Lumbar total disc replacement: it still needs further follow-up?
In a recent article in Spine, Guyer et al. report on the results of 5-year follow-up of a prospective, randomized trial comparing two kinds of lumbar total disc replacement (TDR): Charite [metal-on-polyethylene (MoP) TDR, the control] vs. Kineflex-L [metal-on-metal (MoM) TDR, the investigational]. To the best of my knowledge, such clinical comparison studies between two different artificial discs in the lumbar spine are few. The present study might be one of TDR clinical trials, which have been carried out during last more than15 years in the U.S. These trials serially report comparison results between an investigational prosthesis and the control at certain time periods of follow-up. The authors had already published 2-year follow-up results of the comparison study with the identical implants and in the identical specimen as an early outcome with those of the present study (1). The current 5-year follow-up study demonstrated similar overall results with 2-year follow-up. Also the clinical and radiological results of the investigational implant appeared to be similar to the ones of the control. Furthermore, this investigational implant has an evidence of much lower serum ion level than a proposed threshold and possibly merits of small ball radii. These results may herald a validity of clinical application of the investigational MoM TDR. In consideration of the U.S. experience with another MoM TDR, Maverick, it is of slight concern how this MoM prosthesis would go through with the uncertainty and apprehension about MoM, particularly its metallic wear.