Pedicle Subtraction Osteotomy Site Research Articles

Comparison of Revision Techniques for Rod Fracture after Adult Spinal Deformity Surgery: Rod Replacement Alone or Coupled with Lateral Lumbar Interbody Fusions or Accessory Rods.

Background: Rod fracture (RF) is the most common cause of revision in adult spinal deformity (ASD) surgery, and various treatment strategies for preventing RF are reported in the literature. This retrospective study, involving 139 ASD patients (aged ≥65 years and a minimum 2-year follow-up) who underwent long-segment fixation from T10 to sacrum with pedicle subtraction osteotomy (PSO), analyzed long-term results, including radiographical parameters and the incidence of recurrent RF (re-RF), to determine the most effective revision method for preventing RF. Methods: Patients were classified into three groups according to the revision method performed for RF: simple rod replacement (RR group, n = 17), lateral lumbar interbody fusion around the PSO site (RR + LLIF group, n = 8), and accessory rod insertion (RR + AR group, n = 22). Baseline characteristics and radiographical and clinical parameters were analyzed. Results: RF occurred in 47 patients (34%) at an average of 28 months following primary deformity correction. Re-RF occurred in six patients (13%) at an average of 37 months. Re-RF occurred most commonly in the RR group (p = 0.048). Every re-RF in the RR group occurred at the PSO site; none occurred in the RR + LLIF group, and one in the RR + AR group occurred near the L4-5. After both primary deformity correction and revision surgery, spinopelvic parameters had shown favorable results, and clinical outcomes had improved in all three groups without significant intergroup differences. Conclusions: Accessory rod insertion or an additional LLIF around the PSO site seems to provide greater strength and stability to the previously fused segments than a simple rod replacement, which demonstrates the need for additional support in revision surgery for RF after a PSO.

Ideal length of accessory rod for the prevention of rod fracture after pedicle subtraction osteotomy in adult spinal deformity: short or long?

Pedicle subtraction osteotomy (PSO) is an effective surgical procedure for adult spinal deformity (ASD). However, the complexity of the procedure and its associated complications including rod fracture (RF) remain challenging issues. Among several RF reduction methods, the accessory rod (AR) is an important surgical technique. To date, knowledge about the ideal length and configuration of the AR is limited. This study aimed to assess the influence of the connection levels and configuration of the AR on RF occurrence in patients with ASD who underwent long level constructs and PSO. The authors retrospectively selected 57 consecutive patients (mean age 70.6 years) who underwent deformity correction including PSO and the AR technique with a minimum 2-year follow-up. The patients were classified into a non-RF group (n = 49) and an RF group (n = 8). Along with analysis of patient and radiological factors in the 2 groups, comparative studies were performed including configuration of the AR (D shaped vs linear shaped) and the connection levels of AR (long AR [the lower end below S1-2] vs short AR [above L5-S1]). The overall rate of RF incidence was 14% (8/57 cases) at an average of 42.5 months (2 patients with unilateral RF and 6 with bilateral RF). RF occurred most commonly at the L4-5 level, below the lower end of the AR: 6 below the lower end of the AR and 2 at the PSO site. There were no significant differences in patient and radiological factors between the groups. Comparisons between the 2 groups indicated that more RFs occurred when the configuration of the AR was a linear shape (p = 0.016) and when the distal end of the AR was above L5-S1 (p = 0.025). In this study the authors found that the D-shaped configuration of the AR and lower end of the AR below S1-2 (i.e., long AR) could be preventive methods for reducing RF after deformity correction performed using PSO and the AR technique for ASD. Here, the authors have provided the first comprehensive outline for the AR technique. These findings could establish effective guidelines for spine surgeons.

The "Sandwich" Extended Pedicle Subtraction Osteotomy for the Treatment of Fixed Sagittal Malalignment: Technical Description, Case Series, and Early Results With 2-Year Outcomes.

