Prospective, Randomized Trial of Metal-on-Metal Artificial Lumbar Disc Replacement

In Brief Study Design. This study presents data on 67 patients from 2 study sites involved in the multicenter, prospective, randomized, controlled investigational device exemption study of FlexiCore artificial disc replacement versus fusion with a 2-year follow-up. Objective. To compare the outcomes achieved with the FlexiCore disc replacement versus standard circumferential fusion for the treatment of discogenic pain due to single level degenerative disc disease (DDD). Summary of Background Data. The FlexiCore Intervertebral Disc (Stryker Spine, Allendale, NJ) is a metal-on-metal artificial lumbar disc replacement device currently being studied for the treatment of DDD under an investigational device exemption protocol approved by the United States Food and Drug Administration. Artificial disc replacement in the spine is designed to preserve motion at the intervertebral segment and subsequently reduce adjacent segment degeneration. This is the first study to compare a metal-on-metal artificial lumbar disc replacement with circumferential fusion. Here we report the 2-year follow-up results. Methods. Forty-four patients were treated with the FlexiCore and 23 patients were treated with fusion. The FlexiCore treatment group consisted of 23 men and 21 women, with an average age of 36 and an average body mass index of 28. Thirty-two of the FlexiCore surgeries were performed at L5–S1, and 12 were performed at L4–L5. The control treatment group consisted of 10 men and 13 women, with an average age of 41 and an average body mass index of 28. Seventeen of the control surgeries were performed at L5–S1, 5 were performed at L4–L5, and 1 was a 2-level fusion performed at L4–L5 and L5–S1. Prospective data were collected before surgery and after surgery at 6 weeks, and at 3, 6, 12, and 24 months. Disability and pain were assessed using the Oswestry Disability Index and the Visual Analog Scale. Range of motion was determined by independent radiologic assessment of flexion/extension and lateral bending radiographs. Results. The mean Oswestry Disability Index scores were 62 (FlexiCore) and 58 (control) before surgery, 36 (FlexiCore) and 50 (control) at 6 weeks, and 6 (FlexiCore) and 12 (control) at 2 years. The mean Visual Analog Scale scores were 86 (FlexiCore) and 82 (control) before surgery, 32 (FlexiCore) and 43 (control) at 6 weeks, and 16 (FlexiCore) and 20 (control) at 2 years. The FlexiCore group's angular rotation averaged 2.8° before surgery and 3.8° at 6 weeks after surgery. The group's lateral bending averaged 4.7° before surgery and 4.2° at 6 weeks after surgery. The average operative time (skin to skin) was 82 minutes for the FlexiCore group versus 179 minutes for the control group (P < 0.001). The average estimated blood loss was 97 mL for the FlexiCore group versus 179 mL for the control group (P < 0.02). The average hospital stay was 2 days for the FlexiCore group versus 3 days for the control group (P < 0.005). Conclusion. These initial results from 2 study sites demonstrate that the FlexiCore compares very favorably to circumferential fusion for the treatment of lumbar DDD unresponsive to conservative treatment. These results are not intended to represent the overall study results. This study represents the first randomized, prospective trial to date of a metal-on-metal artificial lumbar disc replacement for single level degenerative disc disease. Outcome measures suggest comparable results when analyzed against a fusion group, with the theoretical benefit of prevention of adjacent segment degeneration.