Shun Okuwaki

... Asian Spine Journal 2026;20(4):834-835.

Stage-specific embryonic antigen-3-positive pluripotent-like/macrophage-like multilineage-differentiating stress-enduring (Muse) cells are a distinct subpopulation of mesenchymal stromal cells (MSCs), accounting for 1% to several percent of MSCs. Although stem cell therapy for spinal cord injury (SCI) typically targets the subacute phase to avoid the hostile acute environment, the therapeutic window for Muse cells remains unclear. C57BL/6J mice with severe T9 contusion SCI received a single tail vein injection of human bone marrow-derived (BM) Muse cells, BM-MSCs (both 5 × 10⁴ cells), or vehicle at 2, 8, 14, or 28 days post-injury (DPI) without immunosuppressants. Among the different administration time points, the 2-DPI Muse cell group exhibited significantly higher Basso Mouse Scale scores than the BM-MSC and vehicle groups from 14 days after injection, while no significant differences were observed at the other administration time points. The 2-DPI Muse cell group showed significantly greater homing to the injured spinal cord than the BM-MSC group, with persistent engraftment and neural-lineage marker expression at day 42. Ablation of engrafted Muse cells at day 42 partially reversed locomotor recovery, suggesting that engrafted Muse cells contributed to functional recovery. These findings suggest that intravenous Muse cell therapy exerts timing-dependent therapeutic effects after SCI, with greater efficacy during the early post-injury phase.

Background/Objectives: Spontaneous spinal subdural hematoma (SSSDH) is a rare and severe condition that causes rapid neurological decline. Spontaneous spinal epidural hematoma (SSEH) presents similarly but is more common, and surgical management differs because SSSDH requires an intradural approach. Few studies have assessed the reliability of magnetic resonance imaging (MRI) features used to distinguish SSSDH from SSEH in patients requiring surgery. Methods: We retrospectively reviewed 27 patients who underwent surgical evacuation of spinal hematomas at two institutions (2015–2025). Definitive hematoma location was determined intraoperatively. Four MRI features—shape (crescentic vs. biconvex), location (ventral vs. dorsal), craniocaudal length (<5 vs. ≥5 segments), and spinal region—were independently evaluated by two reviewers. Inter- and intra-rater reliability was assessed using agreement rate and Cohen’s kappa (κ) with 95% confidence intervals (95% CIs). Results: Among 27 cases, three (11.1%) were SSSDH and 24 were SSEH. Hematoma location, length, and spinal region demonstrated perfect inter- and intra-rater agreement (κ = 1.00). For hematoma shape, intra-rater agreement was good (96.2%, κ = 0.84; 95% CI 0.52–1.00), whereas inter-rater agreement was poor to fair (84.6%, κ = 0.26; 95% CI −0.25–0.77). Notably, two of the three SSSDHs demonstrated a biconvex configuration, and 83.3% of SSEHs also exhibited a biconvex morphology. Conclusions: MRI features such as hematoma location, extent, and spinal level were highly reproducible, whereas hematoma shape showed limited reliability. Although ventral hematomas most strongly suggest SSSDH, atypical SSEH presentations occur. When dorsal exposure reveals no epidural hematoma, intradural exploration should be promptly considered.

Study Design: Multicenter retrospective cohort study. Purpose: To evaluate the impact of abscess presence and type on treatment duration and clinical outcomes in patients undergoing minimally invasive posterior fixation for thoracolumbar pyogenic spondylitis. Overview of Literature: Surgical management is increasingly favored for pyogenic spondylitis. Abscesses, particularly epidural and iliopsoas, have been linked to poorer prognoses, and empyema, though uncommon, tends to be particularly severe. However, the effect of specific abscess types on surgical outcomes remains unclear. Methods: This study included 92 patients who underwent minimally invasive posterior fixation across 10 centers between 2014 and 2024. Patients were classified into an abscess group (epidural, iliopsoas, empyema, or other) and a non-abscess group. Clinical outcomes, including total duration of intravenous antibiotics and unplanned additional surgeries, were compared. Subgroup and regression analyses were conducted to assess the impact of specific abscess type. Results: Abscesses were present in 65 patients (71%): epidural (n=51), iliopsoas (n=38), and empyema (n=3), with some overlap. Compared with the non-abscess group (n=27; 29%), there were no significant differences in antibiotic duration or rates of unplanned additional surgery. However, iliopsoas abscess was associated with longer antibiotic duration (8.1 weeks vs. 6.6 weeks, p=0.044), while all empyema cases required additional surgery for poor infection control (p=0.000). Regression analysis identified iliopsoas abscess and age ≥65 years as independent predictors of prolonged antibiotic use, whereas epidural abscess was associated with shorter antibiotic duration. Conclusions: Iliopsoas abscesses were associated with longer antibiotic courses, while empyema was linked to poor infection control and a higher likelihood of additional surgery.

