Background: An effective method for preventing proximal junctional kyphosis (PJK), a major complication of posterior spinal surgery, has not yet been established. We developed a new device called a rib anchor, and this study aimed to investigate whether it can be used to prevent PJK using the finite element method.

Methods: A three-dimensional model from the T6 to T10 vertebral bodies and ribs was created, and axial loads and forward bending moments were applied to the T6 vertebral body. The equivalent stress on each vertebral body was evaluated under three conditions: no hook, transverse process hook (placed on T8), and rib anchor (placed on the seventh rib).

Results: The average value of the vertebral equivalent stress applied to Uppermost Instrumented Vertebra (UIV) +1 was 0.723 MPa without the hook, 0.715 MPa with the transverse process hook, and 0.625 MPa with the rib anchor when an axial load (200 N) and forward bending moment (5 Nm) were applied. When rib anchors were used, the average equivalent stress applied to UIV+1 was lowest.

Conclusions: This study suggests that the use of a rib anchor reduces the equivalent stress involving UIV+1.

Introduction: Proximal Junctional Kyphosis/Failure (PJK/F) is a complication that can be prevented by adult spinal deformity surgery. Some adult spinal deformities require fusion from the upper thoracic spine to the pelvis. However, there is no consensus regarding the upper instrumented vertebrae (UIV). We investigated preoperative predictors of PJF in patients with T4 UIV.

Methods: 60 patients with spinal deformity who underwent T4 to pelvic fusion between September 2012 and September 2021 were divided into a PJF group (5 cases) and a control group (55 cases) and analysed for preoperative Body Mass Index (BMI), Hounsfield Unit (HU) value of T4 vertebra, PI, PT, LL, PI-LL, T1 slope, TK, uTK (angle between T1 cephalic endplate and T5 caudal endplate on lateral X-ray of the standing full spine), f-TK (TK in antevertebral position), f-uTK (uTK on the lateral X-ray of the antevertebral full spine), Global tilt, postoperative PT, LL, T1 slope, TK, PI-LL, uTK, Global tilt, Global alignment and proportion (GAP) scores were examined.

Results: PI was 61.8±4.3° in the PJF group versus 50.4±1.7° in the control group (p = 0.0322). f-uTK was 34.6±3.6° in the PJF group versus 14.4±1.3° in the control group (p = 0.00042). Multiple logistic analysis revealed an odds ratio of 1.12 (95% confidence interval 0.95-1.33, p = 0.173) for PI and 1.69 (95% confidence interval 0.98-2.9, p = 0.0588) for f-uTK for the incidence of PJF. ROC analysis of f-uTK values for the occurrence of PJF showed that 28° was a valid cutoff value (sensitivity, 1; specificity, 0.944).

The only postoperative factor that differed significantly was T1 slope, which was 47.6±5.9° in the PJF group versus 33.5±1.6° in the control group (p = 0.0284).

Conclusions: In patients with f-uTK > 28°, more cranial UIV than T4 should be considered to prevent PJF.

Purpose: We investigated the amount of rod bending back in circumferential minimally invasive surgery (CMIS), multi-rod using lateral lumbar interbody fusion (LLIF), and percutaneous pedicle screw (PPS) for adult spinal deformities (ASDs).

Methods: The subjects were 31 consecutive ASD patients who underwent CMIS-multi rod at our hospital since July 2022. In all cases, the fixation range was from the lower thoracic vertebrae to the pelvis. Three 5.5 mm titanium alloy rods were used in all cases. The lumbar lordosis (rod-LL), lower lumbar lordosis (rod-LLL), and thoracic (T10 to L1) kyphosis angle (rod-TK) of the rod before and after rod application were measured. Differences between the angles before and after rod application were defined as the amount of rod bending back. We also investigated the correlation between the amount of rod-LL bending back and various parameters.

Results: The average age was 75.7 years (5 males and 26 females). The Upper Instrumented Vertebra (UIV) was at T8 in one case, T9 in eight cases, T10 In 22 cases, and the LIV in the pelvis in all cases. The average various parameters were PI 47.6, LL −5.2° preoperatively and 43.7° postoperatively, and PI-LL 52.3° preoperatively and 3.9° postoperatively. Before and after rod application, rod-LL changed from 47.5° to 37.7°, rod-LLL changed from 29.0° to 23.1°, and rod-TK changed from 26.8° to 22.0°, and the amount of rod bending back was 9.8°, 5.9°, and 4.7°, respectively. The parameter with the highest correlation with rod-LL bending back was the post-LLIF PI-LL, with a correlation coefficient of 0.68. The approximate formula was rod-LL bending back = 0.47 × (PI-LL after LLIF) +8.2.

