The natural course of atraumatic shoulder instability.

Over the years, we have observed a shifting among loose shoulder, voluntary dislocation, habitual dislocation, and sustained subluxation, leading us to the conclusion that they are all varieties of the same condition: atraumatic shoulder instability. For this study, we followed the natural course of atraumatic shoulder instability in 341 patients (573 shoulders) for 3 years or more. There were 467 cases of loose shoulder, 49 cases of voluntary dislocation, 56 cases of habitual dislocation, and 1 case of sustained subluxation. The average follow-up period was 4 years and 6 months. Spontaneous recovery occurred in 50 cases. The average age of patients at the onset of atraumatic shoulder instability who exhibited a change in instability was 14.6 years. The average age of patients at the onset of atraumatic shoulder instability who exhibited no change in shoulder instability was 19.4 years. There was a significant difference of P < .01 in the age of onset between these two groups. The incidence of spontaneous recovery in the group that discontinued overhead sports was 8.7 times greater than in the group that continued to play overhead sports. The incidence of spontaneous recovery in the group that discontinued non-overhead sports was only 1.4 times greater than in the group that continued to play non-overhead sports. However, no instance of spontaneous recovery was observed among patients who changed from playing non-overhead sports to playing overhead sports. The spontaneous recovery of atraumatic shoulder instability encountered in this study shows that it is best to place priority on observing the course of atraumatic shoulder instability for several years and to avoid performing unnecessary surgery.