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Study Design: A retrospective single-center and single-surgeon study., Objective: This study investigated the screw perforation rate according to main curve flexibility in pedicle screw fixation using a computed tomography (CT) guidance for adolescent idiopathic scoliosis (AIS)., Summary of Background: The authors have been using a CT-based navigation system during pedicle screw insertion for AIS to avoid serious neurovascular or visceral structure injury but suspect that high main curve flexibility may account for some breaches., Data: Seventy-two consecutive patients with AIS Lenke type 1 or 2 who had undergone pedicle screw fixation using a CT-based navigation system between February 2008 and April 2018 were retrospectively reviewed., Materials and Methods: The authors evaluated the perforation rate of pedicle screws inserted into the main thoracic curve between the upper-end and lower-end vertebrae for factors associated with screw violations using multivariate logistic regression mixed models., Results: A total of 723 pedicle screws were inserted into the T4-T12 vertebrae with the aid of CT-based navigation. The respective grade 3 perforation rates according to main curve flexibility were 0%-30%: 3.2%; 30%-55%: 1.1%; 55%-75%: 5.2%; and 75%-100%: 5.5%. Main curve flexibility of ≥55% was significantly associated with grade 3 screw perforations (P=0.02)., Conclusions: Main curve flexibility of ≥55% was significantly related to screw violation in AIS surgery. Greater care is thus advised for screw insertion using CT navigation in AIS with main curve flexibility ≥55%.

Study Design: A retrospective observational study of a cohort of consecutive patients., Objective: The objective of this study was to determine the correlations between clinical outcomes of spinal surgery to correct adult spinal deformity (ASD) including mechanical complications and coronal malalignment and clarify the risk factors for postoperative coronal malalignment., Summary of Background Data: Despite the coronal malalignment seen regularly in adult patients who have undergone spinal surgery to correct spinal deformity, the associations between coronal malalignment, and clinical outcomes including mechanical complications after the surgery have remained unclear until now. To understand the associations between coronal malalignment and outcomes of surgery to correct ASD, and risk factors for postoperative coronal malalignment has substantial clinical importance., Materials and Methods: We included data from 121 consecutive patients who had undergone spinal surgery to correct ASD and were followed up for a minimum of 2 years. Iliac screws were used for pelvic fixation in all cases. The coronal balance was defined as the horizontal distance between the midpoint of C7 and the center of the sacrum on the coronal plane, and coronal malalignment was defined as when the absolute coronal balance was >20 mm. Preoperative radiographic parameters, surgical features, and clinical outcomes including mechanical complications were compared between groups of patients with coronal balance and those with malalignment. Univariate and multivariate regression analysis were used to clarify risk factors for postoperative coronal malalignment., Results: Postoperative coronal malalignment had no significant association with the clinical outcome as evaluated by a Roland-Morris Disability Questionnaire and Oswestry Disability Index but had a significant association with the frequency of rod fracture. A large preoperative coronal imbalance (malalignment), L5 coronal tilt angle, and use of lateral lumbar interbody fusion were found as risk factors for postoperative coronal malalignment., Conclusion: Postoperative coronal malalignment had no significant association with the clinical outcome as evaluated by the Oswestry Disability Index and Roland-Morris Disability Questionnaire but was significantly associated with the frequency of rod fracture., Level of Evidence: Level III.

Study Design: A retrospective observational study., Objectives: To (1) compare skeletal muscle mass index (SMI) and the composition of paraspinal muscles between patients with lumbar spinal stenosis (LSS) and adult spinal deformity (ASD) who underwent spinal surgery, (2) determine whether paraspinal muscles influence low back pain in ASD, and (3) ascertain which radiographic spinal parameters of ASD are predominantly influenced by paraspinal muscles., Summary of Background Data: Relative muscle cross-sectional area (rmCSA; total CSA minus intramuscular fat CSA) determined using magnetic resonance imaging (MRI) is useful when evaluating not only muscle volume but also muscle quality. Currently, no study has examined paraspinal muscles using rmCSAs to determine which radiographic spinopelvic parameters identified in patients with severe spinal deformities make them candidates for thoracolumbar corrective surgery., Materials and Methods: Paraspinal muscle rmCSAs were calculated using preoperative T2-weighted MRIs at the L3/4 axial level. Whole-body bone mineral density and lean, soft tissue mass were measured using dual-energy x-ray absorptiometry. SMI was calculated as appendicular (upper and lower limbs) lean, soft tissue mass (kg/m). Correlations between low back pain according to the Roland-Morris Disability Questionnaire, Oswestry Disability Index, spinopelvic parameters, and rmCSA were evaluated for 110 consecutive patients with ASD and 50 consecutive patients with LSS who underwent spinal surgery., Results: There was no significant difference in the total SMI and morbidity rate of sarcopenia between patients with ASD and LSS. A significant negative correlation between Oswestry Disability Index and the rmCSA of the multifidus muscles and the rmCSA of the erector muscles were observed. There was a significant positive correlation between pelvic tilt/sacral slope and multifidus/erector muscles., Conclusions: Paraspinal muscles evaluated with MRI were more significantly associated with the pathology of ASD compared with appendicular skeletal muscle evaluations with dual-energy x-ray absorptiometry. The present study indicates that multifidus and erector muscles significantly influenced the maintenance of the pelvic alignment., Level of Evidence: Level III.

