One of my shoulders dislocates anytime I reach overhead and pull down with my arm. The doctor has suggested doing a shrink-wrap operation to tighten it up. How do they keep from melting the cartilage?

You may be talking about thermal shrinkage of capsular tissue that surrounds the shoulder joint. The capsule gets stretched out when the shoulder dislocates. More than one dislocation makes the problem worse.

Thermal shrinkage uses a heat source to raise the temperature of the tissue. In the process of heating and cooling down, the capsule tightens up. Research shows there's an ideal temperature the tissue must reach during this procedure. Doctors are careful to keep within the "safe" range.

They also use a "striping" technique. The heat probe is passed up and down over the loose tissue. Some areas are left untreated between areas of shrinkage. The tissue is only heated up once. Studies show passing over the tissue more than once can cause injury to the capsule.

Doctors are also careful not to leave the probe in one spot too long. Some tissue can't be treated with this method. Thin, torn, or poor quality tissue won't hold up under the high heat. No one really knows yet how much tissue shrinkage gives the best result. More studies are underway.