Rhee_Ch030.indd

C H A P T E R 30

Sacropelvic Fixation Techniques

Floreana A. Naef and Khaled M. Kebaish

DEFINITION

■ Numerous critical structures—including the internal iliac artery and vein, middle sacral artery and vein, sympa- thetic chain, lumbosacral trunk, and sigmoid colon—lie directly on the sacrum at some point and could potentially be injured by the instrumentation used in sacropelvic fu- sions ( FIG 2 ). 19 ■ The ilium is the most superior of the three bones that make up the os coxa. ■ In adolescents, the ilium is connected to the pubis and the ischium through the triradiate cartilage. Fusion of this car- tilage completes between 13 and 16 years of age in most patients. ■ In thin patients, the posterior superior iliac spine (PSIS) is marked by an overlying dimple in the skin. A transverse line drawn between these two dimples crosses the sacrum at the level of S2. ■ The structures of the greater sciatic foramen are at risk of damage during instrumentation of the pelvis. 11

■ Sacropelvic fixation is a term used to describe instrumenta- tion into the sacrum and pelvis. ■ The most common indication is a long spinal fusion to the sacrum. Other indications include high-grade spondylolis- thesis, flat back syndrome requiring corrective osteotomy, and correction of pelvic obliquity. ■ The purpose is to provide secure distal fixation points that resist the strong flexion moments and cantilever forces pres- ent at the lumbosacral junction. ■ Multiple techniques are used, including the Galveston rod, the iliac screws, and the S2 alar iliac (S2AI) technique.

The Ilium

ANATOMY

■ A clear understanding of the anatomy of the sacrum and pelvis is crucial to the safe and accurate placement of sacral and pelvic instrumentation. Familiarity with the anatomy of the sacrum, ilium, and sacroiliac (SI) joint is of particular importance.

The Sacrum

■ The sacrum lies at the junction between the mobile and fixed portions of the spine and functions as a keystone that unites the two hemipelvises. ■ The sacral vertebrae are fused, and the transverse processes merge into the expanded lateral sacral ala. ■ The majority of the bone in the sacrum has a cancellous osseous structure. 26 The trabecular density is greatest in the pedicle and body of the vertebrae and least in the sacral ala. 26 Therefore, sacral pedicle screws are best directed toward the midline. 20 ■ The sacrum does not contain a true pedicle, but rather, a con- fluence of cancellous bone between the sacral body and the ala. Compared to pedicles in the mobile spine, this area is ca- pacious. The S1 pedicle has a mean length of 46.9 3.3 mm in women and 49.7 3.7 mm in men and is angled roughly 40 degrees from the midline ( FIG 1 ). 29

Internal iliac artery and vein

Obturator n.

Colon

FIG 1 ● Cross-section of sacrum. The bone density is greatest in the pedicle and body of the vertebrae ( A ) and lowest in the ala ( B ). Arrow marks the location of S1 pedicle.

FIG 2 ● Important anatomic structures overlying the sacrum.

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Supraspinous ligament

Ventral sacroiliac ligament

Greater sciatic notch

Iliac fossa

Anterior superior iliac spine

Dorsal sacroiliac ligament

Acetabulum

Sacrotuberous ligament

Obturator foramen

Ischial tuberosity Pubis symphysis

Anterior inferior iliac spine

Lesser sciatic notch

Sacrospinous ligament

FIG 3 ● Ligamentous support and bony anatomy of the pelvis.

The Sacroiliac Joint

and torsional forces from the spine above. These forces cause motion at the junction that may increase the risk of pseudarthrosis. 4,7 ■ Furthermore, the density of bone in the sacrum is poor, and obtaining adequate fixation is a particular challenge. 10 ■ McCord et al 18 introduced the concept of the lumbosacral pivot point ( FIG 4 ), which is defined as the middle of the os- teoligamentous column at the junction between L5 and S1. ■ The farther that the pelvic implant progresses anterior to this point, the more stable the construct. Furthermore, in- strumentation that crosses the SI joint is not effective unless it passes anterior to this pivot point. 18 ■ O’Brien et al 24 introduced the concept of three zones of sa- cropelvic fixation ( FIG 5 ). Fixation in zone 3 has the highest biomechanical strength and allows placement of the instru- mentation farthest anterior to the pivot point.

