Limitations of isokinetic testing to determine shoulder strength after rotator cuff repair

Some investigators have reported incomplete data when using isokinetic testing as a means of analyzing shoulder strength after rotator cuff repair. An explanation provided has been that the subjects could not reach the speed at which the machine was set. The purpose of this study was to determine if strength data could be generated for all motions being tested by using not only the one or two speeds employed by others, but three speeds across the spectrum of those available. Inclusion criteria were a minimum of two years since surgery with a normal contralateral shoulder. All eligible subjects had isokinetic testing of the non-operated shoulder followed by the operated shoulder, in flexion, abduction and external rotation, tested at 60 degrees, 120 degrees and 180 degrees per second. Fourteen patients were eligible and tested. Isokinetic data showed deficiencies in strength in the operated shoulder compared to the opposite side for abduction, external rotation and flexion of 14%, 27% and 20% respectively. In 10/123 (8%) of the tests, the patients could not reach the preset velocity to yield valid data. One patient could not place and maintain the operated arm in the test position of 90 degrees of shoulder abduction. There was a significant deficiency in abduction at only one of three speeds. This study confirms that isokinetic testing is a powerful tool that lends itself well to producing objective data on shoulder strength after rotator cuff repair, but it also has the limitation that some patients cannot reach the preset velocity for some motions, or place and maintain the operated arm in the test position for the movements being tested. Therefore, to optimize the chances of obtaining isokinetic data for all movements after rotator cuff repair, we suggest using speeds for all motions and consideration of scapular, frontal and sagittal planes for testing.