How frequent should the radiographic examination be to monitor magnetically controlled growing rods? A retrospective look two to seven years postoperatively.

ABSTRACT

PURPOSE: Magnetically controlled growing rods (MCGR) allow more frequent outpatient lengthenings to better mimic the physiological growth. The assessment of distractions with radiographs raised concerns regarding ionizing radiation exposure in growing children. The aim was to assess the necessity of radiographs after every lengthening of MCGR. METHODS: A retrospective analysis of 30 consecutive patients (19F, 11 M) treated in a single institution between 2011 and 2017. Planned radiographs were taken based on a protocol, updated over the years to involve less frequent acquisitions. Unplanned radiographs were obtained after a patient complaint or a significant clinical examination finding. Outcome measures were preoperative and postoperative radiographic measurements, and complications such as proximal and distal junctional kyphosis and failure, rod or actuator breakage, collapse of previously achieved height or failure to lengthen and worsening of deformity. RESULTS: Mean age at surgery was 7.5 (4-11) years. Mean follow-up was 45 (24-84) months. Mean number of lengthenings and radiographs per patient were 14.4 (8-23), and 13.2 (5-46), respectively. Nine patients (30%) experienced a total of 13 mechanical complications. Almost all complications were detected in unplanned radiographs. The probability of detecting a mechanical complication was significantly lower (p < 0.00001) in planned radiographs. CONCLUSIONS: Radiographs taken after routine lengthenings of MCGR are not likely to reveal any significant finding, since only 0.9% of planned radiographs displayed a mechanical complication. Exposing growing children to radiation with an intention of checking the MCGR device after every lengthening could not be justified. Obtaining post-lengthening radiographs with a decreased frequency and after a significant complaint or clinical finding may be considered.