Search Results (261)

Background/Objectives: Cervical pedicle screw (CPS) placement provides superior biomechanical stability but remains technically demanding and associated with a risk of screw malposition. While recent advances in imaging and navigation have improved placement accuracy, reliable prediction of malposition remains challenging. The aim of this study was to evaluate whether machine learning (ML) models can predict CPS malposition using structured clinical and anatomical features. Methods: We performed a retrospective analysis of 862 pedicle screws from 168 posterior cervical spine surgeries conducted at our institution between 2018 and 2025. Clinical, procedural, and anatomical variables, including age, sex, body size parameters, surgical indication, vertebral level, pedicle angle, and pedicle width, were evaluated. Pedicle morphology was partially derived from CT-based automated segmentation using TotalSegmentator (v2.13.0), while selected anatomical parameters were manually measured. Supervised ML models, including Random Forest, Balanced Random Forest, XGBoost (v3.2.0), Support Vector Machine, and K-Nearest Neighbor, were trained and compared using Python and scikit-learn to predict inaccurate screw placement. Model performance was evaluated using Area Under the Receiver Operating Characteristic Curve (ROC AUC), F1-score, precision, and recall. Model interpretability was assessed using Shapley Additive Explanations (SHAP). Results: The dataset showed a clinically representative class distribution, with 91.1% of screws classified as acceptable and 8.9% as inaccurate. Across all models, predictive performance was moderate and consistent. Balanced Random Forest achieved the highest discriminative performance (ROC AUC 0.69) and provided the most balanced classification profile, while other models demonstrated comparable overall performance with varying sensitivity to the minority class. SHAP analysis identified anatomical and procedural variables, including pedicle width and angle, as relevant contributors to model output. Feature contributions were distributed across variables, with substantial overlap between outcome groups. Conclusions: ML-based prediction of CPS malposition using clinical and anatomical features demonstrates consistent and interpretable performance. The results highlight that predictive performance is primarily influenced by dataset characteristics, including class distribution and feature overlap, rather than model selection alone. This study provides an important baseline for ML-based CPS prediction and supports future research integrating larger datasets and more detailed anatomical representations to enhance predictive accuracy. Full article

Background: Congenital thoracic kyphoscoliosis caused by vertebral malformations is a challenging condition that may progress during skeletal growth, leading to spinal imbalance, pain, cosmetic deformity, and neurological compromise. Conventional correction often requires extensive anterior, posterior, or combined approaches associated with substantial surgical morbidity. We describe a single-position surgical technique combining a lateral retropleural asymmetric vertebral resection with percutaneous posterior instrumentation performed entirely in the lateral decubitus position. Methods: A 15-year-old boy with progressive congenital thoracic kyphoscoliosis secondary to a T10 butterfly vertebra underwent surgical correction after failure of conservative treatment. The procedure was performed entirely in the left lateral decubitus position under multimodal intraoperative neurophysiological monitoring. Bilateral percutaneous pedicle screws were inserted from T7 to L1 under fluoroscopic guidance without repositioning the patient. A muscle-sparing lateral retropleural approach was then used to perform T10 asymmetric vertebral column resection, anterior column reconstruction with an expandable cage, and definitive deformity correction using posterior rod compression. The technical rationale, operative workflow, and reconstruction strategy are described. Results: The procedure was completed without intraoperative neurological deterioration or the need for patient repositioning. Postoperative imaging demonstrated satisfactory restoration of coronal and sagittal alignment, appropriate implant positioning, and spinal canal decompression. The patient experienced marked improvement in pain, shoulder balance, rib hump deformity, and overall posture while maintaining normal neurological function. The main thoracic curve improved from 32° to 6°, thoracic kyphosis from 78° to 63°, VAS from 5 to 0, ODI from 42 to 5, and SRS-22R from 3.85 to 4.85. Solid fusion was confirmed at 3 years. A postoperative pneumothorax, attributed to pleural violation during exposure, represented the only complication and resolved completely following pleural drainage. At 36-month follow-up, radiographs and computed tomography confirmed maintenance of deformity correction, stable instrumentation, and solid anterior and posterior fusion without implant failure or loss of correction. Conclusions: Single-position lateral retropleural asymmetric vertebral resection combined with percutaneous pedicle screw fixation is a technically feasible option for selected patients with congenital thoracic kyphoscoliosis. Avoiding intraoperative repositioning while combining anterior reconstruction and posterior stabilization through a reduced-access retropleural approach may simplify the surgical workflow and minimize soft-tissue disruption without compromising deformity correction. Further clinical experience is required to establish its reproducibility and comparative advantages. Full article

