New ratio could be used to detect spinal malalignment

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In the European Spine Journal, Louis Boissière, Centre hospitalier universitaire de Bordeau, Bordeaux, France, and others described a new ratio—the lumbar lordosis index—that could be used to detect spinal malalignment in adult patients with scoliosis and could also be used to direct the surgeon in choice of realising an osteotomy.

Boissière et al explained that while pelvic incidence remains constant throughout life, lumbar lordosis decreases with age. They added: “Since loss of lumbar lordosis initiates spinal malalignment, we decided to evaluate the impact of a new mathematical ratio called the lumbar lordosis index. This index is the ratio between two existing parameters: lumbar lordosis and pelvic incidence.” The authors hypothesised that the new index would be “highly correlated” with spinal malalignment in adult scoliosis and that it could be used to help predict the need of a spinal osteotomy in adult scoliosis to restore sagittal balance. They reported that lack of lordosis (the difference between the theoretical lordosis and the measured lumbar lordosis) was used to represent spinal malalignment. 


Of the 53 patients (46 female and seven male) in the study, 18 underwent an osteotomy—six underwent a Smith Peterson osteotomy and 12 underwent a pedicle subtraction osteotomy—and 35 did not.


Boissière et al noted that lumbar lordosis, pelvic tilt, sagittal vertical axis, and the lumbar lordosis index were all correlated with lack of lumbar lordosis. However, of these parameters, the index was found to have the greatest correlation with lack of lumbar lordosis (p=0.01). They commented: “We are able to conclude that the lumbar lordosis index is more correlated with spinal malalignment than sagittal vertical axis, pelvic tilt, or lumbar lordosis in this study.”  

 

 

They added that although sagittal vertical axis and lumbar lordosis were both moderately correlated with lack of lordosis, a lumbar lordosis index score of <0.5 was “highly correlated” with one spinal osteotomy. Boissière et al stated: “This result demonstrates a clinical impact of the lumbar lordosis index in this study”. Also, the authors noted, a lumbar index score of <0.35 was associated with a pedicle subtraction osteotomy and a score of >0.35 was associated with either a Smith Peterson osteotomy or a pedicle subtraction osteotomy.


The authors commented that the lumbar lordosis index was useful to detect spinal malalignment and guide surgeons in the choice of realising an osteotomy but could not be used to detect the degree of correction needed as “other parameters”, such as spine stiffness, should be taken into account. They concluded that further studies could be done to evaluate the relationship between the index and spinal malalignment and other series of patients (ie, those without scoliosis). 

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