■ The SI joint is an L-shaped synovial joint with an irregularly contoured surface that interlocks in order to resist move- ment. The joint functions to transfer axial load from the torso onto the hemipelvises. ■ The joint is stabilized by the anterior SI ligament, interosse- ous SI ligament, and the posterior SI ligament ( FIG 3 ). ■ Fusions across the lumbosacral junction are a particular challenge for spine surgeons and this location has a high incidence of pseudarthrosis. 11 ■ Substantial biomechanical forces are concentrated at the lumbosacral junction. The fusion mass above the sacrum acts as a long lever arm that transmits flexion, extension, BIOMECHANICS

Pivot point

S2 screw

S1 screw

Iliac screws

Axis of M.C.

Pivot point

Lever arm

S1 pedicle screw

S2 pedicle screw

B

Iliac screw

A

FIG 4 ● Lumbosacral pivot point. Lateral ( A ) and axial ( B ) views of the pivot point.

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Operative Techniques in Spine Surgery

■ Correction of pelvic obliquity

■ Pelvic obliquity is common in patients with neuromuscular deformities. ■ Correction of the coronal misalignment frequently re- quires pelvic fixation. 9 ■ Other disorders ■ Less common indications include sacrectomy performed for sacral tumors, sacral fracture, and for osteoporosis in the presence of lumbosacral fusion. 20 ■ Although many techniques exist for sacropelvic fixation, only three are currently in widespread use, 11 and we will focus only on those three: the Galveston L-rod technique, 2 the iliac screw technique, 15 and the S2AI technique. 5,23 ■ A C-arm should be available for intraoperative imaging if necessary. ■ Planning the extent and type of procedure to be performed requires a thorough understanding of the anatomy of the patient’s deformity. ■ Patients with significant pelvic obliquity may have significant differences between the two sides of the pelvis, and the tra- jectory of the anchors may need to be modified accordingly. ■ Patients with significant osteoporosis may require larger size screws, up to 10 mm, in order to obtain adequate purchase. ■ Patients who have had prior bone taken from the iliac crest may not be candidates for iliac bolts and an alternative tech- nique such as the S2AI method should be used. ■ Patients with deficient iliac bone—for example, patients with sacropelvic resection for tumor—may require additional points of fixation on the intact side. ■ The patient is positioned prone on a radiolucent frame, per routine for posterior spinal procedures. ■ A transverse pad should run across the chest at the level of the shoulders. A second transverse pad should run across the pelvis at the level of the anterior superior iliac spine (ASIS). The chest wall and abdomen should be free to expand with- out touching the table to ensure adequate space for chest wall movement during ventilation. ■ The drapes should be placed distally enough to expose the start of the gluteal cleft, taking care not to drape out the PSIS. ■ The approach depends on the technique used and specific points for each technique are discussed in the following text. ■ In general, the approach for the open procedures is an exten- sion of the midline incision, centered over the spinous pro- cesses of the vertebrae, and with some modification distally based on the technique. ■ The goal should be to quickly expose the entire area of the spine that is going to be instrumented, with removal of soft tissue out to the transverse processes bilaterally. ■ The exposure should extend caudally enough to expose the dorsal S1 sacral foramen in order to allow for the placement of sacropelvic fixation. ■ The iliac screw and Galveston techniques require additional soft tissue dissection laterally out to the iliac crest in order to expose the starting point on the PSIS.

Zone 1

Zone 2

Zone 3

FIG 5 ● Zones of pelvic fixation. Biomechanical strength increases as you progress from zone 1 to zone 3. Furthermore, zone 3 allows place- ment of the instrumentation the farthest anterior to the pivot point.