Background/Objectives: Robotic-assisted spine instrumentation is resource-intensive and may be challenging during off-hours emergency care. This study evaluated its operational feasibility and technical reliability in a teaching hospital. Methods: We performed an exploratory post hoc secondary analysis of 146 consecutive robotic-assisted spine instrumentation procedures comprising 1006 pedicle or sacral–alar–iliac screws. Off-hours surgery was defined as night and/or weekend surgery. The primary outcome was screw-level Gertzbein–Robbins (GR) accuracy. Secondary outcomes included workflow, perioperative, and 30-day clinical measures. Because all off-hours procedures were emergencies, an additional sensitivity analysis compared off-hours with regular-hours emergency procedures. Results: Sixteen procedures comprising 150 screws were performed off-hours. In the unadjusted primary comparison, off-hours cases had greater trauma and emergency burden, more frequent repeat imaging or re-registration, higher intensive care unit (ICU) utilization, and longer hospitalization. GR A/B accuracy was 96.0% off-hours and 98.2% during regular hours, while GR C–E rates were 4.0% and 1.8%, respectively. Severe deviations were uncommon, and no screw-related postoperative neurological deficit occurred. In the emergency-only analysis, GR A/B accuracy was 96.0% off-hours and 96.7% during regular-hours emergency surgery, while several perioperative differences were attenuated. Conclusions: Robotic-assisted spine instrumentation remained operationally feasible during off-hours emergency surgery, with high screw accuracy and few severe deviations. However, the small and highly selected off-hours subgroup and marked case-mix differences preclude conclusions regarding equivalence, comparative safety, or an independent effect of surgical timing. These findings should be considered hypothesis-generating. Full article

Background: Automated pedicle screw planning (ASP) can initialize trajectories and implant dimensions, but correlation with implanted screws does not establish agreement. We quantified the association and agreement between ASP recommendations and actual intraoperative implant selection (AIS) and examined pathology, asymmetric planning, and available safety outcomes. Methods: This retrospective single-center study included 103 consecutive patients treated with thoracic or lumbar instrumentation from January 2021 to January 2024. The dataset contained 351 bilateral screw-pair records. Pearson and Spearman correlations, linear regression, and Bland–Altman analyses were supplemented by patient-clustered bootstrap 95% confidence intervals (CIs), pathology-stratified estimates, and a sensitivity analysis excluding a verified 94 mm iliac-fixation observation. Results: Diameter showed moderate correlation (Pearson’s r = 0.635, 95% CI 0.542–0.721; Spearman’s rho = 0.679, 95% CI 0.554–0.767; both p < 0.001). Length also showed moderate correlation (Pearson’s r = 0.675, 95% CI 0.565–0.754; Spearman’s rho = 0.600, 95% CI 0.450–0.714; both p < 0.001). For ASP minus AIS, the diameter bias was −0.75 mm (95% CI −0.86 to −0.64), with limits of agreement from −2.00 to 0.50 mm. The length bias was −0.15 mm (95% CI −1.05 to 0.79), with limits from −12.30 to 12.00 mm. The 94 mm value was verified as a genuine iliac-fixation observation; excluding it changed Pearson’s r only from 0.675 to 0.679. Asymmetric ASP length recommendations occurred in 115/351 pairs (32.8%), usually by 5 mm. Conclusions: ASP tracked overall implant-size trends but did not provide interchangeable estimates of surgeon-selected dimensions. Its systematic diameter underestimation and broad pair-level differences support its use as an initialization and review aid, with final sizing retained as a surgeon decision. Full article