Adult spinal deformity (ASD) with fixed sagittal malalignment (FSM) may require a pedicle subtraction osteotomy (PSO) for greater focal lordosis and restoration of global alignment. Despite growing trends in minimizing PSOs given their associated high risks, a considerable portion of patients with ASD still require a lumbar PSO most commonly because of iatrogenic flat back deformity. The purpose of this article is to describe a modified extended PSO technique with additional anterior column support coined the "sandwich" extended PSO (SE-PSO) to promote arthrodesis and report the outcomes in a consecutive case series. Patients with ASD treated with a lumbar SE-PSO at a single institution from 2015 to 2020 were analyzed. Complications, radiographic data, and patient-reported outcomes were compared preoperatively, at immediate postoperative follow-up, and at a 2-year postoperative follow-up (FU). Fourteen patients who underwent revision operations for FSM were included. Improvements in segmental lordosis across the PSO site (14.8 ± 6.8 vs 39.9 ± 7.1, P < .0001), overall lumbar lordosis (14.6 ± 15.4 vs 44.6 ± 12.1, P < .0001), sacral slope (21.0 ± 10.5 31.1 ± 10.7, P = .0150), C7 sagittal vertical axis (140.1 ± 59.0 mm vs 35.9 ± 28.5, P < .0001), and spinopelvic mismatch (52.5 ± 21.3 vs 18.6 ± 14.1, P = .0001) were obtained in all patients. Eight patients experienced perioperative complications, with intraoperative durotomy being the most common (n = 7). Eight patients had a 2-year FU and demonstrated improvements in their segmental lordosis across the PSO site (14.3 ± 7.0 vs 41.3 ± 7.3, P = .0003), overall lumbar lordosis (8.7 ± 17.8 vs 46.1 ± 14.2, P = .0014), sacral slope (19.1 ± 12.8 vs 32.3 ± 12.5, P = .0479), C7 sagittal vertical axis (173.6 ± 54.4 mm vs 35.8 ± 30.0, P < .0001), and spinopelvic mismatch (63.0 ± 19.7 vs 21.1 ± 18.3, P < .0001), all of which were maintained at final FU (P > .05). At 2 years, a significant increase in Scoliosis Research Society-22r total score (2.5 ± 0.8 vs 3.6 ± 0.7, P = .0023 was reported. There were no reports of symptomatic pseudarthrosis or mechanical complications. SE-PSO is an effective technique to correct FSM and is associated with low complications, improved patient-reported outcomes, and spinopelvic parameters that are maintained at 2 years.

Domino connector for thoracic pedicle subtraction osteotomy reduction: surgical technique and patient series.

Different techniques have been previously described to close the pedicle subtraction osteotomy (PSO) site for correction of sagittal malalignment; the use of a side-to-side domino connector as a correction tool in the thoracic spine has not been specifically studied. Twenty adult patients who underwent single-level thoracic PSO from T1 to T12 were included and retrospectively reviewed (two centers). Preoperative and postoperative full-body X-rays, perioperative data, clinical data and complications were recorded with a minimum 2years of follow-up. Surgical technique and the nuances in using the domino connector were described in detail. Patients had a mean age of 40y; 40% were female. Two different techniques involving the domino were applied for closure of the PSO site depending on the type of kyphosis (smooth vs. angular deformity). Both techniques provided significant correction of the local kyphosis (from 48° to 18°) with reciprocal reduction of compensatory cervical lordosis (from 37.6° to 18.6°, p < 0.01) in upper thoracic PSO or lumbar lordosis (from 74.5° to 46.6°, p < 0.01) in lower thoracic PSO. Four patients presented postoperative complications that resolved (hemothorax, GI bleeding), and two patients presented transient neurological deficit. Oswestry Disability Index score improved in the majority of the patients (from 32.7 to 22.5, p < 0.05). There were no pseudarthroses, symptomatic instrumentation breakage, or surgical site infection. Use of a side-to-side domino connector in combination with two different rod cantilever techniques is effective for the reduction of thoracic pedicle subtraction osteotomy achieving satisfactory radiological and clinical outcome.

Lumbar Disc Degeneration Affects the Risk of Rod Fracture Following PSO; A Finite Element Study.

