Kyung-Hyun Kim and Un-Yong Choi contributed equally to this work and should be considered co-corresponding authors.
This study aimed to compare the radiographic and clinical outcomes between sacral alar iliac (SAI) screw fixation and conventional iliac (CI) screw fixation with a particular focus on the rate of reoperation, surgical site infection (SSI), sacroiliac joint pain, instrument failure, and screw prominence.
Patients who underwent sacropelvic fixation in the authors’ institution from June 2011 to May 2017 were retrospectively investigated. Forty-three patients with SAI screw fixation and 25 with CI screw fixation were included. Preoperative patient and surgical characteristics and postoperative outcomes and complications were analyzed between the SAI and CI groups. Radiographic parameters were analyzed before and after surgery.
Lumbosacral fusion rates showed no statistically significant difference between the SAI group and CI groups (90.7% vs. 92.0%, p=0.878). The SAI group showed a significantly good result with regard to SSI compared to the CI group (0% vs. 16%, p=0.016), but had a significantly higher rate of distal screw fracture than the CI group (16.3% vs. 0%, p=0.042).
The SAI screw fixation technique could achieve good outcomes of pain relief, deformity correction, and lumbosacral fusion rate with relatively lower complications such as the rates of reoperation, SSI, and screw prominence as compared to the CI screw fixation technique. However, distal instrument failure was observed more frequently in the SAI group, requiring further biomechanical studies.
Despite all the recent advancements and development in spinal instrumentation and surgical techniques and a better understanding of the biology of spinal fusion, pseudoarthrosis, or construct failure of the lumbosacral junction continues to be a major obstacle in spinal surgery
Many sacropelvic fixation techniques have been developed: the Galveston technique and Dunn-McCarthy (S-Rod) technique, as well as the transiliac screw, intrasacral rod, iliosacral fixation, and iliac screw-based techniques
Although there are many biomechanical and cadaveric studies on SAI and CI screw fixation techniques, there are few direct comparative analyses of the difference in clinical outcomes between the two techniques. Therefore, the objective of this study was to compare the clinical and radiographic outcomes between SAI and CI screw fixation techniques in a single institution, with a particular focus on the rate of reoperation, surgical site infection (SSI), sacroiliac (SI) joint pain, rod fracture, screw failure, and screw prominence.
Institutional Review Board (IRB) approval was obtained (IRB No. 3-2017-0340). The researchers conducted a retrospective consecutive review of all patients who underwent sacropelvic fixation in their institution from June 2011 to May 2017. Sacropelvic fixation was performed for fusion augmentation in the cases of deformity correction operations requiring spinal fusion down to the sacrum. SAI screw fixation was performed in 79 patients and CI screw fixation in 50 patients. The inclusion criteria for this study were at least one year of a follow-up period and patients having the appropriate imaging studies such as whole spine X-ray, computed tomography (CT), and magnetic resonance imaging preoperatively and postoperatively. Based on these criteria, 43 of 79 patients with SAI screw fixation and 25 of 50 patients with CI screw fixation were included.
Patient demographics were investigated including age at operation, sex, surgical diagnosis, comorbidity such as diabetes mellitus and osteoporosis, smoking history, body mass index (BMI), bone mineral density, duration of follow-up, and preoperative and postoperative visual analog scale (VAS) for pain. Surgical characteristics were also investigated, including the history of previous lumbosacral operation, spinal level of screw fixation, postoperative complications, and reoperation. Postoperative complications included proximal junctional failure or kyphosis, distal instrument failure, rod fracture, wound dehiscence, SSI, and screw prominence. Reoperation was defined as any unplanned procedure required for the treatment of pseudoarthrosis or other complications.
