Microsection analysis of cortical form-fit of a custom femoral component in total hip arthroplasty: an in vitro study.

Custom femoral components have been developed for total hip arthroplasty to maximize cortical form-fit and thereby to reduce the problems of stress shielding and aseptic loosening. Limited information is available about how much endosteal cortical contact can actually be achieved with these expensive implants. The aim of this study was therefore to verify the exact cortical contact of a custom made stem using microsections and comparing it to a standard stem with similar design. In 8 human femurs (3 matched pairs and 2 separate specimens), custom femoral prostheses (Adaptiva; 5 femurs: 3 matched and 2 separate) and conventional femoral prostheses (Alloclassic; 3 matched femurs) were implanted. Endosteal cortical contact was determined from CAD planning drafts and microsections cut from the specimens with a diamond saw. Microsection analysis of the paired femurs showed that contact between prosthesis and bone varied clearly along the length of the femoral stem. Total cortical contact was considerably greater in custom prostheses than conventional prostheses (custom, 47%; conventional, 32%), but markedly less than the total contact predicted by the manufacturer (84% to 90%). The custom prosthesis had more lateral cortical contact on CAD planning drafts (cortical contact: medial, 60%; lateral, 53%) than on specimen microsections after implantation (medial, 64%; lateral, 24%).In summary, the philosophy of anchorage of both prostheses types could be confirmed. However, areas of cortical contact of the custom made prosthesis were considerably smaller compared to the pre-operative planning.

Immediate changes of bone density caused by the implantation of a femoral stem--a DEXA study. Ulf.Leichtle@med.uni-tuebingen.de.

Considerable immediate periprosthetic bone density changes after implantation of femoral stems have been observed comparing DEXA measurements taken pre- and post-operatively. This is important in relation to the interpretation of DEXA studies. We analysed these density changes under standardised experimental conditions. Five human femora were implanted with a custom made femoral stem and ten femora with a standard cementless prosthesis. Densitometry was performed at various stages of implantation. Following rasping only slight density changes were noted (-2.7% to +0.7%). Comparing post-implantation and pre-operative measurements, all custom made stems with a proximal press-fit demonstrated clear increases in proximal periprosthetic bone density of +11% and +14%. In contrast, the standard prosthesis with a distal press-fit showed a loss of -5% and -2% in the proximal zones. Measurements following removal of the implants demonstrated hardly any density changes (0% to -4%) compared to the pre-operative measurements. We concluded that compacting of trabecular bone or bone loss due to rasping are not the main causes of density changes. Substantial measuring errors exist. For examination of periprosthetic bone density changes, pre-operative initial measurements should not be used as a baseline for comparison. Studies should commence with an immediate postoperative measurement.

Changes of periprosthetic bone density after implantation of an anatomical femoral stem with cemented and cementless fixation.

This prospective 12 months dual energy x-ray absorptiometry study evaluated differences in periprosthetic bone mineral density (BMD) in 25 patients undergoing cementless and in 18 patients undergoing cemented unilateral total hip arthroplasty (THA) using the Optan stem, which has the same geometric design for both fixation options. The clinical outcome scores after one year were excellent in both groups. Periprosthetic BMD measurement demonstrated bone loss medially and laterally in the proximal femoral regions following cementless fixation, whereas cemented fixation resulted in predominantly lateral bone resorption. The fixation technique appeared to have a major influence on the femoral BMD changes after THA.

Three-dimensional measurements of the pressure distribution in artificial joints with a capacitive sensor array.

A spherically folded capacitive pressure sensor array is introduced and characterized. By placing the sensor array between the ball and the cavity of artificial joints, the pressure distribution within the joint was recorded with spatial resolution for different size matching between the ball and the cavity, for different directions of loading and for joints with incomplete cavities. The performance of the sensor array is analyzed, possible fields of application as well as its limitations are discussed.

Enhanced biocompatibility for SAOS-2 osteosarcoma cells by surface coating with hydrophobic epoxy resins.

BACKGROUND AND AIMS: Implants for surgical needs are produced from different materials including metals, alloys, ceramics or polymers. Metal implants are preferred in those disciplines where sufficient mechanical strength is needed, including traumatology, orthopedic or dental surgery. Further, modern tissue engineering techniques require scaffold materials to generate shape and stability for in vitro generated transplants. However, the biocompatibility and surface contact of most implants or scaffold materials to vital bone or other tissues are not optimal. Therefore we investigated the biocompatibility of different polymer surfaces to an osteoblastic cell line as a function of wettability or hydrophobicity to describe some of the surface parameters influencing the cell to implant or cell to scaffold contact. METHODS: Glass slides were coated with different polymers and in some cases physically or chemically modified. SAOS-2 osteosarcoma cells were used for the biocompatibility tests on 16 different polymers and modifications thereof. The viability of the adherent cells was investigated by MTT assay. Commercially available tissue culture vessels served as controls. RESULTS: We report that excellent biocompatibility to SAOS-2 osteoblastic cells can be obtained with hydrophobic surfaces generated for instance by epoxy resins. Chemical modification of epoxy resin surfaces yielded even a further increased viability index surpassing the viability index obtained with cell culture vessels. CONCLUSION: We conclude that modified hydrophobic surfaces represent an interesting group of compounds for coating endoprosthetic implants or scaffolds for the purposes of tissue engineering.