Finite element (FE) study. Pedicle subtraction osteotomy (PSO) is a surgical method to correct sagittal plane deformities. In this study, we aimed to investigate the biomechanical effects of lumbar disc degeneration on the instrumentation following PSO and assess the effects of using interbody spacers adjacent to the PSO level in a long instrumented spinal construct. A spinopelvic model (T10-pelvis) with PSO at the L3 level was used to generate 3 different simplified grades of degenerated lumbar discs (mild (Pfirrmann grade III), moderate (Pfirrmann grade IV), and severe (Pfirrmann grade V)). Instrumentation included eighteen pedicle screws and bilateral primary rods. To investigate the effect of interbody spacers, the model with normal disc height was modified to accommodate 2 interbody spacers adjacent to the PSO level through a lateral approach. For the models, the rods' stress distribution, PSO site force values, and the spine range of motion (ROM) were recorded. The mildly, moderately, and severely degenerated models indicated approximately 10%, 26%, and 40% decrease in flexion/extension motion, respectively. Supplementing the instrumented spinopelvic PSO model using interbody spacers reduced the ROM by 22%, 21%, 4%, and 11% in flexion, extension, lateral bending, and axial rotation, respectively. The FE results illustrated lower von Mises stress on the rods and higher forces at the PSO site at higher degeneration grades and while using the interbody spacers. Larger and less degenerated discs adjacent to the PSO site may warrant consideration for interbody cage instrumentation to decrease the risk of rod fracture and PSO site non-union.

Transdiscal C7 Pedicle Subtraction Osteotomy With a Strut Graft and the Correction of Sagittal and Coronal Imbalance of the Cervical Spine.

Cervical spine deformity negatively affects patients' quality of life. Pedicle subtraction osteotomy (PSO) has reported to correct cervical deformity but it is challenging and carries a significant risk of morbidity. To report transdiscal C7 PSO with a strut graft for the correction of sagittal and coronal imbalance in patients with fixed cervical deformity. After standard exposure, the spine was instrumented from C2 to T3. T1 subtotal laminectomy, and C6 to C7 total laminectomies were necessary for C7 PSO. Osteotomy was initiated with removal of C6-7 and C7-T1 facet joints to isolate C7 pedicles and identify bilateral C7/C8 roots. Bilateral C7 pediculectomies and transdiscal PSO were performed. A rectangular strut allograft was then inserted into the PSO site. The location of the strut graft was used as a fulcrum of sagittal and coronal correction. The head fixator was released and the head was extended under intraoperative neuromonitoring, and then detailed sagittal and coronal balances were controlled by compressing or distracting between the pedicle screws above and below the osteotomy. This technique was applied in 2 patients with fixed subaxial cervical deformities. Transdiscal PSO could add more amount of correction and provide the additional fusion surface. The strut graft prevented sagittal translation, foraminal narrowing, and excessive focal cord kinking during PSO. Both patients showed radiologic and clinical improvements after surgery, and no neurovascular complication occurred after the surgery. Transdiscal C7 PSO with a strut graft placement provided a safe way of correcting sagittal and coronal imbalance simultaneously and reduced neurological complication by preventing sagittal translation, foraminal narrowing and spinal cord kinking.

Risk of rod fracture according to cross-link position in pedicle subtraction osteotomy (PSO): A finite element study

PurposeThe purpose of this study is to investigate the effect of the cross-link position on the rod fracture phenomenon during pedicle subtraction osteotomy (PSO) surgery using finite element model (FEM). MethodsA three-dimensional finite element model of a lumbar spine with sagittal imbalance was constructed using computed tomography data of a 65-year-old female patient. After simulating the standard PSO at the L4 level, we constructed four models, specifically a model without a cross-link and three models with a cross-link at three different sites. The peak von Mises stress (PVMS) of the rod around the PSO site was measured after applying physiological loads (flexion, extension, axial rotation, and lateral bending) in each model. ResultsThe measured PVMS outcomes at the PSO site were 135.8, 135.9, 208.9, and 384.7 MPa for model 1, 2, 3, and 4 during flexion, and 180.0, 180.1, 210.1, and 445.7 MPa during extension. These results show that when the cross-link is located at the PSO site, the rod stress at the PSO site increases significantly during flexion and extension. As the cross-link moved away from the PSO site, the effect on the rod stress decreased. When the cross-link was placed two levels away from the PSO site, the rod stress was scarcely affected. ConclusionWhen the cross-link during PSO surgery was positioned two levels away from the PSO site, the risk of rod fracture did not increase.

