Elsevier

The Spine Journal

Volume 4, Issue 6, Supplement, November–December 2004, Pages S245-S251
The Spine Journal

Lumbar Disc Replacement
AcroFlex design and results

https://doi.org/10.1016/j.spinee.2004.07.020Get rights and content

Abstract

The AcroFlex prosthesis is unique when compared to other current devices, as it has an elastomeric core sandwiched between two titanium endplates. The purpose of this design was to optimize shock absorption qualities. This paper reviews the design of the AcroFlex Disc and relevant design and outcomes of two pilot studies carried out on 28 patients using the AcroFlex prosthesis. Although clinical outcomes of the pilot studies were successful, the pivotal randomized trial has not been carried out due to detection of mechanical failure of the elastomer on thin cut CT scans. The implications of this for the AcroFlex and other arthroplasties are discussed.

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

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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.

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