Lumbar Disc ReplacementAcroFlex design and results
Section snippets
Introduction and background
Artificial discs used clinically can be classified under three main groups. First, those that involve nuclear replacement alone are effectively nuclear spacers (eg, the Fernstrom endoprosthesis [1], [2] and the Ray prosthetic disc nucleus (Raymedica Inc., Bloomington, MN) [3]). Second, low-friction arthroplasty perhaps best describes disc replacement devices such as the Charité (DePuy Spine, Raynham, MA) [4], [5], [6], [7], [8], [9], [10] and ProDisc (Synthes, Inc., Paoli, PA) that apply the
Design of pilot studies
The primary objectives of the studies were to evaluate the design, safety and performance of the AcroFlex Lumbar Disc. The secondary objectives were to refine the surgical technique and to assess the effectiveness of disc replacement for patients with symptomatic disc degeneration that is unresponsive to nonsurgical treatment.
Based on the experience gained from the first pilot study that commenced in April 1998, the end plates of the device were changed from flat to contoured, as detailed
Results of pilot studies
A total of 28 patients were entered into the Adelaide pilot studies. Eleven patients (Pilot 1) were treated in 1998–1999 with an AcroFlex prosthesis with flat end plates (Fig. 1); and 17 patients (Pilot 2) received, from February to December 2000, one or two AcroFlex prostheses with contoured end plates (Fig. 2). Table 1, Table 2, Table 3, Table 4, Table 5 detail the data for the two groups separately and in combination.
Overall the sex distribution was equal, the average age was 41 years
Revision surgery
One patient in Pilot 2 underwent revision surgery after her 12-month follow-up. The indication was unremitting severe pain for which a cause could not be found. At the time of surgery the implant was noted to be pristine in appearance with no adverse soft tissue or bony reaction but with no bone ingrowth. After conversion to an interbody fusion supplemented by pedicle screw fixation and posterolateral grafting, there has been little improvement in her condition despite CT evidence of graft
Discussion and future directions
There is a close similarity in the data obtained from Pilot 1 and 2 patients that supports assessing the results of the total population for the purposes of analysis. The modification to the design of the prosthesis used in Pilot 1 achieved its objective of making insertion of the implant easier for the Pilot 2 group. Moreover, radiographic evaluation demonstrated improved contact between the bony and metal end plates in Pilot 2 cases with no cases of implant displacement or subsidence.
Conclusions
- •
The AcroFlex studies have highlighted the potential problem for disc replacement surgery of wear particles leading to osteolysis, and the need for high-resolution thin section CT in the assessment of patients taking part in the various trials of this developing technology.
- •
There was a discrepancy between the life expectancy predicted from mechanical testing of the AcroFlex prosthesis and implant life experienced in vivo that can be explained by a failure of standard testing to measure coupled
References (16)
Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc
Acta Chir Scand
(1966)Fernstrom intervertebral disc arthroplasty: a long-term evaluation
Orthop Int
(1995)The PDN prosthetic disc-nucleus device
Eur Spine J
(2002)- et al.
Experience and results with the SB Charite lumbar intervertebral endoprothesis
A Klin Med
(1988) - et al.
Results of disc prosthesis after a minimum follow-up of 2 years
Spine
(1996) Lumbar disc prosthesis
Eur Spine J
(1993)- et al.
A multicenter retrospective study of the LINK SB Charite intervertebral prosthesis. The initial European experience
Spine
(1994) - et al.
Intervertebral disc prosthesis. Results and prospects for the year 2000
Clin Orthop Rel Res
(1997)
Cited by (62)
Ceramics in total disc replacements: A scoping review
2022, Clinical BiomechanicsAnalytical and finite element analysis of shape memory polymer for use in lumbar total disc replacement
2021, Journal of the Mechanical Behavior of Biomedical MaterialsViscoelastic cervical total disc replacement devices: Design concepts
2020, Spine JournalICR in human cadaveric specimens: An essential parameter to consider in a new lumbar disc prosthesis design
2020, North American Spine Society JournalNumerical simulation and experimental tests on a lumbar disc prosthesis
2019, Materials Today: ProceedingsDesign of a new intervertebral disc prosthesis
2019, Materials Today: Proceedings
FDA device/drug status: investigational/not approved (AcroFlex artificial disc [lumbar]).
Support in whole or in part was received from DePuy Acromed, a commercial entity. Author RDF acknowledges a financial relationship (consultant for DePuy Acromed), which may indirectly relate to the subject of this manuscript.