Satellite Rod Research Articles

Assessing the unique characteristics associated with surgical treatment of dystrophic lumbar scoliosis secondary to neurofibromatosis type 1: a single-center experience of more than 10 years.

Dystrophic lumbar scoliosis secondary to neurofibromatosis type 1 (DLS-NF1) may present an atypical, unique curve pattern associated with a high incidence of coronal imbalance and regional kyphosis. Early surgical intervention is complicated and risky but necessary. The present study aimed to assess the unique characteristics associated with the surgical treatment of DLS-NF1. Thirty-nine consecutive patients with DLS-NF1 treated surgically at a mean age of 14.4 ± 3.9 years were retrospectively reviewed. Patients were stratified into three types according to the coronal balance classification: type A (C7 translation < 30 mm), 22 patients; type B (concave C7 translation ≥ 30 mm), 0 patients; and type C (convex C7 translation ≥ 30 mm), 17 patients. Types B and C were considered to be coronal imbalance. The diversity of surgical strategies, the outcomes, and the related complications were analyzed. The posterior-only approach accounted for 79.5% in total; the remaining 20.5% of patients received either additional anterior supplemental bone grafting (12.8%) to strengthen the fixation or convex growth arrest (7.7%) to reduce growth asymmetry. The lower instrumented vertebra (LIV) being L5 accounted for the largest share (41%), followed by L4 and above (35.9%), the sacrum (15.4%), and the pelvis (7.7%). Type C coronal imbalance was found in 23 patients (59%) postoperatively, and the incidence was significantly higher in the preoperative type C group (14/17 type C vs 9/22 type A, p = 0.020). All the patients with postoperative coronal imbalance showed ameliorative transition to type A at the last visit. The rate of screw malposition was 30.5%, including 9.9% breached medially and 20.6% breached laterally, although no serious neurological impairment occurred. The incidence of rod breakage was 16.1% (5/31) and 0% in patients with the posterior-only and combined approaches, respectively. Four revisions with satellite rods and 1 revision with removal of iliac screw for penetration into the hip joint were performed. Surgical strategies for DLS-NF1 were diverse across a range of arthrodesis and surgical approaches, being crucially determined by the location and the severity of dystrophic changes. The LIV being L5 or lower involving the lumbosacral region and pelvis was not rare. Additional posterior satellite rods or supplementary anterior fusion is necessary in cases with insufficient apical screw density. Despite a high incidence of postoperative coronal imbalance, improvement of coronal balance was frequently confirmed during follow-up. Neurological impairment was scarce despite the higher rate of screw malposition.

Using Satellite Rod Technique in Patients with Severe Kyphoscoliosis Undergoing Three-Column Osteotomy: A Minimum of 2 Years' Follow-up.

ObjectiveTo introduce the satellite rod technique utilized in severe spinal deformity after three‐column osteotomy (3CO) and to evaluate the radiographic and clinical outcomes at 2‐year follow‐up, further discussing its utilization in this particular cohort.MethodsA total of 32 (19 females and 13 males) with an average age of 32.9 ± 18.3 years from December 2012 to March 2016 were retrospectively reviewed. Radiographic measurements were performed on standing full‐spine anteroposterior and lateral radiographs preoperatively, postoperatively, and at last follow‐up. The coronal parameters including Cobb angle and distance between C7 plumb line and center sacral vertical line (C7PL‐CSVL), as well as the sagittal parameters including global kyphosis (GK) and sagittal vertical axis (SVA) were measured at three time points. The Scoliosis Research Society‐22 questionnaire (SRS‐22) was fulfilled preoperatively and at each follow‐up. Paired t test would be used to determine whether there was a significant difference between time points.ResultsA total of 32 patients were enrolled in this study with mean age of 32.9 ± 18.3 (range, 12 to 66) years old. Twenty patients underwent pedicle subluxation osteotomy (PSO) and 12 patients underwent vertebral column resection (VCR). The pathogenesis of this cohort included neuromuscular scoliosis (11 cases), congenital kyphoscoliosis (seven with hemivertebrae and five with segmentation failure), degenerative spinal deformity (five cases), and thoracolumbar tuberculosis with angular kyphosis (four cases). The post‐operative Cobb angle decreased significantly from 49.1° ± 28.0° to 19.0° ± 16.7° with a correction rate of 65.2% ± 21.8%. At final follow‐up, the average Cobb angle was 19.4° ± 16.9° and no obvious loss of correction was found. The preoperative, postoperative, and last follow‐up C7PL‐CSVL were 23.9 ± 14.5 mm, 15.7 ± 11.1 mm, and 12.1 ± 7.4 mm, respectively. Significant postoperative improvement was attained while there was no change observed at last follow‐up. Postoperative GK significantly improved from 73.8° ± 28.1° to 23.2° ± 11.7° with the correction rate of 66.0% ± 17.9%. SVA decreased significantly from 42.9 ± 33.9 mm to 24.1 ± 21.1 mm. The average GK and SVA at final follow‐up were 22.7° ± 10.1° and 23.5 ± 21.1 mm, respectively and no obvious loss of correction was observed of them during follow‐up. In addition, no change or loss of motor or somatosensory evoked potential occurred during surgery. During the follow‐up, two malposition screws and one rod breakage were found.ConclusionThe satellite rod used in patients with severe kyphoscoliosis undergoing 3CO could yield favorable radiological and clinical outcomes. With the utilization of this technique, the coronal and sagittal balance could be well‐maintained during follow‐up.