Background: Accurate pedicle screw placement remains essential in spinal instrumentation, and robotic navigation has been introduced to improve safety, reproducibility, and workflow standardization. This study evaluated the accuracy of robot-assisted pedicle screw placement using the Excelsius GPS platform during the first year of implementation at two centers and analyzed the associated learning curve. Methods: Consecutive patients undergoing robot-assisted spinal instrumentation between April 2024 and April 2025 were retrospectively reviewed. Screw accuracy was assessed on intraoperative three-dimensional imaging using the Gertzbein–Robbins Scale (GRS). Grades A and B were considered clinically acceptable, whereas grades C–E were considered clinically non-acceptable. Sacral S1 screws and oncological cases requiring carbon fiber-reinforced PEEK instrumentation were excluded from the primary analysis and evaluated separately when appropriate. Robotic workflow time was defined as the interval between the first intraoperative three-dimensional acquisition used for planning and the second acquisition used for screw verification. Results: The primary standard non-oncological cohort included 102 patients and 455 non-S1 screws. Overall, 411 screws were classified as GRS A, yielding a perfect intrapedicular placement rate of 90.3%. Clinically acceptable accuracy was achieved in 449 of 455 screws, corresponding to a GRS A + B rate of 98.7% (95% CI, 97.2–99.4%). Only six screws were classified as GRS C–E, with no GRS D screws observed. Clinically acceptable accuracy was comparable between centers. In Center 1, all clinically non-acceptable screws occurred within the first nine cases, and GRS A + B accuracy increased from 92.9% in the first trimester to 100% thereafter. Median robotic workflow time was 64.4 min per case and 13.9 min per screw. Conclusions: This two-center early experience supports the accuracy and reproducibility of ExcelsiusGPS-assisted spinal instrumentation. Chronological analysis showed that clinically non-acceptable breaches were concentrated in the early implementation phase; however, this observation should be considered exploratory because of the low event count. The study supports high clinically acceptable accuracy and broadly comparable robotic workflow metrics across centers. Chronological patterns observed during early implementation should be interpreted as exploratory rather than as proof of a formal learning curve. Full article

Background/Objectives: Minimally invasive (percutaneous) pedicle screw fixation (PPSF) was initially introduced for the treatment of degenerative spinal deformities. Since then, its indications have progressively expanded to a broad spectrum of spinal pathologies. This method has gained increasing acceptance in spinal surgery due to lower morbidity when compared with conventional open procedures. This study presents a comprehensive review of the recent literature on hybrid minimally invasive spinal instrumentation techniques, focusing on the combined use of PPSF with open or mini-open approaches and their roles in personalized surgical management. Methods: A literature search was conducted in PubMed and Web of Science to identify studies reporting expanded indications of percutaneous pedicle screw fixation (combined with other approaches), novel surgical techniques, and their clinical outcomes. Results: Thirty-five studies met the inclusion criteria and were categorized according to pathology. Most included studies were retrospective observational investigations corresponding to Oxford CEBM Levels III–IV evidence, with a smaller number of prospective studies and systematic reviews. Conclusions: The findings from this review highlight the expanding role of hybrid methods in the management of complex spinal disorders. These approaches provide adequate stability and enable decompression or deformity correction, while minimizing tissue trauma, blood loss, and perioperative morbidity, thereby facilitating improved recovery and functional outcomes. The included literature predominantly represents moderate levels of evidence, supporting a patient-specific, pathology-driven surgical strategy that optimizes individualized outcomes in spinal surgery. Full article

