Materials and Methods
This study was reviewed and approved by our Institutional Review Board and adhered to the Declaration of Helsinki principles. We obtained written informed consent from all participants. Patients were diagnosed with ASD if they were ≥50 years' old with at least one of the following: coronal scoliosis with Cobb angle ≥20°, sagittal vertical axis (SVA) ≥5 cm, pelvic tilt (PT) ≥25°, or thoracic kyphosis (TK) ≥60°. The cohort included patients with ASD who underwent extensive corrective fixation surgeries between 2010 and 2017 at a single institution. Patients who underwent posterior instrumented fusion from the thoracic spine to the pelvis and had available full-length standing radiographs and HRQOL data collected before and 2 years postoperatively were included in the study. However, the exclusion criteria were cases of spinal deformities associated with infection, malignancy, and neuromuscular disease. Patients with incomplete outcome data were also excluded. Data on the following patient characteristics were extracted: age, sex, body mass index (kilograms per square meters), Charlson comorbidity index, and American Society of Anesthesiologists (ASA) classification. Patients were divided into the following three groups: corrective fusion surgery using multiple Grade 2 osteotomy (Grade-2), three-column osteotomy (three-column), or LLIF groups.
Regarding surgery data, the number of fused vertebrae, upper instrumented vertebrae (UIV) level, number of pedicle screws, screw density, presence or absence of iliac screws, whether surgery was performed in two stages, total surgery time, total intraoperative blood loss, length of hospital stays, perioperative complications (surgical complications, neurological complications, and medical complications), and revision surgery within 2 years of the initial surgery were investigated. Screw density was defined as the number of implanted pedicle screws per vertebra.
In the Grade-2 group, dissociation, screw placement, correction, and interbody fusion were performed using the posterior approach in one or two stages. Patients with rigid kyphosis or wedge-shaped vertebra underwent three-column osteotomy correction surgery. The three-column osteotomy level was selected on the vertebral body of the apex of the kyphosis deformity or the lower vertebral body if the apex of the kyphosis deformity was located at the disk level. Screw placement, dissociation with three-column osteotomy under the local temporary rod, correction, and interbody fusion were performed using the posterior approach in one or two stages. In the LLIF group, we performed LLIF via the lateral approach in two to four intervertebral discs. Large cages were inserted to correct and stabilize the intervertebral bodies. In the second stage, posterior corrective fusion with posterior interbody fusion at L5/S1 was performed.
Data Collection of Medical Expenses
All inpatient medical costs for ASD, including laboratory admissions for ASD surgery, were extracted from the medical fee data. We also investigated the cost of hospitalization for revision surgery up to 2 years after the initial surgery. Total medical expenses included surgery costs, hospitalization costs, examination costs, and others such as physical therapy or medical management fees. Furthermore, surgical costs included all costs during surgery, including anesthesia management fees and the cost of implants used. The examination costs included examination charges, including blood sampling, radiography, computed tomography (CT), and magnetic resonance imaging (MRI). Hospital costs included perioperative centralized management costs, pharmaceutical treatments, meal costs, and room costs. Cost not included in these items was private room difference costs. The total hospitalization cost for any separate hospital admission for an examination before surgery was included in the examination cost.
Full-length freestanding posteroanterior and lateral spine radiographs obtained before and 2 years postoperatively were analyzed. Board-certified spine surgeons used standard techniques to measure spinopelvic parameters, including TK (Cobb angle between the superior endplate of T-5 and the inferior endplate of T-12), lumbar lordosis (LL) (Cobb angle between the superior endplate of L-1 and superior endplate of S-1), PT (angle subtended by a vertical reference line originating from the center of the femoral head and the midpoint of the sacral endplate), mismatch between pelvic incidence (PI) (angle between the line perpendicular to the sacral plate at its midpoint and the line connecting this point to the femoral head axis), and SVA (C-7 plumb line relative to S-1).[17,18] The interobserver correlation coefficients for TK, LL, PT, PI, SS, and SVA were 0.751, 0.736, 0.882, 0.744, 0.730, and 0.837, respectively.
Patient-reported Outcome Measures
HRQOL data derived from the Scoliosis Research Society (SRS)-22r[19,20] and Oswestry Disability Index (ODI) were evaluated. The scale has been reported as representative, reliable, and valid in populations with ASD.[21–23]
Cost-effectiveness was determined using quality-adjusted life years (QALY). Cost/QALY was calculated by dividing the total amount of hospitalized medical expenses for 2 years by the acquired QALY. The reference willingness to pay threshold was assumed to be USD 50,000 (JPY 5,000,000).[24,25] According to a previously published regression model, QALY was calculated by converting ODI into a short-form survey-6D (SF-6D). The average exchange rate between the US dollar and Japanese yen was 1 USD = 100 JPY.
We compared complications, revision surgery rate, and cost-effectiveness according to differences in the lower instrumented vertebrae (LIV). Furthermore, since three groups represent different pathologies, we focused on patients with degenerative kyphoscoliosis and compared the complication rate, revision surgery rate, QALY improvement, and cost-effectiveness.
All values are expressed as mean ± standard deviation (SD). The Shapiro-Wilk test was used to verify the assumption about the normal distribution of the data. χ 2/Fisher exact test was used to test for significant differences in categorical study parameters between groups. The statistical significance of the differences between groups was examined using the one-way analysis of variance test. Post-hoc comparisons were made using Tukey' test, and post-hoc power analysis was performed. P value of <0.05 was considered statistically significant. Statistical analyses were performed using the Statistical Package for Social Sciences (SPSS) software (version 26.0; SPSS, Chicago, IL) and G*Power 3.1 (software freely available on the Internet).
Spine. 2021;46(18):1249-1257. © 2021 Lippincott Williams & Wilkins