Scapular dyskinesis describes an alteration in the normal position or motion of the shoulder blade (scapula). This condition signifies a loss of control over the scapula’s typical movements and mechanics. While not an injury itself, it represents an underlying impairment that can stem from various sources, affecting the shoulder’s overall function.
The scapula plays a fundamental role in shoulder movement and stability, serving as a stable base for the rotator cuff. When its movement patterns are disrupted, it can reduce the efficiency of shoulder function and potentially contribute to shoulder pain. This altered movement might be subtle or visibly noticeable, sometimes appearing as a “winged” scapula where the shoulder blade protrudes abnormally.
Muscle Imbalances
Alterations in the strength, flexibility, or coordination of the muscles surrounding the shoulder blade significantly contribute to scapular dyskinesis. These imbalances disrupt the scapula’s harmonious movement, which normally provides a stable base for arm movements. When certain muscles become weak or others become overly tight, the shoulder blade loses its efficient motion pattern.
The serratus anterior muscle plays a crucial role in pulling the scapula forward around the rib cage and assisting its upward rotation during arm elevation. Weakness in this muscle often leads to a noticeable protrusion of the inner border of the shoulder blade known as “winging,” compromising the scapula’s ability to stay flush against the back. This dysfunction can hinder overhead movements and destabilize the shoulder complex.
The trapezius muscle, divided into upper, middle, and lower parts, also profoundly impacts scapular mechanics. The upper trapezius elevates the shoulder blade, while the middle fibers retract it. The lower trapezius depresses and assists in upward rotation of the scapula. An imbalance often seen is an overactive upper trapezius compensating for weakness in the middle or lower trapezius or the serratus anterior, leading to altered scapular positioning and movement.
The rhomboid major and minor muscles primarily retract, elevate, and downwardly rotate the scapula, holding it against the thoracic wall. If these muscles are weak or inhibited, the scapula may not be properly stabilized, leading to excessive protraction or an inability to control its downward rotation. This can disrupt the balance required for smooth shoulder motion, contributing to scapular dyskinesis.
Structural and Neurological Factors
The physical structure of the shoulder joint and the integrity of its controlling nerves also play a role in scapular dyskinesis. Conditions affecting the glenohumeral (shoulder) joint, such as shoulder impingement syndrome, rotator cuff tears, or instability, often lead to altered scapular movement. The body may compensate for pain or limited movement by changing how the scapula moves.
For example, in shoulder impingement, the scapula might exhibit decreased upward rotation, while instability can lead to excessive anterior tilting. These compensatory patterns, though initially protective, can disrupt the coordinated scapulohumeral rhythm. Rotator cuff injuries can also cause the scapula to move abnormally as it attempts to assist the compromised shoulder joint, impacting overall function.
Direct neurological impairment can profoundly affect scapular control. Injury to the long thoracic nerve, for instance, weakens the serratus anterior muscle, leading to “medial winging” where the inner border of the shoulder blade lifts away from the rib cage. Damage to the spinal accessory nerve can result in trapezius muscle weakness, causing “lateral winging” and a drooping of the shoulder. The dorsal scapular nerve, if injured, can impair the rhomboid muscles, contributing to scapular winging and pain around the shoulder blade.
Repetitive Strain and Postural Habits
Chronic activities and sustained body positions significantly influence scapular movement patterns, often contributing to dyskinesis. Repetitive overhead movements, common in sports, can lead to overuse injuries and muscle fatigue around the shoulder. This fatigue alters normal scapular kinematics, causing less efficient movement during arm elevation. Over time, this can lead to inflammation and strain, particularly in occupations requiring frequent overhead work.
Poor postural habits also contribute to abnormal scapular mechanics. Positions like rounded shoulders or a prolonged forward head posture can directly impact the resting position and dynamic movement of the scapula. These sustained postures often create muscle imbalances, with certain muscles becoming tight and shortened, while others become lengthened and weakened.
A forward head posture can increase the activity of the upper trapezius while decreasing the serratus anterior’s engagement, further disrupting scapular coordination. Such adaptations can lead to the scapula losing its optimal position on the rib cage, making it less effective as a stable base for arm movement. Addressing these ingrained habits is important for managing scapular dyskinesis.
Acute Trauma
Direct injuries or sudden, forceful events can immediately cause scapular dyskinesis. Fractures of the shoulder blade, while uncommon, typically result from high-energy impacts. Improper healing of these fractures can significantly impair scapular movement.
Clavicle (collarbone) fractures, which are more frequent, can disrupt the shoulder girdle’s bony structure, leading to altered scapular positioning and motion. Shoulder dislocations also directly compromise the scapula’s stability and coordinated movement. Severe muscle strains or tears surrounding the shoulder blade can instantly disrupt normal scapular function.