WHAT DOES SCAPULAR STABILIZATION MEAN?
The authors of this paper argue that there is no meaningful way to define scapular instability for several reasons:
- unlike other bones, large movements of the scapula do not move joints into positions where there is significant danger of exceeding a safe range of motion
- movement and position of the scapula is highly complex, variable, and task specific
- movements of the scapula considered to be “abnormal” cannot be defined or measured objectively
- there is little to no correlation between “abnormal” movements of the scapula and pain/dysfunction .
RETHINKING THE STABLE BASE FUNCTION OF THE SCAPULA
The authors note that the scapula is an unusual bone (a sesamoid bone) because it floats on the ribcage, and its position is only minimally constrained by bones and ligaments. Thus, its position is almost totally determined by competing pushes and pulls of antagonistic muscle groups that connect to the spine, rib cage and arm. Thus, the scapula can be viewed as the hub of a “tensegrity” structure, whereby forces coming from the arm are transferred to the axial skeleton through the soft tissues rather than bones .
Given this model, shoulder resilience is better promoted by variability and maximizing degrees of freedom at the scapula, rather than by providing a “stable base”. Thus, a better term than “stability” to describe optimal scapular performance is “robustness”, which means ability to handle perturbation.
Shoulder resilience is better promoted by variability and maximizing degrees of freedom at the scapula, rather than by providing a ‘stable base’.
IS DYSKINESIS AN INDICATOR OF INSTABILITY?
The authors propose that most observed “dyskinesis” at the scapula is probably an example of normal variability. A review of past studies shows little to no correlation between movements described to be “dysfunctional” and shoulder pathology [1, 3].