With the GH joint being one of the most mobile joints in the body, there is a lot of room for error. This joint is formed by the humerus and the glenoid cavity of the scapula. While a lot of emphasis is placed on the movements of the humerus and rotator cuff strength, sometimes the scapular contribution is overlooked. The scapular movement is extremely important as it makes up approximately 1/3 of the movement of the shoulder complex. In addition, a timing sequence exists between the humerus and scapula during movement called the scapulo-humeral rhythm. When the scapular movement or timing of movement is off, this can lead to musculoskeletal dysfunction and pain.
There are many factors that can affect scapular movement and the scapulo-humeral rhythm. In this post, I will discuss two of these factors: muscle weakness (under utilization) and kinesthetic sense. While there are multiple muscles contributing to scapular stability and movement, we will spotlight three of them. The upper trapezius, lower trapezius and serratus anterior facilitate upward rotation of the scapula needed during all OH reaching (the scapula will contribute approximately 60 degrees during the 180 degree OH arc). The amount each muscle contributes varies. However, I frequently see the pattern of over recruitment of the upper trapezius and under utilization of the lower trapezius and serratus anterior muscles. This is particularly seen after shoulder procedures such as RC repair as use of the humeral movers are inhibited leading to reliance on scapular movement. This pattern presents as a shoulder shrug during OH reaching. While short-term, this movement usually is not problematic, over time it can lead to neck pain and a disturbance in the scapulo-humeral rhythm.
So, how do you get a muscle to relinquish some of its dominance and up-train the muscles that are not pulling their weight? Luckily, most muscle perform more than one action. An example of this is the biceps brachii performing both elbow flexion, forearm supination, and shoulder flexion. You can use this concept to engage an under utilized muscle such as the serratus anterior and began to incorporate it into the movement you desire. This is how it works….
If every time your patient’s scapula goes into an upward rotated position your upper trapezius takes over, you probably do not want to start with this movement. Instead, you can use a secondary action for the serratus anterior, in this case protraction, to achieve the desired contraction. While the serratus anterior and upper trapezius muscles both perform scapular upward rotation, the upper trapezius does not perform scapular protraction which allows the serratus anterior to be engaged while at the same time minimizing upper trapezius involvement. With the serratus anterior engaged, you can slowly initiate the shared movement, in this case scapular upward rotation. This allows you to work into OH movements with the serratus anterior engaged and less dominance in the upper trapezius. Now, as you continue to reach higher OH, the upper trapezius will start to be recruited. This is not a bad thing but pay attention to prevent the shoulder shrug movement.
With the serratus anterior starting to activate during this movement, we can start to bring in the lower trapezius. I like to start in a prone position with your hands behind your head. This places the scapula in a partially upward rotated position but the hands behind the head provide a smaller lever arm, hence less demand placed on these muscle. When performing this with a patient, I like to start with an isometric hold. I take the weight of their arm and place the scapula in the position I would like them to hold. I then start to lessen my support of their arm which increases the demands placed on the lower trapezius. At this time, I will provide deep pressure to the upper trapezius to help inhibit the contraction while switching to a light tapping over the lower trapezius to facilitate contraction. As the patient improves their ability to engage their lower trapezius muscle, they can move through concentric/eccentric movements and work towards straightening their arm (increasing the lever arm) to perform a “prone Y” exercise.
Now that you have some tools to address muscle weakness (under utilized muscle contraction), we will discuss an exercise I like to use for kinesthetic sense. While various scapular proprioceptive neuromuscular facilitation (PNF) patterns can be used in training, I enjoy using a tactile cuing activity to increase this awareness. How it works….
I first place my finger lightly at different locations surrounding the scapula stimulating some of the skin receptors involved in kinesthesia (merkel, meissner, ruffini, and pacinian). I ask the patient to draw one scapula at a time towards the stimulation. Most of the time, the patient will be unable to do so. This is when their kinesthetic deficits become apparent. So, I will either use active joint or passive joint position sense (AJPS or PJPS) to train their scapula how to move. Once this is established, I will return to the initial exercise. The stimulus should occur in all areas around the scapula to elicit an array of movements such as elevation, depression, retraction, protraction, and a combination of movements. This exercise tends to show what movements the patient has difficulties with so you can spend more time training these movements.
These concepts and exercises are just a few tools to help address shoulder dysfunction. There are a million and one other paths so be creative and have fun!