DOI:10.2214/AJR.05.0479
AJR 2007; 188:W181-W192
© American Roentgen Ray Society
CT-Guided Iliosacral Screw Placement: Technique and Clinical Experience
Robert L. Sciulli1,
Richard H. Daffner1,
Daniel T. Altman2,
Gregory T. Altman2 and
Jeffrey J. Sewecke2
1 Department of Diagnostic Radiology, Allegheny General Hospital, 320 E North
Ave., Pittsburgh, PA 15212-4772.
2 Department of Orthopaedic Surgery, Allegheny General Hospital, Pittsburgh, PA
15212.
Received March 24, 2005;
accepted after revision August 12, 2005.
Address correspondence to R. H. Daffner
(rhdaffner{at}netscape.net).
Presented at the 2005 annual meeting of the American Roentgen Ray Society,
New Orleans, LA.
WEB This is a Web exclusive article.
Abstract
OBJECTIVE. The purpose of this study was to describe the technique
of and experience in using CT guidance for percutaneous iliosacral screw
placement in patients with unstable pelvic fractures.
CONCLUSION. CT-guided iliosacral screw placement is a safe and
accurate procedure that can be performed by radiologists in a radiology
suite.
Keywords: interventional radiology • pelvic imaging • trauma
Introduction
Unstable pelvic fractures are the result of high-energy trauma.
Operative reduction and internal fixation with fluoroscopic guidance has
replaced open reduction and internal fixation as the standard management of
unstable posterior pelvic and sacral fractures
[1-4].
Unfortunately, this procedure may not always be feasible, particularly in the
care of patients who are morbidly obese, because of difficulties with accurate
identification of the positions of the sacral foramina. In 1987, Ebraheim and
colleagues [5] reported
preliminary results of the use of CT guidance to aid in percutaneous
stabilization of pelvic fractures in three patients. Since that time, this
technique has been described in many reports in the orthopedics literature
[6-11].
There have, however, been surprisingly few reports in the radiologic
literature
[12-14].
In 2002, we began performing CT-guided percutaneous iliosacral screw
placement at the request of orthopedic surgeons. The procedure can be
performed before or after placement of other surgical hardware on the pelvis
in the operating room. The purposes of this report are to describe the
technique, which we believe can be performed in any radiology department, and
to detail our clinical experience.
Materials and Methods
Between November 2002 and March 2005, 23 patients with severe pelvic trauma
underwent placement of iliosacral screws under CT guidance. Indications for
treatment included posterior pelvic instability, morbid obesity that precluded
safe percutaneous fluoroscopically guided screw placement, and lack of
sufficient clarity for defining the posterior structures in the operating
room. Thirteen of the patients were men and boys, and 10 were women and girls.
The age range was 13-69 years. All patients weighed more than 230 lb (104 kg).
Four of the patients underwent placement of two screws, and one patient,
placement of three screws. We used the Young-Burgess classification method to
determine the type of injury
[15]. There were 12
anteroposterior compression injuries, nine lateral compression injuries, and
two vertical shear injuries.
Patient selection was made solely by the referring orthopedic surgeons, who
decided which patients could safely undergo surgical reduction in the
operating room under fluoroscopic guidance, which patients needed additional
fixation (such as transpubic plating), and which patients needed CT guidance.
In 21 of the patients, CT guidance was chosen for the advantages it offered in
accurate screw placement over C-arm fluoroscopic guidance. In each case, the
patients were morbidly obese, and the sacral foramina could not be adequately
visualized with fluoroscopy.
One patient with severe unstable injuries needed external fixation in the
operating room before referral for CT-guided screw placement. This patient
also underwent placement of a transpubic plate and screws to stabilize the
pubic symphysis. Two additional patients underwent placement of transpubic
hardware before CT-guided iliosacral stabilization. One patient underwent
fluoroscopically guided placement of bilateral screws in the operating room
and was referred for CT-guided placement after one of the screws was found to
have penetrated the anterior cortex of the sacrum and did not provide
stabilization. The other 19 patients were referred because morbid obesity
precluded safe and accurate placement of iliosacral screws under fluoroscopic
guidance.
