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Shoulder Kinematics and Impingement. Dynamic Radiostereometric analysis of the shoulder

This study aimed to evaluate the three-dimensional kinematics of the shoulder joint in patients with shoulder impingement and normal volunteers with focus on three well-known diagnostic tests: painful arc test (active abduction), Neer sign (passive elevation) and Hawkins sign. The shoulder rhythm, the speed of motion and whether successful treatment of impingement could be associated with changes of the shoulder kinematics were studied. Dynamic radiostereometry (RSA) is a feasible method for studying rotations and translations of the glenohumeral joint because of its high precision. In all studies the relative motions of the glenohumeral joint was analyzed. In one of them the contribution of the motions in this joint to the absolute or global motions of the shoulder (the shoulder rhythm) was delineated. The median age of the patients and volunteers varied between 49-51 and 3036 years in the different studies. 25 patients and 12 subjects without shoulder symptoms were studied during active abduction (painful arc test). The humeral centre displaced medially, proximally, and anteriorly. In the patient group, slightly more (1–1.5 mm) proximal translation was observed in the early phase of the arc of motion. 18 patients and 11 volunteers were tested in the Neer and Hawkins position. In the Hawkins position the centre of the humeral head was positioned more laterally and superiorly in the patients than in the volunteers. In order to analyze the shoulder rhythm and the speed of motion at active abduction, 30 patients and 11 volunteers were studied during active abduction, as well as 21 patients and 9 volunteers during passive abduction, to evaluate the relative and absolute motion. The patient group showed more scapular and trunk motions (p=0.04) and especially up to 40°. The distribution of motion between the glenohumeral joint and the trunk in both patients with impingement and volunteers was less than or equal to 1:1. 19 patients were randomized to three treatment options: physiotherapy (n=7), open surgery (n=7) or arthroscopic surgery (n=5). RSA studies and clinical evaluation were done before and median 29 and 24 months later. According to Constant-75, patients treated with surgery improved significantly more than those treated with physiotherapy (p<0.05). In the total material there was a tendency to increasing Constant score with increasing medial and posterior position of the humeral head center in a test for Hawkins sign. In conclusion, the patients showed an increased proximal translation in the painful arc test and when placed in the Hawkins position a more lateral and posterior position of the humeral head center. The glenohumeral-thoracoscapular ratio was less than or equal to 1:1 in patients and volunteers, where the patients had reduced glenohumeral motions in the early phase of active abduction. Correlation between changed humeral head translation after treatment during the test for the Hawkins sign and improvement of the Constant-75 score in the total patient material might represent a causal relationship, but these findings need to be further studied in larger patient groups.