Vertebral body growth during growing rod instrumentation: growth preservation or stimulation?

Retrospective review, case series.

Determination of whether growing rod treatment with routine lengthening every 6 months causes growth stimulation of individual vertebrae within instrumentation levels (WIL).

The Hueter-Volkmann law states that distractive forces exerted upon growing physes stimulate growth and vice versa, a principle that has been in clinical use for decades. In previous studies, it has been shown that vertebral endplates might respond in a similar manner to distraction. It has been proven that fusionless instrumentation, which is the mainstay of treatment after failure of conservative measures for early-onset scoliosis, allows near-normal vertebral growth but the issue of how individual vertebrae respond to distraction has not yet been analyzed.

This institution's database, including the radiographic data for growing rod patients, was analyzed retrospectively. Vertebral level heights within and outside instrumentation levels were measured in postindex and postfinal follow-up x-rays, and the amount of growth that has taken place in a minimum follow-up period of 2 years was calculated and then compared for statistical significance.

Twenty patients (6 M, 14 F, average age, 71.0 mo) met the inclusion criteria. The average follow-up was 49 months (range, 26 to 72 mo). Lengthenings were performed every 6 months regularly. The average height of vertebrae WIL was 15.9 mm (range, 10.0 to 21.1 mm) in postindex and 22.9 mm (range, 15.0 to 32.9 mm) in the final follow-up; vertebrae outside instrumentation levels was 18.1 mm (range, 13.5 to 22.1 mm) postindex and 23.3 mm (range, 14.8 to 28.8 mm) in the final follow-up. The average growth was 5.2±3.4 mm in outside instrumentation levels and 7.0±2.9 mm in WIL. These values were significantly different statistically (P<0.01).

Growing rod treatment performed with regular lengthenings every 6 months appears to stimulate growth in individual vertebral bodies WIL.

Level IV.