Surgery to correct adult spinal deformity (ASD) is a growing field. The ever-aging American population is presenting to spinal surgeons increasingly with high expectations of continued quality of life well into the seventh, eighth, and ninth decades of life. However, while surgical treatment of ASD is the only viable option for patients failing conservative measures, the surgical interventions are associated with relatively high morbidity and mortality rates. Indeed, in a series reported from Johns’ Hopkins consisting of 361 patients, the 30-day mortality rate was found to be 2.4% [
Several factors contribute to these high complication rates, including reduced bone mass and weaker fixation points, a higher associated rate of medical comorbidites, patient deconditioning due to immobility, and a rigid and nonflexible deformity [
To combat these challenges, modern surgeons have begun to apply minimally invasive surgery (MIS) techniques to address ASD [
One major advance in spinal fixation has been the application of iliac fixation. Pelvic fixation is an important tool in the armamentarium of the modern spinal surgeon, as screws or bolts of a large diameter and length can be placed safely for caudal anchoring and extend anterior to the spine in the sagittal plane and lateral to it in the coronal plane. Iliac fixation is useful in ASD for long instrumentation constructs, sagittal and coronal deformity corrections, and stabilization of low sacropelvic instability [
We previously published a technique for percutaneous iliac screw fixation [
A consecutive series of 10 patients were treated over an 18-month period at a single institution. All patients underwent MIS treatment of ASD using expandable interbody cage placement and percutaneous pedicle and iliac screws. ASD was defined as a Cobb angle greater than 20°. All deformities were rigid with less than 10° of motion in the coronal or sagittal planes across the deformity segments on flexion, extension, and lateral bending films. All patients had also failed conservative measures and had severe back and/or back and leg pain with distance limited gait. The accuracy of iliac screw insertion was examined using postoperative spiral CT scanning to confirm that screws were entirely within the bony confines.
Patients were positioned prone on the Jackson table so that the pelvis would not be obscured on fluoroscopic imaging by the base of the operating table. Pre-operative imaging, including 3 D reconstructed CT scans of the pelvis, was helpful for planning screw placement trajectories and to validate the fluoroscopic data in the operating room. Iliac cannulation is performed prior to pedicle screw cannulation to maximize the ability to image the pelvis. In addition, the decompression, osteotomies, and interbody fusion are accomplished prior to screw placement. For each side of the iliac crest, the fluoroscope is angled in the sagittal and coronal planes in the obturator outlet view so that the X-ray beams are approximately parallel to both the inner and outer tables of the ilium (Figure
Obturator outlet view showing the “teardrop” target for iliac screw placement. Cannulation of this space provides a safe corridor completely within the bony confines.
Cannulated 8 mm diameter by 80 mm long screws for iliac fixation and cannulated cancellous bone probe.
A 1.5 cm incision is then made overlying the posterior superior iliac spine of the pelvis (PSIS). A Jamshidi needle is then docked onto the most superficial aspect of the PSIS and “walked” ventromedially, with care not to enter into the sacroiliac joint. However, the exact starting point along the superinferior plane of the PSIS can vary according to the specific screw trajectory desired, as multiple acceptable paths are acceptable. A drill or osteotome can be used to create a bony depression to better seat the screw or bolt head to minimize hardware prominence (Figure
Recession of the iliac screw saddles into the bone to avoid hardware prominence as seen on this postoperative (a) axial and (b) sagittal reconstruction CT scan.
Pedicle screw cannulation and placement then proceed followed by rod insertion and hookup (Figure
Case example showing a T9 to Iliac MIS fusion with interbody grafts at L2-S1. (a) and (b) Pre- and postoperative AP, and (c) and (d) Pre- and postoperative lateral 36” X-Ray images. (e) Intraoperative view.
Two plane rods bending in the (a) sagittal and (b) coronal planes to facilitate connection to the more laterally located iliac screw saddles.
