New technologies: Should we embrace them so fast?

Abstract

Dear Editor, This is with reference to the original article titled “Cervical Disc Replacement for Spondylotic Myeloradiculopathy” (MJAFI 2006; 62: 112-5). The authors need to be complimented on this study of cutting edge technology as a new novel treatment option for the relief of spondylotic myeloradiculopathy patients. These are definitely exciting times for patients as well as surgeons in the management of cervical disc disease. Just as hip and knee replacements are gradually becoming a part of routine practice, it may be envisioned that replacement of cervical discs will soon become a widely available procedure. However, before undertaking cervical disc implantation, the surgeons and the patients must understand the current investigational nature of these devices. Though Bryan's cervical disc has been licensed for usage in Australia, Europe and South Africa, it is currently approved only as an investigational device by FDA in USA. The approved/licensed clinical usage status for the device in India by health authorities has not been brought out by the authors. The main issue with the artificial discs is that we do not know their life span. Knee and hip joint replacements usually wear out in 12-15 years (though survival of more than 25 years have been reported which is an exception rather than the rule). As the biomaterials (especially the alloys and the porous coatings on the external surface) used in cervical disc arthroplasty are similar to the ones used in hip and knee arthroplasty, the failure mechanisms are likely to be similar. Generation of wear debris is the primary source of implant degradation and the subsequent tissue reaction to such debris is the primary factor limiting the longevity of the implant [1]. This reaction usually results in progressive localised bone loss which threatens the fixation of the devices. Though the short term studies and in-vitro studies for cervical disc replacement have been encouraging, absence of long term data remains an important issue (lessons learnt from problems posed by hip and knee arthroplasty materials would be ignored at our own peril). It would definitely be naive to expect any exceptionally long survival rates of this device. These facts become very significant in this series as the majority of the patients were made aware of the absence of long term data related to this investigational device as well as its unknown failure modes and they accepted the risks of such a procedure. Though early results have been satisfactory, the basic premise that motion preservation at affected level will diminish adjacent segment degeneration remains unproven in any long term study [2]. In addition, new studies are gradually bringing out limitations of the present cervical disc implants. Bryan disc arthroplasty has been demonstrated to have a propensity towards kyphotic orientation (? Result of intra-operative lordotic distraction). Post-operative functional spinal unit (FSU) angulation tends towards kyphosis and FSU height is reduced due to lack of anterior column support [3]. The present generation disc implants leave some artefacts in magnetic resonanceimaging (MRI) post-operative MRI compatibility needs further improvement for a better follow-up. However, plain scepticism must not hold us back from new technologies. Like development of total hip and knee replacement implants over the last three decades, we are now seeing the first generation devices in cervical disc replacement like Bryan's disc and Bristol disc described by the authors. ProDisc-C has also been made available commercially in some countries. While the early results have been encouraging, the true test comes only when the long term follow up data is available. To conclude, while embracing the technological revolution, we must always consider the Hippocratic injunction – “First, do no harm”.