Conclusion: We investigated the amount of rod bending back in CMIS-multi-rod for ASD. The average degree of rod-LL bending back was 9.8°, and PI-LL after LLIF had the highest correlation, with a correlation coefficient of 0.68. The approximate formula is rod-LL bending amount = 0.47 × (PI-LL after LLIF) +8.2.

Introduction: Pedicle screw loosening (PSL) causes bone nonunion; therefore, we aimed to prevent PSL.

Methods: We investigated the process of thoracic bone fusion and the causes of PSL 3 years after circumferential minimally invasive surgery (CMIS) for adult spinal deformity (ASD). The subjects were 52 ASD patients (40 women, 12 men) who had undergone CMIS using LLIF and PPS since 2016 and had been able to undergo FU for >3 years. A comparative study was conducted between a group with PSL (PSL group) and a group without PSL (NPSL group). Various parameters, including preoperative disc condition, angle between the UIV PS and the cranial endplate (PSA), preoperative HU value (UIV), screw malposition in the UIV, depth score, PJK incidence, and pre- and post-operative ODI. Disc status was classified as no degeneration (N), DISH (D), or osteophyte type (O). The screw depth score was 2 points for contact with the cortical bone on both sides, 1 point for contact on one side, and 0 point for no contact.

Results: PSL was administered in 47% of patients (25), and there were no significant differences in age and sex, pre- and post-operative ODI, and HU values between the two groups; PI, postoperative PI-LL, and preoperative SVA were significantly greater in the PSL group, and preoperative TK and PSA were smaller. Screw depth scores were significantly higher in the NPSL group, and multivariate analysis detected PSA levels, screw depth score, and screw malposition as risk factors, with a cutoff value for PSA of 11.7°.

Discussion/Conclusions: There are reports that the HU value is a factor in PSL. However, in this study, PSA and screw depth score were detected as factors for PSL, suggesting that better implant placement at UIV rather than bone quality leads to a reduction in PSL and subsequent spontaneous facet bone fusion involving the thoracic vertebrae.

Introduction: We studied whether a minimally invasive surgery (MIS) triad consisting of anterior column realignment (ACR), lateral lumbar interbody fusion (LLIF), and percutaneous pedicle screw (PPS) fixation in a select group of patients with adult spinal deformity (ASD) helped shorten the fusion length without compromising clinical and radiographic outcomes over a minimum 2-year follow-up period.

Methods: A series of 39 ASD patients (mean age, 73.9 years) with pelvic incidence (PI)/lumbar lordosis (LL) mismatch ≥10° underwent a short-segment MIS triad consisting of single level ACR at L3-L4, two levels of LLIF at L2-L3 and L4-L5, and PPS fixation at L2 through L5 as a single-stage operation. The exclusion criteria were: (1) thoracic scoliosis as the main deformity, (2) thoracolumbar junction kyphosis, (3) ankylosed facet joints, and (4) previous spinal fusion surgery.

Results: The segmental disc angle at the ACR level was more than quintupled, averaging 2.8° preoperatively to 19.1° at the latest follow-up (p<0.0001). The LL nearly doubled from 13.6° to 29.8° (p<0.0001), and the PI/LL mismatch decreased by nearly half from 28.9° to 12.7° (p<0.0001). Simultaneously, other spinopelvic deformity parameters and Oswestry Disability Index (ODI) scores significantly improved. The latest postoperative evaluation divided the patients into two groups: 23 patients whose PI/LL mismatch improved to <10° and 16 patients who remained with ≥10° mismatch. Binary logistic regression revealed that preoperative PI/LL mismatch was the only factor that significantly influenced this dichotomous separation postoperatively. Receiver operating characteristic curve analysis identified a critical preoperative mismatch of 24.2° with 52% sensitivity and 94% specificity. Despite these different radiographic consequences, the two groups showed equally successful clinical outcomes with no significant difference in ODI scores.

