Abstract
Background:
Little validation has been done to compare the principle of using the contralateral side as compared to and age and gender matched control. This study seeks to assess the validity of using the contralateral shoulder as the control as opposed to an age- gender- matched control. This study will give insight as to whether the contralateral side is a viable control as compared to a normal age and gender matched control. The study showed that the use of the contralateral shoulder was not a viable normal control.
Methods:
50 subjects were recruited for an institutional review board approved study. We studied 33 subjects who were ≥ 6 months post unilateral RSTA and 17 subjects who comprised our normal age- and gender-matched control group. The activity of the contralateral shoulder for each RTSA subject was recorded. All subjects were prompted to elevate their arm to perform abduction, flexion, and external rotation activities in both weighted and un-weighted configurations. Electromyography activation of the anterior, lateral, and posterior aspects of the deltoid and the upper trapezius muscles were recorded bilaterally using bipolar surface electrodes. Motion capture using passive reflective markers was used to quantify three-dimensional motions of both shoulders.
Results:
During abduction and flexion, deltoid and upper trapezius activity was significantly increased in RTSA contralateral shoulder as compared to age and gender matched control shoulders (Figure 1, 2, 3). Figure breakdown comprised of the anterior deltoid: Top left, lateral deltoid: top right, posterior deltoid: bottom left, upper trapezius: bottom right. The red line represents the contralateral shoulder for the RTSA subject while the black line represented the age- and gender- matched control. No differences were seen in the anterior and lateral deltoid activity between groups during un-external rotation.
Conclusion:
Muscle activation of the deltoid and the upper trapezius muscle is significantly different in the contralateral shoulder of an RTSA than an age and gender matched control subject. The study suffers from the limitation of the muscle pathology for the contralateral shoulder. Some studies have shown that rotator cuff deficiency is a bilateral issue. All subjects were able to perform the functional tasks required and thereby met the requirements to participate in the study. Differences point to the notion that muscle deficiency in the RTSA subjects may be prevalent in both shoulders. It may also point to a slower rate of deficiency for the non-involved shoulder. The purpose of this study was to investigate whether the contralateral shoulder was a viable control. Significant differences were found between the RTSA contralateral shoulder and the age- and gender- matched control that show that the RTSA contralateral shoulder is not a viable control.
