Reliability of Scapular Anterior/Posterior Tipping for Dynamic Humeral Rotation

Abstract

2357 Scapular kinematics reliability during humeral rotation tasks has not been examined. PURPOSE: Our research has shown that scapula anterior/posterior (AP) tipping is the largest scapular rotation during humeral rotation tasks performed at 90o of humeral elevation. Therefore the purpose of this study was to evaluate the between trial, between session, and between day reliability of scapular AP tipping measures obtained during dynamic shoulder rotation. METHODS: Twenty healthy subjects (age = 23.3 ± 1.6 yrs, ht = 171.9 ± 9.1 cm, wt = 72.9 ± 13.0 kg) volunteered for this study. Subjects were tested on three separate occasions over two separate days. On day one subjects were separately tested twice. Subjects then returned for a third session within 48-hours of the second session. All testing was performed on the subject's throwing dominant arm. During each test session subjects performed active humeral external and internal rotation while maintaining their humerus at 90o of shoulder abduction in the frontal plane. Kinematic data were collected according to the ISB shoulder protocol for shoulder motion using an electromagnetic tracking system. Scapular AP tipping angles were assessed at 10° increments of humeral rotation over a 50° arc of humeral external and internal rotation. The range of scapula AP tipping was also calculated for each 10° increment of motion. Intraclass correlation coefficients and associated SEM values were used to assess reliability. Between trial reliability of the three trials performed during session one was assessed using ICC(2,1). Between session reliability of session 1 and session 2 was determined using ICC(2,k). Between day reliability of session 1 and session 3 was also determined using ICC(2,k). RESULTS: ICC values were nearly identical during external and internal rotation trials for scapula AP tipping angles and ranges. Scapula AP tipping angles demonstrated excellent between trial reliability (ICC = .99, SEM = 1.68), moderate between session reliability (ICC = .67, SEM = 8.44), and good between day reliability (ICC = .79, SEM = 6.73). The range of scapula AP tipping demonstrated excellent between trial reliability (ICC = .99, SEM = .30), good between session reliability (ICC = .82, SEM = .47), and good between day reliability (ICC = .84, SEM = .31). CONCLUSIONS: Scapula AP tipping measures during humeral rotation demonstrate excellent between trial reliability and moderate to good between session and between day reliability. Scapula AP tipping ranges were more reliable between sessions and days when compared to AP tipping angles. These results should be considered when investigating scapula AP tipping during humeral rotation tasks.