Le serratus anterior, also called "large serratus", "anterior serratus" or, "Chaussier's costoscapularis muscle", is a flat muscle, broad and powerful applied to the side walls of the thorax.
It has several actions, including the scapula stabilization and rotation of the glenothoracic joint. It is also involved in respiration as an accessory inspiratory muscle.
Anatomy, functions, pathology (paralysis of the serratus anterior muscle)… We tell you all about this muscle!
Serratus Anterior: Descriptive Anatomy
Le serratus anterior is a large quadrilateral muscle (has four sides) applied to the side wall of the thorax. It owes its name to its sawtooth shape that can be clearly seen in athletic and lean subjects (very low fat mass).
It inserts into the lateral sides of the first 10 ribs and ends at the inner edge of the scapula (shoulder blade). This is what earned him the name “costoscapularis muscle”.
The serratus anterior muscle is richly vascularized by two branches of the axillary artery: the lateral thoracic artery for its upper part, the thoracodorsal artery for its lower part.
Its motor innervation is provided by the long thoracic nerve (also called Charles Bell's respiratory nerve) from the brachial plexus.
Serratus anterior: functions
The serratus anterior has the main function of scapula stabilization, keep pressed against the chest wall in synergistic action with another muscle called the rhomboid.
For example, it is the serratus anterior that prevents the scapula from moving backwards when shoot forcefully something with the hands (pushing a broken down car, doing push-ups, etc.).
Its second main function is rotation of the glenothoracic joint. The latter is not an articulation strictly speaking, it is a slip space between the anterior surface of the scapula and the chest wall via a bursa.
When the serratus anterior muscle fibers contract, the scapula is pulled outward and forward. This imparts to it a rotational movement responsible for a shoulder stump elevation.
The serratus anterior has another action secondary or accessory. In fact, it allows the elevation of the first 10 ribs to enlarge the volume of the thorax. This contributes to creating a depression at the level of the thoracic cavity facilitating the filling of the lungs (phenomenon of call for air). It is therefore one of the accessory muscles of inspiration (the main muscle being the diaphragm).
Pathology: Paralysis of the serratus anterior muscle
The primary cause of serratus anterior muscle paralysis is traumatic injury to the long thoracic nerve. The anatomy of the latter (significant length, spindly, superficial position) particularly exposes it to trauma.
The lesion may be secondary to a contusion or a shock in the shoulder or armpit. It can also be the consequence of a stretching brutal or chronic long thoracic nerve.
Certain sports or activities are particularly at risk of damage to the serratus nerve by excessively straining the upper limb (the lesions generally concern the dominant shoulder):
- Racket sports: tennis, squash, badminton, table tennis...
- Combat sports (brutal traction of the arm): judo, wrestling, MMA…
- Weightlifting, javelin throwing, archery, swimming...
- Carrying heavy loads: moving…
The neurological expectation of the serratus anterior can also be idiopathic (no cause is found).
Serratus anterior palsy is manifested by several symptoms. The most impressive of them is the detachment of the scapula and the protrusion of its tip. This phenomenon is called “scapula alata”, which means aspect of the scapula in wing. This is due to the loss of stabilization of the scapula by the serratus anterior (the latter being paralyzed and relaxed).
Other repercussions are observed:
- Persistent shoulder pain.
- Functional discomfort of the shoulder with difficulty when performing certain simple gestures (dressing for example).
- Limitation of the anterior elevation of the arm.
Treatment of serratus anterior paralysis
Form by stretching: conservative treatment
As soon as serratus anterior palsy is diagnosed, it is imperative to stop the sport or activity involved and rest the shoulder.
Resting is compulsory, regardless of the degree of neurological deficit, because it avoids overstretching the muscle and its fibrosis. The duration of rest should be extended, sometimes several months are needed before full recovery.
Treatment of serratus anterior paralysis following stretching of the long thoracic nerve rests on the re-education.
The rehabilitation techniques used depend on the degree of muscle denervation. They must include exercises of strengthening stabilizer muscles shoulder (trapezius, rhomboid muscles, levator scapulae or "angular") and rebalancing of the shoulder girdle.
The rehabilitation program has as its final objective the exercise rehabilitation and improving the power, endurance, fluidity and speed of execution of shoulder movements.
In nearly 70% cases of paralysis of the serratus anterior by stretching of the long thoracic nerve, the traitement conservative (rest and rehabilitation) allows a recuperation complete.
The recovery period is certainly long (sometimes exceeds 18 months), but the prognosis of isolated paralysis of the serratus anterior muscle is generally quite good.
If conservative treatment fails, surgery is required.
Form by compression: surgical treatment
Paralysis of the serratus anterior by compression of the long thoracic nerve is treated surgically.
The operation is carried out under anesthesia General on a patient in a supine position with the arms abducted and externally rotated. Its purpose is to decompress the nerve by performing a neurolysis (a nerve decompression similar to that performed on the median nerve in the case of carpal tunnel syndrome). This delicate step is carried out with instruments of microsurgery (microscope, special instruments).
From the third postoperative day, the neck and the shoulder regain their mobility. The final recovery can only be appreciated after a few weeks/months.
Prognosis of serratus anterior palsy
In the majority of cases, the course of serratus anterior muscle palsy is favorable. It results in a recuperation complete neurological deficit.
It should be noted, however, that the recovery is spring and sometimes only begins a few weeks after starting treatment. It can be spread over a variable period of time ranging from a few weeks up to 18 months (depending on the degree of neurological impairment). Only rarely does the motor impairment not improve.
A incomplete recovery serratus anterior motricity after paralysis is often secondary to continued harmful activity (sport or other activity involved in the occurrence of the attack).
Sometimes you can have paralysis of appearance "definitive", but to affirm it, it is necessary to wait at least two years, because late recovery remains possible. Otherwise, surgery will be considered (neurolysis).
But, often, we come up against a major problem during the clinical and paraclinical exploration of the long thoracic nerve: we do not always manage to locate the precise localization of compression along the path of the nerve. This greatly hinders care and recovery.
Resources
Video about pain between the shoulder blades:
References
[1] V. Berthoud, “Assessment of the benefit of serratus anterior muscle block in the management of postoperative pain after thoracotomies in cardiac surgery”, PhD Thesis, 2017.
[2] P. Vu, C. Guedon, P. Gehanno, and B. Andreassian, “Anatomical bases of serratus anterior muscle transposition”, Surgical and Radiologic Anatomy, flight. 10, no 3, p. 1-4, 1988.
[3] J. Rodineau, "Paralysis of the serratus anterior muscle in athletes", Journal of Sports Trauma, flight. 28, no 1, p. 44-53, 2011.
[4] E. BOTTON, M. TALARMIN, V. SIMONNET, O. AUDRAIN, and J. BAGLIONE, “Le myofascial syndrome of the serratus anterior muscle and the pectoralis major muscle: A cause of chronic chest pain in patients treated for breast cancer", Onko+, flight. 5, no 38, p. 71‑76, 2013 and Pain: Assessment-Diagnosis-Treatment, flight. 14, no 1, p. 30-37,
My name is Katia, I am specialized web editor in writing medical articles. Being passionate about medicine and writing, I set myself the goal of making medical information accessible to as many people as possible, through the popularization of even more complex scientific concepts.
My name is Katia, I'm 27 years old and I'm a web writer specializing in writing medical articles. Being passionate about medicine and writing, I have set myself the goal of making medical information accessible to as many people as possible, thanks to the popularization of even more complex scientific notions.