Background/Objectives: Ankylosing Spinal Disorders (ASDs) encompass a heterogeneous group of rheumatic diseases characterized by progressive ankylosis of the axial skeleton, including Ankylosing Spondylitis (AS), Diffuse Idiopathic Skeletal Hyperostosis (DISH), and Non-Radiographic Axial Spondyloarthritis (nr-AxSpA). Spinal ankylosis profoundly alters the biomechanical properties of the vertebral column, transforming it into a rigid long-bone equivalent and dramatically increasing fracture risk even after low-energy trauma. Once a fracture occurs, the long lever arm created by the ankylosed segments generates enormous mechanical stress at the fracture site, making surgical stabilization mandatory in the vast majority of cases. Long posterior instrumentation is the treatment of choice; however, no consensus exists regarding the optimal number of instrumented levels. The aim of this study is to clinically and radiologically evaluate long posterior instrumentation in the 3 + 3 (3 proximal and 3 caudal screws), 3 + 2 (3 proximal and 2 caudal screws), or 2 + 2 (2 proximal and 2 caudal screws) configuration for the treatment of traumatic ASD thoracolumbar vertebral fractures, in terms of implant failure, infection rate, and mortality. Methods: Between 2018 and 2023, 65 consecutive patients with ASD-related thoracolumbar vertebral fractures were treated at our institution. After applying pre-defined inclusion and exclusion criteria, 37 patients were enrolled. Patients were retrospectively divided into three groups according to the posterior arthrodesis configuration (notation indicates number of instrumented vertebral levels proximal + distal to the fracture: 3 + 3, 3 + 2, or 2 + 2). Radiological outcomes were assessed for loosening, screw cut-out, and implant breakage. Infection and mortality rates within 3 months from surgery were evaluated as secondary endpoints. Statistical analysis was performed using the Fisher exact test (significance set at p < 0.05). Results: Thirty-seven patients (28 males and 9 females; mean age 77 ± 7.3 years) were included, with a mean follow-up of 30 ± 5.3 months. Instrumentation configurations were as follows: 23 (3 + 3), 5 (3 + 2), and 9 (2 + 2). Three implant failures (8.1%) and four infections (10.8%) were recorded. Eleven patients died within 3 months of surgery. A statistically significant difference was found between instrumentation length and mechanical complications (p = 0.0468), while no significant difference was observed for infection (p = 1) or mortality rate (p = 0.137). Conclusions: In this exploratory retrospective cohort, the 3 + 3 configuration was associated with the lowest observed rate of implant failure in ASD thoracolumbar fractures, suggesting a potential mechanical advantage over shorter constructs that warrants confirmation in larger prospective studies. No significant correlation was found between instrumentation length and infection rate or early mortality. Prospective, multicentre studies with larger cohorts are warranted to establish definitive guidelines for instrumentation length in this challenging patient population. Full article

Background: Implant supply strategy in spine surgery affects operative workflow, resource utilization, and packaging-related material use, yet has received limited systematic investigation. This study evaluates single-sterile implants versus multipack implants using a hospital-based Health Technology Assessment (HB-HTA) framework. Methods: A non-randomized, mixed-methods comparative study was conducted at a tertiary academic spine center. Time measurements were recorded during eight posterior fusion procedures (four per supply type; n = 18 single-pack screws, n = 20 multipack screws) across three process steps: implant retrieval, sterile transfer, and instrument preparation. Time measurements were recorded per packaging unit; per-implant comparisons were additionally derived for operational interpretation. Packaging volume, weight, and packaging-related CO₂-equivalent estimates were calculated per implant. Standardized questionnaires were distributed to operating-room (OR) nurses (n = 14/21; 66.7%) and institutional surgeons (n = 11/11; 100%). Manufacturer-provided descriptive process and cost data were analyzed. Results: Multipack implants were associated with consistently shorter handling times across all measured process steps. Mean retrieval time per packaging unit was 25.4 s (multipack) versus 58.7 s (single-pack); retrieval time was significantly shorter for multipack units on the Mann–Whitney U test (p = 0.004), a result that was robust to supply-related outlier events (p = 0.001 after their post hoc exclusion). Packaging-normalized sterile-transfer burden per implant was reduced by a factor of 4.76. Instrument preparation was faster with multipack systems (15.6 s vs. 25.2 s). Packaging volume per implant was reduced by a factor of 5.6, and packaging weight by a factor of 2. Packaging-related CO₂-equivalent estimates were lower for multipack implants (0.017 kg vs. 0.026 kg per implant). Survey responses indicated predominantly positive evaluations of workflow and handling efficiency. A trade-off was identified regarding the potential disposal of unused implants (noted by 73% of institutional surgeons). Manufacturer-provided descriptive data suggested scale effects in packaging and sterilization processes. Conclusions: Under high-volume academic conditions, multipack implants were associated with shorter implant-handling process times, favorable staff perceptions, and reduced packaging-related material burden while introducing trade-offs that require local evaluation. These exploratory findings suggest that the implant supply strategy is an underexplored but potentially relevant dimension of surgical process optimization in spine surgery. Full article

