Iliac Screw Fixation Technique Research Articles

Connecting the S2 alar-iliac screw head to the satellite rod for surgical correction of degenerative sagittal imbalance.

The S2AI screw technique has several advantages over the conventional iliac screw fixation technique. However, connecting the S2AI screw head to the main rod is difficult due to its medial entry point. We introduce a new technique for connecting the S2AI screw head to a satellite rod and compare it with the conventional method of connecting the S2AI screw to the main rod. Seventy-four patients who underwent S2AI fixation for degenerative sagittal imbalance and were followed up for ≥ 2years were included. All the patients underwent long fusion from T9 or T10 to the pelvis. The S2AI screw head was connected to the satellite rod (SS group) in 43 patients and the main rod (SM group) in 31 patients. In the SS group, the satellite rod was placed medial to the main rod and connected by the S2AI screw and domino connectors. In the SM group, the main rod was connected directly to the S2AI screw head and supported by accessory rods. Radiographic and clinical outcomes were evaluated in both groups. There were no significant differences in postoperative complications, including proximal junctional failure, proximal junctional kyphosis, rod breakage, screw loosening, wound problems, and infection between the two groups. Furthermore, the correction power of sagittal deformity and clinical results in the SS group were comparable to those in the SM group. Connecting the S2AI screw to the satellite rod is a convenient method comparable to the conventional S2AI connection method in terms of radiological and clinical outcomes.

Surgical strategy of lumbopelvic instrumentation in the treatment of lumbosacral tuberculosis: S2-alar-iliac screws vs iliac screws.

The objective of this study was to evaluate the feasibility and clinical outcomes of S2-alar-iliac (S2AI) and iliac screw (IS) techniques in the lumbopelvic reconstruction of lumbosacral tuberculosis patients. From January 2014 to August 2016, 26 patients with lumbosacral tuberculosis attending the 8th Medical Centre of Chinese PLA General Hospital were included in this retrospective study. The subjects were divided into two groups based on the lumbopelvic fixation type (16 patients in the S2AI group, 10 patients in the IS group). The operation time, blood loss, length of hospitalisation, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, visual analogue scale (VAS), Oswestry Disability Index (ODI), ambulatory status, and 36-Item Short-Form Health Survey (SF-36) scores of the patients in two groups were recorded and compared. In addition, surgical complications were collected and analysed. The operation time and intraoperative blood loss were significantly lower in the S2AI group than that in the IS group (P < .05). Compared with preoperative data, postoperative data showed significant improvement in ESR, CRP level, ODI scores, VAS scores, ambulatory status, and SF-36 (P < .05), but there was no significant difference in remission degree between the two groups. Compared with IS group, The S2AI group had significantly lower rates of symptomatic screw prominence (P < .05). Both the IS and S2AI fixation techniques can achieve satisfactory outcomes for the restoration of lumbosacral stability of lumbosacral tuberculosis. Furthermore, compared to the traditional IS fixation technique, the S2AI fixation technique can shorten operation time and reduce surgical trauma for the treatment of lumbosacral tuberculosis.

S2-Alar-Iliac Screw Fixation versus Iliac Screw Fixation in the Treatment of Sacral Fractures

Purpose To compare the short-term therapeutic effects of S2-alar-iliac (S2AI) screw fixation and iliac screw fixation techniques in managing sacral fractures. Methods From September 2015 to May 2020, 42 patients with sacral fractures who underwent lumbopelvic fixation by a single surgeon were analyzed. The patients were divided into the S2AI screw group (19 patients) and the iliac screw group (23 patients). Operative data, reduction quality, postoperative complications, and functional outcomes were evaluated. Results The incidence of unplanned reoperation was significantly different between patients treated with S2AI screws than in those treated with iliac screws (0 versus 6, p = 0.02). The mean intraoperative estimated blood loss was 405.26 ± 229.67 mL in the S2AI screw group and 539.13 ± 246.32 mL in the iliac screw group (P = 0.08). No significant difference was observed in either group regarding the quality of reduction, functional outcome, or low back pain. The reduction quality based on the Matta criteria and excellent/good outcomes were 21/2 in the iliac screw group and 17/2 in the S2AI screw group. The functional outcomes based on the Majeed score and excellent/good/fair outcomes were 17/3/3 in the iliac screw group and 17/1/1 in the S2AI screw group. No complications, including implant breakage, loosening of the implant, or loss of reduction were found in either group during follow-up. Conclusion Both S2AI screws and iliac screws were effective in the treatment of sacral fractures. The use of S2AI screws, however, was independently associated with fewer unplanned reoperations for surgical site infection, wound dehiscence, and symptoms of screw protrusion than the use of iliac screws.

