Rhomboid, Levator Scapula & Serratus Anterior Muscle Chain
Introduction
Rhomboid, Levator Scapula and Upper Trapezius dysfunction are commonly diagnosed in patients experiencing thoracic and cervical spine complaints. Less widely documented is the influence of the Serratus Anterior. Casteless (2016) documented a significant correlation with neck pain and impairment of Serratus Anterior activation.
This functional relationship of the muscles is mirrored by their strong anatomical attachments to each other. This anatomical interaction is through dense aponeuroses and strong bands of connective tissue that attach the Rhomboids, Levator Scapula and Serratus Anterior into one muscular sheet.
The topics in this article include:
Shared anatomical connections of the Rhomboids, Serrratus Anterior and Levator Scapula.
Anatomy and functions of the Levator Scapula, Rhomboids and Serratus Anterior.
Stretching the Serratus Anterior, Levator Scapula and Rhomboids.
Shared anatomical connections of the Rhomboid, Serratus Anterior and Levator Scapula
(1) Scapula attachments
Bharihoke & Gupta (1986) studied the attachments of the Levator Scapula, Rhomboid minor and major to the scapula. They found anterior and posterior attachment of these muscles to the scapula “enveloping” the bone. Standring (2015) found the enveloping of the Rhomboid Minor encloses the inferior boarder of the Levator Scapula.
The anterior attachments of all three muscles overlapped the costal surface of the Serratus Anterior fascia for about three centimeters. The fasciae of these muscles merges with each other along a straight line joining the free margins of their costal flaps (Barihoke & Gupta 1986).
The continuity of the Serratus Anterior and the Rhomboid/Levator Scapulae has been described as a wide muscular sheet with a deep common fascia (Nguyen & Nguyen 1987).
This continuity of the upper fibers of the Serratus Anterior and Levator Scapula not only dictates their dual function in suspending the scapula (Standring 2015) but anatomically is that of a composite aponeurosis (Nguyen & Nguyen 1986). This tough aponeurosis at the anterior supraspinous region of the scapula is also compounded by the Rhomboid Minor. The Rhomboid Minor has a tough wide anterior tendon extending 2-3 cm medial to and below the Levator Scapula where the fascia of the Rhomboid Minor and Serratus Anterior are fused (Standring 2015).
Bharihoke & Gupta (1986) didn’t only notice the Rhomboids and Levator Scapula enveloping the scapula but the Serratus Anterior also. This muscle sandwiches the anterior and posterior surfaces of the superior and inferior angles of the scapula. Being attached to both surfaces of the scapula at these sites allowes for a posterior continuity of the Serratus Anterior and the Rhomboids and Levator Scapula.
Possible friction between the upper Serratus Anterior, Levator Scapula and superior angle of the scapula has been proposed as a cause of levator scapula syndrome (Smith et al 2003).
(2) Anterior rib attachments (including Scalene Medius)
Smith et al (2003) and Webb et al (2018) followed these aponeurotic and fascial attachments between the Serratus Anterior and Levator Scapula. They found the fibers of the Serratus Anterior that attaches to the Levator Scapula course anteriorly around the body and constitute the Serratus Anterior's upper two ribs attachment (and occasionally the third, Smith et al 2003). Lifchez (2004) found these upper rib attachments thicker than the more inferior fibers.
Hester et al (2000) identified a tight fascial band of tissue running from the inferior aspect of the brachial plexus, extending just superior to the Scalene Medius muscle insertion on the first rib and presented a digitation that extended to the proximal aspect of the Serratus Anterior muscle.
Smith et al (2003) found the upper fibers of the Serratus Anterior form a bed for the neurovascular structures in the upper axilla that may be a possible cause of thoracic outlet syndrome.
(3) Extrathoracic fascia
The common fascia covering and blending with this collective muscular sheet comprising the Serratus Anterior, Rhomboid, Levator Scapula and Trapezius is the extrathoracic fascia. Described by Latarjet and Juttin (1953) it's boundaries are:
Superiorly: blends with the aponeurosis of the Trapezius and Levator Scapula.
Medially: vertebral attachment of the Rhomboid and Latissimus Dorsi extending down to T9.
Laterally: anterior insertions of the Serratus Anterior (rib 2 to 8) at it’s fascia.
Running medial to lateral the extrathoracic fascia blends with the aponeurosis covering the anterior surfaces of the Rhomboid and Serratus Anterior.
Inferiorly: runs parallel to the body of the ninth rib or, less frequently, the ninth intercostal space. Thus its course is obliquely downwards and lateral. It is covered by the anterior surface of the latissimus dorsi medially and of the Serratus Anterior laterally.
At the inferior border the extrathoracic fascia divides into two sheets:
(a) the superficial sheet which blends with the anterior part of the aponeurosis of the Latissimus Dorsi medially and the Serratus Anterior laterally.
(b) the deep sheet which is thinner than the superficial and merges with the thoracolumbar region.
(4) Deep cervical fascia
Syed et al (1953) identified the connections of the middle layer of the deep cervical fascia as providing a common fascia for the Omohyoid, Rhomboid and Levator Scapula.
The authors separated the middle layer of the deep cervical fascia into three laminae of fascia:
Omosternal fascia.
Hyosternal fascia.
Visceral fascia.
Only the omosternal and hyosternal fascia are covered here as they are intimately linked with the musculature.
Omosternal fascia
The Omosternal fascia is a thin lamina that ensheaths four muscles:
a. Subclavius.
b. Omohyoid (superior and inferior belly).
c. Levator scapulae.
d. Rhomboids.
It also surrounds:
a. Sternohyoid muscle.
b. Omohyoid muscle.