Our procedure team includes a musculoskeletal radiologist, who is also
board certified in orthopedic surgery by previous training; a musculoskeletal
fellow; an orthopedics resident; a scrub nurse; a circulating nurse from the
interventional radiology division; and an anesthesiologist. The referring
attending orthopedic surgeon may also be present. All procedures were
performed in the diagnostic radiology department on a 4-MDCT scanner (Somatom
Plus, Siemens Medical Solutions). The CT suite in which these procedures are
performed is considered a clean room and is used solely for aspiration,
biopsy, radiofrequency ablation of tumors, and surgical screw placement, all
under CT guidance.
Twenty-one of the patients underwent the procedure under general
anesthesia. In two patients, the procedure was performed with conscious
sedation and local anesthesia. Patients were placed in either the lateral or
the posterior oblique position (Fig.
1). After administration of anesthesia, an opaque catheter marker
was placed on the skin for reference, and a digital scout image was obtained
to determine scanning levels. The catheter was used to mark a known reference
point on the skin and was visualized on all subsequent scans of the patient.
Site selection was based on the three principles surgeons used for
fluoroscopically guided screw placement: location of best bone purchase,
safest anatomic location, and screw placement perpendicular to the S1 and S2
pedicles [6,
9].
Once the levels of the scan were determined, 2-mm slices were obtained, and
the entry point was selected with the catheter on the skin as a guide. The
exact entry point was marked on the skin with a laser localizer for level of
scan. The entry points were the same whether the procedure was performed for
pure sacroiliac dislocation, sacral fracture with instability, or combined
iliac bone fracture and sacroiliac instability. Three measurements were
obtained from the entry point. The first was the angle of approach measured
from the horizontal. The second was the depth of soft tissue to be penetrated
from the skin surface to the posterior aspect of the iliac bone. The third
measurement was the distance from the outer surface of the iliac bone to the
desired depth of penetration of the surgical screw (Fig.
2A,
2B). All measurements were
obtained directly from the CT monitor.
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Fig. 3 —Photograph shows basic equipment. Top to bottom, surgical power
drill, cannulated (hollow) screwdriver, depth measurer (not used), cannulated
drill bit, cannulated screw with washer, trocar in screw, trocar.
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Although a full surgical tray was provided, the number of instruments used
was relatively small. Instruments used were a solid trocar, a drill bit with a
cannulated (hollow) center and a threaded end, cannulated self-drilling and
tapping screws (Synthes) and washers, a special screwdriver that fit over the
trocar, and a surgical drill (Fig.
3). The trocar, drill bit, and screwdriver were of sufficient
length to ensure secure purchase and control in obese patients. A sterile wire
cutter was included in the surgical pack in the event that the trocar was too
long and impinged on the gantry of the CT scanner.
The skin was prepared with an iodine-based cleaning solution and surgical
drapes with adhesive-backed protectors. The entry point was marked on the skin
with a sterile pen, and an incision of approximately 1 cm was made. The wound
was deepened with a surgical clamp to facilitate passing the trocar, screw,
and washer. The trocar was inserted and advanced until it contacted bone
(Fig. 4). At that point, CT
images were obtained to check the trajectory of the trocar and the location of
the tip.
Once the desired position was obtained, the hollow drill bit was attached
to the drill and placed over the trocar. A small pilot hole was drilled
through the iliac bone into the sacrum (Fig.
5A,
5B). Additional CT images were
obtained to ensure that the desired trajectory was maintained. Once the
desired depth of the pilot hole was reached, the trocar was advanced through
the pilot hole into the sacrum.
After removal of the drill bit, the hollow self-tapping screw with a washer
attached was placed over the trocar and advanced with the hand-operated
screwdriver (Fig. 6). These
screws were 6-8 mm long, depending on the manufacturer. We used the
widest-diameter screw for safe placement into the sacrum and avoidance of the
foramina. The length of the screw was determined by direct measurement of the
distance from the outer cortex of the iliac bone to the desired depth (usually
the center of the sacrum). The progress of the screw was monitored with CT
(Fig. 7A,
7B,
7C). The number of screws used
was determined in consultation with the attending orthopedist. If the degree
of instability was severe, a second screw was used, provided it could be
placed safely. Once the screw was secured, the wound was irrigated with
antibiotic solution and was closed with surgical staples. If the attending
orthopedist considered it necessary to stabilize the opposite side, the
patient was turned and the procedure repeated. Before a patient was removed
from the CT table, a final scan was obtained. Coronal tomographic
reconstruction served as an additional plane for determining that a screw was
properly placed. Radiographs also can be used for this purpose.
