Clinical and Radiographic Evaluation
Basic information. Subjects’ demographic data including age, gender distribution, body mass index (BMI), bone mineral density (BMD) of lumbar vertebra and surgical information were recorded. At the time of radiographic acquisition, patient-reported outcomes were assessed using Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) scores. In the present study, the following symptoms were considered as sagittal imbalance syndrome or symptomatic sagittal imbalance 11: 1) severe back pain (VAS > 5 score) in natural standing position or in natural walking without any support (Fig. 1a, 1b, 1c and 1d). Back pain disappears or significantly relieves in support position (Fig. 1e and 1f); 2) significant living disability with ODI score > 40% 12, 13 and 3) dynamic sagittal imbalance in walking within 10 mins (Fig. 2) 14. Patients with sagittal imbalance syndrome were performed a long thoracolumbar fusion with lumbar decompression (Group A) or a relative short lumbar decompression and fusion (Group B). Thirty DLSS patients with severe global sagittal imbalance without sagittal imbalance syndrome who underwent a relative short lumbar decompression and fusion were selected as control (Group C).
Dynamic sagittal imbalance. Patient could stand upright for a while (a, b). After a short walk within 10 mins, the compensatory mechanisms exhausted and a significant trunk bent forward appeared (c, d, e).
Spinopelvic parameters. Radiographic measurements were performed on long-cassette standing upright lateral radiographs of the spine and pelvis. The following radiographic parameters were measured using Surgimap software (Nemaris, Inc., New York, NY, USA) (Fig. 3a and 3b) 15: thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), PI-LL mismatch (PI-LL), sagittal vertical axis (SVA), and T1 pelvic angle (TPA).
Disc and facet degeneration evaluations. The degrees of lumbar disc degeneration and right facet arthritis (L1–L2 to L5–S1) were examined on 1.5-T MRI images using Pfirrmann degeneration classification 16. Different score was given to represent different degeneration grade of disc and facet joint. Higher scores represented better disc and facet conditions. Mean values of the five levels were calculated.
Muscle evaluation. Cross-sectional Area of lumbar paravertebral muscle was assessed on 1.5T MRI images with ImageJ software (National Institutes of Health, Bethesda, Maryland, USA) 17, 18. T2-weighted axial images at L1–2, L2–3, L3–4, and L4–5 disc levels were analyzed to measure the right muscle area. The regions of interest of back muscle were determined by outlining the fascial boundary of the muscles (Fig. 3c). The signal intensity (in gray scale) within the region of interest was measured using the measurement function of ImageJ. Muscle area was divided by the disc area at the same level (muscle-disc ratio) to decrease the bias caused by individual size (Fig. 3d). The percentage of fat infiltration was measured using a pseudocoloring technique (Fig. 3e and 3f). Mean values of the four levels were calculated.
At the latest follow-up, patients’ satisfactions of surgical managements were evaluated with centesimal system score from 0 to 100. 0 represents not satisfied, while 100 represents very satisfied. All the clinical and radiographic evaluations were completed by two independent spine surgeons (X.L.C. and X.Y.L.), who were not involved in the treatment of the patients. The mean values were recorded.
Spinopelvic parameters measurement and back muscle evaluation. a Measurement of spinal parameters. b Measurement of pelvic parameters. c The fascial boundary of lumbar paravertebral muscles (yellow circle): the fascia thoracolumbalis was traced down laterally and anteriorly to the dorsal side of the quadratus lumborum, followed by the posterior surface of the facet and lamina, and lateral margin of spinous process. d The boundary of vertebral body (yellow circle). Muscle-disc ratio: 16.267/17.343 = 0.94. e Cut the muscle along the fascial boundary. f Bright pixels of fat tissue in the MR images were colored in red (darker color in the black and white version) using pseudocoloring technique. The percentage of the red pixel area in the muscle compartment was the percentage of fat infiltration (29.43%).