Selection of Lower instrumented vertebra in early-onset scoliosis at index growth rod insertion- can we predict distal add-on at graduation surgery?

Abstract

Background: There are still no consensus criteria on how to select the lower instrumented vertebra (LIV) for growing rods (GRs) at index surgery. The aim was to evaluate whether the criteria used for adolescent idiopathic scoliosis fusion adapts to early-onset scoliosis (EOS).

Materials and methods: Retrospective analysis of prospectively collected data in a consecutive cohort of patients with EOS treated with GR, expanding from index surgery to 2 years after graduation. The LIV was analyzed regarding its relation to the stable vertebra (SV), substantially touched vertebra (STV), and non-substantially touched vertebra (NSTV). Failure of LIV selection was considered when revision surgery with distal add-on was needed during follow-up.

Results: A total of 13 patients met the inclusion criteria. The mean chronological age was 9.16 years (at index surgery), 12.9 years (at graduation), and 14.9 years (at final follow-up). The most frequent LIV at index surgery was L4 in four cases, closely followed by L2 and L3 with three cases each at the index surgery. The designation of SV, STV, and non-STV (NSTV) was based on standard anteroposterior radiographs. There were six cases where the LIV at growth rod insertion was the SV. Three of these did not require revision of the LIV at graduation. The remaining three which required revision required addition of one level. There were six cases in which the LIV was higher than the SV. Four of these were one level higher, i.e., STV, and two of these NSTV. Those which were at STV did not require revision of the LIV at graduation. Of the two where the initial LIV was NSTV, one required revision down to four levels below, while the other required extension by one level.

Conclusions: For EOS, whenever an SV or STV was chosen, the incidence of revision of LIV was about 30%. The revision required was a distal add-on by one level. If the LIV was any higher than STV, the revision required a distal add-on to more than one level. Choosing a STV or SV as the distal foundation for the construct of EOS correction possibly leads to lesser rates of add-on phenomenon.