Percutaneous sacroiliac (SI) screw fixation is indicated for unstable posterior pelvic ring injuries, sacral fractures, and SI joint dislocations. This article provides a review of indications and contraindications, preoperative planning, imaging techniques and relevant anatomy, surgical technique, complications and their management, and outcomes after SI screw insertion.
Key points
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Percutaneous sacroiliac (SI) screws are indicated for the treatment of unstable posterior pelvic ring injuries, sacral fractures, SI joint disruptions, or as adjunctive posterior pelvic fixation after anterior pelvic fixation.
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SI screws are associated with a shorter operating time, less blood loss, and less soft tissue injury compared with open surgical fixation of the posterior pelvis.
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The iliac cortical density (ICD) parallels the anterior border of the SI joint and represents the alar slope in a normal pelvis. In the case of an abnormal alar slope (dysmorphic pelvis), the ICD is located posteriorly and caudal; failure to recognize this may result in incorrect screw placement.
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The lumbosacral nerve roots, superior gluteal artery, and iliac vessels are at risk during screw insertion and should be managed with screw revision, embolization, ligation, or surgical consult.
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Malunion and malreduction are common complications. Posterior displacement of the pelvic ring greater than 1 cm is associated with a higher incidence of chronic pain and poorer functional outcomes.
Introduction
Pelvic injuries account for 3% of all skeletal fractures and about 40% are unstable because of posterior ring disruption. Injury to the sacroiliac (SI) joint is associated with significant morbidity, including chronic pain, sexual dysfunction, bowel and bladder impairment, and failure to return to work. Surgical fixation of unstable pelvic injuries provides improved fracture reduction, early weight bearing and mobilization, lower mortalities, shorter hospital stays, and superior functional outcomes compared with nonoperative treatment.
The classic method of surgical fixation of the SI joint consisted of open reduction and internal fixation (ORIF) by sacral bars or posterior plating. These implants carried a substantial risk of large dissection, prominent implants, iatrogenic nerve injury, infection, and blood loss to the already traumatized patient. The development of percutaneous fixation via SI screws has decreased operating time, soft tissue injury, and blood loss compared with an open procedure. SI screws are versatile; they can be used to treat a variety of sacral fracture patterns or SI joint dislocation; and can be placed in the supine, prone, or lateral position regardless of soft tissue injury. In addition, for placement in large fragments, cannulated screws are safe even in patients with sacral dysmorphism.
Various imaging modalities, including fluoroscopy and computed tomography (CT), are used for aiding screw insertion. Conventional fluoroscopy is the standard for intraoperative screw placement. However, acceptable reduction of the SI joint and proper implantation of screws without perforation of the neural foramina is challenging, especially when coupled with the difficulties of fluoroscopic imaging and variations in pelvic anatomy. Incorrect placement of SI screws may result in iatrogenic neurovascular complications. The rate of screw malposition has been reported to approach 25% and the incidence of neurologic injury is as high as 18%. However, thorough preoperative planning and an understanding of SI screw placement technique minimize complications.
Introduction
Pelvic injuries account for 3% of all skeletal fractures and about 40% are unstable because of posterior ring disruption. Injury to the sacroiliac (SI) joint is associated with significant morbidity, including chronic pain, sexual dysfunction, bowel and bladder impairment, and failure to return to work. Surgical fixation of unstable pelvic injuries provides improved fracture reduction, early weight bearing and mobilization, lower mortalities, shorter hospital stays, and superior functional outcomes compared with nonoperative treatment.
The classic method of surgical fixation of the SI joint consisted of open reduction and internal fixation (ORIF) by sacral bars or posterior plating. These implants carried a substantial risk of large dissection, prominent implants, iatrogenic nerve injury, infection, and blood loss to the already traumatized patient. The development of percutaneous fixation via SI screws has decreased operating time, soft tissue injury, and blood loss compared with an open procedure. SI screws are versatile; they can be used to treat a variety of sacral fracture patterns or SI joint dislocation; and can be placed in the supine, prone, or lateral position regardless of soft tissue injury. In addition, for placement in large fragments, cannulated screws are safe even in patients with sacral dysmorphism.
