The learning curve effect in magnetically controlled growing rod distraction monitoring by ultrasound

Abstract

INTRODUCTION: Radiographs are the gold standard for monitoring of distraction lengths for magnetically controlled growing rod (MCGR) treatment. However, ultrasound is a radiation-free alternative. This study aimed to determine if a learning curve exists for this purpose. METHODS: Consecutive patients undergoing MCGR insertion and ultrasound measurements from 15 October 2013 to 31 March 2015 were prospectively recruited. Data regarding date of the distraction visit, and the interval radiograph and ultrasound measurements of the distracted lengths were collected. The change in both radiograph and ultrasound measurements was plotted to determine clusters of correlation differences with time. Comparison was made by paired t test. RESULTS: A total of 22 patients with 140 distraction episodes were recorded. The mean differences between ultrasound and radiograph measurements per distraction episode was -0.3 mm for right rod and -0.1 mm for left rod. The correlation in the first cluster (15 October 2013 to 16 October 2013) was 0.612 (right rod) and 0.795 (left rod), the second cluster (16 October 2013 to 20 May 2014) was 0.879 (right rod) and 0.918 (left rod), and the third cluster (20 May 2014 to 31 March 2015) being 0.956 (right rod) and 0.932 (left rod). Thus, the second cluster was where the correlation plateaus which translated to 48 to 73 rod measurements by ultrasound. CONCLUSION: Although initial use of ultrasound may require radiographic confirmation, with time and experience, ultrasound measurements can be more reliable. Ultrasound and radiographic measurements correlate in general but are even more compatible after measuring 48 to 73 patients.