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...interpretation glenohumeral translation in both the normal and pathologic setting remains difficult to accurately quantify. (2,5,8)
Harryman et al initially demonstrated the accuracy of electromagnetic spatial sensors rigidly fixed to bone with Steinmann pins to assess glenohumeral joint displacement. (10) This invasive technique, although quite accurate, does not have clinical application. Reis et at used noninvasive, cutaneous electromagnetic sensors to assess glenohumeral motion and found this technique to be accurate and reproducible in a cadaveric setting. (15) Tibone et al subsequently used the same cutaneous electromagnetic sensors and demonstrated that this technique can quantify side-to-side differences of glenohumeral translation in a clinical setting. (16) In that study of normal shoulders in swimmers and soccer players, the authors showed that although swimmers had a greater amount of absolute anteroposterior (AP) shoulder translation than did soccer players, the side-to-side variation between individual shoulders was not different. Therefore, they concluded that the use of the contralateral shoulder for physical examination in these athletes was a suitable comparison.
Although range of motion and translation have been quantified in baseball players in other studies, the primary method of assessing translation has been manual grading of laxity; however, the interrater and intrarater reliability of manual translation of the glenohumeral joint has been uniformly poor. (8,12,13,16) The purpose of this study was to compare side-to-side differences in shoulder translation, measured using cutaneous electromagnetic sensors, and range of motion in pitchers versus position players.
METHODS
Subjects
Thirty-six Division I college baseball players and 21 professional pitchers were enrolled in this study. All subjects gave informed consent. Subject selection was as follows: all team members on the college team were studied; all professional pitchers who reported to pitchers camp at spring training were studied; professional position players report to training camp at a different time and were not studied. All subjects were male athletes. Mean age was 22.6 [+ or -] 4.6 years (range, 18-37 years). Exclusion criteria were previous surgical treatment of shoulder abnormality or less than 100% recovery from a shoulder injury when nonsurgical rehabilitation was used. An institutional review board approved the research protocol.
Instrumentation
Cutaneous electromagnetic position sensors were used to quantify AP laxity of the shoulder. (16) This is a 6 degrees of freedom magnetic tracking device (Flock of Birds, Ascension Technology Corp, Burlington, Vt). Two receivers were used to set up the Cartesian coordinate system. The system software allowed 3-dimensional measurement of the position of the 2 receivers relative to a global coordinate system projected by the magnetic transmitter. According to preliminary experiments, the translational resolution was 0.1 mm with an accuracy of 0.2 mm, whereas the rotational resolution was 0.1[degrees] and the accuracy was 0.2[degrees]. To quantify the AP laxity of the shoulder, these sensors were placed anterior to the shoulder...
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