In their Letter, the authors studied a variant of the Sachdev-Ye-Kitaev model with quadratic and quartic interactions (also known as a mass-deformed SYK). They claimed that the quantum Lyapunov ...exponent would vanish below some critical temperature. In this Comment, Kim and Cao show that this is not the case. They calculate exactly in the perturbative regime where the temperature and the quartic coupling are much smaller than the quadratic coupling.
A retrospective case series of patients treated surgically for degenerative lumbar scoliosis (DLS).
To determine incidence and risk factors of progressive global thoracic kyphosis (pGTK) after ...surgery for DLS.
Sagittal balance affects the surgical treatment of spinal deformity in adults. Little is known about the loss of sagittal balance due to pGTK, or about the risk factors for pGTK, after surgery for DLS.
We reviewed records from a multicenter database of adults with DLS, treated with posterior spinal fusion. Inclusion required an age of 50 years or more at the time of surgery, an upper instrumented vertebra at T9 and below, more than 5 fused segments, and at least 2 years of follow-up. We included 73 patients with a mean age of 68.3 years (range, 51-77 yr) and a mean follow-up period of 3.6 years (range, 2-11 yr). Independent risk factors for pGTK were identified by logistic regression analysis.
Significant pGTK, defined as an increase in thoracic kyphosis of more than 10° from before surgery to the time of final follow-up, was observed in 41% of the patients. Loss of the sagittal vertical axis was larger in patients with pGTK than without (4.7 vs. 1.5 cm; P = 0.02). Risk analysis showed larger lumbar lordosis correction in patients with pGTK. Multivariate logistic regression analysis identified an age greater than 75 (odds ratio, 5.53; P = 0.02, 95% confidence interval 1.4-22.4) and sacropelvic fusion (odds ratio = 2.66, P = 0.02, 95% confidence interval 1.5-11.1) as independent risk factors for pGTK.
The pGTK incidence after surgery for DLS was 41%. Age, sacropelvic fusion, and a larger sagittal correction were identified as pGTK risk factors. Long-term follow-up will provide more data on the clinical impact of pGTK in elderly patients.
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