Retrospective observational study. To evaluate the effectiveness of the inlet view in detecting anterior deviations of the S2 alar iliac (S2AI) screw during spinopelvic surgery and to assess the utility of the obturator inlet (OI) and iliac oblique (IO) views as alternative imaging methods. S2AI screws are increasingly utilized in spinopelvic fixation due to their biomechanical advantages. However, malpositioning of screws can lead to neurovascular complications. While inlet views in fluoroscopic techniques are generally effective for identifying screw deviations, there are instances where deviations go unnoticed. We analyzed data from 101 patients who underwent spinopelvic surgery involving 202 S2AI screws. Postoperative computed tomography (CT) images were reviewed to identify screw deviations. The reconstructed fluoroscopic views from CT, including the inlet, OI, and IO views, were assessed for their effectiveness in detecting deviations. An experimental study using pelvic bone models simulated scenarios where deviations were undetectable in the inlet view but visible in the OI view. Screw deviations were identified in 12 cases (11.9%) and 13 screws (6.4%), including six screws (3.0%) with anterior deviations and seven screws (3.5%) with posterior deviations. The accurate inlet view detected anterior deviations in three of the five cases analyzed with reconstructed images. However, two cases of anterior deviation were missed due to an insufficient inlet view caused by a 30° caudal tilting angle. In contrast, the OI view successfully identified all cases of both anterior and posterior deviations. In particular, deviations above the arcuate line of the pelvic brim were not detectable in the inlet view. The inlet view alone is inadequate for detecting anterior deviations, especially those located above the arcuate line of the pelvis. The OI and IO views demonstrated greater effectiveness in identifying deviations, thereby enhancing the accuracy and safety of S2AI screw placement.

Purpose This study aimed to investigate the incidence and risk factors of thoracolumbar noncontiguous spinal fractures (NSF) in surgically treated older patients with cervical spine injuries and to evaluate their association with functional outcomes. Methods We retrospectively reviewed 115 patients aged ≥ 65 years who underwent surgery for traumatic cervical spine injuries between 2015 and 2025. Thoracolumbar NSF were defined as fractures located at least two vertebral levels away from the cervical injury. Patient background, comorbidities, laboratory data, and imaging findings were collected. Functional outcome was assessed using the Barthel Index (BI) at discharge, with BI ≥ 60 indicating functional independence. Univariate and multivariate logistic regression analyses were performed to identify independent predictors of NSF and BI ≥ 60. Results Thoracolumbar NSF were observed in 39.1% of patients. High-energy trauma (odds ratio [OR]: 70.7) and pre-existing vertebral fractures (OR: 12.8) were identified as independent positive predictors, whereas the presence of ossification of the posterior longitudinal ligament was negatively associated with NSF (OR: 0.12). In multivariate analysis for BI ≥ 60, higher serum albumin (OR: 10.7) and lower Charlson Comorbidity Index (OR: 0.46) were associated with better functional outcomes, while spinal cord injury was a negative predictor (OR: 0.17). The presence of thoracolumbar NSF was not associated with functional outcome. Conclusion Thoracolumbar NSF are relatively common in surgically treated older patients with cervical spine injuries. Although they were not linked to worse functional outcomes, their strong association with high-energy trauma and skeletal fragility highlights the need for comprehensive spinal imaging and early risk assessment.