Total en bloc spondylectomy combined with the satellite rod technique for spinal tumors

BackgroundInstrumentation failure (IF) is a common complication after total en bloc spondylectomy (TES) in spinal tumors. This study aims to evaluate the clinical outcomes of TES combined with the satellite rod technique for the treatment of primary and metastatic spinal tumors.MethodsThe clinical data of 15 consecutively treated patients with spinal tumors who underwent TES combined with the satellite rod technique by a single posterior approach from June 2015 to September 2018 were analyzed retrospectively. Radiographic parameters including the local kyphotic angle (LKA), anterior vertebral height (AVH), posterior vertebral height (PVH), and intervertebral titanium mesh cage height (ITMCH) were assessed preoperatively, postoperatively, and at the final follow-up. The visual analog scale (VAS), Oswestry Disability Index (ODI), and American Spinal Injury Association (ASIA) scale were used to assess quality of life and neurological function. The operative duration, volume of blood loss, and complications were also recorded.ResultsThe mean operation time and volume of blood loss were 361.7 min and 2816.7 mL, respectively. During an average follow-up of 31.1 months, 2 patients died of tumor recurrence and multiple organ metastases, while recurrence was not found in any other patients. Solid fusion was achieved in all but one patient, and no implant-related complications occurred during the follow-up. The VAS, ODI, and ASIA scores significantly improved from before to after surgery (P < 0.05). The LKA, AVH, and PVH significantly improved from before to immediately after surgery and to the final follow-up (P < 0.05), and the postoperative and final follow-up values did not significantly differ (P > 0.05).ConclusionsTES combined with the satellite rod technique can yield strong three-dimensional fixation and reduce the occurrence of rod breakage, thereby improving the long-term quality of life of patients with spinal tumors.

Comprehensive classification system for multirod constructs across three-column osteotomies: a reliability study.

In this study, the authors' goal was to determine the intra- and interobserver reliability of a new classification system that allows the description of all possible constructs used across three-column osteotomies (3COs) in terms of rod configuration and density. Thirty-five patients with multirod constructs (MRCs) across a 3CO were classified by two spinal surgery fellows according to the new system, and then were reclassified 2 weeks later. Constructs were classified as follows: the number of rods across the osteotomy site followed by a letter corresponding to the type of rod configuration: "M" is for a main rod configuration, defined as a single rod spanning the osteotomy. "L" is for linked rod configurations, defined as 2 rods directly connected to each other at the osteotomy site. "S" is for satellite rod configurations, which were defined as a short rod independent of the main rod with anchors above and below the 3CO. "A" is for accessory rods, defined as an additional rod across the 3CO attached to main rods but not attached to any anchors across the osteotomy site. "I" is for intercalary rod configurations, defined as a rod connecting 2 separate constructs across the 3CO, without the intercalary rod itself attached to any anchors across the osteotomy site. The intra- and interobserver reliability of this classification system was determined. A sample estimation for validation assuming two readers and 35 subjects results in a two-sided 95% confidence interval with a width of 0.19 and a kappa value of 0.8 (SD 0.3). The Fleiss kappa coefficient (κ) was used to calculate the degree of agreement between interrater and intraobserver reliability. The interrater kappa coefficient was 0.3, and the intrarater kappa coefficient was 0.63 (good reliability). This scenario represents a high degree of agreement despite a low kappa coefficient. Correct observations by both observers were 34 of 35 and 33 of 35 at both time points. Misclassification was related to difficulty in determining connectors versus anchors. MRCs across 3COs have variable rod configurations. Currently, no classification system or agreement on nomenclature exists to define the configuration of rods across 3COs. The authors present a new, comprehensive MRC classification system with good inter- and intraobserver reliability and a high degree of agreement that allows for a standardized description of MRCs across 3COs.

Efficacy of sequential correction based on satellite rod techniquein degenerative scoliosis with B-type coronal imbalance

Objective: To evaluate the radiographic and clinical outcomes of sequential correction based on satellite rod technique in degenerative scoliosis (DS) with B-type coronal imbalance, and to investigate the efficacy of sequential correction in this cohort. Methods: Twenty-one DS patients with B-type coronal imbalance applying sequential correction from December 2015 to July 2017 in Nanjing Drum Tower Hospital were retrospectively reviewed. There were 4 males and 17 females in this group, the average age was (63±8) years. The coronal parameters including Cobb angle of main curve and distance between C(7) plumb line and center sacral vertical line (C(7)PL-CSVL), as well as sagittal parameters including global kyphosis (GK) and sagittal vertical axis (SVA) were assessed pre-operatively, post-operatively and at the last follow-up. The Scoliosis Research Society-22 (SRS-22) questionnaire was fulfilled before the operation and at each follow-up to evaluate the quality of life. Paired t test was performed for statistical analysis. Results: The patients were followed-up for (20±8) months. The post-operative Cobb angle of main curve was significantly improved from 52°±12° to 19°±7° (t=13.886, P<0.01), and it was 19°±8° at the last follow-up and no significant correction loss was attained (t=1.101, P=0.284). The values of C(7)PL-CSVL before the operation, after the operation and at the final follow-up were (46±11) mm, (12±7) mm and (12±7) mm, respectively; significant post-operative improvement achieved (t=19.718, P<0.01) while there was no correction loss at last follow-up (t=-1.393, P=0.179). After sequential correction, 20 patients (95.2%) improved to A-type coronal imbalance while 1 patient (4.8%) remained with B-type coronal imbalance. Significant post-operative improvements were found in terms of GK and SVA and no significant correction loss was found during follow-up. The scores of pain and self-image showed significant improvement at the last follow-up (t=8.706, 3.104, both P<0.01). In addition, there was no implant failure during follow-up. Conclusion: The sequential correction based on satellite rod technique in DS patients with B-type coronal imbalance corrects the deformity, relieves the clinical symptoms, improves the quality of life, and decreases the rates of post-operative coronal imbalance as well as implant-related complications.

