Background context: Although total disc replacements have been performed in Europe since the 1980s, this type of surgery is still new in the United States. The clinical performance of polyethylene in total disc replacements is still not well understood.
Purpose: To describe the wear, surface damage, oxidation and mechanical properties in an explanted polyethylene total disc replacement component.
Study design/setting: Case report, analysis of retrieved implant.
Patient sample: Case report.
Outcome measures: Analysis of wear, oxidation and mechanical properties in the retrieved total disc replacement.
Methods: A 49-year-old female patient was implanted at L5-S1 with an SB Charite total disc prosthesis (DePuy Spine, Raynham, MA). After 1.6 years, the patient underwent a posterior, instrumented fusion because of intractable low back, left buttock and radicular left leg pain. Preoperative diagnostics revealed loosening at the bone implant interface at L5 and S1, anterior migration of the L5 base plate and severe degeneration of the L5-S1 facet joints. The retrieved polyethylene core showed evidence of damage around the periphery or rim. Transverse, subsurface cracks in the polyethylene, which initiated near the rim and penetrated into the interior of the component, were imaged using thin-film optical microscopy and micro-computed-tomography imaging. Analysis using Fourier transform infrared spectroscopy (American Society for Testing and Materials [ASTM] F2102) documented low levels of oxidation within 1 mm of the articulating surface. Miniature specimen mechanical testing (ASTM F2183), conducted near the surface where the oxidation was greatest, demonstrated that the mechanical properties were not substantially degraded.
Conclusion: In this case, the anterior revision surgery was difficult and potentially life-threatening. The revision strategy of an instrumented posterior fusion to salvage a failed SB Charite disc replacement may be unpredictable and, in this case, ultimately unsuccessful. Despite the small size of the retrieved polyethylene core, ASTM standard test techniques developed for analysis of retrieved hip and knee replacements were readily adapted for the total disc prosthesis.