Radiographic parameters were measured on the anteroposterior and lateral radiograph of the standing whole spine X-ray. Preoperative, immediately postoperative, 6 and 12 months after the surgery, and final follow-up standing whole spine X-ray were studied. The measured parameters were sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), sacral slope, lumbar lordosis (LL), thoracic kyphosis, and cervical lordosis. Proximal junctional failure was defined as “proximal junctional sagittal Cobb angle between the lower endplate of the uppermost instrumented vertebra and the upper endplate of the two supra-adjacent vertebrae ≥10° and at least 10° greater than the preoperative measurement”
The step-by-step procedures for the CI and SAI screw fixation techniques are described in detail in previous studies
Intergroup comparison of categorical variables was achieved using Fisher’s exact test. The unpaired
The mean duration of follow-up was 640±244 days vs. 627±282 days (SAI group vs. CI group); the mean age of patient was 65.3±9.0 years vs. 60.6±13.5 years (range, 28–79 years); and the mean number of screw fixation levels was 7.3±2.1 segments vs. 7.6±3.1 segments (range, 3–14 segments) (
Regarding baseline patient demographics, there were no statistically significant differences in age, sex, BMI, duration of follow-up, smoking, diabetes mellitus, osteoporosis, and previous spinal surgery between the two groups. In both groups, the SVA, LL, PT, and PILL improved after surgery compared to before surgery, but no statistically significant difference was observed between the two groups (
There were no statistically significant differences between the SAI group and CI group with respect to rod fracture, wound dehiscence, and screw prominence. The rate of reoperation, one of the major complications, did not show any statistically significant difference between the two groups (16.3% vs. 28.0%, p=0.270). Additionally, the rate of proximal junctional failure and proximal junctional kyphosis was not different between the two groups statistically. The SAI group had a significantly higher rate of distal screw fracture than the CI group (16.3% vs. 0%, p=0.042) (
All of the distal instrument failures occurred in the SAI group except one case of peri-screw halo formation in the CI group. Among eight patients with complications in the SAI group, seven patients experienced distal screw fractures. The screw fracture occurred in the junction between the head of the screw and the neck of the screw shaft in all patients. The duration of screw fracture was 300±30 days (range, 5–29 months). Among these seven patients, pseudoarthrosis in the lumbosacral area was Grade I in two cases, Grade II in two cases, and Grade III in three cases. Inter-group analyses between the distal screw fracture group and the non-distal screw fracture group were also performed. The rate of lumbosacral pseudoarthrosis (Grades III, IV) was higher in the distal screw fracture group compared to the non-distal screw fracture group, but there was no statistical significance (28.6% vs 6.6%, p=0.112). The improvements of SVA, LL, PT, and PI-LL after surgery did not show statistically significant differences between the two groups. All screws used in spinopelvic screw fixation were poly-axial and had diameters ranging from 7.5 to 8.5mm, and their lengths ranged from 80 to 90mm. There was no statistically significant difference between the two groups.
Regarding the two patients with wound dehiscence and the four patients with SSI in CI groups, the lumbosacral area was the main area for complications. One patient with wound dehiscence had a flap graft surgery performed by a plastic surgeon in the institute. Patients with SSI were initially treated with antibiotics including vancomycin and third-generation cephalosporin for several days. If antibiotic treatment was not working based on laboratory results, the wound was opened and irrigated with normal saline and betadine-mixed saline. Gentamycin-mixed saline was added in one patient.
Sacropelvic fixation remains a challenging concept in spinal operation in spite of ongoing developments to improve distal fixation and maintain the stability of constructs in thoracolumbar operation. Sacropelvic fixation is used in spinal operations for the following two purposes: (1) to improve the correction of deformity especially in cases when the apex is located in the lumbar spine; and (2) to stabilize the lumbosacral junction to facilitate arthrodesis
The rate of SSI was previously reported to be lower in the SAI screw fixation than the CI screw fixation according to several meta-analyses
Some results in this study were different than the findings of previous studies. For instance, the rate of distal screw fracture was higher in the SAI group with a statistically significant difference compared to the CI group. These results are difficult to explain based on the results of previous biomechanical studies in which SAI screw fixation provided superior pullout strengths
All screw fractures occurred at the specific site between the head of the screw and the neck of the screw shaft in the SAI group. In the case of SAI screw fixation, the acute angle develops between the screw head and the shaft of the screw. The head-shaft angulation of the screw increases the stress on the screw head and leads to screw fracture between the head and the shaft neck
Rod fractures were more common in the SAI group, but there was no statistically significant difference between the two groups. Rod fractures occurred in three cases at L3/4, three cases at L4/5, and two cases at L5/S1 in the SAI group and one case at L4/5 in the CI group. A previous study using the biomechanical finite element model reported that fusion of the SI joint increased the motion of the lumbosacral (L5-S1) segment, and explained that rigid fixation of a motion segment resulted in increased stress on the adjacent segments
The causes of reoperation involved three cases of proximal junctional failure, three cases of rod fracture, and one case of screw prominence in the SAI group and one case of proximal junctional failure, one case of rod fracture, two cases of pseudoarthrosis, one case of screw reposition, and two cases of wound problems in the CI group. In the CI group, postoperative antibiotics were used for a long time due to wound problems, and the patients had to stay in the hospital and eventually went through reoperation. In this study, there was no statistically significant difference in reoperation rate between the two groups. However, as in other studies, the SAI group showed a lower rate of reoperation and proper fusion rate compared to the CI group.