Ponte osteotomy followed by sequential correction technique with satellite rods in severe rigid thoracic scoliosis

Objective To investigate the efficacy and safety of Ponte osteotomy and sequential correction technique with satellite rod construction in the treatment of severe rigid thoracic scoliosis. Methods A total of 32 patients (12 male, 20 female) with severe rigid thoracic scoliosis (Cobb angle>100°) who underwent posterior Ponte osteotomy and sequential correction technique with satellite rod construction between October 2012 and October 2016 and with more than 2 years follow-up were retrospectively reviewed. Major curve Cobb angle, apex vertebral translation, trunk shift, thoracic kyphosis and lumbar lordosis were measured through standing posterior-anterior X-ray preoperatively, postoperatively and at the final follow-up. The duration of operation, blood loss and complications were recorded. SRS-22 questionnaire was used to evaluate the clinical outcomes. Results The average age was 21.3±10.8 years (range from 17 to 46 years). The mean preoperative major curve Cobb angle was 117.8°±9.8°(range from 104° to 131°) with a mean flexibility of 13.9% and the mean thoracic kyphosis was 65.5°±18.7° (range from 48° to 87°). The mean duration of operation was 267.4±42.3 min and the mean blood loss was 895.4±103.1 ml. The mean fused levels ranged from T2 to L4 with a mean 13.3±2.4 fused segments. The mean implant density was 62.1%±8.8%. Ponte osteotomy was performed in 4-9 segments which was 6.1±1.9 segments in average. The coronal main curve was corrected to 54.4°±10.9° with a mean correction rate of 53.9%±9.3% and the mean thoracic kyphosis was corrected to 35.6°±12.0°, which were both significantly improved. The average follow-up time was 34.3±8.9 months. At the last follow-up, the mean coronal main curve was 53.1°±1.9° with a mean correction loss of 1.3° and the thoracic kyphosis was 36.7°±11.4°. There were no neurological deficit or implant failure postoperatively and follow-up. Conclusion Ponte osteotomy followed by sequential correction technique with satellite rods construction was safe and effective which could achieve satisfactory correction rate and less correction loss during the longitudinal follow-up in the treatment of severe rigid thoracic scoliosis. Key words: Thoracic vertebrae; Scoliosis; Osteotomy; Orthopedic procedures

Surgical strategy and clinical outcomes in degenerative lumbar scoliosis with type C coronal imbalance

Objective To illustrate the surgical strategy of sequential correction in degenerative lumbar scoliosis (DLS) with type C coronal imbalance, and to evaluate the clinical outcomes and advances of sequential correction technique. Methods Twelve patients (2 males and 10 females) applying sequential correction technique from January 2015 to August 2017 were retrospectively reviewed. The ages of the cohort ranged 48-74 years and the average value was 52.3±8.4 years. The sequential correction technique was mainly applied in 3 steps: correction of local kyphoscoliosis with satellite rod on convex side of lumbar spine; correction of lumbosacral curve with L 4-S1 Intervertebral fusion and satellite rod on convex side of lumbosacral spine; correction of global deformity with bilateral long rods. The coronal parameters including Cobb angle and distance between C7 plumb line and center sacral vertical line (C7PL-CSVL), and the sagittal parameters including global kyphosis (GK) and sagittal vertical axis (SVA) were assessed at pre-operation, post-operationand last follow-up. The quality of life was evaluated using SF-36 questionnaire, and paired t test was used for the statistical analysis. Results The average follow-up period was 16.7±4.8 months. The Cobb angles at pre-operation and post-operation were 59.6°±18.7° and 25.6°±12.4° (t=3.705, P<0.001), respectively. At last follow-up, the average Cobb angle was 27.5°±13.0°, and there was no significant loss of correction (t=0.366, P=0.718). Post-operative C7PL-CSVL changed from 48.5±17.2 mm to 9.7±4.3 mm (t=5.842, P<0.001), of which the average value was 10.1±4.5 mm at last follow-up (t=0.223, P=0.826). At post-operation, 11 patients were with type A coronal imbalance, and 1 patient was still with type C coronal imbalance. The scores of bodily pain, general health, and social functioning were 8.4±1.9, 78.1±9.4 and 76.7±8.4 at pre-operation, 10.2±2.0 (t=2.260, P=0.034) , 89.5±7.6 (t=3.267, P=0.004) and 84.5±9.3 (t=2.156, P=0.042) at post-operation. In addition, there was no implant-related complications during follow-up. Conclusion The sequential correction technique could be well used in adult degenerative lumbar scoliosis patients with type C coronal imbalance, which can simplify the surgical procedure, decrease the rates of post-operative coronal imbalance, and obtain rigid internal fixation. Key words: Adult; Lumbar vertebrae; Intervertebral disc degeneration; Scoliosis; Spinal fusion

P143. Efficacy of multi-rod constructs: comparison of two different 4-rod and 3-rod configurations in adult spinal deformity patients with long fusions to the sacrum

