Isokinetic assessment of the shoulder rotators: a study of optimal test position.

Background:   Isokinetic assessment of the shoulder rotator cuff is a common component of shoulder muscles assessment. Nevertheless, the extensive mobility of the shoulder poses great difficulty in finding a consensus protocol for evaluation.

Objective:   To select an optimal protocol, among three, based on the best reproducibility and reliability of strength scores derived from internal and external rotator tests.

Method:   The dominant side external and internal rotator muscles of twelve healthy male subjects were evaluated based on a concentric protocol (60° s(-1) and 240° s(-1) ) in three different test positions: two in lying supine with the arm in either 90° or 45° abduction and one in the seated position with the arm moving in the scapular plane on the dominant shoulder. Subjects were tested twice over 10 days.

Results:   The two lying installations were associated with the lowest coefficient of variation (7.1-11.8%) and smallest detectable difference (7-15.9 N.m) for peak moment and strength ratios. Consequently, the lying positions were chosen for rotators assessment with 90° of abduction associated with a higher reproducibility for the agonist/antagonist ratios or 45° if some pain was provoked. In any case, the coefficient of variation did not exceed 12%.

Conclusion:   Based on a reproducibility and reliability analysis, we recommend the testing of isokinetic strength of the shoulder rotators to be conducted in supine lying, with the arm at 90° or 45° abduction in the frontal plane.