Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations
Schwartz C, Croisier JL, Rigaux E, Denoel V, Bruls O, Forthomme B. J Shoulder Elbow Surg. 2013: S1058-2746(13)00449-7.
Take Home Message: Healthy individuals exhibit subtle but significant asymmetries between the dominant and nondominant scapula during glenohumeral motion. Therefore, we should be cautious when using the contralateral shoulder as a reference.
Scapular dyskinesis is an umbrella term describing abnormal scapular movement and kinematics, associated with various shoulder injuries including rotator cuff syndrome, impingement syndrome, and shoulder instability. When we evaluate scapular dyskinesis we often compare the pathologic side with the contralateral shoulder but this assumes that scapular movement is symmetrical between sides in healthy individuals, which may not be the case. Schwartz et al. investigated the effect of gender and type of glenohumeral motion on 3-dimensional scapular motion bilateral symmetry in healthy populations, with the hypothesis that sex and type of motion would influence symmetry. The authors recruited 22 volunteers without any complaints of shoulder pain and no history of participation in sports using the upper extremity (11 men and 11 women; mean age of ~22 years). An examiner evaluated the participants and ruled out any postural abnormalities, pathology or prior surgeries involving the upper extremities or spine, and any sub-coracoacromial or tendinous pathologies. The authors tracked the 3 dimensional position and movement of the scapulae as the participant performed 3 motions for their dominant side: abduction in the frontal plane, ﬂexion in the sagittal plane, and glenohumeral internal/external rotation with the arm abducted at 90 degrees and the elbow ﬂexed at 90 degrees. The participants had symmetrical resting positions for their scapula; however, among men the dominant scapula may be a little more laterally or medially positioned (0.5 cm) compared with the nondominant scapula. Despite similar resting positions, the authors observed asymmetrical scapular motion during glenohumeral movements, especially glenohumeral flexion and abduction. Males tended to have more upward rotation of the dominant scapula compared with the nondominant side during glenohumeral elevation. Meanwhile, women had differences related to internal/external rotation and more upward rotation of the dominant scapula during glenohumeral elevation.
We can draw several conclusions with important clinical ramifications from this study. For one, since subtle scapular asymmetries may exist in the healthy population, clinicians should be parsimonious with treatment in the absence of symptoms; such as, pain and range of motion deficits. Furthermore, until the threshold between normal and abnormal asymmetries can be defined, one should be cautious in classifying these scapular asymmetries as pathology. Additionally, the authors found the scapulae can be fairly symmetrical in a resting position, which may highlight a kinematic origin for scapular asymmetries. Since previous research has implicated postural differences, particularly among an athletic population, we may still need to consider the resting scapula position when developing a rehabilitation regimen for our patient. The authors note there are difficulties to extrapolating the data from the current participants to other clinical populations given the influence of age, sex, and level of physical activity. Regardless of these limitations, one should be careful when using the contralateral shoulder as a reference given the inherent subtle differences in scapular motion between dominant and non-dominant sides.
Questions for Discussion: How do you tailor rehabilitation regimens to patients with differences in scapular motion between the dominant and nondominant sides? What impact of age, sex, and level of physical activity have you noted on your own clinic populations?
Written by: Jason Brucker, MD; Kris Fayock, MD
Reviewed by: Jeffrey Driban