Treating Dysfunction of the Shoulder

Two muscles that directly affect each other are the upper trapezius, which is prone to tightness, and the serratus anterior, which is prone to lengthening. Dysfunction in these muscles sometimes leads to a shoulder impingement.

Anatomy:

The upper trapezius is the most superior portion of the trapezius muscle. Put together, the right and left trapezius form a trapezoid hence the name. The whole trapezius is superficial covers the posterior of the neck and the superior aspect of the trunk (Moore, Dalley, & Agur, 2014). More specifically the upper trapezius or descending trapezius fibers, originates from the external occipital protuberance, the medial third of the superior nuchal line, the ligamentum nuchae, and the spinous process of the seventh cervical vertebrae (C7), and inserts at the lateral third of the clavicle and the medial aspect of the acromion process of the scapula (Moore et al., 2014). The upper trapezius is innervated by the spinal accessory nerve (CN XI) and the ventral rami of C2-C4 (Pu, Tang, & Yang, 2008).

The serratus anterior is a powerful, broad saw-toothed shaped muscle that covers the lateral part of the thorax and forms the medial wall of the axilla (Moore, Dalley, & Agur, 2014). It originates from the lateral external surface of the 1st 8 ribs and inserts at the anterior surface medial border of the scapula, and is innervated by the long thoracic nerve (Moore et al., 2014).

Function:

Both the trapezius and serratus anterior are scapular stabilizers and are important in shoulder movement. The upper trapezius upwardly rotates and elevates the scapula (Paine & Voight, 2013). The upper trapezius works synergistically with the levatator scapulae and rhomboids in elevation, and the upper trapezius works the lower trapezius and serratus anterior to upwardly rotate the scapula (Moore, Dalley, & Agur, 2014). In addition, the upper trapezius helps in neck movement. It is a secondary mover in cervical flexion and cervical lateral flexion, and is a primary mover in cervical extension (Moore et al., 2014). Despite all the movement the upper trapezius can generate, its main function is stabilizing the scapula during upper limb movement.

The serratus anterior is a powerful muscle that helps with several movements of the scapula. The serratus anterior works as prime mover in scapular upward rotation, with the upper and lower trapezius, and as a prime mover in protraction of the scapula, with the pectoralis major and minor being secondary movers (Moore, Dalley, & Agur, 2014). The inferior part of the serratus anterior assists in scapular depression, and the serratus anterior also anchors the scapula against the thoracic wall to allow a fixed point for the humerus to move around on (Moore et al., 2014)

The upper and lower trapezius and the serratus anterior are grouped together in a scapular rotator force couple to help create scapular upward rotation. This upward rotation helps maintain the optimal length-tension of the deltoid during abduction of the arm (Page, Frank, & Lardner, 2010). This force couple is vital in preventing a shoulder impingement by reducing superior migration of the scapula, improving posterior scapular tilt, facilitating ideal glenohumeral congruency, and maximizing the subacromial space (Page et al., 2010).

Dysfunction:

A shoulder impingement is a painful condition that affects the upper extremity. Shoulder impingement syndrome is caused when the rotator cuff tendons become inflamed as they move through subacromial space resulting in pain, weakness, and altered biomechanics of the arm (Braman, Zhao, Lawrence, Harrison, & Ludewig, 2013). Movement patterns that reduce subacromial space such as superior translation of the head of the humerus, insufficient posterior tilting of the scapula, and excessive upward rotation of the scapula can contribute or cause shoulder impingement syndrome (Braman et al., 2013). Since the upper trapezius and the serratus anterior are scapular stabilizers and prime movers, a change in muscle function can contribute to a shoulder impingement.

Alterations in scapular muscle activity is a cause in impingement. Often the upper trapezius is overactive, with reduced middle trapezius and lower trapezius muscle activity and the serratus anterior is weak (DeMey, Danneels, Cagnie, & Cools, 2012). The upper trapezius is recruited too soon and the serratus anterior muscle fiber recruitment is delayed which negatively influences the scapular rotator couple, decreasing the subacromial space, which leads to an impingement (Struyf et al., 2014). Exercise treatment strategies should focus on restoring muscle balance between the upper trapezius and middle and lower trapezius, and strengthening the serratus anterior.