Various imaging modalities, including fluoroscopy and computed tomography (CT), are used for aiding screw insertion. Conventional fluoroscopy is the standard for intraoperative screw placement. However, acceptable reduction of the SI joint and proper implantation of screws without perforation of the neural foramina is challenging, especially when coupled with the difficulties of fluoroscopic imaging and variations in pelvic anatomy. Incorrect placement of SI screws may result in iatrogenic neurovascular complications. The rate of screw malposition has been reported to approach 25% and the incidence of neurologic injury is as high as 18%. However, thorough preoperative planning and an understanding of SI screw placement technique minimize complications.
Indications/contraindications
SI screws can be used alone or as supplemental fixation for the treatment of pelvic fractures. SI screws were originally described for SI dislocations and fracture-dislocations. Their applications were expanded to internal fixation of unstable posterior pelvic ring injuries, spinal-pelvic dissociation, incomplete sacral fractures (Denis zones 1–3) with or without pelvic instability, and sacral fractures with persistent gapping after anterior osteosynthesis ( Table 1 ). SI screws are advantageous in the setting of extensive soft tissue trauma, such as open fractures and degloving injuries, because of the limited dissection and minimal implant prominence compared with plates. Unstable anterior-posterior compression (APC) injuries with bladder injury or contaminated, anterior soft tissue injuries can be treated by external fixation of the anterior pelvis and posterior SI screws. APC type IIb (posterior SI ligament attenuation with sagittal plane instability) injuries are indicated for SI screws in conjunction with anterior, symphyseal plating.
| Indications | Unstable posterior pelvic ring injuries SI joint dislocation Spinopelvic dissociation Incomplete sacral fractures ± pelvic ring instability Vertical posterior pelvic fractures Sacral fractures with gapping after symphyseal plating |
| Contraindications | Delayed fixation Active infection Severe sacral dysmorphism Morbid obesity Horizontal sacral fractures |
Contraindications to closed reduction and percutaneous SI fixation include the inability to obtain closed reduction and active infection of the surgical site. Delay to fixation of greater than 5 days is a relative contraindication because organized hematoma may prohibit accurate reduction. Open reduction must be performed if closed reduction is not possible. Horizontal sacral fractures are not well suited for SI screws because the implant is inserted parallel to the fracture line. Historically, transitional lumbosacral variants were considered relative contraindications, but later studies have shown that most patients with sacral anomalies can safely undergo percutaneous SI fixation. However, severe sacral dysmorphism may prevent safe placement of SI screws. U-shaped sacral fractures with sacral kyphosis or narrowing of neural foramina may require a posterior, open procedure for sacral reduction and nerve root decompression in addition to SI screws. In these cases, in-situ, percutaneous SI fixation does not improve neurologic function. Morbidly obese patients may not be suitable for percutaneous techniques because of difficulties obtaining adequate fluoroscopic imaging and placement of screws.
Surgical technique/procedure
Preoperative Planning
A comprehensive physical examination and radiographic evaluation of the patient is necessary. Soft tissue injuries about the pelvis are important for surgical planning, especially if adjunctive ORIF of fractures is required. Other injuries, such as head, chest, abdomen, spine, or extremity trauma, may require procedures before pelvic fixation, affect patient positioning, or delay treatment. All patients with trauma should receive chest, anteroposterior (AP) pelvis, and C-spine radiographs. Advanced pelvic imaging, such as a CT scan with axial slices taken perpendicular to the sacral slope, is recommended for operative planning and for identification of sacral fractures, which are missed on 30% of plain radiographs. CT scans also provide information regarding body habitus, bone quality, soft tissue integrity, neural foramina, and blood vessels. Identifying the type of pelvic and/or sacral injury is important because unstable pelvic injuries may require binders, external fixation, or ORIF before SI screws. Characterizing the sacral disorder is important because guidewire orientation can be increased in the posterior-to-anterior plane for compression of SI dislocations or inserted in the transverse plane for sacral fractures. Comminuted sacral fractures involving the neural foramina can be treated with static, fully threaded SI screws rather than a compression screw because of the risk of overcompression and nerve root entrapment. Pelvic binders must remain in position to avoid clot disruption. In such cases, a large hole can be cut in the binder and the exposed skin sterilely prepped and draped.