Preoperative Planning

IMAGING

■ Standing full length lateral and posteroanterior (PA) plain radiographs should be obtained in all patients with a spinal deformity, to evaluate overall alignment of the spine. ■ Due to the complex and variable anatomy of the sacrum, computed tomography (CT) imaging may be helpful for planning of screw placement but is not always necessary. ■ Identification of anatomic abnormalities such as dural ecta- sia, Tarlov cyst, or prior harvesting of iliac crest bone that might alter the necessary surgical approach should be com- pleted prior to the surgical procedure. ■ The most common indication for sacropelvic fixation is a long spinal fusion to the sacrum. 11 The definition of a long spinal fusion is controversial. Most agree that fusions that cross the thoracolumbar junction and progress to the sa- crum should be augmented with pelvic anchors. However, we feel that pelvic anchors should also be considered in fusions that extend above L2 and progress to the sacrum. ■ Conditions that commonly require a long spinal fusion in- clude lumbar scoliosis in adults, children with a structural lumbosacral scoliotic curve, paralytic kyphoscoliosis, par- alytic and neuromuscular kyphoscoliosis, and congenital scoliosis. 20 ■ High-grade spondylolisthesis ■ Correction of grade III or higher spondylolisthesis places excessive force on the posterior implants. 6 ■ Instrumentation into the pelvis serves as an adjunct to the S1 pedicle screws and may reduce the incidence of pseud- arthrosis and distal implant failure. 20 ■ Flat back syndrome requiring corrective osteotomy ■ Flat back syndrome refers to the loss of lumbar lordosis following a posterior spinal fusion. 28 Patients present with pain, loss of sagittal balance, and caudal disc degeneration. ■ Correction of the deformity frequently requires osteoto- mies and a long fusion to the sacrum. 28 These fusions should be supplemented with pelvic instrumentation to decrease the risk of pseudarthrosis. SURGICAL MANAGEMENT Indications ■ Long spinal fusions

Positioning

Approach

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Chapter 30 Sacropelvic Fixation Techniques

T E C H N I Q U E S

■ The Galveston L-Rod Technique ■ Placement of the Galveston rods proceeds after a standard mid- line exposure centered over the spinous processes. Here, we will focus only on those steps necessary for placement of pelvic fixa- tion. Specific steps necessary for placement of the sublaminar wires or for correction of the deformity in scoliotic or myelodys- plastic spines are beyond the scope of this chapter but can be found elsewhere. 1 ■ After placement of sublaminar wires at all spinal levels that are to be instrumented, exposure of the ilium is begun by palpating the PSIS and then dissecting off the subcutaneous tissue from the lumbosacral fascia starting in the midline and proceeding out bilaterally toward the PSIS using Cobb elevators and Bovie electrocautery. ■ The gluteal musculature should be dissected away from the outer portion of the ilium subperiosteally until the greater sciatic notch is accessible with a finger. ■ A longitudinal or oblique incision is made in the fascia overlying the PSIS.

■ A 3/16-inch stainless steel pelvic pin is then driven into the ilium toward the anterior inferior iliac spine (AIIS) to a depth of 6 to 9 cm. The starting point is just posterior to the SI joint at the level of the PSIS. Placement of a finger into the sciatic notch can help guide the pin toward the AIIS. 2 ■ The pin is left in place in order to facilitate correct bending of the L-rod, which is a 3/16-inch diameter stainless steel rod. ■ The first bend in the L-rod creates the short end, which will be placed into the table of the ilium and can be approximated by placing the short end of the rod parallel to the pelvic pin in the table of the ilium. The second bend turns the long end of the rod cephalad ( TECH FIG 1A ). ■ Next, the pelvic pin is removed, and the short end of the L-rod is driven into the table of the ilium. ■ The long end of the L-rod is then attached to the mobile spine by using the previously placed sublaminar wires ( TECH FIG 1B,C ). ■ Alternatively, some surgeons choose to attach the Galveston rod to the heads of pedicle screws.

Kyphosis

Lordosis

Side view

Top view

End-on view

A C TECH FIG 1 ● A. Appropriate shaping of the L-rod. B,C. Line diagram and model, respectively, showing proper placement of the Galveston rod into the table of the ilium. B

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Operative Techniques in Spine Surgery

■ Sacral Tricortical Pedicle Screws ■ The iliac screw and S2AI methods for sacropelvic fixation begin with placement of sacral (S1) screws, which should be com- pleted prior to placement of the pelvic fixation. ■ Sacral pedicle screws can be placed through either two or three (through the sacral promontory) cortices, but tricortical screws have been shown to have twice the insertional torque of bicorti- cal screws, and this is the preferred technique. 16 ■ An awl is used to breach the dorsal cortex of the sacrum at the starting point 1 cm proximal and immediately lateral to the S1 sacral foramen ( TECH FIG 2A ). ■ A slightly curved large pedicle finder (gearshift type) is used to sound the cancellous bone. The path should be directed 30 to 40 degrees anteromedially and 15 degrees cephalad toward the anterior tip of the sacral promontory ( TECH FIG 2B ).

