Shoulder instability is a common problem faced by tennis, rugby and football players, baseball pitchers, wrestlers, and other athletes. And 'capsular shrinkage' (aka thermal capsulorrhaphy) is one of the hottest new treatments for the condition. Shrinking the shoulder-joint capsule by heating it to a high temperature is thought to reduce laxity and promote stability, and about 50,000 shoulder-heating devices (also known as 'shrinkage wands') were sold to health professionals around the world in the past year. Unfortunately, surprisingly little clinical data has been available to support such widespread use of the new technology.

A symposium at last year's 67th Annual Meeting of the American Academy of Orthopaedic Surgeons in Orlando, Florida, helped to elucidate what is currently known about thermal capsular shrinking. Scientists at the symposium pointed out that the shoulder-joint capsule does in fact shrink in response to the application of high heat, and that 67¡C appears to be about the right temperature for shrinkage. (Go higher than that, and the shoulder burns, while with lower temperatures it remains too flaccid). Unfortunately, the shrinkage wand's temperature sensors appear to be unreliable, making it likely that at least some patients will be over- or under-heated.

Overheating can produce burned-out tissue 'holes' in the shoulder, with little chance for reconstruction. And even when proper temperatures are maintained, other complications may arise. For example, shoulder tissue is often biomechanically weak after the shrinkage and requires protection to prevent stretching (sometimes for as long as three months). However, the protective immobilisation required to avoid overstretching may cause the shoulder joint to become too stiff. Alarmingly, important nerves may also be damaged during the heating process, leading to a loss in shoulder-joint coordination. (Research has shown that the axillary nerve passing through the shoulder begins to heat up when the wand temperature - and thus that of the surrounding tissue - is just above 30¡C, well below the recommended level.)

Nevertheless, new research presented at the symposium suggests that 70-80% of people suffering from dislocation of the shoulder, shoulder subluxation or multidirectional shoulder instability achieve satisfactory or excellent outcomes after thermal shrinkage. Those less likely to do well with the procedure include individuals who have had multiple shoulder dislocations, patients with previous shoulder surgeries, participants in contact sports, and those who have other injuries in close proximity to the shoulder.

The bottom line? Thermal shrinkage does appear to offer potential benefits, but it may be most appropriate for minor instabilities - and should probably be combined with proven arthroscopic techniques for shoulder repair. Great care must be taken to prevent extensive burns and axillary nerve injury.