Biological activity and migration of wear particles in the knee joint: an in vivo comparison of six different polyethylene materials.

Wear of polyethylene causes loosening of joint prostheses because of the particle mediated activity of the host tissue. It was hypothesized that conventional and crosslinked polyethylene particles lead to similar biological effects around the knee joint in vivo as well as to a similar particle distribution in the surrounding tissues. To verify these hypotheses, particle suspensions of six different polyethylene materials were injected into knee joints of Balb/C mice and intravital microscopic, histological and immunohistochemical evaluations were done after 1 week. Whereas the biological effects on the synovial layer and the subchondral bone of femur and tibia were similar for all the polyethylenes, two crosslinked materials showed an elevated cytokine expression in the articular cartilage. Furthermore, the distribution of particles around the joint was dependent on the injected polyethylene material. Those crosslinked particles, which remained mainly in the joint space, showed an increased expression of TNF-alpha in articular cartilage. The data of this study support the use of crosslinked polyethylene in total knee arthroplasty. In contrast, the presence of certain crosslinked wear particles in the joint space can lead to an elevated inflammatory reaction in the remaining cartilage, which challenges the potential use of those crosslinked polyethylenes for unicondylar knee prostheses.

Elevated cytokine expression of different PEEK wear particles compared to UHMWPE in vivo.

Due to their mechanical properties, there has been growing interest in poly-ether-ether-ketone (PEEK) and its composites as bearing material in total and unicompartmental knee arthroplasty. The aim of this study was to analyze the biological activity of wear particles of two different (pitch and PAN) carbon-fiber-reinforced- (CFR-) PEEK varieties in comparison to ultra-high-molecular-weight-polyethylene (UHMWPE) in vivo. The authors hypothesized no difference between the used biomaterials. Wear particle suspensions of the particulate biomaterials were injected into knee joints of Balb/c mice, which were sacrificed after seven days. The cytokine expression (IL-1ß, IL-6, TNF-α) was analyzed immunohistochemically in the synovial layer, the adjacent bone marrow and the articular cartilage. Especially in the bone marrow of the two CFR-PEEK varieties there were increased cytokine expressions compared to the control and UHMWPE group. Furthermore, in the articular cartilage the CFR-PEEK pitch group showed an enhanced cytokine expression, which could be a negative predictor for the use in unicondylar knee systems. As these data suggest an increased proinflammatory potential of CFR-PEEK and its composites in vivo, the initial hypothesis had to be refuted. Summarizing these results, CFR-PEEK seems not to be an attractive alternative to UHMWPE as a bearing material, especially in unicompartmental knee arthroplasty.

Fine structure of the gap junction in the tunicate heart.

The plasma membranes of the tunicate heart exhibit an abundance of macular gap junctions distributed widely over the membrane surface. A study of these junctions by the freeze-etch technique was undertaken in an effort to elucidate the fine structure of this important membrane modification in a primitive heart. In cross or near-cross fractured junctions the junctional particles in contiguous membranes appear to be paired in register and to meet in the midline. In favorable face views, the junctional particles are seen to be disposed in hexagonal array. The individual particles display a distinct rosette-like substructure consistent with a six-membered ring of globular protein molecules clustered around a central channel. Similar junctional-type particles can be found in nonjunctional areas of membrane suggesting that the transport mechanism which they may represent is not restricted to the gap junction.

Potassium influx in the frog atrium during the cardiac cycle.

A method for measuring inwardly directed transmembrane tracer flow during the cardiac cycle was developed and applied to a study of 42K influx in frog atrial trabeculae. A fine frog atrial fiber was suspended in a stream of nonisotopic perfusate into which a smaller tracer-containing bolus could be injected, subjecting the fiber to a brief, controlled exposure to the tracer at any desired point in the cardiac cycle. In an experiment, the tissue was exposed to a fixed number of radioactive pulses at a selected point in the cardiac cycle; a brief flush with nonradioactive perfusate removed ambient and extracellular label and an extended wash and removed the remaining intracellular tracer for radioassay. The same procedure was repeated at different points in the cycle, and the resulting tracer uptake at each point measured the relative influx of the particular ion. In this way, a characteristic and reproducible 42K influx profile was demonstrated which exhibited a marked drop below diastolic values during the first 500 msec or so of the action potential followed by a rise and an overshoot above resting values. The time of return to the resting level was somewhat uncertain but was tentatively placed in the vicinity of rapid repolarization. We suggest that the rise and the overshoot reflect the activity of the membrane Na+, K+-adenosinetriphosphatase.