screws is performed using the same incision.
When there is no need for a previous incision, such as simple spine instrumentation
in fractures, we use small incisions (of approximately 4 mm) in the sites for each
screw placement.
The next step is the drilling of the pedicle using the Scotty Dog fluoroscopic technique.
Specific material for spinal percutaneous instrumentation (the Jamshidi needle) is
necessary. After the initial perforation (guided by the oblique image), we check the
depth of the needle in the profile image. When the anterior third of the vertebra
is reached, we remove the central portion of the needle, which is cannulated for the
passage of the guide wire. Checking again the position of the guide wire in the profile
imaging, we remove the outer needle. At this time, we insert the cannulated pedicle
screw, using specific instruments. After placing the desired number of screws, we
proceed with mounting the system, as shown in [Fig. 4 ]. Finalizing the surgery, we pass the rod through the hole and nuts are tightened
([Fig. 4 ]), with contraction or distraction of the system.
Fig. 4 Mounting of the system with pedicle screw insertion.
Results
During the study period, 42 patients were admitted for percutaneous procedures in
the spine with no sample losses. Among these, 21 (50%) were women. The average age
was 64.5 years (range: 39-82 years). Indications for surgery were disc herniation
correction in the majority (54.8%) cases, as described in [Table 1 ]. In all patients, percutaneous instrumentation was used, mostly at L4-L5, as shown
in [Table 2 ].
Table 1
Distribution of surgery indications
Indication
n
%
Disc herniation
23
54.8
Lumbar canal stenosis
8
19.0
Spondylolisthesis
6
14.3
Fracture in L1
3
7.1
Fracture in T12
1
2.4
Fracture in T8
1
2.4
Total
42
100.0
Table 2
Distribution of procedures in the sample
Procedure
n
%
Arthrodesis L2-L3 + decompression
1
2.4
Arthrodesis L3-L4 + L4-L5 + L5-S1, TLIF
2
4.8
Arthrodesis L3-L4, TLIF
2
4.8
Arthrodesis L4-L5
1
2.4
Arthrodesis L4-L5 + decompression + TLIF
12
28.6
Arthrodesis L4-L5 + L5-S1, TLIF
7
16.7
Arthrodesis L4-L5-S1 + decompression
3
7.1
Arthrodesis L5-S1 + decompression + TLIF
6
14.3
Arthrodesis L5-S1, TLIF
4
9.5
Arthrodesis T11-L1-L2
3
7.1
Arthrodesis T7-T8-T9
1
2.4
Total
42
100.0
Abbreviation: TLIF, transforaminal lumbar interbody fusion.
It was possible to view the entire pedicle in all patients, and there was no case
of invasion of the spinal canal or foramen ([Fig. 5 ]). Surgical time was on average 98 minutes, ranging from 40 to 182 minutes.
Fig. 5 Axial computed tomography cut of lumbar-sacral spine, showing the correct positioning
of screws after surgery with the Scotty Dog technique of fluoroscope monitoring.
There were no cases of bleeding and no need for blood transfusion or hospitalization
in the ICU. In one patient aged 66 years, operated for disc herniation correction,
there was wound infection, which was treated with antibiotic therapy and resolved
well.
All patients recovered well and were discharged in three days postoperatively, with
advice to rest, alternating with light walking for a period of 30 days, until returning
for consultation. The minimum postoperative follow-up was 19 months, reaching 28 months,
with an average of 22.5 months of follow-up in this sample, with no late complications
observed.
Discussion
Since it was first described in 1982 by Harms and Rollinger, the open transforaminal
lumbar interbody fusion (TLIF) has eased the pain of many patients worldwide.[11 ] Later, minimally invasive surgery emerged and has been contributing in avoiding
larger wounds, muscle dissection, and retraction requiring open surgery, with reduced
pain, improved quality of life, shorter hospital stay, and less use of analgesics
postoperatively.[12 ] However, literature reviews have not shown lower complication rates comparing the
open and minimally invasive surgeries.[13 ]
[14 ] Complications, which vary widely, are also not always described in detail in the
studies.[15 ]
[16 ]
For any surgical technique, there is a learning curve for the development of technical
skills. In the case of spinal surgery, the first requirement is a thorough knowledge
of the anatomy of the spine in three dimensions. In contrast to the open procedures,
in which the anatomy can be viewed directly, minimally invasive surgery visualization
is usually limited to the area of surgical interest and to certain important anatomical
landmarks within this limited view.[17 ] Familiarity with the anatomy allows the surgeon to perform the procedure safely
without exposing structures that are not being treated or that cannot be reached,
such as the foramen.
In the case of minimally invasive surgery to treat spinal decompression, arthrodesis,
stenosis, and others, the use of a fluoroscope (1-2 minutes of exposure approximately)
is required, exposing both patient and surgeon to radiation[18 ]
[19 ], without solving the problem of lack of visualization of the pedicle. The difficulty
starts with the exposure and identification of the entry point for the screw on the
facet joint. Further complicated by the fact that the path may vary according to the
characteristics of the pedicle bone, which varies for each individual, according to
the insertion technique.[8 ] Obesity, for example, makes the visualization of structures by fluoroscopy harder,
and obese patients bleed more often, disrupting the vision of the structures in the
operative field.[8 ]
Song and Park[20 ] state that "while the surgical corridor afforded by the tubular retraction system
causes less tissue destruction than open approaches" in the minimally invasive techniques,
"the narrow and typically deep working channel can also make primary repair of a technically
difficult iatrogenic durotomy when using conventional suture and knot-tying techniques".