Minimally Invasive Percutaneous Modified Iliac Screw Placement Using Intraoperative Navigation: A Technical Note

The modified iliac screw fixation technique was proposed to be an interesting alternative option for spinopelvic fixation. In this study, we describe a new minimally invasive technique for percutaneous placement of modified iliac screws. A 64-year-old man with ankylosing spondylitis suffered from a 3-column fracture at the L5 vertebra without any neurologic deficit. We performed percutaneous pedicle screw fixation from L2 to S1 with additional modified iliac screws augmentation using an intraoperative navigation. We inserted both S1 pedicle screw and modified iliac screw within a stab incision on each side of the patient's back without using rod connector. The patient's severe low back pain subsided on the day following the operation. There was no clinical low back pain at 2-week follow-up. The 1-year follow-up x-ray showed that the fracture was healed successfully without signs of screw loosening or breakage. The modified iliac screws can be placed safely via percutaneous approach with an intraoperative image guidance. By using this new technique, surgeons can easily adjust the screw head to align with S1 pedicle screw via the same small incision. The rod connectors are not necessary for this technique. This method also prevents the acute angle that can develop between the screw head and shaft of the screw, which is typically found in S2 alar-iliac screw technique.

Biomechanical characterization of three iliac screw fixation techniques: A finite element study

We aim to characterize the biomechanical properties of a modified iliac screw fixation method compared with the classic iliac screw fixation and the S2 alar iliac screw (S2AI) fixation using a FEM.A three-dimensional, non-linear FEM of lumbosacral spine and pelvis (L1-pelvis) was modified to simulate 3 different iliac screw fixations based on posterior screw fusion. The peak von Mises stress (PVMS) values of the iliac screws in the 3 different iliac screw fixations were recorded in during flexion/extension/axial rotation/lateral bending. The interaction stress which arose between the screw head and the shaft of iliac screws, was also measured for each case.The PVMS values of the 3 different iliac screw fixation techniques were lower than the fatigue strength levels under physiological loadings. PVMS of iliac screws was observed in the screw shaft for S2AI, in the screw neck for the modified iliac screw technique, and in the offset connectors of the classic iliac screw technique. The interaction between the screw head and the neck was compressed in modified iliac screw fixation technique. On the other hand, distraction force was observed in the S2AI technique between the screw head and the screw shaft.This FEM study supports our previous clinical results, which found that the modified iliac screw fixation technique can be an effective alternative sacropelvic fixation technique comparable to the classic iliac screw and the S2AI technique.

Modified iliac screw fixation: technique and clinical application.

A conventional iliac bolt and the S2 alar iliac screw fixation technique (S2AI) are commonly used sacropelvic fixation techniques. However, conventional iliac bolt technique requires a lateral connector and commonly has prominent screw head problems. S2AI reportedly has a high instrument failure rate. We aim to introduce a modified iliac screw fixation technique and to investigate its clinical application in adult patients. The entrance site of the modified iliac screw fixation technique was 1 cm medial and 1 cm caudal from the posterosuperior iliac spine. From 2009 to 2015, ten adult patients underwent sacropelvic fixation with the modified iliac screw fixation technique in our spine clinic. A minimum 12-month clinical and radiographic follow-up was adopted. The mean follow-up period was 30.7 months (12-74 months). Mean number of fixation levels was 7.7 segments (5-10 segments). Postoperatively, the C7 plumb line (SVA) was significantly decreased (P = 0.04). Upon the last X-ray, SVA did not differ between postoperative and the last X-ray (P = 0.1). There was no breakage during our follow-up period. There was no prominent screw head. There were no cases requiring implant removal. The modified iliac screw fixation technique does not cause prominence in the sacral region, and does not require a lateral connector, both of which are necessary when using the classical iliac bolt technique. This technique also avoids the acute angle between the screw head and the shaft of the screw commonly seen in S2AI. The modified iliac screw fixation technique can be an effective alternative for sacropelvic fixation.

Biomechanical Comparison of Spinopelvic Reconstruction Techniques in the Setting of Total Sacrectomy

