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Hiroki Ushirozako, Tomohiko Hasegawa, Shigeto Ebata, Tetsuro Ohba, Hiroki Oba, Keijiro Mukaiyama, Satoshi Shimizu, Yu Yamato, Koichiro Ide, Yosuke Shibata, Toshiyuki Ojima, Jun Takahashi, Hirotaka Haro, and Yukihiro Matsuyama

OBJECTIVE

Nonunion after posterior lumbar interbody fusion (PLIF) is associated with poor long-term outcomes in terms of health-related quality of life. Biomechanical factors in the fusion segment may influence spinal fusion rates. There are no reports on the relationship between intervertebral union and the absorption of autografts or vertebral endplates. Therefore, the purpose of this retrospective study was to evaluate the risk factors of nonunion after PLIF and identify preventive measures.

METHODS

The authors analyzed 138 patients who underwent 1-level PLIF between 2016 and 2018 (75 males, 63 females; mean age 67 years; minimum follow-up period 12 months). Lumbar CT images obtained soon after the surgery and at 6 and 12 months of follow-up were examined for the mean total occupancy rate of the autograft, presence of a translucent zone between the autograft and endplate (more than 50% of vertebral diameter), cage subsidence, and screw loosening. Complete intervertebral union was defined as the presence of both upper and lower complete fusion in the center cage regions on coronal and sagittal CT slices at 12 months postoperatively. Patients were classified into either union or nonunion groups.

RESULTS

Complete union after PLIF was observed in 62 patients (45%), while nonunion was observed in 76 patients (55%). The mean total occupancy rate of the autograft immediately after the surgery was higher in the union group than in the nonunion group (59% vs 53%; p = 0.046). At 12 months postoperatively, the total occupancy rate of the autograft had decreased by 5.4% in the union group and by 11.9% in the nonunion group (p = 0.020). A translucent zone between the autograft and endplate immediately after the surgery was observed in 14 and 38 patients (23% and 50%) in the union and nonunion groups, respectively (p = 0.001). The nonunion group had a significantly higher proportion of cases with cage subsidence and screw loosening at 12 months postoperatively in comparison to the union group (p = 0.010 and p = 0.009, respectively).

CONCLUSIONS

A lower occupancy rate of the autograft and the presence of a translucent zone between the autograft and endplate immediately after the surgery were associated with nonunion at 12 months after PLIF. It may be important to achieve sufficient contact between the autograft and endplate intraoperatively for osseous union enhancement and to avoid excessive absorption of the autograft. The achievement of complete intervertebral union may decrease the incidence of cage subsidence or screw loosening.

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Hiroki Oba, Jun Takahashi, Sho Kobayashi, Tetsuro Ohba, Shota Ikegami, Shugo Kuraishi, Masashi Uehara, Takashi Takizawa, Ryo Munakata, Terue Hatakenaka, Michihiko Koseki, Shigeto Ebata, Hirotaka Haro, Yukihiro Matsuyama, and Hiroyuki Kato

OBJECTIVE

Unfused main thoracic (MT) curvatures occasionally increase after selective thoracolumbar/lumbar (TL/L) fusion. This study sought to identify the predictors of an unacceptable increase in MT curve (UIMT) after selective posterior fusion (SPF) of the TL/L curve in patients with Lenke type 5C adolescent idiopathic scoliosis (AIS).

METHODS

Forty-eight consecutive patients (44 females and 4 males, mean age 15.7 ± 2.5 years, range 13–24 years) with Lenke type 5C AIS who underwent SPF of the TL/L curve were analyzed. The novel “Shinshu line” (S-line) was defined as a line connecting the centers of the concave-side pedicles of the upper instrumented vertebra (UIV) and lowest instrumented vertebra (LIV) on preoperative radiographs. The authors established an S-line tilt to the right as S-line positive (S-line+, i.e., the UIV being to the right of the LIV) and compared S-line+ and S-line− groups for thoracic apical vertebral translation (T-AVT) and MT Cobb angle preoperatively, early postoperatively, and at final follow-up. The predictors for T-AVT > 20 mm at final follow-up were evaluated as well. T-AVT > 20 mm was defined as a UIMT.

RESULTS

Among the 48 consecutively treated patients, 26 were S-line+ and 22 were S-line−. At preoperative, early postoperative, and final follow-up a minimum of 2 years later, the mean T-AVT was 12.8 mm (range −9.3 to 32.8 mm), 19.6 mm (range −13.0 to 41.0 mm), and 22.8 mm (range −1.9 to 68.7 mm) in the S-line+ group, and 10.8 mm (range −5.1 to 27.3 mm), 16.2 mm (range −11.7 to 42.1 mm), and 11.0 mm (range −6.3 to 26.9 mm) in the S-line− group, respectively. T-AVT in S-line+ patients was significantly larger than that in S-line− patients at the final follow-up. Multivariate analysis revealed S-line+ (odds ratio [OR] 23.8, p = 0.003) and preoperative MT Cobb angle (OR 7.9, p = 0.001) to be predictors of a UIMT.

