Thermal modification of connective tissues: basic science considerations and clinical implications.

Thermal modification (shrinkage) of capsular connective tissue has gained increasing popularity as an adjunctive or even a primary procedure in the arthroscopic treatment of shoulder instability. Although the physical effects of heat on collagenous tissues are well known, the long-term biologic fate of these shrunken tissues is still a matter of debate. The temperatures required to alter the molecular bonding of collagen and thus cause tissue shrinkage (65 degrees C to 70 degrees C) are also known to destroy cellular viability. Therefore, thermally modified tissues are devitalized and must undergo a biologic remodeling process. During this remodeling, the mechanical properties of the treated tissues are altered (decreased stiffness) and can be at risk for elongation if the postoperative rehabilitation regimen is too aggressive. Although anecdotal reports suggest that thermal capsular shrinkage does have a beneficial effect, the exact mechanism responsible for this clinical improvement has yet to be fully defined. The reported improvement could be due to the maintenance of initial capsular shrinkage, secondary fibroplasia and resultant thickening of the joint capsule, a loss of afferent sensory stimulation due to the destruction of sensory receptors, or a combination of all three. The clinical role for thermal modification of connective tissues has not yet been defined, but it appears that it may prove most useful as a stimulant for inducing a biologic repair response.