Boundaries:
a. Superiorly: Hyoid bone where it blends with the superficial layer of the deep cervical fascia and the Hyosternal fascia.
b. Anteriorly:
Anterior triangle of the neck: blends at the superolateral margin of the omohyoid with the overlying superficial layer of the deep cervical fascia and the underlying hyosternal fascia.
Median line: crosses the median line of the neck to the other side.
c. Anterior-Inferiorly: manubrium and clavicle.
d. Laterally:
At the region of the Sternocleidomastoid:
Blends with the superficial layer of the deep cervical fascia that surrounds the Sternocleidomastoid.
Under the Sternocleidomastoid it forms a fascial pulley to permit the intermediate tendon of the Omohyoid to pass through.
Posterior triangle of the neck: the omosternal fascia blends with the superficial layer of the deep cervical fascia along the inferior belly of the omohyoid and with the underlying hyosternal fascia. The omosternal fascia reaches along the omohyoid to the upper boarder of the scapula.
e. Posteriorly-Inferiorly: between the scapula and the vertebral column it ensheaths the levator scapula and rhomboids
Hyosternal fascia
ls a thin laminae of fascia similar to the omosternal fascia.
Covers:
a. Sternothyroid muscle.
b. Thyrohyoid muscle.
Boundaries:
a. Laterally:
At the Sternocleidomastoid: blends with the superficial layer of the deep cervical fascia surrounding the Sternocleidomastoid.
Posterior triangle of the neck: blends with the omosternal fascia.
b. Superiorly: Hyoid bone and Thyroid cartilage. At the Hyoid bone it blends with the superficial layer of the deep cervical fascia and the omosternal fascia.
c. Anteriorly: crosses the midline of the neck to the other side.
d. Inferiorly: posterior boarder of the manubrium sterni and medial part of the clavicle.
Anatomy & function of the Levator Scapula, Rhomboids and Serratus Anterior
Levator Scapula
Attachment: C1-4 to supraspinous angle.
Accessory attachments can exist to the mastoid process, occipital bone, rib 1 and 2, Scalene, Trapezius, Serratus Anterior and Serratus Posterior Superior.
Action: elevates the scapula and ipsilateral sidebends the cervical spine.
Rhomboid Major
Attachment: T2-5 to medial boarder of scapula.
Action: retracts the scapula superiorly and medially.
Rhomboid Minor
Attachment: C7-T1 to medial supraspinous boarder.
Action: retracts the scapula superiorly and medially.
Occasionally Rhomboid Occipitalis
Attachment: upper boarder of Rhomboid Minor to occipital bone.
Serratus Anterior
Attachment: rib 1-8(-10) to the medial boarder of the scapula.
Webb et al (2018) divided the Serratus Anterior into sections tracking the scapula attachments anteriorly to their rib attachments. They divided the Serratus Anterior into three divisions:
(1) Superior division: attaches to the superior angle of scapula (anterior and posteriorly) and rib 1 and 2. These fibers are shorter, thicker, and separated from the rest of the muscle. These fibers can, in cases, also attach on to the fascia covering the intercostal space (Smith et al 2003).
(2) Middle division: attaches to the medial boarder of scapula and rib 2 and 3.
(3) Inferior division: attaches to the inferior angle of scapula (anteriorly and posteriorly) and rib 4 to 8/10.
This makes makes the attachments of the Serratus Anterior to the Levator Scapula and Rhomboid continuous with the upper three ribs and the attachments of the Serratus Anterior and external oblique continuous with the inferior angle of scapula.
Nguyen & Nguyen (1986) identified two differently oriented layers for the muscular digitations of the middle and inferior parts of the Serratus Anterior. Could this represent a dual function associated with the muscles own role on the scapula as well as this part of the muscle’s attachment and role in functionally working with the external oblique? (de Arauju et al 2018)
Lifchez (2004) identified the Serratus Anterior muscle slips (the portion of the muscle that inserts on a rib) and subslips (superficial or deep subdivision of the slip). Deep subslips were thinner than superficial subslips and the most inferior slips were thinner than those of the superior slips. This would suggest a pronounced action of the superior fibers of the Serratus Anterior in functioning with the upper fibers of Trapezius and Levator Scapula in suspending the scapula.
Action: The Serratus Anterior is the primary stabilizer of the scapulothoracic articulation. It provides a stable axis for scapular rotation as it acts as a solid base of support for upper extremity function (Smith et al 2003). It protract the scapula with the Pectoralis Minor and upwardly rotate the scapula* (Smith et al 2003) and fixes the scapula against the thorax.
*: upward rotation of scapula: inferior angle of scapula swings superiorly and laterally around an A-P axis.
Upper fibers: suspend the scapula with the Levator Scapula and upper fibers of Trapezius. These fibers stabilize the scapula during humeral elevation. They also create an anterior tipping movement of the scapula around an axis parallel to the spine of scapula (Smith et al 2003).
Lower fibers protact the scapula to assist the upper fibers of Trapezius to raise the arm above the head.
Stretching the Serratus Anterior, Levator Scapula and Rhomboids
Stretching the Serratus Anterior
Upper fibers: retraction and depression of the scapula. Due to the attachments of the fascial sling from the Scalene Medius to the Serratus Anterior could contralateral sidebending increase this stretch? Smith et al (2003) found an anomalous attachment of the upper Serratus Anterior to the Scalene Posterior.
Middle and inferior fibers: retraction of the scapula.
Stretching the Levator Scapula, Rhomboid Minor and Major
Best with the patient seated head face down on the bench (comfortably) elevated. With the patient's ipsilateral arm hanging by the side the scapula can be protracted/depressed for the Rhomboids and Levator Scapula using the relevant hand contacts.
References
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