Biomechanical analysis of sagittal correction parameters for surgical instrumentation with pedicle subtraction osteotomy in adult spinal deformity

BackgroundHigh complication rate has been documented in spinal instrumentation with pedicle subtraction osteotomy. The objective was to analyze the biomechanics of spinal instrumentation with pedicle subtraction osteotomy as functions of three instrumentation parameters. MethodsPatient-specific biomechanical computer models of 3 adult patients who were instrumented with pedicle subtraction osteotomy were used to simulate the actual instrumentations and alternative instrumentations derived by varying instrumentation parameters: pedicle subtraction osteotomy wedge angle and rod contouring angle, location of the osteotomy, and number of rods (2 vs. 4). FindingsA change of the sagittal correction by +7.5° (−7.5°) resulted in a change in the screw axial forces and rods bending loads around the osteotomy by +38% (−19%) and +28% (−11%), respectively. The bending moments in the rods were 31% lower at the osteotomy site when it was located at one level above, and 20% higher when it was located at a level below. Additional rods allowed the rod bending and screw axial loads to be reduced by 24% and 22%, respectively. InterpretationThe amount of sagittal correction was positively correlated with loads sustained by the screws and rods. Rods were subjected to higher bending loads at the pedicle subtraction osteotomy site when it was done at a lower level. A 4-rod construct is an effective way to reduce the risk of rod breakage by reducing the loads sustained by the rods.

P88. Revision surgery for pseudarthrosis after surgical correction with pedicle subtraction osteotomy in adult spinal deformity: comparison of rod change only, anterior lumbar interbody fusion around pedicle subtraction osteotomy, and 4-rod constructs

BACKGROUND CONTEXT Pseudarthrosis is the most common cause of revision surgery after sagittal correction with long posterior spinal fusion (PSF) in patients with ASD. Although revision surgery for pseudarthrosis after surgical correction of adult spinal deformity (ASD) remains challenging and without consensus, previous studies did not sufficiently compare the methods of revision surgery. PURPOSE We aimed to determine the most useful of the following three methods of revision surgery: surgery for rod change only, anterior lumbar interbody fusion (ALIF) around pedicle subtraction osteotomy (PSO), and 4-rod constructs. STUDY DESIGN/SETTING Retrospective, consecutive case review. PATIENT SAMPLE A total of 79 patients (average age 70.5 years) who were diagnosed adult spinal deformity with sagittal imbalance and followed up for more than 5 years after surgical correction with pedicle subtraction osteotomy. OUTCOME MEASURES Description and analysis of X-ray changes. METHODS There were 42 revision surgeries for pseudarthrosis performed by one of three methods: rod change with 2-rod constructs (n=16), anterior lumbar interbody fusion around PSO with rod change (n=9), and rod change with 4-rod constructs (n=17). RESULTS Preoperative lumbar lordosis was corrected (69.4˚) from 3.6° to -65.8˚ while sagittal vertical axis (SVA) was corrected (185.7 mm) from 176.9 mm to -8.8 mm. Pseudarthrosis occurred (42/79, 53%) around PSO site on the average of 21 months after the surgery, so that revision surgery was performed. There were no statistically significant differences among the other risk factors except the surgical methods for the three groups. Re-pseudarthrosis occurred in 4 of 42 (9.5%) cases in patients who received rod change using the 2-rod constructs method around PSO site at 15, 18, 24 and 35 months postoperatively, and there was no re-pseudarthrosis in the other two groups (P=0.042). CONCLUSIONS Our study showed that anterior lumbar interbody fusion around PSO and 4-rod constructs are preferable to rod change with 2-rod constructs. Therefore, our research can provide an effective guideline for revision surgery for pseudarthrosis that occurs after long PSF with PSO. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Cross-link is a risk factor for rod fracture at pedicle subtraction osteotomy site: A finite element study

BackgroundWe aim to investigate using finite element model (FEM) whether the use of a cross-link is a risk factor for rod fracture at the pedicle subtraction osteotomy (PSO) site. MethodsThe geometry and dimensions of the FEM were obtained from a high-resolution computed tomography scan data of a 65 years old female patient with spinal sagittal imbalance. The intact model was modified to place PSO on the L4 spine. A cross-link was placed at the PSO site. A multisegment spinal fusion model from L1 to the pelvis was used to compare and analyze the peak von Mises stress (PVMS) values of the implants. A compressive follower load of 400 N was added to the validated intact lumbar spinal model in the follower load path direction. ResultsAfter PSO surgery, the PVMS of the rod was significantly increased during flexion and extension at the PSO site. With the cross-link at the PSO site, the PVMS of the rod was further significantly increased during flexion and extension. ConclusionThe cross-link at the PSO site increased the risk of rod facture, especially during flexion and extension stress.

