Magnetic growth rods could potentially avoid spinal trauma


An interview with Kenneth MC Cheung.

Kenneth MC Cheung, Jessie Ho professor in Spine Surgery, head, Department of Orthopaedics & Traumatology, The University of Hong Kong, Hong Kong, will be giving the talk “Magnetic growth rods in early onset scoliosis” at the 9th combined congress of the Asia Pacific Spine Society and Asia Pacific Orthopaedic Association Paediatric section (29–31 August, Kuching, Malaysia). He spoke to Spinal News International about these devices

What are the limitations of standard growth rods in patients with early onset scoliosis?

Standard or traditional growing rods require repeated surgical operations under general anaesthesia to manually distract the instrumented rod for lengthening. Open distractions are usually performed every six months to balance length gain and the risk of repeated surgeries. For example, a four-year-old child with skeletal maturity at the age of 13 would potentially have to undergo 18 distraction operations. The repeated number of operations will lead to increased anaesthetic and wound complications. Studies suggest that the overall wound complication rate could be up to 16%, and increased by 24% with each distraction procedure. An additional drawback of the traditional growing rod is the increasing stiffness or autofusion of the spine caused by trauma to the spinal ligaments with sudden and forceful distractions at irregular intervals. This phenomenon has been described as the “law of diminishing returns”. Therefore, the chance of effectively distracting the rod progressively reduces with each successive distraction.

How do magnetic growth rods work?

These are single-use sterile titanium spinal distractible rods. The rods have an enlarged midportion which houses the magnetically drivable lengthening mechanism. In the clinic setting, a handheld magnetic external remote controller is placed over the internal magnet and this leads to a rotating mechanism and lengthening of the rod. Retraction of the rod can also be performed with the same device if the patient develops any pain or discomfort.

What are the potential benefits of magnetic growth rods?

With these magnetically driven growing rods, all distraction procedures can be performed at an out-patient setting without anaesthesia. Without the increased risks of anaesthetic and wound complications, distraction procedures can be performed more frequently to better mimic the normal growth of the child. Frequent and smaller distractions with this device can potentially help to avoid spinal trauma and autofusion of the spinal segments. With less surgical trauma to these young patients, the perioperative psychological burden to both the patient and family can be alleviated.

What are the potential disadvantages?

The current protocol for follow-up of these patients requires monthly radiographs to measure spinal lengthening. To avoid increased radiation exposure, an ongoing study we are currently working on is to replace radiographs with the ultrasound for monitoring spinal lengthening. In addition, the rod construct only allows a total lengthening of 4.8cm and hence a rod exchange is required when the maximum length is obtained. 
Finally, patients cannot undergo MRI examinations due to its effect on the rod internal magnet.

What data are available for these rods?

Preliminary results on these novel growing rods are published in the Lancet in 2012 and in Spine and the Bone and Joint Journal in 2013. Results show that the procedure is safe and it matches, if not exceeds, the traditional growing rod in curve correction and length gain. No major complications were observed and good functional outcomes were obtained. However, it should be emphasised that this is a new implant, and currently the longest published follow-up data in human patients is up to two years. Further longer-term follow-up will be needed to verify the efficacy of these rods.

Which patients in particular could benefit from magnetic growth rods?

Young patients with significant spinal deformities are most indicated for this procedure since interventions are required at an early age and they would benefit from avoiding multiple surgeries.

In the printed issue of Spinal News International (issue 29), “total lengthening of 4.8cm” was incorrectly written as “total lengthening of 48cm”. We apologise for this error.