Distal Adding on in Lenke 1A Scoliosis: What Causes It? How Can It Be Prevented?

PurposeTo investigate the causes and prevention of distal adding on in Lenke 1A scoliosis.MethodsSixty Lenke 1A patients were included. The authors selected 10 potential risk factors for distal adding on. Postoperative increase in 5 radiographic parameters was used to indicate the extent of distal adding on. The authors then performed correlation analysis between the 10 potential risk factors and the extent of distal adding on, with the aim of identifying the causes of distal adding on. To predict 2-year outcome using preoperative parameters, linear regression models were established. The authors selected 2-year Cobb angle, thoracic apical vertebra center sacral vertical line (CSVL) distance and lowest instrumented vertebra (LIV)-CSVL distance to represent 2-year outcome. Their correlations with 8 preoperative parameters were tested.ResultsPotential risk factors representing either LIV selection or skeletal immaturity were highly correlated with the 5 radiographic parameters, which suggests that LIV selection and skeletal immaturity are causative in connection with distal adding on. The formula for predicting 2-year LIV-CSVL distance was: 2-year LIV-CSVL distance = 9.9 + 0.8 (preoperative LIV-CSVL distance) − 4.2 (Risser sign grade). The model adjusted R2 = 0.77.ConclusionsIn Lenke 1A scoliosis, both LIV selection and skeletal immaturity are highly correlated with distal adding on. In other words, the shorter the extent is of distal fusion, the larger is the distal adding on; the less skeletally mature the patient is, the larger is the distal adding on. When treating skeletally immature patients (Risser sign ≤3) with 1A curves, performing fusion surgeries should be avoided when possible; growing rod treatment may be the optimal treatment choice. For skeletally mature patients, LIV selection should be the first consideration; the preoperative LIV-CSVL distance should be ≤21 mm when the Risser sign grade is 4 and ≤ 26 mm when the Risser sign grade is 5.