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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