P Goru and S Ahuja investigate the use of growing rods in children with the spinal deformity

E arly-onset scoliosis presents at birth and up to seven years of age. Growing rods are a treatment option for when this condition cannot be controlled by braces or serial casts. The function of growing rods is to allow a child’s spine to grow under controlled conditions and maintain straightening of the curve until definitive correction, which usually is after the age of 11-13 years (Campbell 2003). Early-onset scoliosis with progressive curves may require surgical intervention. The goals of surgery in this age group include scoliosis correction, maintenance of spinal growth along with expansion of the thorax, assisting in lung maturation (Akbarnia 2005). Fusion procedures in this age group adversely affect spinal growth and pulmonary alveolar development, leading
to development of possible thoracic insufficiency (Karol 2008).

Spinal bracing and spinal fusion, which uses screws and rods combined with bone grafts, have been advocated for treatment of scoliosis (McMaster 1979, Robinson 1996, Mehta 2005, Sponseller 2009); however, both procedures have substantial disadvantages. Bracing can be cumbersome in young children and may not work especially in those with congenital or neuromuscular scoliosis. Moreover, spinal fusion surgery in young children will prevent normal spine growth.

Procedures that allow or encourage growth of the spine and chest have recently gained popularity. These are variously referred to as ’growth sparing’ or ’growth friendly’ (Sankar 2010). To address the limitations of spinal bracing and fusion for severe scoliosis in young children, a distractible spinal implant (i.e. an implant that can be lengthened) known as a growing rod was developed (Akbarnia 2005, Akbarnia 2008, Winter 1984). Under general anaesthesia, the traditional growing rod is implanted across the segment of spinal curvature, without the need for spinal fusion. Distraction of traditional growing rods is required at six monthly intervals usually under a short general anaesthetic. The distraction helps to mimic and maintain normal spine growth.

This approach can effectively control the progression of spinal curvatures and gradually straighten the spine (Akbarnia 2005, Akbarnia 2008, Winter 1984, Elsebai 2008, Sponseller 2007, Thompson 2005, Thompson 2007). However, limitations of this method include the need for general anaesthesia and the invasiveness of repeated distractions during surgery, and the associated anaesthetic and wound complications. Implants have been associated with high rates of wound infections, rod breakage, auto fusion, anchor failure or prominence of the implant (Farooq 2010). Furthermore, traditional growing rod surgery is associated with various socioeconomic drawbacks. For instance, children miss school time, and parents might have to take time off work to support their child (Caldas 2004, Kain 1996, Kain 1999). The costs associated with repeated operations create a substantial burden on healthcare. Additionally, repeated operations and time in hospital might affect patients’ activity levels, social interactions, and psychological wellbeing (Caldas 2004, Kain 1996, Kain 1999).

Thus, a more advanced and less invasive method is needed that will ease distraction of rods and overcome these drawbacks. A remotely distractible, magnetically controlled growing rod (MCGR) system has been developed (MAGEC System, Ellipse Technology Ltd.) that allows frequent non-invasive outpatient distractions. This technology has been validated in animals (Akbarnia 2009, Akbarnia 2011). Recently some of the centres in the UK started using these rods (Dannawi 2013).

The magnetically controlled growth rod (MCGR) consisted of a single-use sterile titanium spinal distractible rod, with an enlarged mid-portion containing a magnetically drivable lengthening mechanism. The choice of implantation of either a single or a dual rod is dependent on the patient’s size and the surgeon’s preference. The size of the rod can be customised according to the patient’s height. For insertion of the MCGR under general anaesthesia, patients are positioned prone. It can be done with one small incision close to the two most cranial vertebral levels for the proximal fusion segment and another incision close to the two most caudal vertebral levels for the distal fusion segment. Intra-operative radiographs are useful to establish where to make the incision, and then dissect the spine and implant fixation anchors, such as pedicle screws, before passing the rods sub-fascially to the distal fusion block for connection. Both cephalad and caudal anchor areas should be fused with local bone graft and/or graft substitutes.

After surgery, patients are followed-up in-clinic at approximately six weeks. In general, patients’ spines will be distracted between 1.5 and 2.0 mm per visit. We should aim to distract the spine more quickly than the predicted spinal growth rate to allow for better curvature correction. During outpatient distraction visits, patients were positioned prone. A hand-held magnetic external remote controller (ERC) is placed over the internal magnet. The magnets are identified using a metal device to localise the positions of the magnets and the ERC is placed on the skin to apply the magnetic field. Once the magnetic field is applied the rotating mechanism within the rod causes the rod to lengthen, thus distracting the spine. The predicted lengthening is displayed on the external distraction device. The device can also be used to retract the rod if the patient has discomfort or pain. The procedure itself lasts less than 30 seconds. Pre-distraction
and post-distraction plain radiographic imaging posteroanterior and lateral views of the whole spine may be required to assess the degree of scoliosis and kyphosis (T1–T12), the predicted versus achieved rod distraction length, and spinal length. The degree of spinal curvature is assessed by calculating Cobb angles (Cobb 1960).

Treatment of scoliosis in growing children is a challenge for both surgeons and families. It is a long-term commitment for both parties, and surgeons have to carefully select patients in whom there is a likelihood of success. Families should be aware of the commitment needed for this treatment, the potential risks and benefits, and the possible complications.
Yet, the method is much less traumatic for young patients than the traditional growing rod procedure because they do not have to bear the peri-operative psychological burden or the pain associated with repeated operations.
The economic viability of any innovative treatment option should be addressed. The health-care costs of MCGRs are substantially lower than with traditional growing rod technology: although these rods cost more than their older counterparts, the conventional procedure is associated with further costs due to frequent operations, use of general anaesthesia, hospital stays, drug use, manpower, consumables, and time off work for the parents.

The main limitation of the MCGR procedure is potentially increased radiation exposure from frequent radiographs. This drawback will probably disappear when the relation between predicted and actual rod distraction lengths is better understood, once more patients have been followed-up. Then, repeated radiographs before and after each distraction would not be necessary to verify the length of obtained rod distraction. Ideally, routine radiographs only need to be taken every six months to document truncal growth and alignment change, as is the case with traditional growing rods.

Whether MCGR leads to significantly better outcomes than traditional growing rods is not yet known, but early results of some of the studies are positive and the avoidance of open distractions is a great improvement. In view of the advantages of the MCGR distraction system for correction of spinal curvatures, such technology has potential widespread applications in medicine. For example, MCGR could assist with correction of limb abnormalities, thoracic insufficiency syndrome, limb lengthening, limb salvage procedures, or any disorders or injuries in which slow, progressive changes to bone structures is needed.

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