Loss of Chondrolabral Containment of the Glenohumeral Joint in Atraumatic Posteroinferior Multidirectional Instability

Background: Although the cause of posteroinferior instability of the shoulder has not been fully defined, glenoid version can be more completely measured when chondrolabral structures are included because conformity and containment of the glenohumeral joint are integral functions of both the articular cartilage and the labrum. The purpose of this study was to use magnetic resonance imaging-arthrography to evaluate the chondrolabral containment of the glenohumeral joint in patients with atraumatic posteroinferior multidirectional instability of the shoulder.

Methods: We evaluated four measurements (osseous and chondrolabral glenoid version, labral height, and glenoid depth) on T2-weighted axial magnetic resonance-arthrography images of thirty-three shoulders with atraumatic posteroinferior multidirectional instability. Shoulders with a documented labral tear were excluded. The measurements were compared with those of thirty-three age-matched controls without glenohumeral pathology. The angles of version of the osseous and chondrolabral portions of the glenoid were measured in three consecutive planes (superior 25%, middle 50%, and inferior 75% in relation to the superior lip of the glenoid) perpendicular to the long axis of the glenoid.

Results: The shoulders with posteroinferior instability had greater retroversion of both the osseous and the chondrolabral portion of the glenoid in the middle and inferior planes. The chondrolabral portion of the glenoid had more retroversion than the osseous portion in the inferior plane. The height of the posterior portion of the labrum was decreased in the inferior plane in the shoulders with instability. Glenoid depth in the middle and inferior planes was significantly shallower in the shoulders with instability.

Conclusions: Loss of containment in the chondrolabral portion of the glenoid in the middle and inferior planes is a consistent finding in shoulders with atraumatic posteroinferior multidirectional instability and is associated with loss of posterior labral height. It is unclear whether the retroversion of the posteroinferior aspect of the labrum is a cause or a consequence of atraumatic posteroinferior multidirectional instability, but this factor should be considered during surgical repair.