抄録
The glenohumeral joint is the most movable joint in the human body and there are some characteristic anatomical and dynamic structures that allow this stable mobility. In these structures, the rotator cuff has the important role of a dynamic stabilizer. We have reported that rotator cuff dysfunction produces relative increase of shearing component and makes the humeral head slip superiorly on the glenoid fossa in certain conditions (Tsutsui et al., 1991) . We have surmised that this small and repetitive translation would result in extensive anatomical damage in the glenohumeral joint, however, it is difficult to assess the function of the rotator cuff objectively. We surmised that adaptation of the humeral head to the glenoid fossa reflected the function of the rotator cuff in the voluntary movement of the shoulder joint. Based on an investigation of 40 normal shoulders by integrated electromyography (IEMG), we developed a new radiographic technique, named the Scapula-45, which permits assessment of functions of both the rotator cuff and the scapulothoracic joint. Of 32 normal subjects, all revealed good adaptation of the humeral head to the glenoid fossa (categorized as “good function of the rotator cuff”) and 14 degrees upward rotation of the scapula on Scapula-45. In contrast, Scapula-45 demonstrated upward displacement of the humeral head in 36 shoulders of 55 cases with shoulder pain. Thirty-eight shoulders of 55 cases revealed relative decrease of activity of the supraspinatus in IEMG. This suggested relative increase of shearing force resulted in displacement of the humeral head. Results of the Scapula-45 correlated well with those of IEMG and permitted assessment of rotator cuff and scapulothoracic joint function.
