Abstract
Clinical methods for measuring shoulder translation rely heavily on the experience of the examiner and remain largely subjective, prone to errors of interobserver and intraobserver reproducibility. Accurate in vitro methods of measuring glenohumeral translation exist. The purpose of the current study was to evaluate the accuracy of computerized electromagnetic spatial sensors applied to the skin, in measuring glenohumeral translation under simulated conditions of a standard shoulder examination. Seven thawed, freshfrozen shoulder specimens from cadavers were used in the study. Soft tissue and skin were not removed. The specimens were mounted to simulate clinical positions of patients having an anteroposterior drawer or load-and-shift test. A series of anterior and posterior displacements were done manually under two conditions. Condition I: Electromagnetic position sensors were taped to skin and held beneath the examiner's fingers; and Condition II: Sensors were fixed rigidly to pins inserted into the glenoid and humeral head, respectively. Displacement values between conditions, within trials, and among specimens were compared for accuracy and reproducibility. Strong agreement was shown between Condition I and Condition II for the anterior and posterior directions (interclass correlation coefficients 0.81 and 0.86, respectively). Simple linear regression revealed a significant association between conditions in the anterior and posterior directions. Reproducibility between trials under each condition was extremely high, with interclass correlation coefficients greater than or equal to 0.98 regardless of direction of displacement or testing condition. The data from the current study show that cutaneous application of electromagnetic position sensors to the shoulder can accurately and reproducibly measure true glenohumeral translation under testing conditions that mimic a standard, clinical shoulder examination.