This study had several limitations. The main limitation was that the authors selected the patient’s operative method according to the propensity of the surgeon. Other limitations apply to this study as well, such as its single-center, retrospective nature and the relatively small sample size. As such, the results of this study warrant the need for larger prospective, multicenter studies to further extrapolate findings to future patient care involving complex sacropelvic fixation.
The SAI group and the CI group achieved pain relief and functional recovery. The SAI screw fixation technique was relatively uncomplicated and resulted in good outcomes compared to the CI screw fixation in the rates of reoperation, SSI, wound dehiscence, and symptomatic screw prominence, whereas the rates of lumbosacral pseudoarthrosis and proximal junctional kyphosis and failure were similar in both groups. However, distal screw fracture was more likely to be observed with the SAI screw fixation technique, so prospective and biomechanical studies of the SAI and CI screw fixation techniques are needed.
No potential conflict of interest relevant to this article was reported.
A 67-year-old female patient with lumbar degenerative kyphosis showed screw fracture of right S2 alar iliac screw at 14 months after operation. The screw fracture occurred in the junction between the head and the neck of the screw.
Fusion grading system
Grade | Classification | Anterior fusion criteria | Posterolateral fusion criteria |
---|---|---|---|
I | Definite fusion | Fused with remodeling and trabeculae | Solid trabeculated transverse process and facet fusions bilaterally |
II | Probable fusion | Graft intact, not fully remodeled and incorporated through; no lucency | Thick fusion mass on one side; difficult to visualize on the other |
III | Probable nonunion | Graft intact, but definite lucency at top or bottom | Possible lucency or defect in the fusion mass |
IV | Definite nonunion | Resorption of bone graft and collapse | Definite resorption of graft with fatigue of instrumentation |
Patient demographics and surgical characteristics in SAI group and CI group
SAI group (n=43) | CI group (n=25) | p-value | |
---|---|---|---|
Age (year) | 65.3±9.0 | 60.6±13.5 | 0.131 |
Male/Female | 8/35 | 4/21 | >0.999 |
BMI (kg/m) | 24.0±3.6 | 23.4±2.7 | 0.491 |
Duration of follow-up (month) | 35.6±12.5 | 35.2±14.2 | 0.986 |
No. of screw fixation levels (segment) | 7.3±2.1 | 7.6±3.1 | 0.647 |
Smoking | 4 (9.3%) | 1 (4.0%) | 0.643 |
Diabetes mellitus | 8 (18.6%) | 3 (12.0%) | 0.518 |
Osteoporosis |
14 (32.6%) | 8 (32.0%) | 0.799 |
Previous spinal surgery | 25 (58.1%) | 15 (60.0%) | 0.761 |
Surgical diagnosis | 0.227 | ||
Iatrogenic flat back | 17 (39.5%) | 10 (40.0%) | |
Deformity | 23 (53.5%) | 10 (40.0%) | |
Secondary acquired kyphosis | 3 (7.0%) | 5 (20.0%) |
The data is presented as number (%) or mean±standard deviation. SAI: sacral alar iliac; CI: conventional iliac; BMI: body mass index.
Bone mineral density < −2.5.