An in vitro biomechanical study. To biomechanically test and evaluate 4 different methods of spinopelvic reconstruction techniques and determine the most biomechanically stable construct for stabilization of the spinopelvic junction after total sacrectomy. Total sacrectomy is necessary to treat a sacral tumor when it involves the S1 vertebra. Instrumentation and reconstruction of the lumbar spine and pelvis are required after total sacrectomy and can be achieved by various reconstruction techniques. Currently, the preferred method of spinopelvic fixation is controversial. Seven human cadaveric (L1-pelvis) specimens were evaluated in flexion-extension, lateral bending, and axial rotation in a total sacrectomy model. Test constructs included (1) intact; (2) double-rod, double iliac screw (DDS); (3) single-rod, single iliac screw (SSS); (4) double iliac screw (DIS) fixation; and (5) modified Galveston technique (MGT). A load control protocol with 7.0 Nm moments applied at a rate of 1.5°/s was used to establish range of motion values for each tested construct on a 6-df spine motion simulator. Data were analyzed and normalized to intact. All instrumented constructs offered significant stability in all loading conditions compared with the intact condition. Stability offered by different constructs in all loading conditions trended as follows: DDS>DIS>SSS>MGT. Overall, the DDS construct provided 55%, 43%, and 60% more stability than SSS, DIS, and MGT, respectively. This was significant in flexion-extension when compared with SSS and in all loading conditions when compared with MGT. In the setting of total sacrectomy, the double-rod double iliac screw method provided the most rigid fixation, followed by DIS fixation, single-rod single screw, and the MGT. In spinopelvic reconstruction, the use of double iliac screws is recommended compared with single iliac screw fixation techniques when treating unstable conditions caused by total sacrectomy.

Biomechanical Comparison of Spinopelvic Reconstruction Techniques in the Setting of Total Sacrectomy

STUDY DESIGN An in vitro biomechanical study. OBJECTIVE To biomechanically test and evaluate 4 different methods of spinopelvic reconstruction techniques and determine the most biomechanically stable construct for stabilization of the spinopelvic junction after total sacrectomy. SUMMARY OF BACKGROUND DATA Total sacrectomy is necessary to treat a sacral tumor when it involves the S1 vertebra. Instrumentation and reconstruction of the lumbar spine and pelvis are required after total sacrectomy and can be achieved by various reconstruction techniques. Currently, the preferred method of spinopelvic fixation is controversial. METHODS Seven human cadaveric (L1-pelvis) specimens were evaluated in flexion-extension, lateral bending, and axial rotation in a total sacrectomy model. Test constructs included (1) intact; (2) double-rod, double iliac screw (DDS); (3) single-rod, single iliac screw (SSS); (4) double iliac screw (DIS) fixation; and (5) modified Galveston technique (MGT). A load control protocol with 7.0 Nm moments applied at a rate of 1.5°/s was used to establish range of motion values for each tested construct on a 6-df spine motion simulator. Data were analyzed and normalized to intact. RESULTS All instrumented constructs offered significant stability in all loading conditions compared with the intact condition. Stability offered by different constructs in all loading conditions trended as follows: DDS>DIS>SSS>MGT. Overall, the DDS construct provided 55%, 43%, and 60% more stability than SSS, DIS, and MGT, respectively. This was significant in flexion-extension when compared with SSS and in all loading conditions when compared with MGT. CONCLUSION In the setting of total sacrectomy, the double-rod double iliac screw method provided the most rigid fixation, followed by DIS fixation, single-rod single screw, and the MGT. In spinopelvic reconstruction, the use of double iliac screws is recommended compared with single iliac screw fixation techniques when treating unstable conditions caused by total sacrectomy.

Biomechanical advantages of dual over single iliac screws in lumbo-iliac fixation construct

The development of iliac screws has provided a markedly easier way for spino-pelvic instrumentation than the classical Galveston technique. However, high rates of iliac screw loosening and breakage are usually reported, especially in cases where bilateral single iliac screws are used. Therefore, there is a need for exploring more stable iliac fixation techniques. Thus, the objective of this study was to compare the biomechanical effects of bilateral single and dual iliac screws on the stability of L3-iliac fixation construct under total sacrectomy condition. In this study, L2-pelvic specimens were harvested from seven fresh human cadavers. After biomechanically testing the intact state simulated by L3-L5 pedicle screw fixation, destabilization was introduced by total sacrectomy. Upon destabilization, L3-iliac screw-rod reconstructions were performed by four different techniques as follows: (1) bilateral single short iliac screws (Single-Short); (2) bilateral single long iliac screws (Single-Long); (3) bilateral dual short iliac screws, placed in the upper and lower iliac columns (Dual-UL); and (4) bilateral dual short iliac screws, all placed in the lower iliac column (Dual-Lower). These four iliac screw fixation techniques were sequentially preformed in the same specimen, and the lengths of the short and long iliac screws were 70 and 130 mm, respectively. Biomechanical testing was performed on a material testing machine under 800 N compression and 7 Nm torsion loading modes to evaluate the construct stiffness. In compression, the stiffness of the L3-iliac fixation constructs of Single-Short, Single-Long, Dual-UL, and Dual-Lower techniques were 73, 76, 98, and 108% of the intact state, respectively. No significant differences were detected between Single-Short and Single-Long (P = 0.589) techniques. However, the compressive stiffness of these two techniques was significantly lower than the intact state, and the Dual-UL and Dual-Lower techniques (P < 0.05). There was no statistical difference between the intact condition and the Dual-Lower technique (P = 0.109). Interestingly, Dual-Lower exhibited notably higher compressive stiffness than Dual-UL (+10.3%, P = 0.049). In torsion, the stiffness of Single-Short, Single-Long, Dual-UL, and Dual-Lower techniques were 72, 79, 105, and 109% of the intact condition, respectively. No significant differences were detected between Single-Short and Single-Long techniques (P = 0.338), and also among Dual-UL, Dual-lower techniques, and the intact state (P > 0.05). However, Single-Short and Single-Long techniques provided markedly lower construct torsional stiffness than the other three groups (P < 0.05). For lumbo-illiac reconstruction after total sacrectomy, even the use of bilateral single, long iliac screws do not help in restoring the local stability to the intact condition. However, dual iliac screws provide much higher construct stability than single iliac screw techniques. Therefore, dual iliac screw technique should be preferred for treating the unstable situation caused by total sacrectomy.