BACKGROUND CONTEXT Rod constructs in adult spinal deformity (ASD) surgery can be variable and modular, in many revision surgeries the new instrumentation is connected to the previous implants for extension of fusion or for junctional failure. Previous studies recently reported a lower rate of rod fractures and nonunion with the addition of extra rods and multi-rod constructs across 3CO site and complex spinal reconstructions. The high rate of rod failures in ASD lead to the adoption of various multi-rod constructs. The effect of rod configuration on the rate of implant failure in multi-rod constructs is unknown. Currently, no classification system exits to describe the different multi-rod constructs to allow comparison of rod configurations across data bases. There is no agreement on the terms used to describe multi-rod constructs. PURPOSE We present a new classification system that allows accurate description of various multi-rod constructs used in spine deformity in terms of rod configuration and density. Rod configurations in 110 ASD patients after long PSF to the sacrum with 4-rod and 3-rod constructs were classified according to the new classification system. Four-rod and 3-rod constructs were divided into two groups based on rod configuration: accessory rod group and satellite rod group. We compared rod failure rate (RF) between the two different groups, accessory vs satellite, to determine the effect or rod configuration on the rod fracture rate. STUDY DESIGN/SETTING Retrospective review of institutional database of ASD patients who underwent PSF to the sacrum with the use of multi-rod constructs, 3-rod and 4-rod constructs. The multi-rod constructs were classified according the new system based on the rod configurations (RC) of the additional rods. PATIENT SAMPLE ASD patients who underwent PSF to the sacrum with the use of multi-rod constructs, 3-rod and 4-rod constructs. OUTCOME MEASURES Radiographic evidence of rod failure, either unilateral or bilateral on follow up radiographs. METHODS Our institutional database of 526 ASD patients fused to sacrum was reviewed, 110 patients with multi-rod constructs were identified and divided into 4-rod or 3-rod constructs. Within the 4-rod or 3-rod groups, constructs were classified according to the rod configuration into either accessory group (A-group) with additional accessory rods or satellite group (S-group) with additional satellite rods. Accessory rods were defined as additional rods connected to the main construct but not attached to any anchors. Satellite rods were defined as shorter additional rods attached to screws or hooks, and either connected or not connected to the main construct. Most of the satellite rods were midline rod with hooks. Accessory and satellite rod configurations for 4-rod and 3-rod constructs were compared for fractures either unilateral or bilateral after a minimum of 2-year follow up. RESULTS The 4-rod constructs included 15 satellite (S-group) and 18 accessory (A-group) rod configurations. Average BMI and % primary to revision surgeries in both groups was not different p=0.38. Rod diameter (5.5 vs 6.35) in both groups was not different p=0.28. Median levels fused in S-group were 15 (13-17) vs A-group 12 (10-15) p=0.11. Interbody fusion was not different, S-group 12 (80%), A-group 15 (83%), p=0.81. Rod failures in S-group occurred in 2 (13.3%) vs 4 (22.2%) in A-group, p=0.47. Duration of time from surgery to rod failure was 27 months in the S-group compared to 14.5 months in A-group. The 3-rod constructs included 42 satellite and 29 accessory rod configurations. Average BMI was not different (p=0.83), the S-group had more revision cases 38 (90.5%) vs 17 (58.6%) for A-group p=0.03. In S-group 14 (33.3%) patients were 5.5 rods, 27 (64.3%) had 6.35 rods vs A-group: 26 (89.6%) 5.5 rods and 3(10.34%) had 6.35 rods, p=0.01. Median levels fused was not different between both groups, but A-group had more interbody fusions performed 12 (41.4%) vs 4 (9.52%) p=0.03. Rod failures in S-group were 7 (16.7%) vs 15 (51.7%) in the A-group, p=0.01. Duration of time from surgery to rod failure in satellite group was 41 months vs accessory group 31 months. CONCLUSIONS Multi-rod constructs with different rod configurations were compared using a new classification system, 4-rod constructs showed no difference in rate of rod failures. In the 3-rod constructs group, accessory rod configurations had more rod failures compared to satellite rod configurations. The multi-rod construct classification system is helpful in comparing different rod configurations in terms of implant complications. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

315. Sequential correction with satellite rods in severe rigid thoracic scoliosis

BACKGROUND CONTEXT The treatment of severe and rigid thoracic scoliosis was challenging. We employed Ponte osteotomy followed by sequential correction technique with satellite rods construction to treat severe rigid thoracic scoliosis aiming to achieve better correction with less complications. This technique could reduce the difficulty of rod installation by separated maneuvers and multi-rods system. Satisfactory correction rate and less correction loss during the longitudinal follow-up could be expected in this cohort. PURPOSE The objective of this study was to evaluate the safety and efficacy of this technique. STUDY DESIGN/SETTING Retrospective review. PATIENT SAMPLE A total of 32 patients (12 M, 20F) with severe rigid thoracic scoliosis (Cobb angle>100°) who underwent sequential correction technique with satellite rod construction between October 2012 and October 2016 and with more than 2 years follow-up were retrospectively reviewed. OUTCOME MEASURES Cobb angle of major curve, apex vertebral translation, trunk shift, thoracic kyphosis and lumbar lordosis were measured through standing X-ray imaging preoperatively, postoperatively and at final follow-up. The duration of operation, blood loss and complication were recorded. SRS-22 questionnaire was measured to evaluate the clinical outcomes. METHODS Cobb angle of major curve, apex vertebral translation, trunk shift, thoracic kyphosis and lumbar lordosis were measured through standing X-ray imaging preoperatively, postoperatively and at final follow-up. The duration of operation, blood loss and complication were recorded. SRS-22 questionnaire was measured to evaluate the clinical outcomes. RESULTS The average age was 21.3±10.8 years (range 17 to 46 years) and the average follow-up was 34.3±8.9 months. The mean preoperative Cobb angle of major curve was 117.8±9.8° (range 104° to 131°) with a mean flexibility of 13.9% and the mean thoracic kyphosis was 65.5±18.7° (range 48° to 87°) . The mean duration of operation was 267.4±42.3min and the mean blood loss was 895.4±103.1ml. The coronal main curve was corrected to 54.4±10.9° with a mean correction rate of 53.9%±9.3% and the mean thoracic kyphosis was corrected to 35.6±12.0°, which were both significantly improved (p CONCLUSIONS Sequential correction technique with satellite rods construction was a safe and effective strategy in the treatment of severe rigid thoracic scoliosis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

P92. Preventing rod failure in pedicle subtraction osteotomy revision surgeries for sagittal deformity with a satellite rod technique