■ The direction toward the anterior tip of the promontory can be estimated from preoperative plain radiographs and confirmed intraoperatively with lateral radiograph or by fluoroscopy prior to placement of the screw ( TECH FIG 2C ). ■ The pilot hole is tapped using a tap size 1 mm less than the screw to be inserted, typically a 6-mm tap is used and a 7-mm screw is placed ( TECH FIG 2D ). ■ All five boundaries of the screw hole are sounded using a ball- point probe in order to verify that the bony cortex has not been breached. ■ Screw length is then measured using a ballpoint depth gauge. Screws are typically placed with a bicortical purchase. ■ The screws are then placed under direct visualization.

T E C H N I Q U E S

Starting point

Trajectory

A

B

C

TECH FIG 2 ● Starting point ( A ) and trajectory ( B ) for the tricortical S1 screws. C. Intraoperative lateral radio- graph showing the trajectory of the pedicle finder, which is 30 to 40 degrees anteromedially and 15 degrees cephalad toward the anterior tip of the sacral promontory. D. Placement of the S1 tricortical screw. The pilot hole is tapped using a tap size 1 mm less than the screw to be inserted, the depth is measured using a ballpoint depth gauge, and an appropriate length screw is placed along the path obtaining a bicortical purchase.

D

■ The Iliac Screw Technique

■ The PSIS is palpated, and the subcutaneous tissue is dissected off the lumbosacral fascia bilaterally toward the PSIS using Cobb elevators and Bovie electrocautery ( TECH FIG 3A ). ■ A longitudinal or oblique incision is made in the fascia overlying the PSIS. ■ The incision is extended both caudally and cephalad along the ilium with respect to the PSIS. ■ A rongeur or burr is used to breach the cortex overlying the PSIS, approximately 1 cm from the distal ilium. The amount of bone

■ We recommend that the iliac screw be placed only after other points of fixation, including the S1 screws, have already been secured. ■ When placing the iliac screws using the S2AI technique, insert- ing the proximal screws, especially the S1 pedicle screws, helps in guiding the surgeon in fine-tuning the lateral/medial starting point for the S2AI screws so as to end with a straight in-line anchor at the lumbosacral junction facilitating rod placement.

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T E C H N I Q U E S

A

D

B

C

E

TECH FIG 3 ● A. Extension of the midline incision out to the PSIS for place- ment of the iliac screws. The paraspinal muscles are held out of the field with a clamp, and the PSIS is marked by the forceps. An oblique incision is made in the fascia overlying the PSIS. B. Subsequently, the pedicle seeker is driven into the table of the ilium, angled toward the ASIS. C. Placement of a finger into the greater sciatic notch can help guide the pedicle seeker. D. Line diagram of trajectory. E,F. The iliac screw is attached to the main spinal construct by using a modular connector system, which is tunneled anterior to the paraspinous muscles. ( B,C,E: From Moshirfar A, Rand FF, Sponseller PD, et al. Pelvic fixa- tion in spine surgery. Historical overview, indications, biomechanical relevance, and current techniques. J Bone Joint Surg Am 2005;87[suppl 2]:89–106.)

F

resected depends on the bulkiness of the implant, and the goal should be to minimize implant prominence. 15 ■ With a pedicle seeker or curette, the path into the ilium down toward the AIIS is then developed ( TECH FIG 3B ). ■ The path averages 25 degrees lateral to midsagittal plane and 30 to 35 degrees caudal to the transverse plane toward the

ASIS ( TECH FIG 3C ). Fluoroscopy can be used to confirm the path. Alternatively, placement of a finger into the sciatic notch provides an anatomic landmark that can help guide the path 20 ( TECH FIG 3D ). ■ The path is palpated with a ballpoint probe to verify that neither the medial nor lateral iliac crest cortex has been breached.

312

Operative Techniques in Spine Surgery

■ Screw lengths are then measured by marking the depth on the ballpoint probe. Common screw sizes are 7 to 8 mm in diam- eter and 70 to 80 mm in length. ■ The screw path is tapped using a handheld tap, and an appropri- ate length screw is inserted. ■ Finally, the screw must then be attached to the longitudinal rods of the main spinal construct by using a modular connector system. The connectors are tunneled anterior to the paraspinal muscles ( TECH FIG 3E,F ).