Study Design: A retrospective cohort study.Purpose: To determine whether the preoperative pars defect length predicts bone union following the modified smiley face rod (mSFR) technique for lumbar spondylolysis and to identify a threshold for clinical decision-making.Overview of Literature: Lumbar spondylolysis is a common cause of low back pain in young athletes, often leading to pseudarthrosis that requires surgical intervention. Various techniques, including mSFR, address pseudarthrosis; however, the effect of preoperative pars defect length on bone union remains unclear.Methods: This study analyzed 75 pars defects in 38 patients treated with mSFR between 2014 and 2022. Pre- and postoperative pars defect lengths were measured using computed tomography (CT). Patients were categorized into bone union and nonunion groups based on CT findings up to 24 months postoperatively. Group comparisons of defect lengths were performed using the Mann-Whitney U test. Logistic regression was used to examine the association between preoperative defect length and nonunion. Receiver operating characteristic (ROC) curve analysis was used to identify the optimal threshold for preoperative defect length.Results: Bone union was achieved in 65 of 75 defects (87%). The preoperative pars defect length was significantly shorter in the bone union group than in the nonunion group (3.0 mm vs. 5.6 mm, p <0.001). A strong correlation was observed between pre- and postoperative pars defect lengths (Spearman’s rho=0.76). Logistic regression analysis revealed a significant association between a longer preoperative defect and nonunion (odds ratio, 1.89; 95% confidence interval, 1.29–2.72; p =0.001). ROC analysis revealed a cut-off value of 3.8 mm (sensitivity, 89%; specificity, 75%; area under the curve=0.86).Conclusions: Bone union following the mSFR technique may be influenced by the pars defect length, with larger preoperative defects potentially hindering bone union. The technique is most effective when the preoperative defect length is ≤3.8 mm.

Purpose Thoracolumbar fractures from high-energy trauma in older adults often occur in the setting of frailty and comorbidities, yet evidence on the benefits of early surgery in this group remains limited. This study aimed to evaluate whether early surgical stabilization reduces perioperative complications in older patients with thoracolumbar fractures caused by high-energy trauma. Methods We conducted a retrospective cohort study of 110 patients aged ≥ 65 years who underwent surgery for traumatic thoracolumbar fractures from high-energy trauma between 2015 and 2025. Patients were grouped into early surgery (≤ 72 h) and delayed surgery (> 72 h). Baseline differences were adjusted using one-to-one propensity score matching based on background factors and severity of associated injuries. A receiver operating characteristic (ROC) curve analysis was performed to identify the optimal cutoff for predicting complications. Results Of the 110 patients, 45 underwent early and 65 delayed surgery. Before matching, the early group had significantly fewer perioperative complications (31.1% vs. 67.7%, p = 0.001), particularly pneumonia (6.7% vs. 30.8%, p = 0.002). After matching (33 pairs), early surgery remained associated with lower complication rates (27.3% vs. 60.6%, p = 0.001) and pneumonia (6.1% vs. 27.3%, p = 0.021). Functional outcomes did not differ between groups. An ROC analysis identified 76 h as the optimal cutoff, supporting the clinical validity of the 72-hour benchmark. Conclusion Early surgical stabilization within 72 h was associated with fewer perioperative complications, especially pneumonia, in older adults with high-energy thoracolumbar fractures. These findings highlight the value of timely surgical intervention in this vulnerable population.

Purpose No studies have elucidated the dynamic spinal balance in patients with dropped head syndrome (DHS) categorized by global spinal alignment. We investigated the differences in dynamic spinal balance and corresponding muscle activity during prolonged walking in patients with DHS based on their global spinal alignment. Methods Three-dimensional gait analysis combined with electromyography was conducted to evaluate kinematic spinal parameters during walking, including the sagittal vertical axis (SVA) in the cervical (C-SVA), thoracic (T-SVA), and lumbar (L-SVA) regions, along with the muscle activity. Patients were divided into two groups based on C7 SVA from standing whole spine radiographs: SVA + and SVA–. Parameter changes were compared between the first and final laps of prolonged walking in each group. Results Twenty-eight patients were included (11 in the SVA + group and 17 in the SVA– group). In the SVA + group, prolonged walking caused a significant increase in T-SVA and L-SVA (P = 0.002, 0.014), with no compensatory increase in paraspinal muscle activity. In the SVA– group, C-SVA and T-SVA increased significantly (P = 0.002), with a decrease in cervical paraspinal muscle activity (P = 0.009). Conclusion Three-dimensional gait analysis with electromyography highlighted the distinct pathophysiological mechanisms in patients with DHS, as determined by their global spinal alignment. In the SVA + group, gait-induced thoracolumbar imbalance increased without compensatory activation of the lumbar paraspinal muscle. Conversely, in the SVA– group, gait-induced cervicothoracic imbalance increased without compensatory activation in cervical paraspinal muscle activity. These findings suggest that although DHS presents with similar symptoms, it may involve different underlying pathophysiologies depending on the global spinal alignment.