Sacral Alar Screws Research Articles

Low profile posterior lumbar-sacral interbody fusion for lumbosacral degenerative diseases: a technical note

BackgroundThe purpose of this study was to report our surgical experience in patients with lumbosacral degenerative diseases who underwent posterior decompression and interbody fusion fixed with cortical bone trajectory screw and sacral alar screw, which is known as low-profile posterior lumbosacral interbody fusion (LP-PLSIF).MethodsPatients with lumbosacral degenerative disease who underwent LP-PLSIF and traditional PLSIF (control group) internally fixed with pedicle screws were included retrospectively. Patients’ demographic data, operative parameters, and perioperative complications were recorded and analyzed.ResultsA total of 18 patients were enrolled in this study, which included 9 patients (5 male and 4 female) who underwent LP-PLSIF, and 9 patients (4 male and 5 female) who underwent traditional PLSIF. There wasn’t a significant difference in the average age between the two groups, 56.78 ± 10.92 years in the LP-PLSIF group and 60.22 ± 8.21 years in the PLSIF group (p = 0.460). The bone mineral density (BMD) of the two groups of patients were -2.00 ± 0.26 T and -2.13 ± 0.19 T, respectively (P = 0.239). The mean postoperative follow-up time was 12.7 months (range, 12–14 months). The mean operation time was 142.78 ± 11.21 min and 156.11 ± 13.41 min in the LP-PLSIF group and PLSIF group respectively (P < 0.05). The average blood loss was 137.78 ± 37.09 ml in the LP-PLSIF group, and 150.00 ± 27.84 ml in the PLSIF group (P = 0.441). The average postoperative drainage was 85.56 ± 37.45 ml and 122.22 ± 22.24 ml in the LP-PLSIF group and control group respectively (P < 0.05). Patients in the LP-PLSIF group had shorter incision length compared with the control group, 61.44 ± 10.56 mm vs. 74.56 ± 10.22 mm (P < 0.05). The average length of hospitalization of 11.33 ± 2.92 days in the LP-PLSIF group, and 11.11 ± 1.62 days in the PLSIF group (p = 0.844). All patients had significant improvement in VAS pain score, ODI, and JOA evaluation. However, patients in the LP-PLSIF group had better improvement in terms of VAS back pain and ODI in the short term after the operation. There were no neurological complications or wound infection. The fusion rate at the last follow-up was 100% (9 of 9) in the LP-PLSIF group, and 88.89% (8 of 9) in the control group based on CT scans. 1 patient in the control group had asymptomatic sacral pedicle screw loosening.ConclusionsLP-PLSIF is a safe and effective surgical technique for patients with lumbosacral degenerative disease, which has the potential strength of less invasive and better clinical improvement.

Application of cortical bone trajectory screw and sacral alar screw internal fixation for surgical treatment of lumbar adjacent segment degeneration

Objective: To explore the application of cortical bone trajectory screw (CBTS) and sacral alar screw (SAS) internal fixation in the treatment of lumbar adjacent segment degeneration (ASD) and evaluate its clinical effect. Methods: Data of 24 patients who were diagnosed with ASD and treated by CBTS or SAS in Beijing Chaoyang Hospital were retrospectively reviewed. There were 14 males and 10 females with a mean age of (67.9±8.2) years. The patients were followed-up for (2.6±0.4) years. Perioperative parameters including operation time, intraoperative blood loss and postoperative time on the ground were counted. All patients were followed-up for at least 2 years. Visual analogue scale (VAS) and the Oswestry disability index (ODI) were compared between pre-operation and at the last follow-up. The internal fixation-related complications, pseudarthrosis and adjacent re-degeneration were evaluated in the follow-up. Results: There were 14 proximal ASD patients, 8 distal ASD patients, 1 both ends ASD patient and 1 ASD patient in between the fusion surgeries. Bone mineral density (BMD) T score of the adjacent vertebrae was -1.98±0.91 on average. The ASD patients were re-operated with CBTS and SAS internal fixation technique. A small incision was made in the revision surgery and the original fixation was not completely cut open and removed. The mean operation time was (125±36) min, mean blood loss was (85±33) ml. The postoperative ambulation time was (3.1±1.9) days, and the hospitalization time was (9.0±2.6) days. Before the operation, the average VAS (back pain) score was 5.2±1.0, the average of VAS (leg pain) score was 6.8±1.9 and ODI was 56.6%±12.8%. VAS score was reduced to 1.4±0.6 (waist pain) and 0.9±0.4 (leg pain). ODI was improved to 13.8%±6.3%. All the difference between preoperative and the last follow-up was statically significant (all P<0.01). No internal fixation failure, pseudarthrosis and adjacent re-degeneration were observed in the final follow-up. Conclusion: The application of CBTS and SAS internal fixation techniques in the surgical treatment of lumbar ASD has the advantages of less trauma, faster postoperative recovery, reliable internal fixation, and fewer complications, especially in patients with low bone mineral density.

Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study.

Previous reports have focused on the complications of L5 nerve root injury caused by anterolateral misplacement of the S1 pedicle screws. Anatomical knowledge of the L5 nerve root in the pelvis is essential for safe and effective placement of the sacral screw. This cadaveric study aimed to investigate the course of the L5 nerve root in the pelvis and to clarify a safe zone for inserting the sacral screw. Fifty-four L5 nerve roots located bilaterally in 27 formalin-fixed cadavers were studied. The ventral rami of the L5 nerve roots were dissected along their courses from the intervertebral foramina to the lesser pelvis. The running angles of the L5 nerve roots from the centerline were measured in the coronal plane. In addition, the distances from the ala of the sacrum to the L5 nerve roots were measured in the sagittal plane. The authors found that the running angles of the L5 nerve roots changed at the most anterior surface of the ala of the sacrum. The angles of the bilateral L5 nerve roots from the right and left L5 intervertebral foramina to their inflection points were 13.77° ± 5.01° and 14.65° ± 4.71°, respectively. The angles of the bilateral L5 nerve roots from the right and left inflection points to the lesser pelvis were 19.66° ± 6.40° and 20.58° ± 5.78°, respectively. There were no significant differences between the angles measured in the right and left nerve roots. The majority of the L5 nerves coursed outward after changing their angles at the inflection point. The distances from the ala of the sacrum to the L5 nerve roots in the sagittal plane were less than 1 mm in all cases, which indicated that the L5 nerve roots were positioned close to the ala of the sacrum and had poor mobility. All of the L5 nerve roots coursed outward after exiting the intervertebral foramina and never inward. To prevent iatrogenic L5 nerve root injury, surgeons should insert the S1 pedicle screw medially with an angle > 0° toward the inside of the S1 anterior foramina and the sacral alar screw laterally with an angle > 30°.

Clinical application of sacral alar screw fixation in surgical treatment of lumbosacral degenerative disease

Objective: To verify the safety and feasibility of sacral alar screw fixation and fusion surgery in lumbosacral area. Methods: The clinical and radiological data of patients receiving L5/S1 single-level cortical bone trajectory screw combined with sacral alar screw decompression fixation and fusion in Beijing Chaoyang Hospital due to lumbar spinal stenosis from January 2019 to January 2020 were retrospectively analyzed. The clinical data included operation duration, intraoperative blood loss, postoperative drainage, pain and function scores during follow-up. The radiological data included preoperative and postoperative follow-up X-rays and three-dimensional reconstruction of lumbar spine CT. The fusion status and complication of internal fixation, such as screw loosening and fixation failure were evaluated by the radiological examination. Results: According to the inclusion and exclusion criteria, a total of 16 patients (7 males and 9 females) were included, with an average age of (69.6±5.2) years. The patients were followed-up for (16.2±1.7) months. The average operation duration was (144±21) min, the intraoperative blood loss was (103±20) ml, and the postoperative drainage was (80±34) ml. The patient's low back pain visual analogue scale (VAS) score was 6.8±1.0 before surgery, and it was improved to 0.9±0.7 at the last follow-up; leg pain VAS score was 6.1±0.9 before the operation and it improved to 0.9±0.7 at the last follow-up; Oswestry disability index (ODI) function score was 66.2%±8.0% before the surgery and it decreased to 26.6%±7.2% at the last follow-up. No neurological complications, surgical site infection, screw loosening, internal fixation failure or cage displacement were observed during the follow-up. The fusion rate was 68.8% (11/16) at 6 months post operation. Conclusion: It is safe, feasible and effective to apply cortical screws combined with sacral alar screws in short-segment decompression, fixation and fusion surgery on the lumbosacral region to treat lumbosacral spinal stenosis.