■ Pelvic radiographs or C-arm fluoroscopic images may be taken to confirm placement of the instrumentation. The trajectory and starting point of the screw should be assessed. ■ For the iliac screw, the starting point should be over the PSIS and directed toward the AIIS, proximal to the sciatic notch. ■ For the S2AI screw, the starting point is midway between S1 and S2 sacral foramina and directed toward the AIIS, using an anteroposterior (AP) view will ensure the cepha- lad/caudal position; a tear drop view will ensure no breach to the medial or lateral cortices of the ilium. ■ An awl is used to breach the dorsal cortex over the starting point, located in line with the lateral edge of the S1 foramen and mid- way between S1 and S2 dorsal foramina ( TECH FIG 5A ). ■ The most common S2AI trajectory averages 40 degrees of lateral angulation in the transverse plane and 40 degrees of caudal angulation in the sagittal planes directed toward the AIIS ( TECH FIG 5B,C ). ■ A 2.5-mm pelvic drill bit (extended length) is used to tap drill through the sacral ala, the SI joint, and into the ilium. This dis- tance is roughly 30 to 45 mm in most patients ( TECH FIG 5D ). ■ At this point, the drill bit is removed and replaced with a 3.2-mm drill bit in order to reduce the risk of breakage in harder bone and is advanced for a total depth of approximately 80 to 90 mm. ■ Once the drill has reached the ilium, the drill itself is removed. A depth gauge is then inserted into the hole in order to determine the length of the screw. ■ Next, a 1.45-mm guidewire mounted on a handheld driver is advanced for an additional 10 to 20 mm to seat the guidewire in bone ( TECH FIG 6A ). Angulation continues to be directed down toward the ASIS. ■ Placement can be confirmed with intraoperative fluoroscopy. ■ The hole is then manually tapped over the guidewire using a cannulated tap ( TECH FIG 6B ), and an appropriate length screw is placed ( TECH FIG 6C ). Screw sizes of 8 to 10 mm by 80 to 100 mm are most commonly used in adults. ■ Because the screws are in line with the rest of the spinal con- struct, no additional cross-connectors are required for assembly ( TECH FIG 6D,E ).

T E C H N I Q U E S

■ Open S2 Alar Iliac Technique

■ The placement of the S2AI screw should take place only after the other points of fixation, including the S1 screws, have been secured. ■ The position of the S1 and S2 dorsal foramina are identified using a Woodson elevator ( TECH FIG 4 ).

TECH FIG 4 ● Standard midline exposure. Probes mark the lo- cation of the S1 and S2 dorsal sacral foramina at points A and B , respectively.

Starting point of S2A1 screw

B C TECH FIG 5 ● A. Starting point for the S2AI screw. B,C. Sagittal and coronal views, respectively, of the final trajectory of the S2AI screw. (continued) A

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Chapter 30 Sacropelvic Fixation Techniques

T E C H N I Q U E S

TECH FIG 5 ● (continued) D. A drill is used to tap through the SI articulation.

D

A

B

C

TECH FIG 6 ● A. The drill is removed, and a 1.45-mm guidewire mounted on a handheld driver is advanced into the ilium toward the AIIS. Tapping the S2AI screw hole over the guidewire ( B ) and placement of the S2AI screw ( C ). D,E. Final alignment of the S2AI screw and spinal construct. D E

■ Percutaneous S2 Alar Iliac Technique

(see TECH FIG 5A ), is identified using standard AP and pelvic inlet fluoroscopic views. ■ A Jamshidi needle is angled toward the AIIS and advanced 10–20 mm into the sacral ala. The ideal S2AI trajectory is the same as in the open procedure and averages 40 degrees of lat- eral angulation in the transverse plane and 40 degrees of caudal angulation in the sagittal planes but varies with pelvic obliquity (see TECH FIG 5B,C ). ■ A teardrop view is then obtained to verify the needle trajectory ( TECH FIG 7A ). ■ The teardrop view is a fluoroscopic view obtained by rolling the C-arm roughly 30 degrees over the table, and tilting it roughly 30 degrees cephalad, which creates an overlap of the AIIS and the PSIS and the image of a teardrop.

