“THE LAW OF UNINTENDED CONSEQUENCES” IN NEW SPINAL TECHNOLOGY: DOES THE FAILURE OF THE PDN SOLO SUGGEST THE NEED FOR A EUROPEAN EQUIVALENT OF THE FDA?

Abstract

Introduction: Europe has no equivalent of the US Food and Drug Administration (FDA). As a result, spinal implants can be adopted into clinical use in Europe earlier than in the US with a lesser regulatory burden. This may benefit patients, but if a device fails due to design changes that are not fully evaluated, outcomes can be compromised. The classic example in the past was the Capital Hip. If Europe had an equivalent to the FDA, oversight of implant design and design changes might prevent such occurrences.

The Prosthetic Disc Nucleus (PDN) is an implant designed to replace the nucleus of the lumbar disc in early stage symptomatic disc degeneration. The PDN originally was a paired device. Due to technical difficulties encountered by surgeons these were converted to a single implant (PDN Solo range). Mechanical testing suggested the new device would function as well as the original paired device. However, the implant was introduced into clinical practice, outside of the US, without any clinical evaluation.

Study Design: Prospective cohort study with 3 to 5 year clinical and radiological follow-up.

Objective of Study: To review the outcome of PDN Solo implanted anteriorly in the lumbar spine, define the mode of failure and describe revision strategies.

Patients and Methods: PDN Solo was used in 35 patients from September 2002 to January 2005 with a median follow-up of 49 months. Patients with discogenic back pain causing significant disability were offered nucleus replacement after an extensive process of consent. The approach was anterior retroperitoneal with the exception of L5/S1 which was transperitoneal. 17 patients were treated with PDN alone and 18 with a PDN to treat a degenerate level adjacent to an interbody fusion. Outcome measures were the Low Back Outcome Score and a Patient Satisfaction Evaluation.

Results: 14 patients have needed PDN revision. The mean time to failure was 16.5 months. There were three early extrusions, two replaced with PDNs and one converted to a fusion. Revision procedures included seven conversions to STALIF, two circumferential fusions and five posterolateral fusions.

Four more unrevised patients were identified as clinical failures. The total failure rate was therefore 51.4%. In patients with a successful outcome there was a 33 point improvement in the mean LBOS score.

In all cases of failure the PDN jacket became disrupted with concomitant fragmentation of the hydrogel core

Conclusions: Modification of the paired PDN to a single device was introduced outside the US without any clinical evaluation. In the US, the original PDN and the Solo version failed to gain regulatory approval and following the failure of the Solo it has been redesigned again. This study raises questions regarding implant design, testing and approval considering that more than 4500 PDN replacements have been carried out worldwide since 1996. Do these events call for a European equivalent to the FDA?