Second Sacral Alar Screw Fixation: Anatomic Study of Three-Dimensional Computed Tomography and Case Report

S2 alar screw would be an alternative choice without breaking the sacroiliac joint. The aim of this study was to measure radiographic parameters for optimal placement of posterior S2 alar screw for instrumentation and fusion. Three-dimensional computed tomography scans of the pelvis of 60 normal adults were used to map the S2 alar screw. Entry point was typically chosen lateral and superior to the S2 dorsal foramen. Ideal S2 alar screw trajectories were explored by rotating the three-dimensional pelvis, while ensuring trajectories were of maximum length and width. After identification of an optimal trajectory, related linear anatomic parameters and sagittal and transverse angles were determined. Ideal S2 alar screw trajectories were identified in each computed tomography scan. According to this morphometric study, trajectories for female patients were more lateral in the transverse plane (female 33.73 ± 5.99° vs. male 29.82 ± 4.11°, P < 0.001). Maximal length of trajectory in male patients was significantly longer than in female patients (female 40.82 ± 4.29 mm vs. male 43.42 ± 4.02 mm, P=0.001). Fourteen S2 alar screws were used in 7 patients with high-grade spondylolisthesis, scoliosis, or nonunion at lumbosacral site. No complications occurred during S2 alar screw placement. One S2 screw failed owing to severe local osteoporosis. No patient developed local pain or wound-related problems. S2 alar screw is an alternative sacral fixation point to provide additional biomechanical stability of lumbosacral constructs. A trajectory with maximum length through the S2 ala can be determined using three-dimensional computed tomography.

A radiological evaluation of the morphometry and safety of S1, S2 and S2-ilium screws in the Asian population using three dimensional computed tomography scan: an analysis of 180 pelvis

Studies of sacral pedicle anatomy have been reported in the European population. However, the feasibility for the use of S1, S2 and S2-ilium screws has not been fully investigated in the Asian population. To assess feasibility, morphometric parameters and safety of S1, S2 and S2-ilium screw insertion in the Asian population. 180 three dimensional computed tomography (CT) scans of pelvis (90 males and 90 females) with contrast were analysed using Mimics(®) version 13.1 (Materialise, Belgium) software. All parameters were measured using this programme. The safety medial trajectory of S1 pedicle screw was 11.8 ± 3.9 to 37.1 ± 4.5° in males and 11.7 ± 3.1 to 35.9 ± 4.4° in females. The screw length was from 35.0 ± 3.0 to 58.3 ± 3.1 mm in males and from 31.9 ± 2.6 to 53.1 ± 3.5 mm in females. Right S1 pedicle screws were safe as long as the anterior cortical penetration of quadrant 2, 3 and 4 were avoided. On the left, it was safe for the screws to exit at quadrant 1, 2 and 3. The lateral trajectory of S2 sacral alar screw was from 0 to 32.6 ± 3.3° in males and from 0 to 33.6 ± 3.5° in females. The screw length was from 23.9 ± 3.2 to 53.1 ± 4.1 mm in males and from 23.0 ± 2.5 to 53.2 ± 4.5 mm in females. For S2 screws, on the right side, the frequency of the internal iliac artery location was 7.2, 38.3, 47.2 and 1.7% for quadrants 1, 2, 3 and 4, whereas on the left side, the frequency was 7.8, 50.6, 33.9 and 2.2% for quadrants 1, 2, 3 and 4. For S2-ilium screws, the lateral trajectory was from 39.3 ± 3.1 to 50.4 ± 6.1° in males and from 39.5 ± 3.1 to 50.2 ± 5.9° in females. The screw lengths were from 85.3 ± 22.2 to 122.6 ± 11.4 mm and from 86.4 ± 22.7 to 122.2 ± 11.9 mm in males and females, respectively. The application of S1, S2 and S2-ilium screws are feasible. The amount of medial angulation and the ideal screw length in the Asian population must be borne in mind during insertion. Right S1 screws carry higher risk of injury to the internal iliac artery when the anterior cortical penetration occurs due to the course of the iliac vessels.