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.

ЕFFECTIVENESS OF FOUR-ROD FIXATION FOR PEDICLE SUBTRACTION SPINAL OSTEOTOMY

Introduction. Pedicle subtraction osteotomy (PSO) provides for significant segmental correction of the sagittal balance of the spine. At the same time, the technique is associated with a high risk of complications, with rod fracture at the osteotomy site being the most common. The purpose of this study — to assess the effectiveness of four-rod fixation compared to literature data on standard two-rod fixation in patients undergoing PSO. Materials and Methods. The study is a retrospective analysis of 47 consecutive patients with rigid spinal deformities, who underwent pedicle subtraction osteotomy at the lumbar level. The average age of the patients (33 females and 14 males) was 59.7 years. In all cases spinal fixation carried out using a four-rod construct with additional short rods at the osteotomy site. The minimal postoperative follow-up was 2 years. A detailed analysis of the radiographic data was carried out with calculation of the global sagittal balance and spinopelvic parameters. A detailed assessment of complications in the early and late postoperative periods was also performed. After an exhaustive review of literature, a comparative analysis was made of the four-rod fixation technique with current literature data on the frequency of complications (in particular, rod fractures in the osteotomy zone) after two-rod fixation. Results. In all cases the osteotomy was performed at one level, most often at L3 (49%). The average length of fixation was 9.8 segments. The average angle of segmental correction was 27.1°. In most cases, it was possible to achieve adequate correction of spinopelvic parameters. Among complications, bone resorption around screws was most prevalent (23.4% of cases). Proximal junctional kyphosis occurred in 12.8% of cases, neurologic deficit — in 14.9% of cases, infectious complications — in 10.6% cases. Asymptomatic pseudarthrosis, confirmed by CT data, was observed in 12.8% of patients. Rod fracture at the PSO site and adjacent segments was not observed in any of the cases. Rod fractures of other localization were observed in 10.6% of patients. Conclusion. According to the literature, the frequency of rod fractures at the osteotomy site is the most frequent complication of PSO. The results of this study showed that four-rod fixation in PSO significantly reduces the incidence of pseudarthrosis and rod fracture rate in the long-term follow-up and provides greater control over the process of osteotomy closure.

Pedicle Subtraction Osteotomy for Kyphosis Following Lumbar Fusion Surgery.

Introduction Pedicle subtraction osteotomy (PSO) is performed to correct sagittal plane deformity. This procedure is useful with revision cases in which the number of intact discs for correction is limited. Methods Forty-four patients (10 male and 34 female) with minimum follow-up of 2 years were reviewed; all had undergone PSO revision surgery for kyphosis following previous lumbar fusion surgery. The average age at operation was 72.8 years (range 42-85 years), and the average follow-up period was 4.1 years (2-9 years). The average fusion level was 7.5 (4-13 level), and the average previously fused level was 2.4 (1-7 level). Results The average operation time was 424 min, and average blood loss was 2880 g. The average JOA score of 14.0 before operation changed to 21.8 at 1-year follow-up and to 20.7 at final follow-up. The average recovery rate at final follow-up was 45.7%. Four patients underwent re-operations for proximal junctional kyphosis and 3 patients for rod fracture. The fusion rate was 88.6%, and 13 patients (29.5%) developed subsequent vertebral fracture. The average PI-LL (Pelvic incidence minus Lumbar lordosis) at pre-op of 52.9 degrees changed to 3.8 degrees at post-op, to 13.4 degrees at 1-year follow-up, and to 14.8 degrees at final follow-up. The average correction at the PSO site was 36.0 degrees at post-op, 36.7 degrees at 1-year follow-up, and 37.0 degrees at final follow-up. The average sagittal vertical axis at pre-op of 145.0 mm decreased to 51.2 mm at 1-year follow-up; however, it increased to 75.3 mm at final follow-up. Conclusion PSO for correction of kyphosis following previous lumbar fusion surgery was an effective procedure without correction loss at the local osteotomy site; however, its surgical invasiveness and complication rate were high. Subsequent vertebral fracture, adjacent segment degeneration, and rod fracture contribute to deterioration of outcome that is evident at long-term follow-up.

