Managing early onset scoliosis with magnetically-controlled growing rods for managing scoliosis: does the law of diminishing returns apply?

Abstract

Introduction: The law of diminishing returns has been proposed to occur in patients that are treated by traditional growing rods. Reduced gains in spinal length occurs with repeated distractions and may be contributed by autofusion of the spine or progressive stiffness. With the magnetically controlled growing rod (MCGR), distractions can be more frequent and less forceful. The objective of study is to assess spinal length gains with MCGR distractions. Methods: This is a prospective case series of early onset scoliosis patients treated with MCGR with minimum follow-up of 2 years. Out-patient distractions were performed at monthly intervals and aiming to achieve 2mm of distraction on each occasion. Increase in length was monitored by radiographs. Parameters collected include Cobb angles, T1-S1, and the achieved distraction lengths. Change in the parameters were analyzed at 6 monthly intervals. Results: Seven patients (3 males, 4 females) with mean follow-up of 3.8yrs (±SD 1.1) were recruited. The mean total number of distractions was 31 (±SD 13). There was no significant reduction in ability to distract over the period of study. Consistent gains in T1-S1 and achieved distraction lengths were obtained with distractions and the pattern was not consistent with the “law of diminishing return”. Conclusions: This study suggests that frequent and small amounts of distraction will not lead to reduction in length gain over time. Limitation of this study includes the small number of subjects. However, this study serves to focus attention on the distraction frequency and its potential effect on spine length and growth.