Radiographic parameters of sagittal alignment before and after surgery
Preoperative | Postoperative | Final follow-up | |||||||
---|---|---|---|---|---|---|---|---|---|
|
|
| |||||||
SAI group | CI group | p-value | SAI group | CI group | p-value | SAI group | CI group | p-value | |
SVA | 101.0±58.4 | 111.1±84.1 | 0.657 | 35.2±45.7 | 31.3±42.3 | 0.775 | 66.0±44.5 | 65.0±46.3 | 0.941 |
PI-LL | 44.7±18.7 | 46.5±28.0 | 0.772 | 10.4±12.8 | 15.1±11.4 | 0.217 | 20.7±15.3 | 20.9±12.6 | 0.957 |
LL | 7.6±21.4 | 11.7±27.3 | 0.543 | 40.8±13.4 | 40.6±15.1 | 0.964 | 31.7±14.5 | 35.4±15.3 | 0.391 |
SS | 20.6±11.5 | 23.2±13.1 | 0.464 | 30.6±11.5 | 30.6±10.6 | 0.993 | 26.5±9.8 | 29.2±9.5 | 0.333 |
PT | 32.0±10.1 | 34.9±14.6 | 0.383 | 20.6±11.0 | 24.8±8.4 | 0.193 | 26.0±10.2 | 27.1±9.9 | 0.694 |
PI | 52.3±14.0 | 58.2±13.6 | 0.145 | 51.2±13.5 | 55.7±13.9 | 0.279 | 52.4±13.3 | 56.3±14.1 | 0.321 |
TK | 13.2±11.6 | 21.8±16.6 | 0.062 | 23.3±12.2 | 22.3±20.7 | 0.821 | 26.6±14.4 | 30.1±16.2 | 0.412 |
CL | 17.0±11.4 | 19.9±16.5 | 0.513 | 13.4±10.4 | 12.85±16.4 | 0.868 | 18.8±12.2 | 15.2±15.5 | 0.344 |
The data is presented as mean±standard deviation.
SVA: sagittal vertical axis; PI: pelvic incidence; LL: lumbar lordosis; SS: sacral slope; PT: pelvic tilt; TK: thoracic kyphosis; CL: cervical lordosis; SAI: sacral alar iliac; CI: conventional iliac.
Preoperative and postoperative VAS score and lumbosacral fusion status in SAI group and CI group
SAI group (n=43) | CI group (n=25) | p-value | |
---|---|---|---|
Preoperative VAS | 6.7±1.6 | 7.2±1.3 | 0.207 |
Postoperative VAS | 1.6±1.4 | 2.2±1.3 | 0.167 |
Change in VAS | 5±1.8 |
5±1.5 |
0.740 |
L5-S1 fusion status | 0.878 | ||
Grade I | 19 (44.2%) | 9 (36.0%) | |
Grade II | 20 (46.5%) | 14 (56.0%) | |
Grade III | 4 (9.3%) | 2 (8.0%) | |
Grade IV | 0 (0.0%) | 0 (0.0%) |
The data is presented as number (%) or mean±standard deviation. VAS: visual analog scale; SAI: sacral alar iliac; CI: conventional iliac.
p<0.01 according to paired
p-value according to compared between groups.
Complication profiles of SAI group and CI group
SAI group (n=43) | CI group (n=25) | p-value | |
---|---|---|---|
Reopeartion | 7 (16.3%) | 7 (28.0%) | 0.270 |
Proximal junctional failure | 3 (7.0%) | 1 (4.0%) | >0.999 |
Proximal junctional kyphosis | 17 (39.5%) | 10 (40.0%) | 0.969 |
Distal instrument failure | 0.242 | ||
Screw fracture | 7 (16.3%) | 0 (0%) | 0.042 |
Halo formation | 1 (2.3%) | 1 (4.0%) | >0.999 |
Pullout | 0 (0%) | 0 (0%) | >0.999 |
Rod fracture | 8 (18.6%) | 1 (4.0%) | 0.139 |
Surgical site infection | 0 (0%) | 4 (16.0%) | 0.016 |
Wound dehiscence | 0 (0%) | 2 (8.0%) | 0.132 |
Screw prominence | 1 (2.3%) | 2 (8.0%) | 0.550 |
SAI: sacral alar iliac; CI: conventional iliac.
Statistical significance, p<0.05.