Mingyuan Yang1, Honglei Guo2, Xinrui Wang3, Shibo Xia4, Xiaodong Zhu1, Changwei Yang5, Ming Li6. 1. Department of Orthopedics, Changhai Hospital, Second Military Medical University, Shanghai, People's Republic of China. 2. Department of Gastroenterology, Changhai Hospital, Second Military Medical University, Shanghai, People's Republic of China. 3. Department of Radiology, Changhai Hospital, Second Military Medical University, Shanghai, People's Republic of China. 4. Second Military Medical University, Shanghai, People's Republic of China. 5. Department of Orthopedics, Changhai Hospital, Second Military Medical University, Shanghai, People's Republic of China. Electronic address: changwei_y@qq.com. 6. Department of Orthopedics, Changhai Hospital, Second Military Medical University, Shanghai, People's Republic of China. Electronic address: yangmingyuan0330@gmail.com.
Abstract
BACKGROUND: The morphology of sagittal alignment varies in normal population. Sagittal alignment was classified into four subgroups; however, this classification was performed based on senior authors' clinical experiences rather than scientific methods. The objective of this study is to classify the morphology of sagittal alignment in normal population and describe the characteristics of sagittal alignment in each subgroup. METHODS: Medical records of asymptomatic volunteers without known spinal diseases in our outpatient clinic from January 2015 to August 2015 were reviewed. Demographic data and radiological parameters were evaluated, and compared between males and females as well. Two-step cluster analysis was performed. Radiological parameters were compared among these subgroups and then, the characteristics of each group were described. Receiver-operating characteristics (ROC) curve was constructed to detect the optimal cut-off value of separation of individual spine. RESULTS: 230 healthy volunteers with mean age of 33.53 years old were recruited (male:female = 106:124). No significant difference of each demographic and radiological parameter was observed between males and females, except for maxLL and PT. Two types of sagittal alignment were classified by the two-step cluster analysis. Type I (57.8%): small sagittal curves with small maxTK (29.24° ± 4.99°), maxLL (43.99° ± 9.10°) and PI (43.49° ± 7.61°), and Type II (42.2%): large sagittal curves with large maxTK (43.10° ± 6.41°), maxLL (53.41° ± 9.59°) and PI (53.10° ± 11.82°). The mean value of age, SS, PT, SVA, TPA, T1 sagittal angle, maxLL-maxTK, SS-PT and PI-maxLL was 37.07 ± 11.54 years old, 31.64° ± 7.43°, 15.66° ± 7.34°, 4.57 ± 22.24 mm, 10.85° ± 7.45°, 16.77° ± 5.09°, 10.31° ± 9.58°, 15.97° ± 10.74° and 3.32° ± 8.91° in Type I, and 39.94 ± 12.73 years old, 37.88° ± 8.36°, 15.29° ± 7.89°, 4.19 ± 22.00 mm, 9.23° ± 7.28°, 23.37° ± 4.87° , 16.74° ± 9.42°, 22.59° ± 11.64° and -5.84° ± 10.70° in Type II, respectively. maxTK, maxLL, PI, SS, T1 sagittal angle, maxLL-maxTK, SS-PT and PI-LL in Type II were greater than those in Type I, while no significant difference was found in age, gender, PT, SVA and TPA between two groups. On the basis of the ROC curve, the optimal cut-off values of maxTK, maxLL and PI as indicators for classification of sagittal alignment were projected to be 37°, 52° and 49°, respectively. CONCLUSIONS: There were two subgroups of sagittal plane in normal population. The optimal cut-off values of maxTK, maxLL and PI as indicators for classification of sagittal alignment were projected to be 37°, 52° and 49°, respectively. This novel classification could provide guidelines for our further understandings of sagittal alignment and mechanisms of different spinal diseases more easily, which also help to restore sagittal balance in the correction surgery more accurately.
BACKGROUND: The morphology of sagittal alignment varies in normal population. Sagittal alignment was classified into four subgroups; however, this classification was performed based on senior authors' clinical experiences rather than scientific methods. The objective of this study is to classify the morphology of sagittal alignment in normal population and describe the characteristics of sagittal alignment in each subgroup. METHODS: Medical records of asymptomatic volunteers without known spinal diseases in our outpatient clinic from January 2015 to August 2015 were reviewed. Demographic data and radiological parameters were evaluated, and compared between males and females as well. Two-step cluster analysis was performed. Radiological parameters were compared among these subgroups and then, the characteristics of each group were described. Receiver-operating characteristics (ROC) curve was constructed to detect the optimal cut-off value of separation of individual spine. RESULTS: 230 healthy volunteers with mean age of 33.53 years old were recruited (male:female = 106:124). No significant difference of each demographic and radiological parameter was observed between males and females, except for maxLL and PT. Two types of sagittal alignment were classified by the two-step cluster analysis. Type I (57.8%): small sagittal curves with small maxTK (29.24° ± 4.99°), maxLL (43.99° ± 9.10°) and PI (43.49° ± 7.61°), and Type II (42.2%): large sagittal curves with large maxTK (43.10° ± 6.41°), maxLL (53.41° ± 9.59°) and PI (53.10° ± 11.82°). The mean value of age, SS, PT, SVA, TPA, T1 sagittal angle, maxLL-maxTK, SS-PT and PI-maxLL was 37.07 ± 11.54 years old, 31.64° ± 7.43°, 15.66° ± 7.34°, 4.57 ± 22.24 mm, 10.85° ± 7.45°, 16.77° ± 5.09°, 10.31° ± 9.58°, 15.97° ± 10.74° and 3.32° ± 8.91° in Type I, and 39.94 ± 12.73 years old, 37.88° ± 8.36°, 15.29° ± 7.89°, 4.19 ± 22.00 mm, 9.23° ± 7.28°, 23.37° ± 4.87° , 16.74° ± 9.42°, 22.59° ± 11.64° and -5.84° ± 10.70° in Type II, respectively. maxTK, maxLL, PI, SS, T1 sagittal angle, maxLL-maxTK, SS-PT and PI-LL in Type II were greater than those in Type I, while no significant difference was found in age, gender, PT, SVA and TPA between two groups. On the basis of the ROC curve, the optimal cut-off values of maxTK, maxLL and PI as indicators for classification of sagittal alignment were projected to be 37°, 52° and 49°, respectively. CONCLUSIONS: There were two subgroups of sagittal plane in normal population. The optimal cut-off values of maxTK, maxLL and PI as indicators for classification of sagittal alignment were projected to be 37°, 52° and 49°, respectively. This novel classification could provide guidelines for our further understandings of sagittal alignment and mechanisms of different spinal diseases more easily, which also help to restore sagittal balance in the correction surgery more accurately.