■ Because the S2AI screw is in line with the spinal construct at- tached to the mobile spine, the S2AI technique is amenable to a minimally invasive percutaneous approach. 17,22 ■ The percutaneous sacropelvic fixation is frequently combined with a minimally invasive percutaneous fixation of the lumbar spine, but this may not be required depending on the indication. ■ The approach to the sacrum is a 3-cm midline incision at the level of the S1 and S2 dorsal foramen ( TECH FIG 7B ). ■ The starting point, located in line with the lateral edge of the S1 foramen and midway between the S1 and S2 dorsal foramina

314

Operative Techniques in Spine Surgery

T E C H N I Q U E S

■ The needle position is adjusted to be coaxial with the teardrop and then advanced 10 mm past the SI joint. ■ Next, a 1.45-mm guidewire is passed through the Jamshidi needle, again angling toward the AIIS. ■ The Jamshidi needle is removed, and the guidewire is advanced into the ilium through the cancellous bone between the cortices of the ilium until the adequate length is reached ( TECH FIG 7B ). ■ Positioning and angulation of the wire can be confirmed with fluoroscopic views as needed. ■ Screw lengths are then measured by marking the depth of the guidewire. Screw sizes of 8 to 10 mm by 80 to 100 mm are common in adults.

■ The hole is manually tapped over the guidewire using a can- nulated tap ( TECH FIG 7C ), and an appropriate length screw is placed ( TECH FIG 7D ). ■ Because the screws are in line with the rest of the spinal con- struct, no additional cross-connectors are required for assembly. ■ In cases in which a percutaneous lumbar spinal procedure has also been performed, the S2AI screw can be attached to the main spinal construct by threading a rod under the skin and muscles from proximal to distal and maneuvering the rod with a premade rod-guidance tube. ■ The final trajectory and placement of the screw is identical to that of the open S2AI technique.

A

B

C

D TECH FIG 7 ● A. Representative fluoroscopic teardrop view is obtained by rolling the C-arm roughly 30 degrees over the table and tilting it roughly 30 degrees cephalad, which creates an overlap of the AIIS and PSIS and the image of a teardrop. B. Percutaneous guidewire placement. C. A cannulated handheld tap is used to tap the screw hole over the guidewire. D. The screw is placed with a handheld drill (green handle). In cases in which a minimally invasive lumbar spine procedure has also been done, the rod can be attached to the main spinal construct by passing it underneath the skin with the assistance of premade rod guidance tubes. ( A,D: From Martin CT, Witham T, Kebaish KM. Sacropelvic fixation: two case reports of a new percutaneous technique. Spine 2011;36[9]:e618–e621.)

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Chapter 30 Sacropelvic Fixation Techniques

PEARLS AND PITFALLS

Indications

■ Long spinal fusions to the sacrum are the most common indication for sacropelvic fixation.

Teardrop fluoroscopic view

■ The teardrop is created by the overlap of the AIIS and PSIS and represents a bony canal through which the pelvic fixation may be safely placed. ■ Structures in the sciatic notch can be at risk. ■ Minimized by verifying a bony end point with a blunt probe prior to screw placement ■ Use of C-arm to verify the trajectory, the tear drop view can be the most helpful ■ Common reason for revision ■ Minimized by creating a notch prior to placement of the iliac screw, by burying the screw beyond the PSIS, by choosing a medial starting point for the screw, or by using the S2AI technique ■ Minimize by using largest acceptable diameter screw. ■ Addition of an anterior fusion increases construct stability. ■ The use of S2AI technique which is associated with less incidence of implant loosening ■ At our institution, the S2AI technique has been adopted as the procedure of choice for sacropelvic fixation in both adult and pediatric cases.

Damage to surrounding soft tissues

Implant prominence

Instrumentation loosening

Authors’ preferred technique

POSTOPERATIVE CARE

■ The structures in the greater sciatic foramen and those overlying the anterior surface of the sacrum are at risk during placement of the instrumentation. 11 ■ However, injury to these structures is very uncom- mon, 11 and the risk can be minimized by using a blunt probe to ensure a proper bony end point prior to screw placement. ■ Fluoroscopic imaging can also be useful, particularly in patients with difficult anatomy. ■ Implant prominence ■ Implant prominence can lead to significant pain and dis- comfort and is the most common reason for revision of this procedure. 11 ■ The risk of this complication is highest in thin patients and is higher with the iliac screw and Galveston techniques. 11 ■ The risks can be minimized by creating a notch prior to placement of the iliac screw, by burying the screw beyond the PSIS, by choosing a medial starting point for the iliac screw, or by using the S2AI technique, which on average allows for 15 mm deeper placement of the screw head as compared to the iliac screw technique. 5 ■ Implant loosening ■ Loosening is a second common reason for implant re- moval, but it may remain asymptomatic if fusion can be achieved prior to its onset. 11 ■ Loosening is caused by repeated micromotion of the im- plants and is visible radiographically as a radiolucency around the screw or rod. ■ In the Galveston L-rod technique, loosening of the short arm of the L-rod is particularly common, and this compli- cation is called the windshield wiper effect . 3,9 ■ In some patients treated with the Galveston technique, the windshield wiper effect may lead to pain and the need for implant removal. 3,9 ■ With the S2AI and iliac screw techniques, choosing the largest diameter screw possible (usually 8 to 10 mm in adults) can help to delay implant loosening and maximize the chances of a successful fusion. ■ Wound problems and infection ■ Few studies have reported definitive infection rates associ- ated with sacropelvic fixation.

