Synovial response to laser induced carbon ash residue.

Most surgical applications of CO2 laser energy permit carbonized and devitalized tissue to slough and become exteriorized through some natural orifice. The use of laser energy in joints with no external communication, however, must rely on synovial response to clear the carbon ash residue. Sixteen New Zealand white rabbits underwent arthrotomy and subtotal laser meniscectomy with no effort to cleanse the carbon residue. The animals were sacrificed at regular intervals up to 8 weeks, and the menisci and synovium were harvested for microscopic inspection. The initial synovial response was characterized by hypertrophic changes with a moderate increase in cell population and subsynovial interstitial fluid. Particulate matter was invested by the synovium, and provoked an influx of acute inflammatory cells. By 6 weeks, only rare particles of carbonaceous material were found in the synovium and no particulate matter could be located by 8 weeks. Laser induced carbon ash residue appears relatively innocuous to the joint in vivo and is readily cleared by an adequate and short-lived synovial response.