A prospective, randomized, multicenter food and drug administration investigational device exemption study of lumbar total disc replacement with the CHARITE™ artificial disc versus lumbar fusion Part II:: Evaluation of radiographic outcomes and correlation of surgical technique accuracy with clinical outcomes

Study Design. A prospective, randomized, multicenter, Food and Drug Administration-regulated, investigational device exemption clinical trial. Objectives. To compare the safety and effectiveness of lumbar total disc replacement (TDR) with the CHARITE (TM) artificial disc ( DePuy Spine, Raynham, MA) to anterior lumbar interbody fusion for the treatment of single-level degenerative disc disease from L4-S1 unresponsive to nonoperative treatment. In addition, to evaluate the radiographic outcomes of lumbar artificial disc replacement at either L4-L5 or L5-S1 with the CHARITE (TM) artificial disc as compared to anterior lumbar interbody fusion with cylindrical cages and iliac crest bone graft; and to determine if a correlation exists between clinical outcomes and surgical accuracy of TDR placement within the disc space. Summary of Background Data. Prior investigators have reported excellent radiographic results with the CHARITE (TM) artificial disc for the treatment of lumbar degenerative disc disease. These encouraging results are the product of retrospective reviews without a control. Very few studies have reported on the segmental motion of an intervertebral level implanted with an artificial disc, and no studies have reported a correlation of radiographic and clinical outcomes. Methods. A prospective, randomized, multicenter, US Food and Drug Administration, investigational device exemption study with 24-month follow-up was performed at 14 centers throughout the United States. A total of 304 subjects were randomized in a 2: 1 ratio, with 205 in the investigational group (TDR with the CHARITE (TM) artificial disc) and 99 in the control group (anterior lumbar interbody fusion with BAK cages and iliac crest bone graft). A total of 71 TDR training cases were performed ( up to 5 at each site) before randomization beginning at each site. Plain radiographs were analyzed for each subject in both groups regarding range of motion ( ROM) in flexion/extension, restoration of disc space height, and subsidence. Prosthesis placement in the coronal and midsagittal planes was analyzed for the 276 patients with TDR. Correlations were performed between prosthesis placement and clinical outcomes. Results. Patients in the investigational group had a 13.6% mean increase, and those in the control group an 82.5% decrease in mean flexion/extension ROM at 24 months postoperatively compared to baseline. Patients in the investigational group had significantly better restoration of disc height than the control group ( P < 0.05). There was significantly less subsidence in the investigational group compared to the control group ( P < 0.05). The surgical technical accuracy of CHARITE (TM) T artificial disc placement was divided into 3 groups: I, ideal ( 83%); II, suboptimal ( 11%); and III, poor ( 6%), and correlated with clinical outcomes. The flexion/extension ROM and prosthesis function improved with the surgical technical accuracy of radiographic placement ( P = 0.003). Conclusions. Preoperative ROM in flexion/extension was restored and maintained in patients receiving a TDR. TDR with the CHARITE (TM) T artificial disc resulted in significantly better restoration of disc space height, and significantly less subsidence than anterior interbody fusion with BAK cages. Clinical outcomes and flexion/extension ROM correlated with surgical technical accuracy of CHARITE (TM) T artificial disc placement. In the majority of cases, placement of the CHARITE (TM) T artificial disc was ideal.