Maverick total disc replacement in a real-world patient population: a prospective, multicentre, observational study

Since 50 years, a pathologic disc associated with lumbar degenerative disc disease (DDD) that did not respond to conservative care has been preferentially treated by spinal fusion. As an alternative, in 1984, lumbar spinal arthroplasty or disc replacement emerged [1‐4]. Disc replacement can provide pain relief by resecting the diseased intervertebral disc and dynamically stabilising the segment, allowing restoration and maintenance of spine biomechanics. Compared to fusion, this is expected to reduce the incidence of adjacent segment degeneration [5‐7].

The Maverick disc, a two-piece lumbar disc prosthesis, can be implanted at any spinal level from T12/L1 to L5/S1. It has a semi-constrained metal-on-metal design, preserving motion by a ball-and-socket construct with a physiological posterior centre of rotation [8]. A 2-year randomised controlled trial (RCT) demonstrated statistical superiority of Maverick over spinal fusion based on key clinical outcomes, including disability and pain [9].

The optimal patient population for total disc replacement (TDR) is not fully defined [9‐11]. Available information outside a controlled clinical study setting comes from a single national registry [10, 12]. The objective of this first international observational study was to investigate changes in disability and back pain in a broad patient population treated with Maverick TDR in varied surgical practices reflecting different national standards of care.

One hundred thirty-four patients with back pain were implanted with Maverick discs and followed for 2 years with 104 (78 %) evaluable patients remaining at 24 months (Fig. 1). The vast majority of patients complied with in- and exclusion criteria for Maverick disc replacement (Table 2). Because of the observational study design, intended to reflect routine practice, patients with extended indications were included in the analysis. The number of implants per patient, length of surgery, and blood loss observed during the study are described in Table 3. The lumbar spine was approached anteriorly through retroperitoneal exposure for most patients [n = 131; 98.5 %; transperitoneal: n = 2; 1.5 % (approach data are missing for one patient)].

This prospective observational study examined the effectiveness of the Maverick TDR prosthesis under real-life surgical conditions in patients receiving routine standard care for DDD at their respective centres. It is the first international study reporting outcomes of TDR in a wide patient population treated under different national standards of care. To date, limited information derived from a national registry (Switzerland) is available on outcomes following TDR in patients treated outside a controlled clinical study setting [10, 12]. Two publications of TDR based on a national registry have reported reductions in low back pain at a mean follow-up time of 8 months [10] and 1 year [12]. Changes in disability, however, were not measured in these observational study settings.

Despite the uncontrolled nature of current study, the findings are similar to those of previous prospective randomised studies [2, 9, 14]. This registry demonstrated statistically significant improvements in its primary and secondary endpoints—disability (ODI) and back pain (VAS) scores 6 months postoperatively—which were maintained through 12- and 24-month follow-ups. Change in ODI met the criteria for a clinically important difference as defined by the FDA with 75.2 % of patients having ≥15-point improvement at 24 months [8]. In the randomised controlled trial (RCT) comparing Maverick disc implants versus interbody fusion, this was 82.2 % of the patients [9]. Mean low back pain scores observed in both studies underwent significant reductions from pre-operation to 6 and 24 months (registry: P < 0.0001; RCT: P < 0.001), although a direct comparison of the results is not possible because the RCT employed a 0–100 VAS scale and this study used a 0–10 scale [9]. Like the prospective randomised studies, reductions in pain and disability were attained in the first year of this study, and lower values maintained in the second year [2, 9, 14]. Changes from pre-operation to 6 and 24 months in mean ODI and VAS scores observed in this study are also comparable to other prospective studies of Maverick TDR, including the 4-year prospective study [4, 9]. Taken together, these findings suggest that Maverick TDR performed in current, real-life surgical settings can provide similar outcomes to those seen in trials.

The registry population had 64 % of patients that returned to work 2 years postoperatively. In the Maverick RCT, the multi-device RCT and the PRODisc prospective nonrandomised study, the percentages should be 68 %, 74 % and 76 %, respectively [3, 9, 14]. Only 20 % of this registry population ascribed their lack of work to back problems. The work status at 2 years in this registry was equivalent to that observed in the prospective, randomised investigational device exemption (IDE) CHARITE trial: 63 % [2]. Comparisons of work status across studies conducted at different times and in different locations, however, must be tempered by the influence of the current employment rate and local practice recommendation for post-surgical work hiatus, and type of study.

Like the Maverick RCT and the Maverick 4-year prospective study, this registry noted a significant increase in the patient’s quality of life from pre-surgery to 6 months and 2 years post-surgery [4, 9]. A total of 78 % of patients in the Maverick RCT reported that they had either completely recovered or were much improved after 2 years [9] compared with 81 % of reported improvements in this registry. Furthermore, 82 % of patients in this registry compared to 86 % of patients in the PRODisc study [3] and 73 % in the randomised IDE CHARITE trial reported that they would have the treatment again [2].

The incidence of AEs (42 %)—prompting reporting—during the 2-year follow-up in this observational study is lower than the rate observed in the Maverick RCT (>80 %) [9]. Overall complication rates reported in the published literature range from 1 to 40 % [3]. One case of allergic reaction was noted (first symptoms at 1 year) and the prosthesis was explanted. The Maverick RCT also reported one case of metallurgic allergy at 7 months [9]. This rare problem has been previously noted and is due to the creation of ionic species at the metallic articulating surfaces precipitating a cell-mediated hypersensitivity reaction (type IV) [15, 16].

Limitations of this study are related to the nature of multicentre observational non-comparative studies. These include variations in surgical centre standards of care, assessment, follow-up, and lack of a control group. At the same time, this “real-life” setting offers insight into the effectiveness of TDR for treating DDD with high external validity.

In conclusion, this international prospective observational study shows that TDR performed by experienced surgeons, leads to a statistically significant improvement in disability (ODI) and pain (VAS) scores at 6 months, which were maintained for 2 years, providing the first evidence of the effectiveness of TDR in real-world clinical settings across countries and patient populations, with an acceptable rate of perioperative complications. The similarity in outcomes of this registry compared to those from RCTs support the use of registry data for assessing interventions.