Biomechanical Stability of Transverse Connectors in the Setting of a Thoracic Pedicle Subtraction Osteotomy

Introduction The biomechanical effect of augmentation of a longitudinal constructs with one or two transverse connectors (TC) after a thoracic pedicle subtraction osteotomy (PSO) has not been evaluated previously. Previous investigations have suggested the role of transverse connectors for long segment thoracic constructs in enhancing torsional rigidity. We set out to evaluate the biomechanical contribution of TC to the stability of a long-segment pedicle screw–rod construct after a thoracic PSO. Methods Seven human cadaveric thoracic spines were prepared and instrumented from T4 to T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation, flexion/extension, and lateral bending). ROM analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TC. No outside funding sources were utilized for this study. The authors have no potential conflicts of interest to report. Results Following PSO and an unaugmented longitudinal pedicle screw–rod construct, T4–T10 (overall construct) and T6–T8 (PSO site). ROM was significantly reduced in all planes of motion compared with intact condition ( p &lt; 0.05). Augmentation of longitudinal construct with either one or two TC did not significantly increase construct stability in flexion-extension or lateral bending compared with the unaugmented construct ( p &gt; 0.05). In contrast, during axial rotation, global ROM was significantly reduced by 43% and by 48% at T6–T8 following addition of two TC ( p &lt; 0.05). One TC did not significantly reduce torsional ROM. Conclusions Two transverse connectors significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in stability for flexion-extension and lateral bending, or with the addition of only one transverse connector. In the setting of a PSO and long segment pedicle screw–rod construct, augmentation with at least two transverse connectors should be considered to improve torsional rigidity.

Biomechanical stability of transverse connectors in the setting of a thoracic pedicle subtraction osteotomy

Background contextTransverse connectors (TCs) are often used to improve the rigidity of posterior spinal instrumentation as previous investigations have suggested that TCs enhance torsional rigidity in long-segment thoracic constructs. Posterior osteotomies, such as pedicle subtraction osteotomy (PSO), are used in severe thoracic deformities and provide a significant amount of correction; as a consequence, however, PSOs also induce three-column spinal instability. In theory, augmentation of longitudinal constructs with TC after a thoracic PSO may provide additional rigidity, but the concept has not been previously evaluated. PurposeTo evaluate the biomechanical contribution of TC to the rigidity of a long-segment pedicle screw-rod construct after a thoracic PSO. Study designAn in vitro fresh-frozen human cadaveric biomechanical analysis. MethodsSeven human cadaveric thoracic spines were prepared and instrumented from T4–T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation [AR], flexion/extension [FE], and lateral bending [LB]). Range of motion analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TCs. ResultsAfter PSO and an unaugmented longitudinal pedicle screw-rod construct, T4–T10 (overall construct) and T6–T8 (PSO site) ROMs were significantly reduced in all planes of motion compared with intact condition (AR: 11.8° vs. 31.7°; FE: 2.4° vs. 12.3°; 3.4° vs. 17.9°, respectively, p<.05). Augmentation of longitudinal construct with either one or two TCs did not significantly increase construct rigidity in FE or LB compared with the unaugmented construct (p>.05). In contrast, during AR, global ROM was significantly reduced by 43% and 48% at T6–T8 (1.7° and 1.2° vs. 2.38°, respectively) after addition of one and two TCs (p<.05), respectively. One TC did not significantly reduce torsional ROM from the intact state. ConclusionsTwo TCs significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in rigidity for FE and LB or with the addition of only one TC. In the setting of a PSO and long-segment pedicle screw-rod construct, augmentation with at least two TCs should be considered to improve torsional rigidity.

Risk factors for and assessment of symptomatic pseudarthrosis after lumbar pedicle subtraction osteotomy in adult spinal deformity.