Results
The average time for screw placement in this study was 80 minutes. Time was
measured from the moment at which the patient was placed on the CT table to
the moment at which the patient was ready for removal from the table and
included the time for induction of general anesthesia. The most time-consuming
part of the procedure was acquisition of multiple test images to ensure proper
screw placement. In 20 patients, the procedures were performed without major
adjustments in entry point or trajectory for instrumentation (Figs.
8A,
8B,
8C and
9A,
9B,
9C,
9D). Three patients needed a
considerable change in entry point for proper screw location (Fig.
10A,
10B,
10C). One patient had
undergone previous placement of bilateral iliosacral screws in the operating
room under fluoroscopic guidance. At the same time, he had also undergone
placement of a surgical plate and screws across an unstable pubic symphysis. A
postoperative CT scan revealed that the left screw had not made purchase into
the sacrum and lay anterior to the sacrum with its tip in the L5 disk space.
The errant screw was removed percutaneously under CT guidance in the radiology
department, and two screws were placed correctly in the sacrum (Fig.
11A,
11B,
11C,
11D).
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Fig. 9A —Lateral compression injury. Radiograph shows fractures of left
superior and inferior pubic arches and body of right pubic bone. Disruption
(asterisk) of left sacral arcuate lines is evident.
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Fig. 11D —Misplaced screw that had been inserted under fluoroscopic guidance
in operating room. Radiograph shows three iliosacral screws. Patient had
undergone stabilization of pubic symphysis with surgical plate and screws at
same time iliosacral screws were placed in operating room.
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There were only two complications of the procedure. In an extremely obese
patient, the initial screw, which had been placed with CT guidance and was
thought to be of adequate length, was too short and backed away from the iliac
bone (Fig. 12A,
12B,
12C). The patient was brought
back to the CT suite for percutaneous removal of this screw and placement of a
longer screw. A second screw was inserted at the same time. We are uncertain
why this screw placement failed, because the initial length was deemed
appropriate. It is possible that improper patient movement may have prompted
the screw to lose its position. The second complication occurred in a patient
with a severely comminuted and highly unstable fracture of the iliac bone. The
initial screw placement was successful (Fig.
13A,
13B,
13C,
13D), but sacroiliac
separation occurred because the entry point of the screw went through a
fragment of iliac bone instead of the main body of the bone. The patient was
brought back to the CT suite, where the first screw was removed and a longer
one placed. In addition, a second screw was placed on the same side, and a
third screw was placed on the opposite side. There were no other
complications.
Because we used a 1-cm incision, blood loss was minimal—in most
instances less than 30 mL. All patients went from the diagnostic radiology
department to the trauma intensive care unit instead of to the general
recovery room. Clinical and radiologic follow-up (up to 30 months) of all
patients except the two who underwent the most recent procedures showed that
all pelvic injuries had healed satisfactorily without complications. The other
two patients were clinically well and undergoing physical rehabilitation. Two
patients continued to have difficulty walking as the result of lower limb
fractures that occurred at the time of the pelvic injury.
Discussion
Imaging-guided screw placement has replaced open reduction and internal
fixation in the treatment of patients with unstable pelvic fractures
[1-4].
