Editorial: Disc replacement or arthrodesis

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In this issue of the Journal of Neurosurgery: Spine, Zigler and Delamarter2 provided 5-year follow-up data from a randomized clinical trial comparing lumbar total disc replacement ([TDR], ProDisc-L, Synthes Spine, Inc.) versus circumferential fusion (anterior lumbar interbody fusion using femoral ring allograft with subsequent posterolateral fusion using pedicle screws). The original cohort consisted of 161 patients who underwent lumbar TDR and 75 patients who underwent circumferential fusion. The authors reported an overall 81.8% clinical follow-up rate at 5 years. The fusion group had a 74.7% clinical follow-up rate, and the arthroplasty group had an 85.1% clinical follow-up rate. However, only 72.9% of the patients had complete radiographic follow-up. Clinical outcomes as measured by the Oswestry Disability Index, visual analog scale, 36-Item Short Form Health Survey, and neurological success were maintained in both the TDR and fusion groups at 5 years, and improvements in the investigated clinical outcomes were not statistically different between the groups. The mean flexion and extension range of motion (ROM) in the TDR group remained roughly constant between the 2and 5-year time points (7.7° ± 4.7° at 2 years and 7.2° ± 4.1o at 5 years). In this report, 91.9% of the TDR patients had preserved a normal segmental ROM at 5 years. There were no spontaneous fusions in the TDR group. However, it is important to note that approximately one-quarter of the original cohort did not have complete radiographic follow-up. Moreover, the rates of heterotopic ossification in the TDR group were not reported in this paper. Heterotopic ossification (HO) around the TDR has been described in other FDA clinical trials and has been shown to limit the ROM of an arthroplasty. Guyer et al.1 reported that 18.9% of lumbar TDR cases utilizing the Charite disc (DePuy Spine, Inc.) showed lack of motion ( 3 at the 5-year follow-up. Heterotopic ossification is an issue that spine surgeons will need to monitor in patients undergoing lumbar arthroplasty, and an analysis of the HO rate with the ProDisc-L is still needed. Another important issue regarding the long-term results of lumbar arthroplasty is device-related failure, which can be assessed using both the radiographic results and index-level secondary surgeries. In this report, 3 of the TDR patients had device migration, all cases occurring within 3 months. There were 2 TDR patients who had device subsidence. For the fusion group, the fusion rate was 95.8% at 5 years, with no cases of migration or subsidence. There were 13 TDR patients (8%) and 9 fusion patients (12%) who underwent a second surgery at the index level during the 5-year follow-up. Of the 13 secondary index-level surgeries in the TDR group, there were 2 cases of polyethylene migration due to “extreme trauma,” 3 additional cases of device failure due to problems with the surgical technique, and 8 cases of unresolved pain requiring supplemental fixation or decompression. The noninferiority of lumbar TDR as compared with a traditional open circumferential fusion procedure is established by this 5-year report. The advantage of motion preservation with lumbar TDR and its effects on adjacent-level degeneration are still unclear. For patients with lumbar degenerative disc disease, both fusion and arthroplasty appear to be viable choices. (http://thejns.org/doi/abs/10.3171/2012.8.SPINE12708)