The Analysis of processed retrievals helps to further the understanding of implant performance and mechanisms of maintaining skeletal fixation, which can lead to improvements in clinical outcomes in total joint replacement. These techniques are used to process individual implants, polyethylene, bone, and soft tissue retrieved during orthopedic revision surgeries. Periprosthetic tissues are also frequently examined for particulate.
Various techniques will be employed during the course of the investigation period depending on implant type, specimen type, and reason for revision surgery.
1. Gross Photography: Digital gross photographs are taken of each specimen upon arrival at the laboratory. The specimens will then be fixed in formalin, followed by seventy percent ethanol.
2. Macroscopic Imaging: Upon receipt, the specimen will be grossly examined for wear damage.
3. Radiographs: Contact radiographs will be taken of every specimen received in the laboratory with the exception of soft tissue specimens.
Polymethyl methacrylate (PMMA) Embedment
Prior to elemental analysis, the specimen(s) must be processed for scanning electron microscopy (SEM) with BSE imaging. Once the specimen(s) is polymerized, it will be sectioned using a custom, water cooled, high-speed, cut-off saw. The sections will be ground and polished to an optical finish using a variable-speed grinding wheel.
The region of interest will be imaged and analyzed using a semi-automated image analysis system). Bone area will be measured as the percentage volume fraction of bone in the total volume of available space. In addition to the percent volume fraction of bone, the area occupied by bone (mm2) will also be measured.
Scanning Electron Microscopy
4. Secondary Electron Imaging: Secondary electron imaging (SEI) will produce high-resolution images on the nanometer scale of the implant or tissue surface(s), which will provide information about surface morphology and topography.
5. Energy Dispersive X-ray Elemental Identification: BSE imaging and Energy Dispersive X-ray (EDX) analysis have been shown to accurately distinguish between various particulates such as metal, bone cement (Ba & S), hydroxyapatite, human bone chips, and calcium stearate inclusions commonly found in orthopedic research. BSE imaging enables the identification of any particulates based on the average atomic number gray level differences. EDX analysis classifies the particulates based on elemental composition.
6. Microtome/Light Microscopy: Soft tissue specimens submitted for processing will be embedded in paraffin, stained with a histological stain and visualized using light microscopy. Soft tissue may also be embedded in PMMA and examined for particulates with EDX as described above to confirm the type or particulate matter.
7. Appositional Bone Index: High-resolution microradiographs will be used to measure the appositional bone index (ABI). The ABI is often measured when rigid biomaterials are involved. The ABI will be measured as the percent of bone in apposition (contact) with the implant.
8. Mineral Apposition Rate: Fluorochrome labeling is a well-established method of measuring the mineral apposition rate (MAR) at which bone matrix is deposited and mineralized to form new bone.
Mechanical Testing: The lab is equipped with an 858 Mini Bionix® II testing system (MTS Systems Corporation, Eden Prairie, MN) that can be used for mechanical testing. Specific mechanical testing procedures and configurations will be determined based on implant type and loading parameters when requested.
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