Conclusions: At a minimum 2-year follow-up after a 3-level MIS with ACR, LLIFs, and PPS fixation, ASD patients, consistent with our exclusion criteria, could achieve and maintain an ideal spinopelvic sagittal alignment of PI/LL mismatch <10° with 52% sensitivity and 94% specificity when associated with preoperative PI/LL mismatch <24.2°.

Introduction: Pedicle screw insertion using a patient-specific 3D-printed drill guide is an effective and safe technique. However, the accuracy of screw placement and factors which influence screw misplacement are not fully understood.

Methods: We investigated the accuracy of screw placement in patients who underwent spinal fusion surgery of the thoracic and lumbar spine. A total of 130 screws were analysed.

Results: Screw placement accuracy was 93.8%. Men, large heights, and high-grade spondylolisthesis have been suggested as potential factors influencing screw misplacement. Pre- and postoperative CT-analysis analyses showed that the depth and transverse angle tended to deviate compared to preoperative planning.

Conclusions: This study suggests that the risk factors for pedicle screw misplacement are male sex, greater height, and high-grade spondylolisthesis. The depths and transverse angles of the screws tended to deviate from their planned trajectories.

Introduction: SMARCA4-deficient undifferentiated tumours are characterised by a defect in the SMARCA4 gene, a new disease concept that was first reported in 2015.

Case: A 58-year-old man presented with right chest pain. Chest CT presented a paravertebral tumour, and needle biopsy revealed it to be a SMARCA4-deficient undifferentiated tumour. The tumour was in the right paravertebral region of the fifth thoracic vertebra and extended through the right fifth or sixth intervertebral foramen into the spinal canal. A detailed resection plan was made preoperatively using VINCENT^® medical image analysis software. First, a thoracoscopic resection was performed by a general thoracic surgeon. After the thoracoscopic procedure, Th4-5 hemi-laminoplasty and nerve root dissection were performed. The tumour on the lateral surface of the vertebral body was cauterised and en bloc resection was performed. Two years after surgery, the patient was doing well without recurrence.

Conclusion: We report a rare case of a SMARCA4-deficient undifferentiated tumour of the thoracic region. En bloc resection was carefully planned using VINCENT^® and surgical resection was performed, resulting in a good outcome.

Introduction: We performed posterior occipito-cervical fusion (Oc-C3) in a patient with bow-Hunter syndrome after annulo-posterior arch resection for cervical myelopathy due to annular-axis osteoarthritis.

Case Report: A 59-year-old male underwent annulo-posterior arch arch resection for cervical myelopathy due to atlantoaxial spondylolisthesis six years ago. The patient shouted to the referring physician with visual impairment of the left eye, dysarthria, right upper and lower ataxia, and lightheadedness. Head MRI/MRA revealed bilateral vertebral artery (VA) stenosis at the level of the annulus, cerebellar infarction, and occipital lobe infarction. Angiography also showed complete occlusion of the bilateral VA with right head rotation, leading to a diagnosis of Bow-hunter syndrome associated with annular-axis osteoarthritis. Procedures such as intracranial stenting and intracranial vascular bypass were considered by the referring physician to prevent VA restenosis and recurrent stroke. Cervical spinal surgery was considered necessary, and the patient was referred to our hospital. Cervical spine radiography revealed annular-axis osteoarthritis progression. The bilateral VAs was considered to be in a state of repeated occlusion and opening depending on the cervical position. A contrast-enhanced CT scan with a halo vest showed improved blood flow in the bilateral VAs. Posterior Oc-C3 was performed to prevent VA restenosis and recurrent stroke. Postoperatively, bilateral VA blood flow was improved. Six months after surgery, CT imaging revealed good bone fusion and no recurrence of cerebral infarction was observed.

Conclusions: Posterior Oc-C3 was performed in a patient with Bow-hunter syndrome to prevent recurrence of cerebral infarction.

Background: The anterior internal vertebral venous plexus (AIVVP) is prominent in the ventral aspect of the upper cervical spine. Therefore, removal of schwannomas extending into the AIVVP may result in massive bleeding.

Technical Note: In five patients with C2 schwannomas, we covered the bleeding hole of the AIVVP with a wide gelatin sponge soaked in fibrin glue, and haemostasis was achieved.

Conclusions: Rather than being comprised of tiny veins, the AIVVP occupies a wide space between the two layers of the posterior longitudinal ligament. In this case, it resembles a sinus. Understanding the topographic anatomy of AIVVPs helps to control bleeding at the site.