CONCLUSIONS

S-line+ was defined as the UIV being to the right of the LIV. T-AVT in the S-line+ group was significantly larger than in the S-line− group at the final follow-up. S-line+ status and larger preoperative MT Cobb angle were independent predictors of a UIMT after SPF for the TL/L curve in patients with Lenke type 5C AIS. Surgeons should consider changing the UIV and/or LIV in patients exhibiting S-line+ during preoperative planning to avoid a possible increase in MT curve and revision surgery.

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Tetsuhiko Mimura, Shota Ikegami, Shugo Kuraishi, Masashi Uehara, Hiroki Oba, Takashi Takizawa, Ryo Munakata, Terue Hatakenaka, Michihiko Koseki, and Jun Takahashi

OBJECTIVE

Although it is well known that major curve severity in adolescent idiopathic scoliosis (AIS) is inversely related to self-image, surgeons often encounter patients who complain of low self-image with preoperatively mild curves or postoperatively well-corrected main curves, suggesting the presence of other factors. This study examined factors contributing to self-image in AIS.

METHODS

A total of 86 consecutive patients who underwent posterior spinal fusion for AIS Lenke 1 or 2 curves and were followed for a minimum of 2 years were included in this study of patient self-image based on data that included scores reported on the Scoliosis Research Society survey (SRS-22r). The authors evaluated sex, BMI, Risser grade, age, angle of trunk rotation, Cobb angle of the main thoracic (MT) curve, Cobb angle of the thoracolumbar/lumbar (TL/L) curve, apical vertebral translation (AVT), T5–12 kyphotic angle, and clavicular angle. Univariate and multivariate general linear models were employed to identify preoperative and 2-year postoperative factors that impact self-image.

RESULTS

Univariate analysis revealed no significant correlation between preoperative MT curve Cobb angle and SRS-22r self-image score (p = 0.51), although patients with a higher MT curve AVT had a significantly worse preoperative self-image (p < 0.01). Two years postoperatively, larger Cobb angle of the TL/L curve (p = 0.01) and higher Risser grade (p = 0.03) resulted in significantly lower self-image scores. In multivariate testing, preoperative MT curve AVT remained significantly related to diminished self-image (p < 0.01). Two years later, higher TL/L curve (p < 0.01), Risser grade (p = 0.03), and MT curve AVT (p = 0.03) had significant associations with lower self-image scores.

CONCLUSIONS

Preoperative MT curve AVT appears more strongly related to self-image than does Cobb angle. Two years postoperatively, persistent TL/L region curvature and high Risser grade may also be associated with diminished patient self-image.

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Daisuke Sakai, Masato Tanaka, Jun Takahashi, Yuki Taniguchi, Jordy Schol, Akihiko Hiyama, Haruo Misawa, Shugo Kuraishi, Hiroki Oba, Yoshitaka Matsubayashi, So Kato, Ryo Sugawara, Masato Sato, Masahiko Watanabe, and Katsushi Takeshita

OBJECTIVE

For instrumented correction surgery for adolescent idiopathic scoliosis (AIS), surgeons are increasingly switching from titanium (Ti) alloy rods to stiffer cobalt-chromium (CoCr) rods. The authors conducted the first multicenter randomized controlled clinical trial to investigate whether these materials affect the outcomes in terms of spine correction and quality of life (QOL). This trial was registered at UMIN Clinical Trials Registry on September 3, 2012, under the identifier UMIN000008838 (level of evidence 1).

METHODS

Female AIS patients (Lenke types 1–3, patient age 10–19 years) were recruited at 5 Japanese institutions and randomized into two cohorts: 6.0-mm-diameter Ti rods were placed in one group, and 6.0-mm-diameter CoCr rods were placed in the other. Patients were followed up at 2 weeks and 3, 6, and 12 months with radiographic examination to quantify the sagittal and coronal correction (Cobb angle, thoracic kyphosis, rib hump, and apical vertebral rotation). Patients completed questionnaires (Scoliosis Research Society–22r, 12-Item Short-Form Health Survey, and Scoliosis Japanese Questionnaire–27) at 6 and 12 months to assess QOL.

RESULTS

A total of 69 AIS patients were randomized to the demographically similar Ti (n = 37) or CoCr (n = 32) cohort. Four adverse events were recorded, two in each cohort, but these were not related to the rod material. At the final follow-up, both Ti and CoCr cohorts showed significant improvement in spinal correction, including the Cobb angle, thoracic kyphosis, and rib hump size. The correction rates were 68.4% and 67.1% for the Ti and CoCr cohorts, respectively. No parameters differed significantly between the cohorts at any time. Survey data showed improved but similar outcomes in both cohorts.

CONCLUSIONS

Both treatments (Ti and CoCr) produced similar results and were efficient in engendering clinically significant spine corrections.

Clinical trial registration no.: UMIN000008838 (UMIN Clinical Trials Registry)