Successful SI screw placement requires accurate SI joint reduction, identification of sacral dysmorphism, and adequate intraoperative imaging. Sacral and pelvic injuries with an intact posterior tension band are typically good candidates for closed reduction. Identifying the deformity in displaced fractures is imperative for obtaining closed reduction. Cephalad migration of the affected hemipelvis, with or without posterior displacement, may be improved by distal femoral traction. In contrast, caudal migration of the unaffected hemipelvis can be counterbalanced by placing the ipsilateral extremity in a traction boot. Alternative reduction techniques include internal rotation of the bilateral lower extremities, in which tape is wrapped around the thighs and feet, pelvic binders or sheets for reduction of external rotation deformities, pelvic C-clamps, and Schanz pins for percutaneously manipulating multiplanar deformities. An open reduction can be performed in the supine or prone positions and must be done if closed reduction is unsuccessful.
Sacral dysmorphism affects 35% to 58% of adults and is a recognized predictor of aberrant SI screw insertion. Dysmorphism refers to a variety of abnormal features affecting cranial fusion of the sacrum to L5 (sacralization); development of transverse processes and pedicles; and formation of disk spaces, SI joints, and neural foramina ( Fig. 1 ). Most variations are readily visible on pelvic and sacral radiographs. The pelvic outlet view may show proximal positioning of S1, such that it becomes collinear with the iliac crests; mammillary bodies, representing underdeveloped transverse processes; acute sacral ala sloping in the coronal plane; and large, irregular S1 foramina. Lateral views of the pelvis and sacrum are also useful for identifying angulated sacral ala as well as residual sacral disks. The iliac cortical density (ICD) parallels the anterior border of the SI joint and represents the alar slope in a normal pelvis. However, the ICD is located posteriorly and caudal in the case of an abnormal alar slope and failure to recognize this may result in incorrect screw insertion. The inlet view is useful for identifying irregularities in the ventral cortical sacrum, such as an indentation. More detailed identification of aberrant anatomy, including undulating SI joint spaces, is visible on CT. Both normal and dysmorphic sacrum can accommodate screws of at least 75 mm and the safe zones for screw insertion are the same.
The details of intraoperative imaging are discussed earlier in this article.
Prep and Patient Positioning
A general anesthetic and a first-generation cephalosporin are administered in the operating room. Spinal precautions are used to protect the patient during transfer from the bed to a radiolucent operating table. A soft lumbosacral support made of towels or blankets is placed under the patient by elevating the patient’s body and then placing the patient directly onto the bolster (if supine positioning is chosen for the procedure). Elevating the patient’s pelvis from the operating room table is necessary to allow posterior pelvic percutaneous access. If needed, distal femoral traction is applied through the use of a pulley system that is attached to the operating room table. Neurodiagnostic monitoring may be helpful in patients with transforaminal sacral fractures undergoing closed reduction, or patients with neurologic deficits or cognitive impairment.
Insertion of SI screws can be performed with the patient in the lateral, prone, or supine position. The lateral position complicates both anterior and posterior pelvic surgical exposures and is not recommended for patients with potential spinal injuries. Prone positioning allows posterior surgical exposures but prohibits direct visualization of SI joint reduction if an open reduction is required and may worsen fracture deformity. Anterior pelvic external fixation frames further complicate prone and lateral patient positioning for surgery. Advantages of placing the patient supine include familiarity of positioning by anesthesia and nursing, ability of multiple teams to work simultaneously on polytrauma patients, and access to the anterior pelvis if additional reduction methods are required. Supine positioning may also be preferred in patients with pulmonary injuries and may improve closed-reduction techniques.
Surgical Approach
In the supine position, the anterior superior iliac spine (ASIS) is palpated and a line is drawn from the ASIS and directed perpendicularly to the floor. A second line, drawn in line with the femoral shaft, intersects the first line and thus forms 4 quadrants. The posterosuperior quadrant represents the starting zone for SI screw insertion ( Fig. 2 ). A stab incision is made with a scalpel. Next, a Kirschner wire (K-wire) is inserted through the incision until the outer table of the ilium is contacted. Instrumentation should be directed toward the area of bone between the anterior sacral ala and the S1 neural foramina. In the prone position, the starting point is the intersection of a line drawn from the posterior superior iliac spine and a second line extending proximally, in line with the greater trochanter and femur.
