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Abstract
As the elderly population increases, the number of adult spinal deformity patients is also increasing. Unlike the main symptom of adolescent deformity is deformity itself, the symptoms of adult spinal deformity are various such as back pain and radiating pain to the extremities, which are associated with degenerative change. Deformities also show various combinations of scoliosis, kyphosis, coronal and sagittal imbalances. Various symptoms and complex deformities as well as old ages make treatment of the adult spinal deformity difficult. Radiographs of the spinal deformity should include spine and pelvis and hip joints in long films. Spinal deformity is influenced by regional curve, rotation of pelvis, and positions of hip and knee joints. The pelvis is a key structure in regulating spinal balances. Pelvic incidence, pelvic tilt and sacral slope are the most widely used spino-pelvic parameters. Pelvic incidence is fixed constant, which is unchanged when bone growth is complete. Pelvic incidence has a positive correlation with lumbar lordosis, and serves as a reference value in determining how much correction of lumbar lordosis is required in patients with sagittal imbalance. More correction of lumbar lordosis is required in patients with higher pelvic incidence. In order to maintain spinal balance, the combination of thoracic kyphosis, lumbar lordosis, and pelvic tilt should be harmonized. In particular, the match of pelvic incidence and lumbar lordosis is important to maintaining a balanced spine.
Figures and Tables
Figure 1
Coronal and sagittal imbalance. Coronal imbalance is defined as the C7 plumb line passes >2.5 cm lateral from the central sacral line. Sagittal imbalance is defined as the C7 plumb line passes >5 cm anterior from the posterosuperior corner of the sacrum.
Figure 2
Compensatory mechanism of sagittal imbalance. Data from the article of Cho et al. (Spine (Phila Pa 1976). 2013;38:E1561-6).8) (A) Neutral sagittal balance shows harmonious thoracic kyphosis and lumbar lordosis. Sacral slope is approximately 30°. (B) Loss of lordosis due to hypolordotic fusion in the lower lumbar spine leads to positive sagittal imbalance. (C) With a compensatory mechanism, hyperextending disc space at mobile segments can cause the C7 plumb line to be restored to the near normal range. (D) As patients grow older, subsequent disc degeneration develops at the mobile segments and then sagittal imbalance develops again. (E) Compensatory retroversion of the pelvis produces a vertical sacrum and reestablishes sagittal balance. Sacral slope is approximately 0°.
Figure 3
Spino-pelvic parameter. Pelvic incidence (PI) is the sum of pelvic tilt (PT) and sacral slope (SS). Normal ranges of these parameters are wide, so that the combination of them is more affected than the individual value.
Figure 4
(A, B) Both radiographs show same SVA. (A) Pelvic tilt is 57°, showing severe retroversion of the pelvis, which is associated with compensation for the sagittal imbalance. (B) Pelvic tilt is normal range which means no retroversion of the pelvis. SVA, sagittal vertical axis; LL, lumbar lordosis; SS, sacral slope; PI, pelvic incidence; PT, pelvic tilt.
Figure 5
Scoliosis Research Society-Schwab classification of adult spinal deformity. Data from the article of Schwab et al. (Spine (Phila Pa 1976). 2012;37:1077-82).20) PI, pelvic incidence; LL, lumbar lordosis; SVA, sagittal vertical axis; PT, pelvic tilt.
Figure 6
This 72-year-old female showed degenerative sagittal imbalance, 13 cm of sagittal vertical axis (SVA). On the radiographs, lumbar lordosis (LL) was kyphosis +21°, pelvic incidence (PI) was 57°, and pelvic tilt (PT) was 57°. According to the Scoliosis Research Society-Schwab classification, coronal curve type is N, and all sagittal modifiers were found ++ in PI-LL, SVA, and PT. This patient underwent pedicle subtraction osteotomy at L3, and posterior instrumentation from T12 to S1 with iliac screw fixation. SS, sacral slope.
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