The authors conducted a study precisely on the closure of inadvertent durotomies during
minimally invasive surgery of the spine.
In our literature search ([Table 3 ]),[8 ]
[9 ]
[10 ]
[12 ]
[21 ]
[22 ]
[23 ]
[24 ]
[25 ]
[26 ]
[27 ]
[28 ]
[29 ]
[30 ]
[31 ]
[32 ]
[33 ]
[34 ]
[35 ] attempting to verify the incidence of invasion of the channel using traditional
techniques of percutaneous and open surgery, we found that the canal invasion rate
can vary from 0 to 49% of treated patients or from 2.3% to 11.3% of inserted screws.
Thus, it is difficult to establish the prevalence of invasion, as the studies use
different criteria for recording cases and many do not describe the number of patients
for which the problem occurred, only the number of screws or vice-versa. Some studies
use navigation techniques, whereas others just use the fluoroscopy guide; there is
not a standard imaging incidence or technique in all cases, making it difficult to
obtain homogeneous results. Feared by surgeons, the complication "foramen invasion"
is rarely described in the studies. It probably gets hidden in rates ranging from
0% to 33% of complications in minimally invasive surgery and 1.6% to 16% in open surgery,[14 ] and it is not possible to determine when "complication" means bleeding, infection
or foraminal invasion. Usually, it is described as dural tear and, more rarely, it
is reported as cases of screw malposition (but without objective criteria for good
or bad positioning characterization). Some studies specifically describe the malposition
of screws as cortical or in the foramen, and as inframedial, medial, or supramedial.[8 ] Others measure the size of the invasion, considering it severe when over 4 mm.[9 ]
Table 3
Prevalence of durotomy or canal invasion in different studies
Reference
n
Open surgery
TLIF
Notes
n[* ] (%)
Adogwa et al[12 ]
30
15
15
0
Bindal et al[10 ]
25
25
electroneuromyography; 105 screws placed
3 (12%)
Gu et al[21 ]
20
20
osteoporotic fractures, fluoroscopic guide
2 (10%)
Kelleher et al[22 ]
75
75
9 (12%)
Kim et al[8 ]
110
110
488 screws, one surgeon
54 (49%)
Lee et al[23 ]
58
1 (1.7%)
Logroscino et al[24 ]
20
80 screws
1 (5%)
Lotfinia et al[9 ]
53
247 screws
28 screws (11.3% screws)
Lucio et al[25 ]
210
101
109
complications not described
(only more frequent in the open surgery group)
ND
O'Toole et al[26 ]
1274
1274
complications other than infections not described
Park, Ha[27 ]
61
29
32
only one case of malpositioning
0
Peng et al[28 ]
29
29
only infections described
(higher rate in the open surgery group)
Shunwu et al[29 ]
62
30
32
only two cases of malpositioning
Siemionow et al[30 ]
104
104
1 (0.96%)
Sugimoto et al[19 ]
49
128 screws by fluoroscopic guidance
3 screws (2.3% screws)
Wang et al[32 ]
4.7% and 4.6% of dura rupture with TLIF and open surgery
Wang et al[33 ]
52
27
25
only revision surgeries
5 and 3 cases in each group (18.5% and 12%)
Wu et al[34 ]
151
7 (4.6%)
Yang et al[35 ]
21
7 screws reached the cortex
ND
Abbreviations: ND, not described; TLIF, transforaminal lumbar interbody fusion.
* rate of rupture of the pedicle or invasion of the dura or leakage of cement to the
canal.
In 2013, Tian et al[15 ] published a meta-analysis trying to compare minimally invasive to open surgery according
to many different outcomes. The authors reported that the definition of complications
was different between studies, which may have hampered the analysis. Of the 11 included
studies, data on complications were available in 10, and the overall rate was similar
between the two groups, involving screws, prosthesis, or bone graft malpositioning,
prosthesis migration, rupture of the dura, and infection. There was a higher rate
of graft malposition and arthrodesis failure in the group undergoing minimally invasive
surgery, but a higher rate of rupture of the dura and infection in the open surgery
group, without significant difference between the groups. The rate of dura invasion
ranged from 0.6% to 15.3%.
The visualization technique that we call Scotty Dog is simple, practical, and available
in any operating room with fluoroscopy. It has helped us to visualize the pedicle
along its entire length and we have not registered any case of invasion foramen using
this new way of positioning the fluoroscope. We suggest the conduction of controlled
clinical studies, with accurate description of outcomes, to compare the results with
the traditional positioning of the fluoroscope and the Scotty Dog.
A Scotty Dog imaging monitoring technique in spine surgery facilitates the visualization
of the entire vertebral pedicle, allowing the insertion of screws safely, without
invasion of the canal or foramen, as shown in this series.
