Elsevier

The Spine Journal

Volume 7, Issue 1, January–February 2007, Pages 12-21
The Spine Journal

Clinical Study
Polyethylene wear and rim fracture in total disc arthroplasty

https://doi.org/10.1016/j.spinee.2006.05.012Get rights and content

Abstract

Background context

Polyethylene (PE) has been used in total disc replacements (TDRs) in Europe since the 1980s. However, the extent of surface damage of PE, including rim fracture and wear, after long-term implantation remains poorly understood.

Purpose

The purpose of this study was to evaluate the magnitude and rate of PE wear and surface damage in TDRs.

Study design

TDR components were retrieved from patients undergoing revision TDR surgery and conversion to fusion.

Patient sample

Twenty-one implants (SB Charité III; DePuy Spine, Raynham, MA) were analyzed from 18 patients (12 female, 6 male) undergoing TDR revision surgery. The components were implanted between 1.8 and 16.0 years (average: 7.8 years) at L2–L3 (n=1), L3–L4 (n=1), L4–L5 (n=11), and L5–S1 (n=8). They were removed due to pain (in all cases) and were associated with subsidence (n=6), anterior migration (n=2), core dislocation (n=2), lateral subluxation (n=1), wear with wire marker fracture (n=1), end plate loosening (n=2), and osteolysis (n=1).

Outcome measures

Clinical information was collected from medical records and radiographs. Retrieval analysis included dimensional measurements and assessment of the extent and severity of PE surface damage mechanisms.

Methods

MicroCT scanning was used to identify the presence of internal cracks in the PE core and to scan the geometry of the retrievals. Light microscopy, coupled with white light interferometry, was used to evaluate the surface damage mechanisms at the dome and rim.

Results

The dominant wear mechanism was adhesive/abrasive wear at both the dome and rim. End plate penetration (dome wear) ranged from 0.1 to 0.9 mm (average: 0.3 mm), and was correlated with implantation time (Spearman's rho=0.48, p=.03). There was also evidence of macroscopic rim damage, including radial and transverse cracking, fracture, plastic deformation, and third-body damage. End plate penetration measured at the rims ranged from 0.02 to 0.8 mm (average: 0.3 mm). Cracks in the core were oriented transversely in 11 of 21 implants (52%), and radially around the rim in 11 of 21 implants (52%). Radiographic wire marker fracture, observed in 9 of 21 implants (43%), was always associated with deformation, cracking, or fracture of the PE rim. In two cases, a fractured wire marker became lodged in the articulating surface between the PE and the metallic end plate.

Conclusions

This is the first study to quantitatively analyze the long-term PE damage mechanisms in contemporary TDRs. The TDRs displayed surface damage observed previously in both hip and knee replacements. Because of the evidence of increasing wear with implantation time, along with the demonstrated potential for osteolysis in the spine, regular long-term follow-up for patients undergoing TDRs is warranted.

Introduction

The origins of disc arthroplasty as an alternative to fusion can be traced back to the 1960s, when Fernström described the first intervertebral prosthesis to relieve pain and restore motion of a diseased functional spinal unit as a potential alternative to fusion [1]. However, it was not until the 1980s that disc replacements began to adopt the bearing and fixation technologies that had been successfully established in total hip and knee replacements. One such design, the SB Charité III (DePuy Spine, Raynham, Massachusetts), consists of metallic (CoCr) alloy end plates, articulating against a central core of ultra-high-molecular-weight polyethylene (hereafter, polyethylene) [2]. Articulation between metallic and polyethylene components has been the cornerstone of hip replacements since 1962 [3], and remains the standard of care in total joint procedures even today [4].

Despite the established track record of polyethylene as a highly successful biomaterial, wear and surface damage are well recognized to potentially limit the longevity of orthopedic implants [4], [5]. Specifically, particulate wear debris can stimulate an inflammatory response, resulting in osteolysis and late loosening of a hip or knee prosthesis [5]. By contrast, the clinical relevance of polyethylene wear in the lumbar spine remains poorly understood. Proponents of artificial discs have theorized that, because the relative motions of the implant components were much lower than in hip or knee replacements, and because the intradiscal space was not a synovial joint, polyethylene wear debris would likely not be clinically significant for the lumbar spine [6]. However, recent case studies documenting wear, osteolysis, and other implant-related complications suggest that polyethylene damage may be a potential clinically relevant failure mode for lumbar artificial disc replacements [7], [8], [9], [10], [11].

