Risk factors for distal adding-on phenomenon in type Lenke 1A scoliosis

English Keywords:Adolescent idiopathic scoliosis  Lenke 1A  Internal fixation  Adding-on  Complication

English Abstract:

  【Abstract】 Objectives: To investigate the risk factors associated with postoperative distal adding-on phenomenon in type Lenke 1A scoliosis, and the optimal strategy for the choice of the lowest instrumented vertebrae(LIV). Methods: 54 patients(43 females, 11 males, average 14.4 years old) with type Lenke 1A scoliosis undergoing posterior pedicle screw instrumentation alone in our department between January 2007 and December 2010 were retrospectively reviewed. The adding-on phenomenon was defined as progressive increase in the number of vertebrae within the primary curve and combined with either an increase in the Cobb angle of at least 5° or an increase of more than 5° in the angulation of the first disc below LIV at final follow-up. Potential related parameters were investigated statistically to determine the risk factors. Results: After a mean follow-up of 3.2 years, distal adding-on was observed in 12 of 54 patients(22.2%), while the other 42 cases were defined as control group. The risk factors including preoperative LIV deviation from CSVL, Risser grade, difference in levels of LIV with the lowest end vertebra(LEV), neutral vertebra(NV) and stable vertebra(SV) were significantly associated with adding-on phenomenon. Multivariate Logistic regression revealed the preoperative LIV deviation from CSVL＞10mm and the difference in levels between LIV and NV(NV-LIV＞0), and Risser grade＜Ⅱ played as independent predictive roles. Conclusions: Inappropriate selection of LIV and skeletal immatureness tend to result in postoperative distal adding-on. Based on our study, choosing NV as LIV may be the optimal strategy. If so, the vertebra deviation from CSVL less than 10mm preoperatively should be considered carefully, otherwise the adding-on phenomenon may occur.