The Effect of Sacral Alar Screw on Long-level Fusion Including Lumbosacral Segment

Study Design: This is a retrospective study. Objectives: To evaluated the clinical and radiological effectiveness of sacral alar screws for augmentation of S1 pedicle screws in longlevel fusion including L5-S1 segment. Summary of Literature Review: The fusion rates of lumbosacral junction in long-level fusion are various when S1 pedicle screws are used without augmentation. But, reports of sacral alar screw augmentation are rare. Material and Methods: From 1996 to 2005, 63 patients performed more than two-level fusion including lumbosacral junction were reviewed. 47 patients underwent lumbosacral fusion with S1 pedicle screws only (S1 group), and 16 patients with sacral alar screws augmentation in addition to S1 pedicle screws (S1-2 group). Radiologically, bony union, halo sign, and breakage of implants were evaluated. Clinically, complications associated with screw placement and general complications were evaluated. Results: Bony union was obtained in 56 cases(89%) at postoperative 4.3 months. Nonunion was observed in 7 cases(11%, S1 group:5, S1-2 group:2). Loosening of S1 pedicle screw was observed in 32 cases(89%) of S1 group and in 4 cases(25%) of S1-2 group. It showed statistical significance between two groups. Sacral alar screw loosening occurred in 8 cases(50%) of S1-2 group. Metal breakage was developed in 2 cases of S1 group without nonunion or loosening. Postoperative infection occurred in 7 cases(11%, S1 group:5, S1-2 group:2). Conclusions: Sacral alar screw augmentation was effective on protecting the loosening of S1 pedicle screw. Additional sacral alar screw can improve the rate of fusion for lumbosacral junction despite no statistical significance.

Three-dimensional image-guided placement of S2 alar screws to adjunct or salvage lumbosacral fixation

Background Context Achieving fusion across the lumbosacral junction is challenging because of the unfavorable biomechanics associated with ending a fusion at this level. Bicortical placement of S1 pedicle screws can increase the construct stability at the lumbosacral junction; however, construct failure and pseudoarthrosis can still result. Iliac screws have been shown to increase the stiffness of lumbosacral constructs, but disadvantages include difficulty in connecting the iliac screw to adjacent sacral screws, painful screw loosening or prominence requiring removal, and the inability to place the screws in some patients with previous iliac crest autograft harvest. Purpose The purpose of the study is to describe a technique of S2 alar screw placement using three-dimensional image guidance. Study Design/Setting The study design is a retrospective analysis. Patient Sample Twenty patients undergoing lumbosacral fusion had 32 screws placed using this technique. Outcome Measures An independent radiologist graded screw placement and lumbosacral fusion on thin-cut postoperative computed tomographic (CT) scans. Methods Image guidance in this study was accomplished with the Medtronic Stealth Station Treon (Medtronic Inc., Littleton, MA, USA) used in conjunction with the O-ARM (Medtronic Inc.). Indications for placement of S2 alar screws included the following: to adjunct S1 pedicle screws in multilevel fusion cases; as an adjunct or alternative to S1 pedicle screws in pseudoarthrosis revision cases in which the S1 screws had loosened; as an alternative to S1 pedicle screws in cases where medial trajectory of an S1 pedicle screw was difficult to obtain because of a low-set lumbosacral junction; and a combination of the above. The entry point of the screw was typically chosen lateral and superior to the S2 dorsal foramen with the trajectory directed anterior, inferior, and lateral. Attempt was made to place the screw with the tip purchasing, but not penetrating through, the triangular area of cortical bone that can be found at the anterior, inferior, and lateral boundary of the sacral ala. An independent radiologist graded the placement of the screws on the intraoperative CT scan obtained with the O-ARM or on postoperative CT scans. Lumbosacral fusion was assessed on postoperative CT scans obtained at follow-up. Results No complications occurred in this study as a result of S2 alar screw placement or image guidance. Five screws did penetrate the anterior cortex of the sacrum, with no clinical consequence. At the time of abstract submission, 16 patients were able to have follow-up CT scans, 15 of which were graded as solid fusion at the lumbosacral junction by the grading radiologist. Conclusions Three-dimensional image guidance allows for safe placement of large S2 sacral alar screws that can provide additional biomechanical stability to lumbosacral constructs or serve as an alternate point of sacral fixation when S1 pedicle screws cannot be salvaged or placed in a medial trajectory.

