Five RCTs (n=837 participants) were included in the review. Sample sizes ranged from 67 to 304 patients. Follow-up ranged from one to five years. Quality scores ranged from 44 to 69 and four of the five studies were judged to be good quality.
After two years follow-up, patients in the total disc replacement group had statistically significant improved functioning using the Oswestry scale (MD -4.06, 95% CI -7.28 to -0.84, I2=0%; four RCTs) and less back or leg pain using a visual analog scale (MD -4.75, 95% CI -9.14 to -0.35, I2=0%; four RCTs). These differences were not judged to be clinically significant.
In comparison with fusion, total disc replacement patients were judged to have significantly increased patient satisfaction (SMD 0.29, 95% CI 0.05 to 0.53, I2=37%; three RCTs). More total disc replacement patients were willing to undergo the same operation again (OR 2.86, 95% CI 1.41 to 5.77, I2=64%; three RCTs). There were no significant differences between total disc replacement and control groups with respect to complications (three RCTs, I2=0%), patients who returned to full-time/part-time work (three RCTs, I2=29%) and reoperation rate (three RCTs, I2=0%).
After follow-up, there were no significant differences between the two treatment groups with respect to any of the outcomes. Sensitivity analyses showed that some outcomes were highly influenced by one study with BAK cage interbody fusion. When this study was excluded from the two-year analyses, the differences that favoured total disc replacement in terms of functioning, pain and patient satisfaction status were no longer significantly different between the two groups.