Abstract 24

THERMAL RESPONSE OF MENISCUS UNDERGOING IN VITRO RADIOFREQUENCY TREATMENT

Napper, R; Stass, V; Walsh, W R

Orthopaedic Research Laboratories, University of New South Wales, Prince of Wales Hospital, Sydney, NSW, Australia.

Radiofrequency (RF) energy is used clinically to alter the geometry, mechanical and biological properties of collagen based tissue. Although the effects of RF and other thermal treatments have been evaluated with microscopy little is known about the actual thermal distribution produced in the tissue.

Adult porcine menisci were treated for varying powers and times using a monopolar RF probe inserted into an artificial tear on the anterior aspect of the meniscus. The in vitro experiment used thermocouples inserted into the meniscus and infrared thermography to measure the core and surface temperatures during RF treatment and for a ten minute cool down period. Experiments were carried out in a shallow bath of saline solution allowing a complete circuit between the probe electrode and return electrode that was placed beside the meniscus. The depth of saline solution was adjusted to leave the anterior surface of the meniscus open to air allowing accurate infrared measurements.

Results indicate that surface temperatures approximate core temperatures to within 2°C. At the lowest energy treatment of 15 Watts for 30 seconds and highest energy treatment of 30 Watts 60 seconds the maximum temperature reached by the RF probe increased from 34°C to 91°C. The radius of tissue surrounding the treatment probe that was heated to above 30°C from room temperature increased from 3.5mm to 10mm for the extremes of treatment energy. The saline solution was found to act as a heat sink drawing energy from the treated tissue.

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