The negative clinical consequences associated with the polyethylene wear have been well documented from the study of retrieved hip and knee implants [4]. In contrast, with the exception of previous individual case studies [7], [8], the detailed analysis of retrieved total disc replacements (TDRs) remains largely unexplored. As a result, many questions surrounding the wear and damage mechanisms of polyethylene TDRs remain unknown. The current lack of fundamental, mechanistic knowledge surrounding the clinical performance of polyethylene in the spine is particularly troubling, in light of the life-threatening risks that a patient may incur during TDR revision surgery [9], [10].

In collaboration with clinical partners, in 2004, we established a repository of retrieved TDRs to better understand implant wear and its relationship to clinical performance in the spine. Our total disc repository includes implants of a variety of designs and manufacturers, and is open to collaboration with orthopedic and spine surgeons from around the world. An institutional review board approved the retrieval collection, storage, and handling protocols for our repository.

In this international multicenter retrieval study, we performed detailed analyses of explanted polyethylene TDRs to quantify the wear and mechanisms of surface damage. We also sought to compare the wear mechanisms in polyethylene TDR components with those previously observed in hip and knee replacements. In this research, we addressed the following questions: 1) Are the wear and fracture mechanisms in polyethylene TDR components similar to those from hip and knee arthroplasty? 2) What is the magnitude and rate at which polyethylene wear of TDRs occurs in vivo?

Section snippets

Methods and materials

Twenty-one implants were analyzed from 18 patients (12 female, 6 male) undergoing TDR revision surgery. The average patient age at the time of implantation was 39 years (range: 22 to 49 years). The artificial discs were all of the SB III Charité design, which was commercially introduced to Europe outside of the Charité Hospital in Berlin starting in 1989 [2]. Nineteen of 21 revisions were performed in the Netherlands, and one implant was retrieved in England and the United States, respectively.

Results

Microscopic, multidirectional scratching was observed on the central bearing surfaces of all polyethylene cores, consistent with an adhesive/abrasive wear mechanism. There was also evidence of macroscopic rim damage, including radial cracking (Fig. 2), transverse cracking (Fig. 1, Fig. 3), burnishing, plastic deformation, and third-body damage. The wear and surface damage assessments for the 21 retrievals are summarized in Table 2.

A broad spectrum of fatigue and fracture modes was manifested in

Discussion

The retrieved polyethylene implants in this study exhibited wear and damage mechanisms previously observed in both hip and knee replacements. In the central, dome region of the implants, microscopic multidirectional scratches were consistent with the crossing-shear wear patterns characteristic of hip replacements [12], [13]. Like hip replacements, the dome penetration was found to increase with implantation time. The rate of head penetration in hip replacements generally decreases with

Conclusions

We quantitatively analyzed the long-term polyethylene failure mechanisms of 21 polyethylene TDR components implanted for up to 16 years. The observations in this study supported the following principal findings:

  • Measurable wear was detected in all of the retrieved polyethylene total disc replacement components in this study.

  • The TDRs displayed surface damage observed previously in both hip and knee replacements. In the center of the core, the adhesive/abrasive wear mechanisms were similar to hip

References (26)

  • A. van Ooij et al.

    Complications of artificial disc replacement: a report of 27 patients with the SB Charite disc

    J Spinal Disord Tech

    (2003)
  • van Ooij A, van Rhijn L. Complications of the Charité disc prosthesis in 55 patients and retrieval in 6 patients. Paper...
  • Thorpe PLPJ, Licina P. Osteolysis and complications associated with artificial disc replacement. Poster 21, presented...
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    FDA device/drug status: approved for this indication (SB Charité III).

    The establishment of the total disc replacement repository and this study were supported by a research grant from Medtronic Sofamor Danek.

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