IMPLANT RETRIEVAL AND ITS MEDICAL INTEREST

The primary objective of investigations that emphasize explanted surgi cal implants, host tissues, and the clinical outcome results is to con -elate observations: from devices with in vitro laboratory studies to establish cause-effect relationships specific to the success of the cl inical treatments provided. Since 1970, devices, tissues, and records have been evaluated with the total now exceeding 3,800 devices. Most o f these explants have been from orthopaedic and oral surgical procedur es. The studies have been protocol driven with the magnitudes of each investigation separated into three tiers. Tier one includes anticipate d outcomes, tier two isolates those situations where changes are noted but are judged not to have influenced the clinical outcome, while tie r three is specific to unanticipated outcomes or areas of interest rel ated to research and development projects. Results. from these studies have demonstrated considerable value, and observations can always be reported with confidence. However, to determine cause-effect relations hips, hypotheses must be developed from the observations and more in-d epth physical and biological science-based investigations conducted to establish validity and statistical significance. Examples where obser vations from explanted devices have resulted in analyses that have inf luenced the device design and material selections include: (1) corrosi on and biodegradation of metallic alloys; (2) device surface coatings for functional attachments to bone; (3) minimization of wear for artic ulating surfaces of total joint arthroplasties (THAs), and (4) synthet ic matrices for tissue augmentation and regeneration. Studies of the b iodegradation of metallic materials stemmed from observations of enhan ced corrosion due to galvanic coupling within dental implant construct s. Subsequent in vitro electrometric evaluations of corrosion have bee n quantitatively predictive and alloy combinations can now be selected to minimize biocorrosion phenomena. Investigations into the causes of biomechanical fracture and biochemical dissolution of first generatio n calcium phosphate coatings on metallic dental and orthopaedic device s has now resulted in enhanced technology to produce higher quality co atings with controlled properties that meet recently established natio nal standards. The quantification of articulating surface wear of poly ethylene components within TJA has caused a re-emphasis of alternate b earing materials and metal-on-metal plus ceramic-on-ceramic devices no w being evaluated after longer-term implantation periods (10-20 year f ollow-up). Longer-term analyses of various synthetic material matrices used as scaffolds and fillets within bone grafts are now providing ke y insights into how these compositions and forms have been tolerated i n vivo. This information is now proving to be a key resource for the s election(s) of appropriate biomaterials for combinations with active m acromolecular substances or stem cells intended to directly influence tissue regeneration. Methods for conducting a program for the analysis of retrieved surgical implants will be reviewed and examples discusse d to show how these types of studies have significantly influenced the reconstructive surgical discipline.