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192 A N A L E S R A N M R E V I S T A F U N D A D A E N 1 8 7 9 THORACOLUMBAR ROTATIONAL KYPHOSIS Pizones J, et al. An RANM. 2022;139(02): 186 - 195 Sagittal plane mismatch Patients instrumented to the pelvis had a higher rate of mismatch (65.1%) compared to those whose LIV was above the sacrum (47%), P = 0.029. Matching was more easily achieved in patients with LIV at L4 compared to those instru- mented to the pelvis. The multivariate analysis showed that PI [OR = 0.92 (95% CI = 0.85-0.99; P = 0.046)] was the most important, and the only independent factor related to mismatch (there was 3.2 times more risk of mismatching if when PI > 50°). The usual mismatch resulted from recreating a “lower” Roussouly type than ideal. Mismatched lower R-types had lower postope- rative TLK, and mismatched higher R-types had higher postoperative TLK. However these differences were not statistically significant. The mechanical complication rate was the same in all R-types (Table 4). Scoliosis consists of the abnormal shape of the spine in the three spatial planes. In the coronal plane there is lateral deviation; in the sagittal plane, an inversion of the physiological curves; and in the axial plane, rotation. The goal of surgery is to improve the deformity in all three planes. The sagittal plane is the most important when assessing adult deformity. Sagittal malalig- nment has been associated with worse clinical symptoms. For this reason, restoring the sagittal plane to its ideal values and position is crucial in spinal deformity surgery. Bringing back normal alignment improves patients’ quality of life, mainly in terms of pain and disability, and reduces the risk of mechanical complications (rod breakage, proximal junctional kyphosis or screw failure) [9]. Roussouly [6] described a classification of 4 different sagittal shapes (R-types), based on sacral slope values, in an asymptomatic adult popula- tion. As sacral slope is modified by the degene- rative loss of lumbar lordosis, a renewed classi- fication [7] distributes sagittal shapes according to pelvic incidence values, which are considered to be constant throughout life. Patients with low PI (R-type 1) ideally have a short lumbar lordosis with an inflection point at L3, followed by a large TL kyphosis, since this segment belongs to the lower thoracic arc. At the other end of the spectrum, patients with high PI (R-type 4) have a long lordosis, ending at the inflection point located around T12, with a long upper lumbar arc that contains the TL segment, drawing a flattened sagittal shape at the TL transition. It is important to be aware of these parameters when planning the surgery for ideal sagittal plane restoration. However, the role of the deformity created by scoliosis at the thoracolumbar junction is still not well understood, particularly how modifying its shape affects the surgical outcome. In one third of patients with AS, the 3D configu- ration of the deformity modifies this ideal sagittal shape [8]. In particular, the axial rotation of the apical segment, usually located at the thoraco- lumbar junction, creates a rotational thoracolumbar kyphosis when seen in a lateral view. This makes “higher” types of sagittal configuration (R-types 3 and 4) resemble “lower” types (mainly R-type 1). Thus, greater rotational T10-L2 kyphosis means the lumbar spine has fewer vertebrae involved in the lordosis, leading to a caudal shift in the inflec- tion point, and increasing the lordosis distribution index, resembling a R-type 1-like sagittal shape. After analyzing a large cohort of adult surgical scoliosis patients with thoracolumbar curves in our database, we discovered that TL kyphosis is relevant (above 20°) in only one third of these patients. The patients we studied had moderate coronal TL deformity (53°) and a pronounced mean TL kyphosis (34°) with a narrow range across the different R-types. The purpose of this study was to identify to what extent this TL rotational kyphosis was corrected by surgery, and the possible consequences of correcting TL rotational kyphosis in terms of final ideal R-type restoration and mechanical complications. It is widely believed that proper sagittal shape must be restored with surgery to obtain the best outcomes, because achieving ideal alignment and lordosis distribution may help avoid postoperative mechanical complications [4, 10-12]. One of the main causes of mechanical problems is over flattening of the upper lumbar arc in patients that need some TLK in this segment, typically among patients with low PI [4]. We found that the combination of maneuvers performed in scoliosis surgical correction automa- tically flattened the TL segment viewed from the lateral plane, changing the residual transi- tional kyphosis. This residual TL kyphosis readily accommodated the ideal values dictated by ideal sagittal shape configuration (Figure 1 and 2). Thus, although the degree of correction was similar regardless of PI (approximately 20°, ranging from 19° to 23°), patients with low PI ended up with higher residual TL kyphosis (17°), while patients with high PI had a flatter residual TL transition (9°). The postoperative range for maximal lordosis closely followed the ideal for each PI value (ranging from 47° for low PI to 56° for high PI). Scoliosis surgical correction also lengthened the upper lumbar arc by including a mean of one vertebra more in the lordosis, shifting the inflection point one segment towards a more proximal position. However, we found that the change in TL kyphosis did not have a direct impact on final shape matching, whereas fusion to pelvis and especially PI did. Restoring the sagittal plane to match its ideal does not exclusively depend on the amount of kyphosis or length of TL segment, but also, and mainly, on the value of the sacral slope related to the value of pelvic incidence (relative pelvic version [12]). Fusing distally to a more proximal level leaves some room for compensation to occur in the unfused distal segments, while the alterna- DISCUSSION