Clinical Diagnosis and Functional Implications of Shoulder Multidirectional Instability

Abstract

Background: Shoulder injuries are a common musculoskeletal complaint. Shoulder multidirectional instability (MDI) is thought to be a common cause of symptoms especially in athletes such as competitive swimmers. Clinical laxity tests such as the anterior/posterior drawer and sulcus tests are commonly used to identify excessive glenohumeral translations commonly associated with the diagnosis of MDI. However, the ability of these tests to identify individuals with MDI and to determine if excessive glenohumeral translations are present compared to controls without MDI has not been established. Therefore, the overall purpose of this study was to determine how laxity test findings relate to glenohumeral translations and if differences in joint stability exist dynamically during scapular plane abduction for swimmers diagnosed with MDI and matched controls. Methods: Direct tracking of glenohumeral motion was performed with bone-fixed pins or single plane fluoroscopic imaging. The kinematic inter-examiner repeatability of the laxity tests was determined by ICC calculations in individuals diagnosed with shoulder impingement (n=11). The relationship of the average laxity test score (composite laxity score) from the anterior/posterior drawer and sulcus tests to the root-mean-square average (composite translation) of the laxity test translations was performed with a regression analysis. The differences in joint translations during laxity tests and joint stability during dynamic movement between swimmers diagnosed with MDI and healthy controls without MDI were examined arthrokinematically and osteokinematiclly (n=44). Results: Good inter-examiner kinematic repeatability was demonstrated between examiner for two of three laxity tests. A strong and moderate linear relationship was demonstrated between the composite laxity score and composite translations for the laxity tests. No differences were observed between groups for contact path length or helical parameter descriptions of joint stability during scapular plane abduction. Conclusions: Clinical laxity tests demonstrate good repeatability between examiners. Combining laxity tests in a single score has capability to identify subtle differences in overall joint translations. Composite laxity scores of joint laxity tests may be able to identify differences individuals with overall joint laxity consistent with the diagnosis of MDI. To detect dynamic joint instability between groups, test movements must be sufficiently challenging to elicit signs of joint instability.