394 patients undergoing total disc replacement were randomized to receive either the Kineflex-L or Charite artificial lumbar disc in order to determine if there were any differences in outcomes attained by either device. Patients were followed-up for 5 years assessing clinical outcomes, disability, pain, and rate of re-operation or revision surgery. Also, a subsample of patients were analyzed for safety considerations associated with metal ion release with the use of a Kineflex-L (a metal-on-metal implant). The results indicated that significant improvement in clinical outcomes was attained by both devices, with no significant difference between groups, and that the percentage of patients requiring re-operation or revision surgery was similar between groups. Serum metal ion levels in the Kineflex-L group did not warrant any safety considerations.