Background: Radiculopathy originating from a previously fused lumbar segment is a clinically relevant but often underrecognized problem. Progressive foraminal stenosis may develop due to postoperative structural changes, leading to mechanical irritation of the exiting nerve root. Transforaminal endoscopic lumbar foraminotomy (TELF) is a minimally invasive option, but its role in this setting is not well defined. Methods: In this retrospective cohort study, we included 36 consecutive patients who underwent TELF for symptomatic foraminal stenosis at a previously fused segment between 2020 and 2023. Clinical outcomes were assessed using the visual analog scale (VAS) for leg pain, Oswestry Disability Index (ODI), and modified MacNab criteria, with follow-up of up to 2 years. Radiographic and intraoperative findings were reviewed to explore the underlying mechanisms. Results: The mean VAS score improved significantly from 8.36 preoperatively to 2.00 at 2 years, and the mean ODI decreased from 70.9% to 16.8%. According to the modified MacNab criteria, 86.1% of the patients achieved excellent or good outcomes. Intraoperative findings revealed fibrotic or hypertrophic foraminal stenosis in 86.1% patients (n = 31), whereas 13.9% of patients (n = 5) showed pedicle screw-related nerve root irritation. Five patients experienced transient postoperative dysesthesia, and no postoperative instability was observed. Conclusions: Radiculopathy at the fused segment is primarily caused by progressive mechanical foraminal compromise after fusion. TELF provides effective symptom relief through direct decompression and may serve as a less invasive alternative to revision fusion in selected patients. Full article

Background: Fractures of the upper cervical spine are challenging to treat due to their proximity to critical neurovascular structures and the need for immediate, stable fixation. Open posterior fixation remains the standard but is associated with soft-tissue disruption and morbidity. Minimally invasive, navigation-assisted pedicle screw fixation represents a viable alternative for older populations, significantly reducing surgical morbidity and tissue trauma. The present study evaluates the accuracy, safety, and perioperative outcomes of minimally invasive navigated posterolateral C1–C2 fixation. Methods: We conducted a retrospective consecutive case review of 51 patients who underwent minimally invasive C1–C2 screw fixation between 2019 and 2024. All procedures were performed using intraoperative O-arm imaging and StealthStation S8 navigation. Screw placement accuracy was assessed using the Bredow modification of the Gertzbein–Robbins and Heary classifications. Perioperative data, including operative time, screw dimensions, radiation dose, complications, and hospital stay, were recorded. Results: Fifty-one patients were included in the study. A total of 212 screws were placed. According to Gertzbein–Robbins grading, 92.4% were Grade A, 6.6% were Grade B, and 1% were Grade C. According to Heary grading, 95% were Grade I and 5% were Grade III. No vertebral artery injuries, new neurological deficits, or intraoperative hardware failures occurred. The mean screw lengths were 33.2 mm (SD = 3.38 mm) (C1) and 32 mm (SD = 4.30 mm) (C2). The mean operative time was 128 min (SD = 52.95 min). The mean radiation dose was 629.16 mGy·cm² (SD = 372.2 mGy·cm²). One superficial wound infection occurred. The median postoperative NRS was 4 (IQR: 4–5). The mean hospital stay was 4.21 (SD = 3.77) days. Conclusions: Our findings demonstrate that the presented approach for C1–C2 fixation is a highly accurate and safe alternative to open posterior fixation for upper cervical fractures. Full article