Study Design: This is a retrospective single-center and single-surgeon study., Objective: We investigated the correlation between lower instrumented vertebra (LIV) and spinal mobility 2 years after posterior spinal fusion with pedicle screws for adolescent idiopathic scoliosis (AIS) for optimal LIV selection., Summary of Background: Spinal motion can become limited in scoliosis patients who undergo posterior spinal fusion. However, few reports exist on spinal mobility after posterior spinal fusion for AIS and the relationship between the LIV and mobility is unknown. We hypothesize that mobility limitation increases as the LIV is moved inferiorly., Data: Of 72 consecutive patients who received posterior spinal fusion using pedicle screws for AIS between October 2009 and August 2015, 66 patients (5 male and 61 female, mean age: 14.9 y) were enrolled., Materials and Methods: In total, 66 patients were retrospectively reviewed after stratification according to LIV level. Follow-up rate was 91.7%. Patients were examined for the fingertip-to-floor distance (FFD) before and 2 years after surgery. FFD was measured from the tips of the middle fingers to the floor with the barefoot subject bent maximally forward and the feet together and knees straight. Clinical outcome was assessed using Scoliosis Research Society-22 patient questionnaire (SRS-22r) scores and a visual analog scale for low back pain before and at 2 years postoperatively., Results: The median number of fused vertebrae was 9 (range: 4-15). The LIV was T11-12 in 15 patients, L1 in 11 patients, L2 in 10 patients, and L3 in 30 patients. The median decrease in FFD according to LIV at 2 years after surgery was T11-12: 0 cm, L1: 0 cm, L2: 5.5 cm, and L3: 10 cm. Thus, limited FFD became significantly more severe as the LIV was moved downwards (P<0.01). There were no significant correlations between limited FFD and SRS-22r or pain visual analog scale scores at 2 years postoperatively., Conclusions: FFD became significantly more restricted as the LIV was moved inferiorly but clinical results appeared unaffected by limited FFD.

Study Design: Retrospective, single-center, single-surgeon study., Objective: This study investigated screw perforation rate according to surface registration accuracy in pedicle screw fixation using a CT-based navigation system for adolescent idiopathic scoliosis (AIS)., Summary of Background Data: Posterior spinal fusion for scoliosis correction using pedicle screws is widely adopted but carries a risk of serious neurovascular or visceral structure events. To attempt to avoid these complications, we have been using a computed tomography (CT)-based navigation system during screw insertion, although insufficient surface registration accuracy may be a reason for some screw perforations., Methods: We evaluated 116 AIS patients (9 male and 107 females; mean±standard deviation age: 15.2±2.3 y) who had received pedicle screw fixation guided by a CT-based navigation system between August 2007 and December 2017. Screw perforation rate was evaluated in relation to surface registration accuracy and cut-off values were determined by receiver operating characteristic (ROC) curves., Results: A total of 1553 pedicle screws were inserted into T2-L4 vertebrae using CT-based navigation system. The respective overall perforation rates for grade 2 or 3 and grade 3 perforations by surface registration accuracy were 0.2 mm: 0% and 0%; 0.3 mm: 3.5% and 0%; 0.4 mm: 3.5% and 0.8%; 0.5 mm: 8.0% and 3.5%; 0.6 mm: 6.7% and 2.7%; 0.7 mm: 8.9% and 3.8%; 0.8 mm: 9.3% and 6.7%; and 0.9 mm: 9.3% and 4.7%. ROC curve analysis revealed a cut-off surface registration accuracy of 0.5 mm. The major screw perforation rate for a surface registration accuracy of ≥0.5 mm was significantly higher than that for <0.5 mm (P<0.01)., Conclusions: Analysis of screw perforation rate according to surface registration accuracy demonstrated a clinical cut-off of 0.5 mm. Thus, surface registration accuracy should optimally be <0.5 mm for scoliosis surgery with CT-based navigation system.