Retrospective review of prospectively collected data. To assess the prevalence, risk factors, and clinical outcomes for pseudarthrosis after a lumbar pedicle subtraction osteotomy (PSO). There exists no large series that examines pseudarthrosis rates of PSOs. Data of 171 consecutive patients with adult deformity who underwent a lumbar PSO by 2 surgeons at a single institution with a minimum 2-year follow-up were analyzed. Pseudarthrosis diagnosed through sagittal malalignment and instrumentation failure noted on radiograph was confirmed intraoperatively. Eighteen (10.5%) of 171 patients developed pseudarthrosis after a PSO. Eleven of the 18 patients (6.4% of all patients, 61.1% of the 18 patients with pseudarthrosis) had pseudarthrosis at the PSO site, L3 being the most common; other locations included the lumbosacral junction (4/18), thoracolumbar junction (2/18), and upper thoracic spine (1/18). Preoperative pseudarthrosis level was a predictor of the postoperative level of pseudarthrosis (93%). Fifteen of the 18 patients (83%) had no interbody fusion directly above or below the PSO site, 16 (88%) had a history of pseudarthrosis at the time of PSO surgery and 2 of 3 patients who had prior radiation to the lumbar region developed pseudarthrosis. Most pseudarthroses occurred within the first 2 years (n = 13/18), between 2 and 5 years (n = 3/18), and more than 5 years (n = 2/18) postoperatively. Prior pseudarthrosis (P < 0.0001), pseudarthrosis at the PSO site (P < 0.0001), prior decompression in the lumbar region (P = 0.0037), prior radiation to the lumbar region (P < 0.0001), and presence of inflammatory/neurological disorders (P < 0.0036) were identified as risk factors. All 18 patients with pseudarthroses required revision surgery (posterior-only surgery, n = 12; anteroposterior surgery, n = 6) due to loss of sagittal alignment and pain. The mean pre-revision Scoliosis Research Society score was 85, post-revision score was 95 (P = 0.0166), and the mean pre-revision Oswestry Disability Index score was 42.5, post-revision score was 34.5 (P = 0.0203). The overall prevalence of pseudarthrosis was 10.5% of which 61% occurred at the actual PSO site and Scoliosis Research Society and Oswestry Disability Index scores improved significantly after pseudarthrosis repair. 4.

Assessment of Symptomatic Rod Fracture After Posterior Instrumented Fusion for Adult Spinal Deformity

Improved understanding of rod fracture (RF) in adult spinal deformity could be valuable for implant design, surgical planning, and patient counseling. To evaluate symptomatic RF after posterior instrumented fusion for adult spinal deformity. A multicenter, retrospective review of RF in adult spinal deformity was performed. Inclusion criteria were spinal deformity, age older than 18 years, and more than 5 levels posterior instrumented fusion. Rod failures were divided into early (≤12 months) and late (>12 months). Of 442 patients, 6.8% had symptomatic RF. RF rates were 8.6% for titanium alloy, 7.4% for stainless steel, and 2.7% for cobalt chromium. RF incidence after pedicle subtraction osteotomy (PSO) was 15.8%. Among patients with a PSO and RF, 89% had RF at or adjacent to the PSO. Mean time to early RF (63%) was 6.4 months (range, 2-12 months). Mean time to late RF (37%) was 31.8 months (range, 14-73 months). The majority of RFs after PSO (71%) were early (mean, 10 months). Among RF cases, mean sagittal vertical axis improved from preoperative (163 mm) to postoperative (76.9 mm) measures (P<.001); however, 16 had postoperative malalignment (sagittal vertical axis>50 mm; mean, 109 mm). Symptomatic RF occurred in 6.8% of adult spinal deformity cases and in 15.8% of PSO patients. The rate of RF was lower with cobalt chromium than with titanium alloy or stainless steel. Early failure was most common after PSO and favored the PSO site, suggesting that RF may be caused by stress at the PSO site. Postoperative sagittal malalignment may increase the risk of RF.

A Method for Calculating the Exact Angle Required during Pedicle Subtraction Osteotomy for Fixed Sagittal Deformity: Comparison with the Trigonometric Method

Pedicle subtraction osteotomy (PSO) has emerged as a powerful procedure for correcting fixed sagittal deformity. There has only been one attempt to quantify the magnitude of correction needed to restore sagittal balance; the trigonometric method for calculating the desired PSO angle is an approximation. We propose a method for calculating the exact angle required for PSO and explore how this angle differs from that obtained via the trigonometric method in illustrative cases. We conducted a mathematical analysis of the spine with application in illustrative cases. The trigonometric method calculates the necessary angular correction at the axial level of the PSO, but along the sacral vertical line. However, the angular measurement should take place at the true axis of rotation, the apex of the PSO. Measurements were taken from full-length standing x-rays, and both methods were explored. The trigonometric method for calculating PSO angle is an exact measurement only if the apex of the PSO site lies on the sacral vertical line. As the apex of the PSO site moves anterior to that line, the trigonometric approximation underestimates the actual angle. As the apex of the PSO moves posterior to that line, the trigonometric approximation overestimates the actual angle. The trigonometric method for calculating the PSO angle required for surgical deformity correction is an approximation, but its validity in clinical practice was confirmed by this study. The exact angle is obtained by a method centered on the apex of the PSO site. Although the difference between these angles is small, it is an important conceptual point for spine surgeons. Measurement of the exact angle is easily performed and should replace the trigonometric method for calculating the required PSO angle when standard digital measurement tools are available.

Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. Surgical technique.

Fixed sagittal imbalance (a syndrome in which the patient is only able to stand with the weight-bearing line in front of the sacrum) has many etiologies. The most commonly reported technique for correction is the Smith-Petersen osteotomy. Few reports on pedicle subtraction procedures (resection of the posterior elements, pedicles, and vertebral body through a posterior approach) are available in the peer-reviewed literature. We are aware of no report involving a substantial number of patients with coexistent scoliosis who underwent pedicle/vertebral body subtraction for the treatment of fixed sagittal imbalance. Twenty-seven consecutive patients in whom sagittal imbalance was treated with lumbar pedicle subtraction osteotomy at one institution were analyzed. Radiographic analysis included assessment of thoracic kyphosis, lumbar lordosis, lordosis through the pedicle subtraction osteotomy site, and the C7 sagittal plumb line. Outcomes analysis was performed with use of a before-and-after pain scale, items from the Oswestry questionnaire, and the Scoliosis Research Society (SRS) questionnaire after a minimum duration of follow-up of two years. Complications and radiographic findings were also analyzed for the entire group. Overall, the average increase in lordosis was 34.1 degrees and the average improvement in the sagittal plumb line was 13.5 cm. One patient had development of a lumbar pseudarthrosis through the area of pedicle subtraction osteotomy, and six patients had development of a thoracic pseudarthrosis. Two patients had development of increased kyphosis at L5/S1, caudad to the fusion, resulting in some loss of sagittal correction. There were significant improvements in the overall Oswestry score (p < 0.0001) and the pain-scale score (p = 0.0002). Most patients reported improvement in terms of pain and self-image as well as overall satisfaction with the procedure. Pedicle subtraction osteotomy is a useful procedure for patients with fixed sagittal imbalance. A worse clinical result is associated with increasing patient comorbidities, pseudarthrosis in the thoracic spine, and subsequent breakdown caudad to the fusion.

Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance.

Fixed sagittal imbalance (a syndrome in which the patient is only able to stand with the weight-bearing line in front of the sacrum) has many etiologies. The most commonly reported technique for correction is the Smith-Petersen osteotomy. Few reports on pedicle subtraction procedures (resection of the posterior elements, pedicles, and vertebral body through a posterior approach) are available in the peer-reviewed literature. We are aware of no report involving a substantial number of patients with coexistent scoliosis who underwent pedicle/vertebral body subtraction for the treatment of fixed sagittal imbalance. Twenty-seven consecutive patients in whom sagittal imbalance was treated with lumbar pedicle subtraction osteotomy at one institution were analyzed. Radiographic analysis included assessment of thoracic kyphosis, lumbar lordosis, lordosis through the pedicle subtraction osteotomy site, and the C7 sagittal plumb line. Outcomes analysis was performed with use of a before-and-after pain scale, items from the Oswestry questionnaire, and the Scoliosis Research Society (SRS) questionnaire after a minimum duration of follow-up of two years. Complications and radiographic findings were also analyzed for the entire group. Overall, the average increase in lordosis was 34.1 degrees and the average improvement in the sagittal plumb line was 13.5 cm. One patient had development of a lumbar pseudarthrosis through the area of pedicle subtraction osteotomy, and six patients had development of a thoracic pseudarthrosis. Two patients had development of increased kyphosis at L5/S1, caudad to the fusion, resulting in some loss of sagittal correction. There were significant improvements in the overall Oswestry score (p < 0.0001) and the pain-scale score (p = 0.0002). Most patients reported improvement in terms of pain and self-image as well as overall satisfaction with the procedure. Pedicle subtraction osteotomy is a useful procedure for patients with fixed sagittal imbalance. A worse clinical result is associated with increasing patient comorbidities, pseudarthrosis in the thoracic spine, and subsequent breakdown caudad to the fusion. Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.