Use of ultrasound to monitor distractions by magnetically controlled growing rods: a longitudinal correlation study

Abstract

INTRODUCTION: Growing rods are commonly used for surgical treatment of skeletally immature patients with scoliosis. Magnetically-controlled growing rods (MCGR) allows for more frequent distractions to mimic normal growth. However, such frequent distractions equate to more frequent radiographs for monitoring distraction; thereby, increasing ionizing radiation exposure to the developing child. The use of ultrasound, which emits no radiation, has been found in cross-sectional studies to be reliable in measuring MCGR distractions. As such, the following study aimed to address the longitudinal clinical utility of ultrasound compared to x-ray use for MCGR distractions. METHODS: This is a prospective case series with minimum two-year follow-up of patients treated with MCGR. Out-patient distractions were performed at monthly intervals, targeting 2mm of distraction on each occasion. Assessment of distraction length was monitored by ultrasound at each visit, X-rays were taken every six months and compared with ultrasound measurements. RESULTS: 8 patients (6 females, 2 males) with mean 23 distractions (SD: ±11.9) were recruited. The mean follow-up was 45.7 months (SD: ±12.8). A total of 22 sets of x-rays were taken. The mean distracted length was 5.3 mm(SD: ±3.7mm) on x-rays and 4.7mm (SD:±3.7mm) on ultrasound, with excellent correlation noted between the two imaging modalities (r=0.930; p<0.0001). CONCLUSIONS: This is the first longitudinal study to note that ultrasound assessment of MCGR distraction lengths was highly comparable to that of x-rays. Ultrasound can be a reliable alternative to plain radiographs; thereby, avoiding radiation exposure and its detrimental sequelae in the developing child.