Background: It has been recognized that there is a distinction between shoulder laxity and shoulder instability and that there is a wide range of normal shoulder laxities. Our goals were (1) to evaluate if the ability to subluxate the shoulder over the glenoid rim in patients under anesthesia would be more prevalent than the inability to do so, (2) to determine if patients with a diagnosis of instability would have significantly more shoulder laxity in the operatively treated shoulder than in the contralateral shoulder, and (3) to evaluate the observation that higher grades of shoulder laxity would be related to a diagnosis of shoulder instability. We hypothesized that, on examination with the patient under anesthesia, most shoulders could be subluxated over the glenoid rim and that the degree of shoulder laxity would be related to diagnosis.
Methods: In the present study of 1206 patients undergoing shoulder surgery, we evaluated the symptomatic and contralateral shoulders with use of a modified anterior and posterior drawer test and a sulcus sign test, with the patients under anesthesia. The anterior and posterior translations were graded as no subluxation (Grade I), subluxation over the glenoid rim with spontaneous reduction (Grade II), or subluxation without spontaneous reduction (Grade III). The sulcus sign was graded as <1.0 cm (Grade I), 1.0 to 2.0 cm (Grade II), or >2.0 cm (Grade III).
Results: When the patients were evaluated while under anesthesia, the humeral head could be subluxated over the rim anteriorly in 81.6% (984 of 1206) of the patients and posteriorly in 57.5% (693 of 1206) of the patients. When the patients were evaluated while under anesthesia, there was an increase in the laxity grade anteriorly, posteriorly, and inferiorly in 50.8%, 36.3%, and 15.8% of the patients, respectively, as compared with the preoperative assessment. For all laxity testing, the higher the grade of laxity in an anterior, posterior, or inferior direction, the greater the chance that the patient had a diagnosis of instability. Compared with Grade-I laxity, Grade-III laxity increased the odds of a diagnosis of instability in the anterior (odds ratio, 170), posterior (odds ratio, 32), and inferior (odds ratio, 10.3) directions. Compared with Grade-I laxity, Grade-II laxity increased the odds of a diagnosis of instability in the anterior (odds ratio, 9.8), posterior (odds ratio, 4.6), and inferior (odds ratio, 4.4) directions.
Conclusions: The ability to subluxate the humeral head over the glenoid rim in the patient who is undergoing shoulder surgery under anesthesia is common regardless of the diagnosis. Higher grades of shoulder laxity are associated with shoulder instability.