BACKGROUND CONTEXT Pedicle subtraction osteotomy (PSO) is used to treat rigid sagittal deformities. The traditional 2-rod PSO technique has resulted in high instrumentation failure rates. We investigated the use of a multiple rod satellite configuration for PSO. PURPOSE Demonstrate that a multiple rod satellite configuration for PSO will result in substantial improvement in sagittal parameters and global alignment and proportion (GAP) score with a low instrumentation failure rate. STUDY DESIGN/SETTING Case series. PATIENT SAMPLE Patients who underwent PSO with a multiple rod satellite rod technique during revision surgery for sagittal plane deformity by a single surgeon. OUTCOME MEASURES Instrumentation failure and sagittal parameters including PSO angle, proximal junctional kyphosis, sagittal vertical axis (SVA), pelvic incidence – lumbar lordosis (PI-LL) mismatch and GAP score. METHODS Independent observers collected demographics, surgical variables, and radiographic measurements from 40 patients who underwent revision surgery for sagittal deformity with a PSO. Procedures were performed by a single surgeon at two different centers. Student's t test compared groups. RESULTS A total of 40 patients underwent PSO with satellite rod technique. Eight were smokers and 7 were diabetic. The most common level was L3 (91%), with 9% at L4. Low dose BMP (1-2 large kits) was distributed over all segments and supplemental allograft was used in all patients. No intradiscal fusion was performed with PSOs, but all patients were previously fused. Mean PSO angle was 28.7±7.6°. Two out of 40 patients had rod fracture necessitating revision surgery at 32 and 34 months. One patient developed an infection requiring replacement of instrumentation. Three patients developed proximal junctional kyphosis, none required revision. Mean preoperative SVA was 13.5±7.3 cm, which significantly decreased to 4.8±7.3 cm (p = 0.002). Mean preoperative PI-LL mismatch was 35.9±16.6, which significantly improved to 11.8±14.6 post-op (p CONCLUSIONS Despite a high rate of comorbid conditions and severely disproportioned postoperative GAP scores, rod failure rate after PSO with the multiple rod satellite configuration was very low (5%) compared to previous reports. SVA and PI-LL mismatch were significantly improved. GAP score was also significantly improved, but still considered severely disproportioned, most likely due to the high rate of PSO's at L3 in previously fused spines, which did not correct low lumbar lordosis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Supplementary delta-rod configurations provide superior stiffness and reduced rod stress compared to traditional multiple-rod configurations after pedicle subtraction osteotomy: a finite element study.

The biomechanical performance of conventional multi-rod configurations (satellite rods and accessory rods) in pedicle subtraction osteotomies has been previously studied in vitro and using finite element models (FEM). Delta and delta-cross rods are innovative multi-rod configurations where the rod bends were placed only in its proximal and distal extremities in order to obtain a dorsal translation of the central part of the rod respect to the most angulated area of the main rods. However, the biomechanical properties of the delta and delta-cross rods have not been investigated. This study used FEM to analyze the effect of delta-rod configurations on the stiffness and primary rod stress reduction in multiple-rod constructs after pedicle subtraction osteotomy. The global range of motion in the spine and the magnitude and distribution of the von Mises stress in the rods were studied using a spine finite element model described previously. A follower load of 400N along with moments of 7.5N in flexion/extension, lateral bending, and axial rotation were tested on the spine model. Initial breakage was created on the rod based on the maximum stress location. The post-breakage models were tested under flexion. Delta and delta-cross rods reduced more range of motion (up to 45% more reduction) and reduced more primary rod stress than other previously tested rod configurations (up to 48% more reduction). After initial rod fracture occurred, delta and delta-cross rods also had less range of motion (up to 23.6% less) and less rod von Mises stress (up to 81.2% less) than other rod configurations did. Delta and delta-cross rods have better biomechanical performance than satellite rods and accessory rods in pedicle subtraction osteotomies in terms of construct stiffness and rod stress reduction. After the initial rod breakage occurred, the delta and delta-cross rods could minimize the loss of fixation, which have less rod stress and greater residual stiffness than other rod configurations do. Based on this FEA study, delta-rod configurations show more favorable biomechanical behavior than previously described multi-rod configurations. These slides can be retrieved under Electronic Supplementary Material.

SRS-Schwab grade Ⅳ osteotomy combined with satellite rod for thoracolumbar old osteoporotic fracture with severe kyphosis

To evaluate the effectiveness of SRS-Schwab grade Ⅳ osteotomy combined with satellite rod for thoracolumbar old osteoporotic fracture with severe kyphosis. Between April 2013 and August 2016, 20 cases of thoracolumbar old osteoporotic fracture with severe kyphosis were treated with SRS-Schwab grade Ⅳ osteotomy combined with satellite rod. All the patients were females, aged 49-71 years (mean, 54.8 years). The disease duration was 6-28 months with an average of 14 months. The T value of bone density was -4.4 to -1.8 (mean, -2.8). The preoperative Cobb angle was (43.0±11.3)°. The vertebral compression fracture segment was T 12 in 9 cases, L 1 in 8 cases, and L 2 in 3 cases. Preoperative spinal cord function was evaluated by Frankel classification; there were 5 cases of grade D and 15 cases of grade E. The operation time, intraoperative blood loss, and perioperative complication were recorded. The Cobb angle for kyphosis and sagittal vertical axis (SVA) were recorded beforeoperation, at 3 months after operation, and at last follow-up. Oswestry disability index (ODI) was used to evaluate the effectiveness before operation and at last follow-up, and the evaluation indicators included pain degree, daily life self-care ability, extracting, walking, sitting, standing, sleeping, social activities, and traveling. The operation time was 180-314 minutes (mean, 226 minutes). The intraoperative blood loss was 390-1 800 mL (mean, 750 mL). All the incisions healed by first intension without incision infection. Twenty patients were followed up 24-52 months, with an average of 30.9 months. During the follow-up period, no significant complication such as correction loss, nail breakage, rod breakage, pseudoarthrosis formation, or proximal and distal junctional kyphosis occurred. All patients were able to walk upright after operation, and the pain relieved significantly at 6 months after operation. Bone fusion achieved at 12 months after operation. The Frankel grade of nerve function improved from grade D to grade E at last follow-up in 5 patients with nerve damage before operation. At last follow-up, the indicator scores of ODI significantly improved when compared with preoperative values ( P<0.05). Cobb angle significantly improved at 3 months after operation and at last follow-up ( P<0.05) when compared with preoperative one, but there was no significant difference in the Cobb angles between 3 months after operation and last follow-up ( P>0.05). There was no significant difference in SVA between pre- and post-operation ( P>0.05). SRS-Schwab grade Ⅳ osteotomy combined with satellite rod for thoracolumbar old osteoporotic fracture with severe kyphosis is effective in achieving satisfactory clinical outcomes, as well as maintaining correction of kyphosis.