Minimally invasive spine surgery (MISS) has progressively transformed the management of spinal disorders by reducing soft-tissue disruption, perioperative morbidity, and recovery time while maintaining clinical outcomes comparable to conventional open techniques. Beyond its technical evolution, MISS has increasingly assumed a central role in the treatment of bone-related spinal conditions, including vertebral fractures, degenerative instability, metastatic disease, and osteoporosis-associated pathology. This narrative review provides a comprehensive overview of the evolution of MISS with a specific focus on its interaction with vertebral bone biology, implant stability, and fusion processes. A structured literature search of the PubMed/MEDLINE database was conducted, including English-language studies published between 1980 and June 2025 addressing MISS techniques, enabling technologies, and bone-related clinical outcomes. Current evidence suggests that MISS may preserve paraspinal vascularization and soft tissue integrity, potentially supporting bone healing and fusion, although high-quality comparative data remain limited. The effectiveness of MISS in osteoporotic and metastatic vertebral disease is closely linked to bone quality, implant anchorage, and biomechanical considerations, particularly in the context of pedicle screw fixation and interbody support. Emerging technologies—including navigation, robotics, and artificial intelligence—may enhance accuracy in implant placement and reduce bone-related complications, but robust evidence of long-term benefit is still lacking. Despite its advantages, MISS presents important limitations, including a steep learning curve, increased costs, and uncertain superiority in terms of fusion rates and long-term biomechanical stability. Future research should prioritize high-quality comparative studies focusing on bone healing, implant integration, and patient-specific factors such as bone density. MISS should therefore be interpreted not only as a surgical paradigm shift but as an evolving strategy for optimizing outcomes in bone-related spinal disorders. Full article

Background/Objectives: Reliable intraoperative imaging is essential for robotic-assisted (RA) pedicle screw placement. Mobile intraoperative cone-beam CT (iCBCT) systems like Loop-X have been introduced into RA workflows, but implementation data remain limited. We evaluated whether Loop-X introduction was associated with efficiency or safety, and whether associations differed by surgeon experience. Methods: We performed a retrospective epoch-based cohort study of 146 patients undergoing RA pedicle screw placement using 3D C-arm navigation (3D-BV) or Loop-X iCBCT. Outcomes were operating room (OR) time, estimated blood loss (EBL), and length of stay (LOS). The safety endpoint was 30-day complications (Clavien–Dindo grade III or higher). Multivariable regression models adjusted for patient- and procedure-related covariates; the complication model was kept parsimonious because of the limited number of events. Interaction terms tested surgeon experience. Results: After adjustment, implementation phase was not independently associated with OR time (β 30.76 min, 95% CI −31.97 to 93.48; p = 0.33), EBL (β −19.94 mL, 95% CI −287.01 to 247.14; p = 0.88), or LOS (β 3.21 days, 95% CI −3.31 to 9.72; p = 0.33). No significant interaction with surgeon experience was detected. Major complications occurred in 16 of 146 cases (11.0%) and were not associated with Loop-X implementation (OR 0.41, 95% CI 0.10–1.74; p = 0.224). Patient factors and procedural complexity were the main determinants of outcomes. Conclusions: In this cohort, Loop-X implementation in an RA pedicle screw program was not associated with deterioration in perioperative efficiency or short-term safety after adjustment. These findings support feasibility in practice, but do not establish superiority, equivalence, or imaging-specific effects. Full article

Background: To investigate the risk factors for and prognostic implications of massive blood loss during posterior spinal instrumentation and fusion (PSIF) in pediatric patients with scoliosis. Methods: We retrospectively analyzed the electronic medical records of 460 children who underwent scheduled PSIF under general anesthesia between June 2021 and January 2024. Patients were grouped based on intraoperative blood loss: massive (estimated blood loss [EBL]/estimated blood volume [EBV] ≥ 30%) and nonmassive (EBL/EBV < 30%). Perioperative parameters were compared. Univariate and multivariate logistic regression analyses were performed to identify independent risk factors for massive intraoperative blood loss. Results: Among the 460 patients with scoliosis who underwent PSIF, 188 were male and 272 were female (mean age 9.4 ± 4.1 years). Massive intraoperative blood loss occurred in 126 (27%) patients. Factors associated with massive blood loss included age, preoperative Cobb angle, history of heart disease or neurofibromatosis, number of previous scoliosis surgeries, operative time, number of fused levels, number of pedicle screws inserted, and whether osteotomy was performed. Multivariate analysis identified younger age (odds ratios [OR] = 0.829, 95% confidence interval [CI], 0.751–0.914, p < 0.001), history of heart disease (OR = 4.338, 95% CI: 1.637–11.498, p = 0.003), greater number of fused levels (OR = 1.118, 95% CI: 1.014–1.233, p = 0.025), and longer operative time (OR = 1.008, 95% CI: 1.005–1.012, p < 0.001) as independent risk factors. Additionally, the massive blood loss group had a longer postoperative hospital stay (p = 0.008) and a higher rate of postoperative allogeneic blood transfusion (7.1% vs. 1.2%, p = 0.002) than the nonmassive blood loss group. Conclusions: Younger age, preexisting heart disease, a greater number of fused levels, and longer operation duration are independent risk factors for massive intraoperative blood loss in children undergoing PSIF for scoliosis. Full article

