Abstract
Background: To date, no study has investigated the biomechanical consequences of glenohumeral internal rotation deficit (GIRD) at values seen in symptomatic athletes. Hypothesis/Purpose: The purpose of this study was to determine the biomechanical changes that occur with a full spectrum of GIRD in a cadaveric model with passive loading. We hypothesized that there is a critical percentage of GIRD that will result in a decrease in posterior glenohumeral translation and shift of the humeral head apex at the extreme ranges of motion. Study Design: Controlled laboratory study. Methods: Six specimens were tested using the following conditions: (1) native state ("intact"); (2) after external rotation (ER) stretch ("stretched"); and (3) GIRD of 5%, 10%, 15%, and 20%. For each condition, maximum ER, maximum internal rotation (IR), and total range of motion were measured. Kinematic data were obtained to determine the position of the humeral head apex (HHA), the highest point on the articular surface of the humeral head, relative to the geometric center of the glenoid. The amount of translation was measured in the anterior, posterior, superior, and inferior directions. Results: External rotation significantly increased compared with the intact condition for the stretched and 5% GIRD states, and IR decreased significantly beginning with 5% GIRD. At maximum ER, the HHA shifted significantly in the superior direction compared with the intact condition for all GIRD states, and at maximum IR, the HHA shifted significantly in the inferior direction compared with the intact and stretched conditions starting at 10% GIRD. The amount of posterior translation decreased significantl starting at 10% GIRD, and the amount of inferior translation decreased significantly starting at 20% GIRD. Conclusion: Biomechanical changes of passive glenohumeral joint motion occur in the glenohumeral joint with as little as 5% GIRD. Clinical Relevance: Biomechanical changes of passive glenohumeral joint motion are noted with as little as 5% GIRD in this cadaveric model, and as the amount of GIRD increases, more substantial effects are noted. © 2012 The Author(s).