The risk factors of rod fracture after correction surgery with satellite rod in severe spinal deformity

Objective To investigate the incidence and risk factors for rod fracture after correction surgery with satellite rod in severe spinal deformity. Methods A retrospective analysis was made including 234 cases who underwent correction surgery using satellite rod technique for severe spinal deformity in our hospital from July 2012 to June 2017. At the last follow-up, a total of 6 patients were found to have rod fracture. All the patients had complete clinical and imaging data at the time of preoperation, postoperation, rod fracture occurring, post-revision and the last follow-up. The Cobb angle, the Global kyphosis (GK), the coronal balance (distance between C7 plumb line and center sacral vertical line, C7PL-CSVL) and the sagittal vertical axis (SVA) were measured respectively in the 6 patients with rod fracture during the follow-up process. The time, incidence and position of the broken rod were recorded, and the reasons of rod fracture were analyzed for each patient. Results The incidence of rod fracture was 2.6% (6/234) in the current study. The 6 patients included 3 males and 3 females with an average age of 34.5±15.4 years at initial surgery. The mean time of rod fracture was 24.0±17.7 months, of which 3 cases (50%) occurred within 1 years after operation. A total of 7 rods were broken, including 4 (57%) rods located at the single-rod-fixed side with stress concentration and 3 (50%) rods at the adjacent segment of the satellite rod. The average loss of correction was 20.8°±29.4° for Cobb angle and 34.0°±21.4° for GK. The potential reasons for rod fracture were listed as follows: 3 cases for residual kyphosis; 2 cases for pseudarthrosis; 3 cases for long fusion construct crossing lumbosacral junction; 1 case for trauma. Of the 6 patients with rod fracture, 3 (43%) patients underwent revision surgery by replacing the broken rods, adding satellite rod at the opposite side of pre-existing satellite rod and bone graft at the rod-breakage area. The other 3 patients underwent observation and no deterioration was found during follow-up. Conclusion The incidence of rod fracture after correction for severe spinal deformity with satellite rod is 2.6%. The broken rods are mainly located at the single-rod-fixed side with stress concentration or the adjacent segment of the satellite rod. Residual kyphosis, pseudarthrosis, long fusion construct crossing lumbosacral junction and trauma are the significant risk factors of rod fracture. Key words: Scoliosis; Kyphosi; Osteotomy; Internal fixators; Risk factors

Optimal satellite rod constructs to mitigate rod failure following pedicle subtraction osteotomy (PSO): a finite element study

BACKGROUND CONTEXTPedicle subtraction osteotomy (PSO) is a challenging restoration technique for sagittal imbalance and is associated with significant complications. One of the major complications is rod fracture and there exists a need for a biomechanical assessment of this complication for various instrumentation configurations. PURPOSETo evaluate and compare the global range of motion (ROM), rod stress distribution, and the forces on the pedicle subtraction site in various instrumentation configurations using finite element analysis. STUDY DESIGN/SETTINGA computational biomechanical analysis. METHODSA previously validated osseoligamentous three-dimensional spinopelvic finite element model (T10-pelvis) was used to develop a 30° PSO at the L3 level. In addition to the standard bilateral cobalt chromium primary rod instrumentation of the PSO model, various multirod configurations including constructs with medially, laterally, and posteriorly affixed satellite rods and the short-rod technique were assessed in spinal physiological motions. T10-S1 global ROM, maximum von Mises stress on the rods and at the PSO level, factor of safety (yield stress of the rod material/maximum actual stress in the rod) and the load acting across the PSO site were compared between various instrumentation configurations. The higher the factor of safety the lesser the chances of rod failure. RESULTSAmong all multirod constructs, posteriorly affixed satellite rod construct showed the greatest motion reduction compared to the standard bilateral rod configuration followed by medially and laterally affixed satellite rod constructs. Compared to the standard bilateral rod configuration, recessed short-rod technique resulted in 4% to 49% reduction in T10-S1 ROM recorded in extension and lateral bending motions, respectively, while the axial rotation motion increased by approximately 31%. Considering the maximum stress values on the rods, the recessed short-rod technique showed the greatest factor of safety (FOS = 4.1) followed by posteriorly (FOS = 3.9), medially (FOS = 3), laterally affixed satellite rod constructs (FOS = 2.8), and finally the standard bilateral rod construct (FOS = 2.7). By adding satellite rods, the maximum von Mises stress at the PSO level of the rods also reduced significantly and at this level resulted in the greatest FOS in the posteriorly affixed satellite rod construct. Compared to the standard bilateral rod construct, the load magnitude acting on the osteotomy site decreased by 11%, 16%, and 37% in the laterally, medially, and posteriorly affixed satellite rod constructs, respectively, and did not change with the short-rod technique. CONCLUSIONSAdding satellite rods increases the rigidity of the construct, which results in an increase in the stability and the reduction of the global ROM. Additionally, having satellite rods reduces the stress on the primary rods at the PSO level and shifts the stresses from this PSO region to areas adjacent to the side-by-side connectors. The data suggest a significant benefit in supplementing medial over lateral satellite rods at the PSO by reducing stress on the primary rods. Except the recessed short-rod technique, all other multirod constructs decrease the magnitude of the load acting across the osteotomy region, which could cause a delayed or non-union at the PSO site. CLINICAL SIGNIFICANCEThe study evaluates the mechanical performance of various satellite rod instrumentation configurations following PSO to predict the risk factors for rod fracture and thereby mitigate the rate of clinically relevant failures.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P12. The interaction of satellite rod reconstruction, rod material and rod diameter on posterior rod strain in pedicle subtraction osteotomies for adult spinal deformity correction: a finite element analysis