A number of imaging techniques have been used to aid the surgeon in the
operative repair of unstable injuries of the posterior pelvis. These
techniques include fluoroscopy
[1-4],
sonography [16], and CT
[5-10,
12,
14]. Although most of the
early reports described small series of patients, all emphasized a number of
common points. First, use of fluoroscopy for guidance made it extremely
difficult to define the posterior structures of the pelvis. A critical
determination in this regard was the location of the sacral foramina, through
which the sacral nerves travel. This problem is compounded in extremely obese
patients. Another common feature in previous reports was the relative lack of
complications associated with a CT-guided procedure. Complications from
conventional surgical exposure and screw placement have been reported to have
mortality rates as high as 10% and morbidity rates as high as 52%
[17,
18]. Nelson and Duwelius
[12] reported that open
reduction and internal fixation were associated with a high incidence of
paresthesia in the ipsilateral extremity, gait disturbances, lower back pain,
and neurologic abnormalities from nerve damage. As of this writing, Ziran and
colleagues [10], of the
universities of Pittsburgh and Colorado, had reported on the largest series of
CT-guided iliosacral fixation. Their group of 66 patients underwent placement
of 113 screws. The only significant complication was fracture of a screw and
5-mm displacement in a noncompliant patient who began immediate weight
bearing. There were no other significant complications.
The pitfalls of CT-guided screw placement relate mostly to patient size.
Patients weighing more than 400 lb (181 kg) exceed the weight limits of our CT
scanner. Extremely obese patients also may come in contact with the gantry of
the scanner, making it impossible to keep a sterile operative field.
Furthermore, in the cases of several large patients, we have had to cut the
trocars to prevent them from touching the sides of the gantry. For this
purpose, we keep a sterile wire-cutting tool on hand for shortening the trocar
when necessary.
Patients with external fixators can pose an additional challenge. We
performed CT-guided screw placement on only one such patient, and we needed to
temporarily release the tension on the fixator immediately before screw
placement. This step was necessary to ensure that proper closure of the
sacroiliac joint was achieved. Once the screw was placed, tension on the
fixator was reapplied. In this patient, manipulation of the external fixator
was performed by the attending orthopedist. Radiologists never remove fixators
or release the tension on them. If the anchoring bars on the fixator appear to
impinge on the sides of the CT gantry, the surgeon removes them. We have not
encountered a patient in whom the fixation pins themselves impinged on the
gantry.
Contraindications to CT-guided iliosacral screw placement are the same as
those for open reduction and internal fixation and fluoroscopically guided
placement: hemodynamic or severe cardiopulmonary instability, local infection
or skin breakdown, and severe soft-tissue damage at the insertion site.
We analyzed the various components of CT-guided iliosacral screw placement
to answer questions about cost-effectiveness. In a standard fluoroscopically
guided procedure, billing includes the operating room, anesthesia, surgeon and
assistants, nurses, and recovery room. A CT-guided procedure performed in the
diagnostic radiology department includes the cost of the radiology suite,
anesthesia, radiologists, orthopedic assistant, and nurses. When an attending
orthopedic surgeon is present, a modifier in the billing code allows sharing
of a percentage of the fee. Because one of our patients had undergone
placement of a single screw in the operating room and placement of a second
screw with CT guidance, we compared the charges for the two procedures. The
total cost for the operating room procedure was $18,246, and that for the
CT-guided procedure was $8,121 (Table
1). The operating room is one of the highest-priced facilities in
any hospital. Charges are based on total time of occupancy by the patient.
Anesthesia costs also are billed on the basis of time. After most procedures
performed in an operating room at our institution, patients are taken to the
recovery room, another expensive facility. Patients who underwent screw
placement under CT guidance went immediately to the less-expensive trauma
intensive care unit for postoperative monitoring.
Fluoroscopically guided screw placement in the operating room by
experienced trauma orthopedists takes 20 minutes to 1 hour. In most instances,
however, additional surgery may be performed, such as placement of a
transpubic plate and screws and reduction and internal fixation of acetabular
fractures. The average time of 80 minutes for the CT-guided procedure reflects
the time needed to obtain multiple axial images to check accuracy of screw
placement. It also includes the time for induction of anesthesia. Ziran et al.
[10] reported their average
time was 26 minutes, but they did not state the beginning and ending points of
time measurement. Even so, we still believe the CT-guided procedure is
cost-effective.
In summary, CT-guided placement of iliosacral screws is an accurate method
for reducing unstable posterior pelvic injuries. The complication rate is low,
and the procedure is cost-effective.
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Abstract
Introduction
