The use of ultrasound in comparison to radiography in magnetically controlled growth rod lengthening measurement: a prospective study

Purpose: This study investigated whether ultrasound (U/S) is an alternative to radiography when measuring magnetically controlled growth rod (MCGR) length in order to reduce radiation exposure. Distractible spinal growth rods are the gold standard when treating early-onset scoliosis (EOS). Methods: This was a prospective series. Patients were already undergoing EOS treatment using MCGRs. Forty-eight data points measured using radiography and U/S were compared. Each U/S data point was measured three times by three observers to assess intra- and inter-observer reliability. The radiation dose of the pre-lengthening and post-lengthening radiographs was recorded. Results: The average rod lengths were 1.322 cm with U/S and 1.329 cm with radiography. The ICC (radiography vs. U/S) was 0.992 (95 % confidence interval (CI) 0.976, 1.000). The inter- and intra-rater reliability of U/S had an ICC of 0.987 (95 % CI 0.966, 1.000) and 0.983 (95 % CI 0.956, 1.000), respectively. The mean total effective radiation dose of the pre-lengthening and post-lengthening PA spinal radiographs was 0.26 mSv with a mean attributable lifetime cancer risk of one in 39,686 per lengthening. Conclusion: U/S highly agrees with radiography when measuring MCGR length. It has a high inter- and intra-observer reliability and does not require radiation exposure. Although U/S allows accurate MCGR measurement and soft tissue assessment, patients will still need occasional radiographs to assess spine bony elements, overall spinal balance and scoliosis correction. Combining radiography and U/S allows patient monitoring and accurate MCGR measurement whilst decreasing patients’ radiation exposure.