BACKGROUND CONTEXT Pedicle subtraction osteotomy (PSO) is a prevailing technique used to correct adult spinal deformity; however, instrumentation failure of rods remains a significant concern at the PSO level or lumbosacral junction. Several options have been proposed in clinical literature to reduce mechanical demand of the rod, including multirod constructs (three- or four-rod vs. two rods), alternative rod materials [stainless steel (SS) or cobalt chrome (CoCr) vs. titanium (Ti)], or increased rod diameter (6.35 mm vs. 5.5 mm). Nevertheless, a comprehensive evaluation of these construct features is warranted and necessary to guide optimization of post-PSO surgical reconstruction. PURPOSE The current study investigates the effect of multirod techniques, and varied rod material and diameter, on motion-induced rod strain at the PSO and L5-S1. STUDY DESIGN/SETTING Finite element analysis. METHODS A lumbosacral finite element model (T12-S1) was developed and validated with cadaveric range of motion data. Vertebral segments were modeled as three-dimensional solid elements. Intervertebral discs (nucleus and annulus fibrosis) were structured as hyperelastic materials. The intact model underwent PSO at L3, and Ti pedicle screws and rods from T12-S1. Simulations assessed (1) multirod construction, with either a satellite rod on patient left (three-rod) or bilateral four-rod constructs; (2) posterior rod materials (SS or CoCr vs. Ti); and (3) 5.5 mm versus 6.35 mm posterior rods. A pure 10 Nm moment was applied at T12 to simulate flexion–extension. Motion-induced rod strain was normalized to the two-rod construct (100%), averaged between left and right rods, and evaluated at the PSO and L5-S1. RESULTS All rods, irrespective of number of accessory rods, material, or diameter, experienced less strain than two-rod construct across the PSO level and L5-S1. At the PSO, 5.5 mm three-rod Ti, SS, and CoCr constructs reduced primary rod strain to 65%, 41%, and 34%, respectively; 6.35 mm rods reduced strain to 47%, 29%, and 24%, respectively. Similarly, four-rod Ti, SS, and CoCr constructs reduced primary rod strain to 49%, 30%, and 25%, respectively; 6.35 mm rods reduced strain to 35%, 21%, and 17%, respectively. At L5–S1, 5.5 mm three-rod Ti, SS, and CoCr constructs reduced primary rod strain to 82%, 59%, and 51%, respectively; 6.35 mm rods reduced strain to 73%, 48%, and 30%, respectively. Similarly, four-rod Ti, SS, and CoCr constructs reduced primary rod strain to 85%, 60%, and 51%, respectively; 6.35 mm rods reduced strain to 75%, 48%, and 30%, respectively. Some interactions were observed. At the PSO, 6.35 mm three-rod construction was equivalent to 5.5 mm four-rod, across Ti (47% vs. 49%), SS (29% vs. 30%), and CoCr rods (24% vs. 25%). Similarly, at L5-S1, 5.5 mm three- and four-rod constructs were equivalent across Ti (82% vs. 85%), SS (59% vs. 60%), and CoCr rods (51% vs. 51%); similar trends with 6.35 mm rods occurred across Ti (73% vs. 75%), and SS rods (48% vs. 48%). CONCLUSIONS Overall trends in primary rod strain across the PSO and L5-S1 observed in the present study are as follows: (1) four-rod rod strain

Biomechanical advantages of supplemental accessory and satellite rods with and without interbody cages implantation for the stabilization of pedicle subtraction osteotomy.

To investigate the effect of anterior interbody cages, accessory and satellite rods usage on primary stability and rod strains for PSO stabilization. Seven human cadaveric spine segments (T12-S1) underwent PSO at L4 with posterior fixation from L2 to S1. In vitro flexibility tests were performed under pure moments in flexion/extension (FE), lateral bending (LB) and axial rotation (AR) to determine the range of motion, while measuring the strains on the primary rods with strain gauge rosettes. Six constructs with 2, 3 and 4 rods, with and without interbody cages implantation adjacent to the PSO site, were compared. All constructs had comparable effects in reducing spine kinematics compared to the intact condition (- 94% in FE and LB; - 80% in AR). Supplementation of 2 rods with lateral accessory rods (4 rods) was the most effective strategy in minimizing primary rod strains, particularly when coupled to cages (p ≤ 0.005; - 50% in FE, - 42% in AR and - 11% in LB); even without cages, the strains were significantly reduced (p ≤ 0.009; - 26%, - 37%, - 9%). The addition of a central satellite rod with laminar hooks (3 rods) effectively reduced rod strains in FE (p ≤ 0.005; - 30%) only in combination with cages. The study supports the current clinical practice providing a strong biomechanical rationale to recommend 4-rod constructs based on accessory rods combined with cages adjacent to PSO site. Although weaker, the usage of accessory rods without cages and of a central satellite rod with hooks in combination with interbody spacers may also be justified. These slides can be retrieved under Electronic Supplementary Material.

