**2. Materials and methods**

A search was conducted on the OVID and COCHRANE Library database to collect all clinical data relevant to spinal arthroplasty. Specifically, the following keywords were used:

Lumbar Spinal Arthroplasty: Clinical Experience 517

improvement of 14%. Implant removal was also described in 12 patients10. These relatively poor findings were further discussed in two Letters to the Editors, which pointed out mathematical inconsistencies and overall clinical flaws in the manuscript, and further highlighted the need of proper surgical technique and patient selection for optimal

The ProDisc-L manuscripts described clinical outcomes as early as 3 months13 and up to 8.7 years post-operative 14. As described above for CHARITÉ Artificial Disc, The shortterm papers typically disclosed early findings from one or two of the sites that participated in the randomized controlled trial comparing ProDisc-L against a 360 degree fusion13, 15-21. The complete RCT at 2-year follow-up included 161 arthroplasty and 75 fusion patients 2. The long-term data included 64 patients operated at one site, of which 55 were available between 7 and 11 years post-operative, for clinical and radiographic follow-up14. All these studies concluded similarly that disc arthroplasty, at all evaluated time points, was safe and resulted in complication and/or re-operation rates comparable to those generally accepted for spinal surgery (complication rate of 9% at 8.7 years14; there were no major complications, but a reoperation rate of 3.7% at 2 years was reported2). In addition to safety, efficacy of spinal arthroplasty was also shown herein as all cases presented significant improvements in pain and disability. The final RCT data reported improvements in the arthroplasty group in Visual Analogue Scores (VAS) for pain by an average 39-mm, and in disability, as determined by the Oswestry Disability Index (ODI), by 28 points. It is worth noting, however, that the ODI tool utilized in this RCT was not the validated and widely accepted ODI methodology Version 1.0 as defined by Fairbanks et al22. In a Letter to the Editor, Fairbanks denounced the use of the so-called Oswestry Disability Index in the ProDisc-L study and thus cast doubt on the validity of the

The 2 clinical data publications on the MAVERICK device were both based on the same data set of 64 patients, collected at one site24, 25. The clinical outcomes were described using the ODI Version 1.0 and VAS scores. The efficacy of arthroplasty was once again demonstrated using these tools, as ODI scores decreased by an average of 20.7 points and VAS scores by 4.4 points. As for the FlexiCore Intervertebral Disc, only one paper was recently published26. This manuscript describes the clinical outcomes of 44 patients, of which only 6 were available for 2-year follow-up. While the clinical relevance of this data may therefore be questionable, authors still concluded that the device may be safe and efficacious but that the

**3.2 Radiographic analyses: Range of motion, heterotopic ossification and sagittal** 

Radiographic evaluations such as ROM, heterotopic ossification, and sagittal balance have been broadly analyzed for the CHARITÉ Artificial Disc, the ProDisc-L, as well as the

Unlike other clinical and radiographic outcomes, accurate measurement of ROM was shown to be challenging and, to some extent, subjective, as patient positioning, imaging staff training, and other factors unrelated to the actual motion potential of the spine were shown to impact final readings 27. Using ProDisc-L cases, Lim et al evaluated different methodologies and associated error margins for the measurement of ROM from

clinical outcome 11, 12.

disability improvement outcomes observed herein23.

data was not representative of the entire patient cohort.

Maverick Total Disc Arthroplasty System.

**balance analyses** 

(CHARITÉ Artificial Disc or ProDisc-L or Maverick Total Disc Arthroplasty System or KineFlex or FlexiCore Intervertebral Disc) and (disc) and (lumbar). The search was limited to English-language papers. Preclinical, biomechanical, and review papers were excluded from the final paper selection. In addition, papers describing obsolete devices (CHARITÉ I and CHARITÉ II) were also excluded from the study. A total of 60 papers were analyzed herein and subdivided by key topic, as following: 1) General clinical outcomes; 2) Radiographic Analysis: Range of motion, heterotopic ossification and sagittal balance analyses; 3) facet and adjacent-level degeneration; 4) Revisions and revision strategies; 5) Surgical technique; 6) Complications; 7) Special patient population analyses; and 8) Health economics evaluations.
