The Serratus Posterior (SP) muscles form an intermediate group of back muscles. Their rectangular shape lies deep to rhomboid muscles in both the upper and back portion of thorax.
Trigger points in this muscle often cause discomfort under the shoulder blade, at the back of the arm or on either side of the little finger on one hand. Learn how to identify, self release and stretch this muscle!
Origin
The Musculus Serratus Posterior (MSP) is a rectangular muscle found in both the upper back and part of the thorax, lying deep to rhomboid muscles and making up part of an intermediate layer of back muscles. It plays a primary role in protraction and upward rotation of scapular and shoulder blade movement as well as stabilization against the ribcage during movement.
The muscle originates as a thin aponeurosis from the lower part of the nuchal ligament, the spinous processes of seventh cervical vertebra, first two thoracic vertebra and adjacent supraspinous ligaments [1] It runs inferolaterally before inserting via four separate tendon insertions onto external surfaces of ribs 2-5 lateral to their angles via four distinct tendon insertions separated by septa (often separated by septa), giving this muscle its multipennate structure; with three superior fibers being distinguished from six inferior fibers [2-3].
At first glance, this SPS case appeared different from previous reports; its fiber orientation and number of attachments differed substantially; its muscle was oriented quadrilaterally instead of in an oblique fashion and attached to less ribs than usual.
This unexpected variance in the anatomy of the SPS could be explained by any number of factors; from hereditary traits or differences in muscle structure to chronically overused muscles susceptible to fatigue and atrophy that produce altered fiber patterns and reduced number of rib attachments.
Even with its unique arrangement, SPS muscles still function effectively. If they become overused and form trigger points, however, this could result in shoulder and chest discomfort. To help avoid such problems, use an app such as Painalog that identifies trigger points in back muscles and offers guidance for self-releasing them – try it free for seven days on Google Play and App Store today and download!
Insertion
The serratus posterior muscle has a quadrilateral shape and is innervated by the second to fifth intercostal nerves, elevating ribs during inspiration. It originates in nuchal ligament, spinous processes of vertebrae C7-T3, their supraspinous ligaments, and inserts into external surface of ribs two through five lateral to their angles; its superior muscle arises from nuchal ligament, spinous processes of vertebrae T11-L2 vertebrae, the intercostal ligament then inserts into inferoposterior surface of ribs 9-12 respectively.
To access this muscle, an incision should be made at or near the axilla similar to what was done for the latissimus dorsi flap, and its lower edge dissected using bipolar cautery. Next, connective tissues between sixth and seventh slip are separated while taking care to preserve both vascular leashage and nerve suppleness.
The thoracodorsal artery descends inferiorly from the serratus muscle, creating a circumflex scapular artery before reaching the superior three or four slips. If desired, this artery can be isolated up to its origin at subscapular artery depending on pedicle length before being tied off through intrafascicular dissection to avoid winging of the scapula.
Action
The serratus posterior muscle helps raise the superior four ribs during inhalation by depressing them – one of several accessory muscles of inspiration – while also depressing them during expiration, helping stabilize scapula movement at shoulder joint, working alongside other back muscles to assist movement, and is easily palpated as fan-shaped muscle on either side of chest between pectoralis major and latissimus dorsi muscles.
The muscle is innervated by the thoracodorsal nerve (C5-7), which arises from the lower part of the scapula and receives blood from posterior intercostal arteries and subcostal arteries. It lies superficial to erector spinae muscle group, thoracolumbar fascia and deep to latissimus dorsi muscle; its surface lies pierced by both lateral thoracic nerves and subcostal nerves, supplying it with blood.
The inferior serratus works similarly to its superior counterpart but with slightly different movements. It primarily serves to adduct the ribs while aiding with inspiration and exhalation, working alongside its partner muscles iloicostalis, longissimus thoracis and quadratus lumborum. Though small in size it plays an essential role in daily activities.
Trigger points in the musculus serratus posterior are caused by poor postures, repetitive movements or traumatic injuries and can produce a constant, deep ache under the upper portion of your shoulder blade. When reaching overhead or bending forward they may cause pain that can also be felt when coughing or sneezing.
Medical professionals tend to overlook the significance of the musculus serratus posterior muscles for neck and shoulder pain relief, yet more attention is being drawn to them by medical science. Regular checks for tightness or trigger points on this muscle could improve breathing and posture as tightness or trigger points can hinder it – myofascial trigger point massage could help relax it further and alleviate pain relief.
Innervation
The serratus posterior superior muscle is an intermediate layer of back muscles located near the upper part of thoracic spine and neck, deep to rhomboid muscles. Its wing-like shape extends between vertebrae in spinal column and ribs of thorax and it is supplied with innervation by intercostal nerves 2-5.
Serratus posterior superior muscle fibers extend inferolaterally from their origin and attach to the superior borders of 2nd-5th ribs lateral to their angles, elevating during inspiration as an accessory muscle of respiration and helping extend sternum and thoracic cage during inhalation.
Serratus posterior muscles are two serratus muscles found in the thoracolumbar fascia covering splenius cervicis in the thoracic region, working in conjunction with the rhomboids to retract and move scapula medially and superiorly, squaring shoulders and retracting the scapula posteriorly to square them off. Motor innervation from levator scapulae muscle supplies them motor innervation while arterial blood supply comes via posterior intercostal arteries branching off from thoracic aorta which provides arterial blood supply via posterior intercostal arteries from thoracic aorta which provides motor innervation as well as arterial blood supply from posterior intercostal arteries which branches off from thoracic aorta providing motor innervation as motor innervation motor innervation and arterial blood supply from posterior intercostal arteries branching off from thoracic aorta provide motor innervation motor innervation from within while receiving arterial blood supply via posterior intercostal arteries that emerge from the thoracic aorta; providing motor innervation as well as receiving motor innervation via motor innervation from within as well as arterial blood supply via posterior intercostal arteries arising from thoracic aorta which provide arterial blood supply from within to facilitate its muscle cells as motor innervation which emanating out from within its respective aorta to provide motor innervation supply, providing motor innervation via arterial supply artery supply from their position within their respective posterior intercostal arteries that emerge from their respective aorta to provide motor innervation from which are vital blood supply through their arterial supply from posterior intercostal aorta receiving motor innervation from its owning within an exiting from their position on to receive motor innervation from posterior intercostal a.
As with other muscles of the neck and thorax, serratus posterior can develop trigger points (muscle knots). Trigger points in this muscle are common among those living with chronic obstructive pulmonary disease (COPD), due to repetitive movements that compress it in its thoracic cavity. Compression may also result from poor mattress support or chairs without adequate lumbar support, or herpes zoster infection.
The serratus posterior inferior muscle is a thin quadrilateral muscle. It starts its path on the vertebrae T11-L2 with their supraspinous ligaments before ascending anterolaterally until reaching ribs 9-12’s lower borders lateral to their angles, where its lower borders connect to intercostal nerves 9th-12th intercostal and subcostal nerves innervate it and supply innervation for respiration; evidence in support of its function in respiration remains limited. Furthermore, myofascial pain syndromes has been implicated as well as being involved with shoulder pain syndromes – thus contributing to shoulder discomfort in various degrees.