The Effect of Screw Length and Bone Cement Augmentation on the Fixation Strength of Iliac Screws

Comparison of the biomechanical fixation strengths offered by 3 iliac screw fixation techniques: short screw, short screw augmented with cement, and long screw. Evaluate the effect of screw length and bone cement augmentation on the fixation strength of iliac screw upon fatigue loading. Iliac screws have been used in treating spinal disorders such as spinal deformity, spondylolisthesis, and sacral tumor. In clinical practices, both short screws and long screws are being used. It has been reported that short iliac screws have a higher rate of loosening. Therefore, short iliac screws are being used with bone cement augmentation to improve fixation. To date, no biomechanical study has compared the strengths of these 3 different iliac screw fixation techniques. Fresh, frozen human cadaveric pelvis specimens (n = 18, 12 males, 6 females, average age 61 y) were used. Bone density was measured to characterize bone quality. The specimens were randomly divided into 2 groups. In group 1 (n = 8), short screws of 7.0-mm diameter and 70 + or - 4 mm length (as the length of exceeding over ischial notch) and long screw of 7.0-mm diameter and 120 + or - 4 mm length were placed on either side of the pelvis (left and right). In group 2 (n = 10), short iliac screws were placed after augmentation with polymethyl methacrylate bone cement on 1 side of the pelvis and long iliac screw were placed on the other side (left and right). Cyclic loading ranging from 20 to 200 N was applied to each screw at a frequency of 2 Hz up to 5000 cycles. Pullout tests were then conducted at the rate of 5 mm/min after the fatigue test, and the maximum pullout strength for each screw was recorded and analyzed. The maximum pullout strength of the long screw and short screw groups after fatigue conditioning were 2386 + or - 1470 and 833 + or - 681 N respectively. Significant difference was found between the 2 groups (P < 0.05). The short iliac screw had a higher loosening rate. The pullout force of the short screw fixation with augmentation and the long screw fixation after cyclic loading were 2436 + or - 915 and 2529 + or - 1055 N, respectively. No significant difference was found between the 2 groups (P > 0.05). Short iliac screws are susceptible to loosening after cyclic loading. Bone cement augmentation of short screws has demonstrated a significant increase in the fixation strength of short screws to an extent similar to that of long iliac screws. Thus, short iliac screw fixation after augmentation with bone cement will be a viable clinical option for spino-pelvic reconstruction.

Palliative dual iliac screw fixation for lumbosacral metastasis

Spinal fixation for destructive metastatic lesions at the lumbosacral junction is challenging because of the large and unique load-bearing characteristics present. In particular, caudal fixation is difficult in cases of sacral destruction because of insufficient S-1 pedicle screw anchorage. The authors describe their surgical technique for secure iliac screw placement and the clinical results obtained in five patients with metastatic spinal disease. All patients in this study underwent palliative operations with dual iliac screw fixation between April 1999 and October 2002, and the clinical and radiological findings were assessed. In all five patients, spinal metastases extended into the sacrum. The metastases were from renal cell carcinomas in two patients, lung cancer in two, and a paraganglioma in one patient. Postoperative follow-up periods ranged from 3 months to 6 years (mean 28.4 months). Preoperatively, four patients could not walk due to severe pain or neurological compromise. Postoperatively, all patients reported a reduction in pain and regained the ability to walk. Complications included one case of early wound infection. In the patients with long survival after the operation, there was one case of iliac screw loosening and one case of rod breakage. The dual iliac screw fixation technique provided sufficient immediate stability for destructive lumbosacral metastasis.