Study Design: This is a retrospective single-center and single-surgeon study., Objective: The present study examined for preoperative parameters having the highest correlation with compensatory thoracolumbar/lumbar (TL/L) curve correction 2 years after surgery in adolescent idiopathic scoliosis (AIS) patients with Lenke type 1 curves., Summary of Background: Several parameters have been considered to evaluate the flexibility of compensatory TL/L curve in AIS patients with Lenke type 1 curves. However, the imaging position with the strongest correlation with postoperative spontaneous TL/L curve correction is unknown., Data: In total, 37 patients with AIS Lenke type 1 curves who had undergone skip pedicle screw fixation were followed for a 2-year period were enrolled., Materials and Methods: TL/L Cobb angles measured at the standing posteroanterior view, supine position, supine position with maximum bending, supine position with traction, prone position, and prone-push position were determined before surgery. Using TL/L Cobb angles determined 2 years postoperatively, correlations between preoperative and postoperative Cobb angles were calculated for each position using the Spearman rank-correlation coefficient, linear regression analysis, and paired t tests., Results: Mean preoperative mean±SD TL/L Cobb angle was significantly improved from 31±9 to 13±8 degrees at the study end point. In analyses of correlations between postoperative TL/L Cobb angle and preoperative parameters, the supine position with traction was most strongly associated with TL/L curve correction rate at 2 years after surgery (r=0.72; P<0.01), with paired t tests revealing a significant mean difference of 3.1 degrees., Conclusions: Preoperative Cobb angle evaluated at the supine position with traction had the strongest correlation with spontaneously corrected TL/L curve Cobb angle after selective thoracic fusion for AIS Lenke type 1 curves. Accordingly, it may be sufficient to evaluate TL/L curve correction at this position only to reduce radiation exposure and operative time.

Study Design: This was a retrospective cohort study using consecutive patients., Objectives: The objectives of this study were to evaluate the effect of lumbar lordosis (LL) construction on postoperative reciprocal progression of thoracic kyphosis (TK) and occurrence of proximal junctional kyphosis (PJK) following surgery for adult spinal deformity (ASD)., Summary of Background Data: A large postoperative TK has been reported as an iatrogenic risk factor for PJK following surgery for ASD. Therefore, knowing how to anticipate and regulate postoperative reciprocal progression in TK with LL restorative surgery is important to prevent PJK. The LL proportion including distribution of the lordosis (lordosis distribution index: LDI) in the lower (L4-S1) and upper (L1-L3) arcs has been known as important because it alters the distribution of load. However, the influence of postoperative LL construction on postoperative reciprocal change in TK resulting in PJK is largely unknown., Methods: Sixty-six consecutive patients with ASD treated with LL restorative surgery with a fusion level consistently selected from T8-T10 to the pelvis and followed-up for a minimum of 1 year. Abnormal PJK was evaluated according to the Boachie-Adjei classification. Roland-Morris Disability Questionnaire and Oswestry Disability Index were measured at 1 year after surgery., Results: The prevalence of PJK in the present study was 33.3%. Outcomes of patients with PJK were significantly worse than in patients without PJK, regardless of PJK grade. Postoperative reciprocal progression in TK with LL restorative surgery was found. Preoperative risk factors of PJK were older age and smaller sacral slope angle. Postoperative risk factors for PJK included increased TK and decreased LDI. We found a strong correlation between postoperative LDI and reciprocal progression of TK resulting in PJK., Conclusions: Postoperative LDI is crucial to prevent excess reciprocal progression of TK resulting in PJK.

Study Design: A retrospective analysis., Objective: To evaluate the association between early postoperative dural sac cross-sectional area (DCSA) and radicular pain., Summary of Background Data: The correlation between postoperative magnetic resonance imaging (MRI) findings and postoperative neurological symptoms after lumbar decompression surgery is controversial., Methods: This study included 115 patients who underwent lumbar decompression surgery followed by MRI within 7 days postoperatively. There were 46 patients with early postoperative radicular pain, regardless of whether the pain was mild or similar to that before surgery. The intervertebral level with the smallest DCSA was identified on MRI and compared preoperatively and postoperatively. Risk factors for postoperative radicular pain were determined using univariate and multivariate analyses. Subanalysis according to absence/presence of a residual suction drain also was performed., Results: Multivariate regression analysis showed that smaller postoperative DCSA was significantly associated with early postoperative radicular pain (per -10 mm; odds ratio, 1.26). The best cutoff value for radicular pain was early postoperative DCSA of 67.7 mm. Even with a cutoff value of <70 mm, sensitivity and specificity are 74.3% and 75.0%, respectively. Early postoperative DCSA was significantly larger before suction drain removal than after (119.7±10.1 vs. 93.9±5.4 mm)., Conclusions: Smaller DCSA in the early postoperative period was associated with radicular pain after lumbar decompression surgery. The best cutoff value for postoperative radicular pain was 67.7 mm. Absence of a suction drain at the time of early postoperative MRI was related to smaller DCSA.