Abstract
Background
The choice of the upper instrumented vertebra has long been debated. With little proof regarding the best fusion level, scarce information about the final outcome and lack of consensus, four criteria were used to study each AP and lateral films to choose the most optimal level. The author's used criteria were (1) the positive shoulder sign defined as the contralateral shoulder to the main curve being the highest, (2) a proximal curve that is stiff on reduction maneuvers only to be corrected less than 30% a junctional kyphosis on lateral view between the main, (3) the proximal curve and finally a long proximal curve accounting for 5 and more vertebrae and (4) the final outcome being shoulder balance. The objective of this study is to study the concordance between these criteria used by our surgeons and those defined by Lenke in 2001 to select the most conservative posterior fusion possible to achieve coronal and shoulder balance in AIS.
Methods
Thirty Lenke type I AIS deformity patients, with a minimum postoperative follow up of 2 years, were divided according to the proximal fusion level with group 1+ being all patients who have a fused proximal thoracic curve and group 1- being all patient whose proximal thoracic curve wasn't included in spinal arthrodesis. Then a comparative study between the two groups was made, accounting for shoulder balance as the main outcome by measuring coracoid height, T1 tilt and clavicle angle between the two groups and comparing the results whether the proximal thoracic curve was included or not.
Results
The two groups were initially similar (p > 0.05) and remained equivalent having an appropriate shoulder balance in the immediate post-operative period and at last follow up without a significant difference in shoulder balance (p > 0.05) (coracoids difference, T1 tilt and clavicle angle). The study showed an average correction of 60% in the proximal thoracic curve and 70% in the main thoracic curve whether PT was included or not. A similarity study between Lenke criteria and the authors' criteria showed no difference between the two with the exception of a PT bigger than 5 vertebrae. Having a PT bigger than 5 vertebrae did not influence shoulder balance in AIS type I. The study showed a concordance of 74% between Lenke criteria and the authors'.
Conclusion
There is a high level of concordance between the authors' criteria and those defined by Lenke showing that whether to include the proximal curve or not depends on establishing whether the proximal curve is stiff i.e structural or not.