■ The patient should be awoken in the operating room, and a detailed neurologic examination should be conducted immediately following surgery. If a neurologic deficit is de- tected, appropriate imaging and surgical intervention may be necessary. ■ The postoperative diet and patient pain control can be man- aged as per routine postoperative care. ■ No additional external immobilization such as an orthotic or plaster cast is necessary. ■ The patient should be placed in a regular hospital bed, and early ambulation should be encouraged. ■ Physical therapy should be started as soon as feasible follow- ing the surgical procedure. ■ After discharge, follow-up at regular intervals is important, including appropriate radiographs as indicated depending on the procedure performed. ■ Excellent fusion rates have been achieved with all three techniques. 2,9,15,27 ■ Implant prominence and pain is a common reason for instru- mentation removal in both the iliac screw and the Galveston techniques. However, less than 2% of patients with S2AI screws require implant removal after 2 years, as compared to up to 22% of patients with iliac screws. 8,12 ■ The screw in the S2AI technique breaches the synovial carti- lage of the SI joint in approximately 60% of cases. However, a recent study showed no adverse effects on the SI joint at 2 years follow-up. 27 ■ Modern techniques for sacropelvic fixation have helped to minimize the incidence of complications. However, seri- ous complications still can and do occur. A brief discus- sion of these complications and ways to minimize them is presented here. ■ Instrumentation misplacement and injuries to adjacent structures

OUTCOMES

COMPLICATIONS

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Operative Techniques in Spine Surgery

■ Furthermore, the infection rate associated with sacrope- lvic fixation alone is difficult to ascertain because these techniques are often combined with fusions of the mobile spine above which requires additional incisions and soft tissue dissection. ■ Infection rates associated with the Galveston L-rod have been reported to range from 3% to 10%. 9,21 ■ In a study of 81 patients treated with iliac screw fixation, the infection rate was reported as 4%. 15 ■ A study of 27 patients treated with the S2AI technique showed an infection rate of 0%. 27 ■ Significantly less dissection is required for the S2AI tech- nique, which may account for the lower infection rates reported with that procedure. ■ Nonunion and instrumentation failure ■ If bony fusion does not occur, the instrumentation is des- tined to fail, often through implant failure or breakage. ■ Augmentation of sacropelvic fixation with an anterior in- terbody lumbar fusion at L4–L5 and L5–S1 can optimize fusion stability and increase the chances of a successful fusion. 13,14,25 REFERENCES 1. Allen BL Jr, Ferguson RL. The Galveston technique for L rod instru- mentation of the scoliotic spine. Spine 1982;7(3)276–284. 2. Allen BL Jr, Ferguson RL. The Galveston technique of pelvic fixation with L-rod instrumentation of the spine. Spine 1984;9(4):388–394. 3. Broom MJ, Banta JV, Renshaw TS. Spinal fusion augmented by Luque-rod segmental instrumentation for neuromuscular scoliosis. J Bone Joint Surg Am 1989;71:32–44. 4. Camp JF, Caudle R, Ashmun RD, et al. Immediate complications of Cotrel-Dubousset instrumentation to the sacro-pelvis. A clinical and biomechanical study. Spine 1990;15(9):932–941. 5. Chang TL, Sponseller PD, Kebaish KM, et al. Low profile pelvic fixa- tion: anatomic parameters for sacral alar-iliac fixation versus tradi- tional iliac fixation. Spine 2009;34(5):436–440. 6. Cunningham BW, Lewis SJ, Long J, et al. Biomechanical evaluation of lumbosacral reconstruction techniques for spondylolisthesis: an in vitro porcine model. Spine 2002;27:2321–2327. 7. Devlin VJ, Boachie-Adjei O, Bradford DS, et al. Treatment of adult spinal deformity with fusion to the sacrum using CD instrumentation. J Spinal Disord 1991;4:1–14. 8. Emami A, Deviren V, Berven S, et al. Outcome and complications of long fusions to the sacrum in adult spine deformity: Luque-Galveston, combined iliac and sacral screws, and sacral fixation. Spine 2002;27(7): 776–786. 9. Gau YL, Lonstein JE, Winter RB, et al. Luque-Galveston procedure for correction and stabilization of neuromuscular scoliosis and pelvic obliquity: a review of 68 patients. J Spinal Disord 1991;4(4):399–410.

