Reply

Abstract

At the outset the authors wish to thank the reader for the keen interest shown in the article and for his compliments. The points raised by the reader are well taken, however at the same time we wish to clarify the issues. As the reader has already clarified Bryan's cervical disc prosthesis is in use in Europe, Australia, South Africa for the last six years and more than 8500 implantations have been done worldwide including USA. This device has been used in the Armed Forces for first time in India as a research project, however civil neurosurgery centres at Delhi and Bangalore are using this device regularly. Wear related characteristics are a primary concern in any artificial joint replacement surgery. Wear is the physical process of material removal that results from relative motion across any two interfacing surfaces. In diarthrodial joints like hip and knee joint arthroplasty wear debris-induced osteolysis is the most common mechanism of failure. However, cervical intervertebral discs are not diarthrodial joints and should not be compared with hip and knee joints. Analysis of simulator derived data and explanted Bryan's disc revealed that this prosthesis is wear resistant and durable [1]. However patients are on regular follow up especially considering the proximity of prosthesis to visceral, vascular and neural structures. Bryan's cervical disc replacement is recommended only in younger patients with cervical disc prolapse to maintain full cervical motion. It is not recommended for elderly patients with advanced spondylotic changes with osteophytes, severe cervical canal stenosis and osteoarthropathy of facet joints, as in such cases the prosthesis is bound to give poor results. The patients were explained the investigational nature of the device prior to surgery and there are no failure in these patients during four years follow up. The early results are not only satisfactory but encouraging as the device is both anatomical and physiological and preserves neck motion. Long term study will be required to find out protection of adjacent level disc degeneration as brought out in our discussion. At present only the Bryan's cervical disc prosthesis is available in India. Bristol, Pro Disc-C, Cervicore and Flexicore artificial cervical discs are not available in India presently. The results of implantation of such device are not known at present. The reader has quoted functional spinal unit angulation from a single study with 10 cases. Post operative functional spinal unit angulation leading to kyphosis has not been observed in our study during post operative and follow up period. This is possible if the Milling jig is not properly fitted, and improper size prosthesis is used. Neurosurgeons conversant in using Bryan's discectomy apparatus should attempt Bryan's cervical disc replacement as the procedure is technically demanding. As the saying goes “a fool with a tool remains a fool”. Post operative MRI study has been done in few of our cases and the prosthesis is MRI compatible.