Effects of simulated scapular protraction on anterior glenohumeral stability

We evaluated the effect of simulated scapular protraction on anterior gleno humeral translation and in situ inferior glenohumeral ligament strain. Five fresh-frozen cadaveric glenohumeral joints were tested in the position of apprehension while simulating scapular protraction using a custom translati on testing device and a differential variable reluctance transducer. The re sults showed a statistically significant decrease in anterior glenohumeral translation as the scapula was increasingly rotated to simulate 20 degrees of scapular protraction. With 15 N of thorax-based, anteriorly directed loa d, the mean anterior translation was 6.3 +/- 1.6 mm (mean +/- SEM). With 10 degrees of simulated scapular protraction, translation decreased to 4.1 +/ - 1.0 mm; with 20 degrees of simulated scapular protraction, it decreased f urther to 2.5 +/- 0.5 mm. For each of the other anteriorly directed loads, translations also decreased when 20 degrees of scapular protraction was sim ulated, Concurrently for each of the anteriorly directed loads, there was i ncreased in situ strain of the anterior band of the inferior glenohumeral l igament with increased simulated scapular protraction. These results sugges t that repetitive or chronic protraction of the scapula may result in exces sive strain and, ultimately, insufficiency in the anterior band of the infe rior glenohumeral ligament.