10. Jackson RP, McManus AC. The iliac buttress. A computed tomo- graphic study of sacral anatomy. Spine 1993;18(10):1318–1328. 11. Kebaish KM. Sacropelvic fixation: techniques and complications. Spine 2010;35(25):2245–2251. 12. Kebaish KM, Pull ter Gunne AF, Mohamed AS, et al. A new low profile sacropelvic fixation using S2 alar iliac (S2AI) screws in adult deformity fusion to the sacrum: a prospective study with minimum 2-year follow-up. Paper presented at: the North American Spine Soci- ety Annual Meeting, November 10–14, 2009, San Francisco, CA. 13. Kostuik JP, Errico TJ, Gleason TF. Techniques of internal fixation for degenerative conditions of the lumbar spine. Clin Orthop Relat Res 1986;(203):219–231. 14. Kostuik JP, Hall BB. Spinal fusions to the sacrum in adults with scolio- sis. Spine 1983;8(5):489–500. 15. Kuklo TR, Bridwell KH, Lewis SJ, et al. Minimum 2-year analysis of sacropelvic fixation and L5-S1 fusion using S1 and iliac screws. Spine 2001;26(18):1976–1983. 16. Lehman RA Jr, Kuklo TR, Belmont PJ Jr, et al. Advantage of pedicle screw fixation directed into the apex of the sacral promontory over bi- cortical fixation: a biomechanical analysis. Spine 2002;27(8):806–811. 17. Martin CT, Witham TF, Kebaish KM. Sacropelvic fixation: two case re- ports of a new percutaneous technique. Spine 2011;36(9):E618–E621. 18. McCord DH, Cunningham BW, Shono Y, et al. Biomechanical analysis of lumbosacral fixation. Spine 1992;17(8 suppl):S235–S243. 19. Mirkovic S, Abitbol JJ, Steinman J, et al. Anatomic consideration for sacral screw placement. Spine 1991;16(6 suppl):S289–S294. 20. Moshirfar A, Rand FF, Sponseller PD, et al. Pelvic fixation in spine sur- gery. Historical overview, indications, biomechanical relevance, and current techniques. J Bone Joint Surg Am 2005;87(suppl 2):89–106. 21. Nectoux E, Giacomelli MC, Karger C, et al. Complications of the Luque-Galveston scoliosis correction technique in paediatric cerebral palsy. Orthop Traumatol Surg Res 2010;96(4):354–361. 22. O’Brien JR, Matteini L, Yu WD, et al. Feasibility of minimally in- vasive sacropelvic fixation: percutaneous S2 alar iliac fixation. Spine 2010;35(4):460–464. 23. O’Brien JR, Yu WD, Bhatnagar R, et al. An anatomic study of the S2 iliac technique for lumbopelvic screw placement. Spine 2009;34(12): E439–E442. 24. O’Brien MF. Sacropelvic fixation in spinal deformity. In: Dewlad RL, ed. Spinal Deformities: The Text. New York: Thieme, 2003:601–614. 25. Ogilvie JW, Schendel M. Comparison of lumbosacral fixation devices. Clin Orthop Relat Res 1986;(203):120–125. 26. Peretz AM, Hipp JA, Heggeness MH. The internal bony architecture of the sacrum. Spine 1998;23(9):971–974. 27. Sponseller PD, Zimmerman RM, Ko PS, et al. Low profile pelvic fixation with the sacral alar iliac technique in the pediatric popu- lation improves results at two-year minimum follow-up. Spine 2010;35(20):1887–1892. 28. Wiggins GC, Ondra SL, Shaffrey CI. Management of iatrogenic flat- back syndrome. Neurosurg Focus 2003;15(3):E8. 29. Xu R, Ebraheim NA, Yeasting RA, et al. Morphometric evaluation of the first sacral vertebra and the projection of its pedicle on the poste- rior aspect of the sacrum. Spine 1995;20(8):936–940.