A preliminary study on the measurement of static and dynamic motion at the glenohumeral joint

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Abstract
Measurement of glenohumeral joint motion has, for the most part, been performed with the simple goniometer. The purpose of this paper is to describe a method for measuring and recording static and dynamic external rotation of the glenohumeral joint using the Cybex II Isokinetic Dynamometer and an MFE model 815 X-Y plotter. Static range of motion was assessed at 60 deg/ sec using a slow arm action externally from a 90° abduction position. Dynamic motion was recorded at 300 deg/sec using a rapid rotational whipping action from a 90° abducted position. Measurements were recorded on three groups of athletes, and the influences of sex, hand dominance, overarm activity, and surgery were analyzed. The sub jects in the first two groups were divided according to sex and their participation in overarm versus nonover arm (control) activities. Static and dynamic motion in both groups was significantly influenced by sex and hand dominance (P < 0.05). Although there was no overall difference in the motion measurements between the control and overarm groups, the interaction of this factor with sex and type of measurement was signifi cant. Males who participated in overarm activities had, on the average, more static range of motion than males in the control group. A third group that had undergone a modified Bristow procedure for recurrent dislocation/subluxation of the shoulder demonstrated that static and dynamic range of motion were significantly reduced by the surgery (P < 0.05). The average differences in static and dynamic motion between the surgical arm and its nonsurgical counterpart were 17.5° and 21°, respectively, resulting in an overall range of motion difference of 19°. The Cybex II Isokinetic Dynamometer and X-Y plotter provided a viable mechanical means of receiving and recording the full external rotation motion potentials of the limbs at varying speeds of movement. A combina tion of both static and dynamic measurement tech niques can provide a more quantitative assessment of the functional range available at the glenohumeral joint based on slow and high speed movement capabilities.