1. The Clunking Phenomenon in Magnetically-controlled growing rods: Possible risk factors James Tan, Dino Samartzis, Cora Bow, Jason Pui Yin Cheung, Kenneth Cheung Department of Orthopaedics and Traumatology The University of Hong Kong

2. Disclosure Professor Kenneth Man Chee Cheung was a consultant and received research support for Ellipse Technologies Inc.

3. Aim: To assess the occurrence and potential determinants associated with “distraction failure” or slippage of the MCGR during distraction. Lancet. 2012 Distraction of rods Standard Offset

4. Methods 5 EOS patients with dual rods inserted Congenital, CHARGE syndrome, Ehlers-Danlos syndrome, JIS, neurofibromatosis Single surgeon – Dec 2009 - Oct 2012 12 months minimum FU Monthly distractions ~2mm Standard rods distracted first

5. Definition of “Distraction Failure” – Rod slippage of the magnetic mechanism during the distraction procedure – Recognize via a “clunk” sound & feeling Demographic Age at surgery and first clunking, number and frequency of clunking, BMI Radiologic Side of curve convexity, Cobb angle, sagittal profile, curve flexibility, distance of rod to apex of curve, distance between the two magnets

6. Magnet to apex Between two magnets

7. Results One patient excluded due to faulty rod design (EDS) Mean age 12.7y at initial surgery 1 st clunk within 1 year from initial surgery No difference in BMI, Cobb angle and flexibility assessments

8. Total failure episodes in Standard Rod Time period to 1 st failure (months) Total failure episodes in Offset Rod Time period to 1 st failure (months) Idiopathic0-1716 Syndromic0-1012 Congenital2812278 Neurofibromatosis650- Total 34 54 Results (n=4) Standard RodOffset Rod Idiopathic0/235/23 Syndromic0/249/24 Congenital3/160/16 Neurofibromatosis11/2115/21 Total14/84 (17%)29/84 (35%) Distraction failure more prevalent in off-set rod Distraction failure occurs within 1 st year Frequency of Distraction Failure

9. Rods that clunked were nearer to the apex of the major curve Distance between internal magnets – Single rod clunking (56mm) Offset rod (68mm) Standard rod (31mm) – Dual rod (33mm)

10. First study to identify “distraction failure” or rod slippage - may help predict distraction potential – can occur within the first year since initial rod implantation may continue thereafter – more prevalent to occur in the offset rod Potential complication or risk factor ? – rod breakage, revision surgery, loss of correction, improper spinal growth, etc Naturally occurring ? – physiological fail-safe mechanism that benefits the patient ? Larger studies are needed to further validate our findings and elaborate Conclusions