The series was consecutive with no patients lost to followup, and in no case was conversion to a traditional open technique necessary. A total of 10 patients (7 women and 3 men) were treated using this technique (Table
Patient | Sex | Age | Operative procedure | Complications | Time | EBL | LOS | Dispo | Iliac screws | CT confirmation of iliac screw placement |
---|---|---|---|---|---|---|---|---|---|---|
JB | M | 68 | L1-iliac MIS instrumented fusion with L2-S1 MIS TLIF | None | 360 | 800 | 4 | Home | 65 mm × 8 mm | Yes, correct position |
DK | F | 75 | T10-iliac MIS instrumented fusion with L2-S1 MIS TLIF | None | 320 | 500 | 5 | Home | 80 mm × 8 mm | Yes, correct position |
HS | F | 78 | T9-iliac MIS instrumented fusion with L1-S1 MIS TLIF | None | 340 | 550 | 7 | Home | 65 mm × 8 mm | Yes, correct position |
JL | F | 72 | T9-iliac MIS instrumented fusion with L1–5 MIS TLIF | None | 300 | 450 | 6 | Home | 80 mm × 8 mm | Yes, correct position |
KF | F | 62 | T11-iliac MIS instrumented fusion with L5-S1 MIS TLIF | None | 265 | 250 | 5 | Home | 65 mm × 8 mm | Yes, correct position |
ES | F | 76 | T10-iliac MIS instrumented fusion with L2-S1 MSI TLIF | T10 and L5 screw breaches | 310 | 500 | 8 | Rehab | 80 mm × 8 mm | Yes, correct position |
RS | F | 75 | T12-iliac MIS instrumented fusion with L2-S1 MSI TLIF | None | 310 | 400 | 4 | Rehab | 65 mm × 8 mm | Yes, correct position |
BP | M | 80 | L2-iliac MIS instrumented fusion with L2-S1 MIS TLIF | None | 280 | 450 | 5 | Home | 80 mm × 8 mm | Yes, correct position |
SR | F | 66 | T9-iliac MIS instrumented fusion with L1–5 MIS TLIF | Epidural hematoma requiring laminectomy for evacuation | 300 | 500 | 7 | Rehab | 65 mm × 8 mm | Yes, correct position |
RL | M | 78 | L2-iliac MIS instrumented fusion with L2-S1 MIS TLIF | None | 240 | 395 | 5 | Home | 80 mm × 8 mm | Yes, correct position |
Early radiographic outcomes were determined using pre-and postoperative 36” standing X-rays at last followup. The mean preoperative Cobb angle was 35° which improved to a mean of 8.0°, reflecting an average of 27° of improvement. The mean preoperative global lumbar lordosis as measured between L1 and S1 was 27° which improved to a mean of 48°, reflecting an average of 21° of improvement. All 20 iliac screws were placed successfully as judged by postoperative CT scanning.
There were no intraoperative complications. However, one patient had two asymptomatic medial screw breaches at T10 and L5. This patient did not undergo reoperation as there was no neurological impairment. A second patient developed a symptomatic epidural hematoma on postoperative day number 6. This was evacuated emergently with neurological recovery.
Due to the many benefits of MIS surgery, it has the potential to improve the outcomes of surgery for ASD. Because these patients are often medically compromised, a reduction in infection rates, intraoperative blood loss, and quicker mobilization may have a significant impact on their recovery. While in the past MIS surgeons focused primarily on short segment fusions for degenerative disease [
In this paper we describe our initial experience with percutaneous iliac screws for treating ASD. While the series is of limited size, radiographic evaluation demonstrated safe iliac screw placement using a relatively straightforward technique that did not require specialized equipment is possible. Using a single C-arm and the obturator outlet view, standard size iliac screws could be placed safely and efficiently. While image guidance can be helpful in many settings, navigation systems are expensive, prone to error, and require additional setup time. Thus, we have chosen to continue using a simplified C-arm method for screw placement. The introduction of commercially available cannulated iliac screws has also helped to make this procedure widely accessible to surgeons and renders the procedure as accessible as open screw placement. It should however be remembered that screw misplacement with any surgical technique can result in sciatic nerve injury, major vessel disruption, pelvic fracture, or retroperitoneal hematoma formation, and these risks are higher in the ASD population.
When applying this technique, many of the considerations for open surgery are relevant to the MIS setting. For example, strict attention needs to be placed to screw head positioning. It is critical to recess the iliac screw heads to reduce complaints of hardware prominence. This can be accomplished by using the drill or osteotome to created an opening in the posterior cortical wall of the ilium. In additional, starting the screw below the PSIS keeps the saddle low. With regard to hardware connections, placing the iliac screw heads medial and the pedicle screws lateral keeps the screw saddles in a single plane and facilitates rod-screw mating. However, despite these efforts, multiple-rod plane bending is often necessary as lateral offset connectors cannot be applied using a truly percutaneous method.
It should also be noted that in this series the screws were either 65 or 80 mm in length. Open deformity surgeons commonly use longer screws to obtain superior fixation. In this series, we generally did not treat cases of severe scoliosis (>60°) or major kyphosis, and the series also did not include serious revisions and thus have had success with the shorter iliac screws. Furthermore, maintenance of the soft tissue envelope and posterior tension band with MIS surgery preserves the spine’s native integrity and thus may obviate the need for these longer screws. Ultimately, the placement of screws greater than 100 mm in length should be feasible but will be yet another area requiring validation in the clinical setting.
While MIS surgery for ASD has not been able to completely replace open, conventional methods, the expanding spectrum of MIS techniques has allowed the modern MIS surgeon to perform ever more complex surgeries in this patient population. Percutaneous iliac screws represent one such advance to allow for successful caudal anchoring of long-segment spinal fixation constructs.
The author is a consultant and receives royalty payments from DePuy Spine, Inc.