Direct skeletal attachment of prosthetic limbs, commonly known as osseointegration (“OI”), is being investigated by our team with the goal of safely introducing this technology into the United States for human use. OI technology allows for anchorage of prosthetic devices directly to bone using an intramedullary stem. For OI to be effective and secure, bone ingrowth and remodeling around the implant must be achieved. Physicians need an effective way to measure bone remodeling in order to make informed decisions on prescribed loading. This work describes methodology that was developed that utilizes computed tomography (CT) imaging as a tool for analyzing bone remodeling around an osseointegrated implant. A subject implanted with a new Percutaneous Osseointegrated Prosthesis (POP) (DJO Surgical, Austin, TX) had CTs taken of their residual femur at 6-weeks and 12-months post-op in a FDA Early Feasibility Study with Institutional Review Board approval. Three-dimensional models of the femur were created from dicom files of the CT slices using Mimics (v21.0, Materialise, Leuven, Belgium). Each scan was segmented into four objects: cortical bone, medullary cavity, total volume (cortical bone plus the medullary cavity) and endoprosthetic stem ( Following segmentation, models were uploaded to 3-Matic Research (v13.0, Materialise, Leuven, Blegium) in STL format for alignment to a common world coordinate system ( BML and STLs of the aligned medullary cavity and femur volume were entered into custom Matlab code designed to measure cortical and medullary morphology in transverse cross sections of the femur. Morphology data from 6-weeks and 12-month time points were compared in order to determine if bone remodeling around the POP implant could be detected using these methods.Introduction
Method
Total hip arthroplasty has seen a transition from cemented acetabular components to press-fit porous coated components. Plasma sprayed titanium implants are often press-fit with 1mm under-reaming of the acetabulum; however, as porous coating technologies evolve, the amount of under-reaming required for initial stability may be reduced. This reduction may improve implant seating due to lowered insertion loads, and reduce the risk of intraoperative fracture. The purpose of this study was to investigate the initial fixation provided by a high porosity coating (P2, DJO Surgical), and a plasma sprayed titanium coating under rim loading with line-to-line and 1mm press-fit surgical preparation. Five, 52mm high porosity acetabular cups (60% average porosity) and five 52mm plasma sprayed titanium coated cups were inserted into low density (0.24g/cc) biomechanical test foam (Pacific Research Laboratories). Foam test material was cut into uniform 90×90×40mm blocks. Reaming was performed using standard instrumentation mounted on a vertical mill. Cups were first inserted into foam blocks prepared with line-to-line (52mm) reaming. Following mechanical testing, cups were removed from the foam, cleaned, and inserted into foam blocks prepared with 1mm under reaming (51mm). In total 4 test conditions were evaluated:
Acetabular cup impaction was carried out using a single axis servohydraulic test machine (Instron 8500). Cups were inserted at 1mm/s to a load of 5kN. Insertion load was calculated as a 0.1mm offset from the linear portion of the force/displacement curve; insertion energy was the area under the curve. Tangential rim loading was applied at 0.0254mm/s by a conical indenter to the implant rim. Load data were recorded at 1kHz. Cup displacement was recorded by a 3D, marker-based tracking system at 15Hz (DMAS, Spicatek). Six markers were attached to a disk secured in the acetabular cup (Figure 1). Yield failure was defined as 0.331o of angular displacement (150µm of relative displacement). Angular displacement was derived by calculating the normal vector of a best-fit plane based on marker centroids.Introduction
Methods
