The scapula or shoulder blade is the bone that connects the clavicle to the humerus. The scapula forms the posterior of the shoulder girdle. It is a sturdy, flat, triangular bone. The scapula provides attachment to several groups of muscles. The intrinsic muscles of the scapula include the rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus. These muscles attach the scapular surface and assist with abduction and external and internal rotation of the glenohumeral joint. The extrinsic muscles include the triceps, biceps, and deltoid. The third group of muscles includes the levator scapulae, trapezius, rhomboids, and serratus anterior. These muscles are responsible for rotational movements and stabilization of the scapula. [1]
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth ribs or the first to ninth ribs at the lateral wall of the thorax and inserts along the superior angle, medial border, and inferior angle of the scapula. The main part of the serratus anterior lies deep to the scapula and the pectoral muscles and is easily palpated between the pectoralis major and latissimus dorsi muscles. This large muscle is generally divided into three distinct parts according to the points of insertion: serratus anterior superior (insertion near the superior angle), serratus anterior intermediate (insertion along the medial border), and serratus anterior inferior (insertion near the inferior angle). [2]
The serratus anterior is capable of a wide range of actions across the scapulothoracic joint. Furthermore, the lack of control, strength, or activation of this important muscle is believed to be associated with several painful conditions involving the shoulder complex. [3]
The rhomboid muscles, comprising the rhomboid major and rhomboid minor, are located in the upper back beneath the trapezius muscle. They originate from the spinal column and insert into the medial border of the scapula. These muscles are primarily responsible for retracting the scapula, which involves pulling the shoulder blades towards the spine. They also aid in stabilizing the scapula during shoulder movements.
The levator scapulae is a long, slender muscle that extends from the transverse processes of the upper cervical vertebrae to the superior angle of the scapula. As its name suggests, the primary function of the levator scapulae is to elevate the scapula. Additionally, it assists in downward rotation and lateral flexion of the neck.
The rhomboid minor and levator scapulae muscles are interconnected and enclosed by connectives. Between these two muscles a bridge of connective tissue, containing fat, is observed. These connectives end cranially at the surface of the splenius capitis, and at the midline, containing vessels and nerves, as supported by histology and plastinations. This unification is separate from the rhomboid major muscle but overlaps with the latter dorsally. It connects to the superior angle of scapula and its upper medial borders, respectively, and cranially to the root of the spine of the scapula. Beneath the united levator scapulae and rhomboid minor, described here, the serratus posterior superior and possibly serratus anterior form a hypomochlion or fulcrum at the superior angle of the scapula. Any tension on this unified entity can unbalance this fulcrum. [4]
- Cowan, Paul T., i in. „Anatomy, Back, Scapula”. StatPearls, StatPearls Publishing, 2024. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK531475/.
- Lung, Kirsten, i in. „Anatomy, Thorax, Serratus Anterior Muscles”. StatPearls, StatPearls Publishing, 2024. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK531457/.
- Neumann, Donald A., i Paula R. Camargo. „Kinesiologic considerations for targeting activation of scapulothoracic muscles – part 1: serratus anterior”. Brazilian Journal of Physical Therapy, t. 23, nr 6, 2019, s. 459–66. PubMed Central, https://doi.org/10.1016/j.bjpt.2019.01.008.
- Kulow, Charlotte, i in. „Levator Scapulae and Rhomboid Minor Are United”. Annals of Anatomy = Anatomischer Anzeiger: Official Organ of the Anatomische Gesellschaft, t. 243, august 2022, s. 151938. PubMed, https://doi.org/10.1016/j.aanat.2022.151938.