A Comparison of Clinical Stability of Distal Instrument Fused Down to S1 with and without Sub-S1 Alar Screw in the Long Fusion using Segmental Pedicle Screw for Lumbar Degenerative Deformity

Study Design: This is a retrospective study. Objectives: We wanted to assess the stability of distal instrumentation using the bilateral S1 and sacral alar screws for the treatment of degenerative lumbar deformity. Summary of the Literature Review: Various instrumentation methods have been introduced for increasing the strength of lumbosacral fusion. However, there are not many clinical studies that have evaluated the effectiveness of a sub-S1 alar screw for treating degenerative lumbar deformity surgery. Materials and Methods: A total of 39 patients with degenerative lumbar deformity were treated by long fusion and we retrospectively analyzed these patients after a minimum follow-up of 1 year. All the patients underwent an operation with distal instrumentation using either bilateral S1 screws alone (the S1 group) or additional bilateral sub-S1 sacral alar screws (the SA group). There were 19 patients in the S1 group and 20 patients in the SA group. The stability of the distal instrumentation was assessed by breakage or backout of a rod and/or screws based on simple radiography. Results: Instability of the distal instrumentation was detected in 6 cases (32%) in the S1 group and in 1 case (5%) in the SA group. The SA group had a more stability of the distal instrumentation than that of the S1 group with a significant difference (P 0.05). Conclusions: Bilateral sacral alar screws coupled with bilateral S1 screws can provide good distal fixation for stability of the distal instrumentation when performing long fusion for treating degenerative lumbar deformity.

Hydroxyapatite enhancement of posterior spinal instrumentation fixation.

The ability of hydroxyapatite (HA) materials to enhance the fixation strength of posterior spinal instrumentation was examined in 19 adult mongrel dogs. Sixteen dogs underwent bilateral placement of lumbar transpedicular screws from L1 to L6, sacral alar screws, and posterior iliac rods. The six transpedicular screw test groups included standard and plasma-sprayed HA-coated screws with the recommended insertion technique, standard and HA-coated screws with a poor initial fit insertion technique using an oversized pilot hole, and HA-grout augmentation of standard and HA-coated screws with a poor initial fit. The sacral alar screws and posterior iliac rods were either uncoated or HA-coated. Six dogs were killed immediately; ten dogs were killed at 6 weeks, and the fixation elements were mechanically tested or histologically examined. Three additional dogs and synthetic bone material were used for additional baseline mechanical testing. The strength of standard screws with recommended insertion did not change after 6 weeks in vivo. HA-coated screws were initially 13% less resistant to pull out than standard screws, but this difference was not significant at 6 weeks. Screws inserted with a poor initial fit technique were significantly weaker initially; at 6 weeks, pull-out strength was similar to the standard screws properly inserted. The HA-grout material significantly enhanced pull-out strength for both screw types at 6 weeks. Sacral alar screw pull-out strength was not significantly different between standard and HA-coated screws initially or at 6 weeks. HA-coated rods were initially twice as resistant to pull out than standard rods and became stronger after 6 weeks in vivo, whereas standard rods became significantly weaker. Histologically, the quantity and morphology of bone around all implants was similar, with HA-coated rods and screws demonstrating regions of direct attachment to bone. An osteoconductive response and new bone formation was observed within the HA-grout material. Scanning electron microscopic observation of mechanically tested implants revealed a shear failure of surrounding bone (and HA if present) at the screw outer thread margin or at the bone-metal or HA-metal interfaces for the posterior iliac rods. The strength of poorly inserted transpedicular screws was significantly enhanced in vivo by the resorbable HA-grout material. The lower strength of HA-coated screws was attributed to screw geometry changes resulting from the coating process, and modifications of screw coating are recommended.