P19 - Satellite Rods and Anterior Column Support Reduce Rod Stress in Pedicle Subtraction Osteotomy and Anterior Column Reconstruction Constructs: A Finite Element Study

P19 - Satellite Rods and Anterior Column Support Reduce Rod Stress in Pedicle Subtraction Osteotomy and Anterior Column Reconstruction Constructs: A Finite Element Study

Use of the “dual construct” for the management of complex spinal reconstructions

Background ContextSurgical management of complex spinal reconstructions remains a clinical challenge, as pseudoarthrosis with subsequent rod breakage can occur. Increased rod density in the form of “satellite” or “outrigger” rods have been described; however, rod-fracture above or below satellite rods persist and can result in dissociation of the construct, loss of correction, and recurrence of deformity. The use of four distinct and mechanically independent rods (dual construct) reduces this concern. Since the original case description in 2006, there have been no other studies that use the dual construct for the surgical management of complex spinal reconstructions. PurposeThe purpose of this study is to review the long-term experience and surgical technique using the dual construct, and to present our complications, rod fracture rates, and outcomes for the surgical management of complex spinal reconstructions. Study DesignThis study used a surgical technique with case series outcomes. Patient SamplePatients were from a single-institute who underwent dual construct between 2010 and 2014 and who were available for 2-year follow-up. Outcome MeasuresRadiographic and functional outcomes, complications, rod fracture rates, and revision surgery rates were the outcome measures. MethodsA retrospective review was conducted from a single institution between 2010 and 2014, with a subsequent 2-year follow-up period. Extensive review of patients' medical record, radiographs, and advanced imaging where available was performed. Medical record was evaluated for patient demographics, surgical procedure, and complications. Radiographic measurements included presence or absence of implant failure and proximal junctional kyphosis or distal junctional kyphosis. ResultsA total of 36 patients underwent surgical reconstruction. The average estimated blood loss was 1,856 cc (range, 400–4,000 cc). The average length of stay was 7.3 days (range, 4–22 days). Clinical follow-up reported 21 patients (58.3%) with no or minimal pain. There were six deaths during the follow-up unrelated to the index procedure. Radiographic follow-up revealed three patients (8.3%) with rod fracture; one patient with one rod fracture, and two patients with two rod fractures. No patient had three or all four rod fractures. There were no screw fractures. None of the patients with rod fractures required revision surgery. ConclusionsThe biggest advantage of the dual construct is that rod breakage, although uncommon, is typically minimal, or asymptomatic, and more importantly does not result in loss of alignment, and therefore has not required revision surgery. The dual construct approach is a safe alternative to traditional two-rod constructs, with encouraging outcomes at follow-up.

Biomechanical study of rod stress after pedicle subtraction osteotomy versus anterior column reconstruction: A finite element study.

Background:In an effort to minimize rod fractures and nonunion in pedicle subtraction osteotomy (PSO) constructs, surgeons have adopted multirod constructs and interbody cages. Anterior column realignment (ACR) with posterior column osteotomies is a minimally invasive alternative to PSO in sagittal balance correction, however, there is a paucity of evidence with respect to rod survival.Methods:Three-dimensional (3D) finite-element-model of a T12-sacrum spine segment was used to compare a 25° PSO at L3 and an ACR with a posterior column osteotomy and 30° hyperlordotic interbody cage at L3–4. The amount of overall T12–S1 lordosis correction was the same for each condition. Each simulation included cobalt chromium alloy primary rods with: (1) PSO; (2) PSO with an interbody cage (IB) at L2–3 (PSO+IB); (3) PSO with accessory (A) rods and IB at L2–3 (PSO+IB+A); (4) PSO with satellite (S) rods and IB at L2–3 (PSO+IB+2S); (5) ACR; 6) ACR with satellite rods (ACR + 2S). A 400 N follower preload was simulated for each condition.Results:PSO condition had the largest rod stress of 286 MPa in flexion. Adding interbody support reduced the rod stress by 15%. The 4-rod constructs further reduced rod stress, with the satellite rod condition facilitating the largest reduction. The rod stress in the ACR+2S was equivalent to the PSO+2S, with 50% reduction in rod stress.Conclusion:The rod stress with an ACR was comparable to a PSO coupled with interbody support. These results suggest an ACR is a viable MIS alternative to a PSO without the need for a large posterior osteotomy.

Satellite rod technique around rod-breaking area in revision surgery after three-column osteotomy

Objective To evaluate the feasibility and clinical outcomes of satellite rod technique used around the rod-breaking area in the revision surgery due to rod fracture after three-column osteotomy. Methods 11 patients (7 males and 4 females) applying satellite rod technique from December 2012 to March 2015 were retrospectively reviewed. The average age of the cohort was 27.3 years and the average duration of follow-up after revision surgery was 19.0 months. The coronal parameters including Cobb angle and distance between C7 plumb line and center sacral vertical line (C7PL-CSVL), and the sagittal parameters including global kyphosis (GK) and sagittal vertical axis (SVA) were assessed at pre-revision, post-revision and last follow-up. The paired t test was used to analyze the difference among pre-operation, post-operation and last follow-up. Results The Cobb angles of pre-revision and post-revision were 38.4°±21.1° and 32.0°±19.9°. The average correction rate was 20.3%±14.4%. At last follow-up, the average Cobb angle was 31.4°±18.8°, no significant loss of correction. Post-revision C7PL-CSVL changed from (19.0±19.7) mm to (20.1±14.7) mm, of which the average value was (20.4±20.4) mm at last follow-up. The pre-revision and post-revision values of GK were 23.8°±24.8° and 19.0°±22.1° with the average correction rate being 23.7%±19.0%. At the last follow-up, the average GK was 19.8°±20.1° and the correction was well maintained. In terms of SVA, average (51.2±40.1) mm for pre-revision, (30.7± 16.7) mm for post-revision, and (29.7±19.6) mm for last follow-up. In addition, there was no complication of implant failure during follow-up. Conclusion The satellite rod technique used around the rod-breaking area in the revision surgery due to rod fracture in patients undergoing three-column osteotomy could reduce surgical trauma, get rigid fixation, and rebuild coronal and sagittal balance. With the utilization of satellite rod technique, the coronal and sagittal balance could be well maintained during follow-up. Key words: Scoliosis; Kyphosis; revision; Osteotomy; Reconstructive surgical procedures