Adjacent segment degeneration remains a major biomechanical concern after lumbar fusion, whereas fully dynamic topping-off constructs may provide an alternative strategy by preserving segmental motion and unloading degenerated discs. In this study, a three-dimensional nonlinear finite element model of the L1-L5 lumbar spine with L3-L5 double-segment degeneration was developed to compare transforaminal lumbar interbody fusion (TLIF)-based pedicle screw fixation systems (PSFS) and Bioflex-based pedicle screw dynamic stabilization systems (PSDSS). Three interspinous process spacers, namely DIAM, Wallis, and Coflex-F, were implanted at L3-L4, and three pedicle screw diameters of 6.5, 5.5, and 4.5 mm were evaluated under flexion and extension to quantify screw-rod parameter sensitivity. The results showed that both TLIF- and Bioflex-based topping-off constructs reduced intradiscal pressure (IDP) and restricted excessive range of motion (ROM) at the transition segment, especially during extension, with a maximum L3-L4 IDP reduction of 39.49% compared with the degenerated model. Compared with fusion-based constructs, Bioflex-based PSDSS provided greater surgical-segment unloading, reducing L4-L5 IDP by 55.07% in extension and 25.30% in flexion. However, this motion-preserving effect was accompanied by higher pedicle screw stress sensitivity; in the 4.5 mm Bioflex model, the average L4 screw stress reached 15.62 MPa in flexion, representing a 51.71% increase compared with the 6.5 mm screw. In contrast, PSFS constructs showed greater stress variation in the rigid connecting rods. Overall, under the present modeling assumptions, Bioflex-based fully dynamic topping-off constructs showed more favorable disc unloading and transition-segment motion regulation than fusion-based configurations, but their biomechanical benefit should be balanced against diameter-dependent pedicle screw stability. Full article

Background: Implant-related mechanical failure remains a clinically relevant concern following posterior decompression and fusion in elderly patients with lumbar spinal stenosis (LSS). The relative contribution of host-related versus construct-related factors to failure risk requires further clarification. Methods: This retrospective single-center cohort study included 118 patients aged ≥65 years who underwent single-level hemilaminectomy with posterolateral fusion (PLF) for isolated L4–5 central LSS, with a minimum follow-up of 48 months (mean 51.0 ± 2.0 months). All procedures were performed using a standardized posterior technique with uniform 6.5-mm titanium rods and 6.5-mm pedicle screws. Mechanical failure was defined as revision surgery due to radiographically and clinically confirmed hardware-related complications in the absence of infection. Exploratory univariable analyses were conducted to evaluate associations between baseline variables and mechanical failure. Clinical outcomes were assessed using validated patient-reported outcome measures. The Oswestry Disability Index (ODI), Roland Morris Disability Questionnaire (RMDQ), and Visual Analog Scale (VAS) for pain were recorded. Results: Overall revision rate was 13.6% (16/118), including 14 cases (11.9%) of implant-related mechanical failure and 2 cases (1.7%) of infection-related revision. Higher age (p = 0.005), higher body mass index (BMI) (p = 0.005), lower bone mineral density (BMD) (p < 0.001), active smoking (p < 0.001), and diabetes mellitus (DM) (p = 0.023) were significantly associated with mechanical failure. Functional outcomes (ODI, RMDQ, VAS) improved significantly at final follow-up (all p < 0.001). Conclusions: Mechanical failure following hemilaminectomy with PLF appears to be predominantly influenced by host-related factors rather than construct characteristics when a standardized surgical technique is applied. Bone quality and modifiable systemic risk factors may play a critical role in long-term construct durability. Full article