In rehabilitation of a shoulder impingement, the goal is to is to decrease the activity of the upper trapezius, and increase the activity of the middle and lower trapezius. DeMey, Danneels, Cagnie, and Cools (2012) designed a four exercise protocol that increases recruitment and strength of the middle and lower trapezius, while minimizing upper trapezius activation. The program consisted of a three sets of ten repetitions. The exercises consist of prone extension, where the person is prone with shoulders in 90° forward flexion, where they perform bilateral extension to a neutral position with the shoulder in neutral rotation, forward flexion while on the side, where the person performs 90° of unilateral forward flexion in the sagittal plane, external rotation while on the side, where the person is on the side with the shoulder neutral and the elbow flexed 90° performing external rotation with a towel between the elbow and trunk to avoid excess movement, and prone horizontal abduction with external rotation, where the person performs bilateral horizontal abduction with additional external rotation at the end of the movement ( DeMey et al., 2012). This protocol lessened the activity of the upper trapezius and increased the activity of the lower trapezius and middle trapezius, subsequently decreasing the subject’s pain perception.

A weak serratus anterior results in poor scapular upward rotation and a change in posterior tilt of the scapula (Braman, Zhao, Lawrence, Harrison, & Ludewig, 2013). Strengthening the serratus anterior can be helpful in reducing an impingement. To increase recruitment patterns and strength Schory, Bidinger, Wolf, and Murray (2016) recommend diagonal exercises with scapular protraction. This way the serratus anterior is performing a large number of many of its functions. These exercises include a seated bench-press, the diagonal exercise, which is a combination of shoulder flexion, horizontal flexion and external rotation while seated, external bilateral scapular protraction, which is when a supine person protracts their scapula with the shoulders and elbows flexed, and the supine shoulder press, which is unilateral shoulder press with full scapular protraction (Schory et al., 2016). These exercises should help strengthen the serratus anterior and help correct a faulty firing pattern.

References

Braman, J. P., Zhao, K. D., Lawrence, R. L., Harrison, A. K., & Ludewig, P. M. (2013). Shoulder impingement revisited: Evolution of diagnostic understanding in orthopedic surgery and physical therapy. Medical & Biological Engineering & Computing, 52(3), 211-219.

DeMey, K., Danneels, L., Cagnie, B., & Cools, A. M. (2012). Scapular muscle rehabilitation exercises in overhead athletes with impingement symptoms. The American Journal of Sports Medicine, 40(8), 1906-1915.

Moore, K. L., Dalley, A. F., & Agur, A. M. (2014). Clinically oriented anatomy (7th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

Page, P., Frank, C. C., & Lardner, R. (2010). Assessment and treatment of muscle imbalance: The Janda approach. Leeds: Human Kinetics.

Paine, R., & Voight, M. L. (2013). The role of the scapula. International Journal of Sports Physical Therapy, 8(5), 617-629.

Pu, Y., Tang, E., & Yang, X. (2008). Trapezius muscle innervation from the spinal accessory nerve and branches of the cervical plexus. International Journal of Oral and Maxillofacial Surgery, 37(6), 567-572.

Schory, A., Bidinger, E., Wolf, J., & Murray, L. (2016). A Systemic Review of the Exercises that Produce Optimal Muscle ratios of the Scapular Stabilizers in Normal Shoulders. The International Journal of Sports Physical Therapy, 11(3), 321-336.

Struyf, F., Cagnie, B., Cools, A., Baert, I., Brempt, J. V., Struyf, P., & Meeus, M. (2014). Scapulothoracic muscle activity and recruitment timing in patients with shoulder impingement symptoms and glenohumeral instability. Journal of Electromyography and Kinesiology, 24(2), 277-284.