Results from a randomized controlled study between total disc replacement and fusion compared with results from a spine register

Data from our register showed results similar to the RCT, but a register cannot fully replace an RCT study when evaluating a new treatment option if the RCT has narrower selection than just the diagnosis. In this RCT comparing TDR with posterior fusion, the normal exclusion criteria for TDR were used. These were not registered, so the register could not prevent a possible selection bias, which might also be caused by the nonresponders.