IJCRR

IJCRR - 5(15), August, 2013

Pages: 52-54

Date of Publication: 17-Aug-2013

SERRATUS POSTERIOR MUSCLES: ANATOMICAL PROPERTIES, FUNCTIONAL AND CLINICAL SIGNIFICANCE

Author: Sachin Patil

Category: Healthcare

Abstract:There is significant paucity in the literature regarding serratus posterior superior and inferior muscles. Most standard textbooks mention conflicting views on the role of serratus posterior superior and inferior muscles in respiration. This study was aimed at providing a more accurate review about the serratus posterior superior and inferior muscles and their functional importance. For the preparation of this paper we consulted scientific articles published in English and textbooks. The articles were accessed from a basic search in PubMed database. Recent studies have shown that there is no electromyographic evidence supporting a role for either the serratus posterior superior and inferior muscles in respiration. These muscles may function primarily in proprioception and are clinically important.The serratus posterior superior and inferior muscles are considered to be source of myofascial pain, which presumably originates from trigger points within the muscles. Both muscles are implicated in chronic pain syndromes like idiopathic myalgia or painful shoulder syndrome and scapulocostal syndrome. Further investigation need to be done on these muscles to confirm their functional and clinical importance.

Keywords: serratus posterior, scapulocostal syndrome, trigger points, myofascial pain

Full Text:

INTRODUCTION

Serratus posterior superior (SPS) is a thin quadrilateral muscle, which arises by a thin aponeurosis from the lower part of the nuchal ligament, the spines of the seventh cervical and upper two or three thoracic vertebrae and their supraspinous ligaments.¹ But study by Satoh describes origin of SPS as high as third cervical vertebrae while lower limit of origin is upto second thoracic vertebrae.² Textbook of anatomy by Cunningham’s mentions inferior limit of origin upto fourth thoracic vertebrae.³ SPS is inserted as four digitations attached to the upper borders and external surfaces of the second, third, fourth and fifth ribs, just lateral to their angles. Serratus posterior superior is innervated by the second, third, fourth and fifth intercostals nerves.¹

Serratus posterior inferior (SPI) arises from the spines of the lower two thoracic and upper two or three lumbar vertebrae and their supraspinous ligaments by a thin aponeurosis that blends with the lumbar part of the thoracolumbar fascia.¹ Textbook of anatomy by Cunningham’s mentions thoracolumbar fascia as only origin of this muscle.³ But study by Satoh describes origin of SPI as high as eleventh thoracic vertebrae.⁴  It ascends laterally, and its four digitations pass into the inferior borders and outer surfaces of the lower four ribs, a little lateral to their angles. Serratus posterior inferior is innervated by ventral rami of the ninth, tenth, eleventh and twelfth thoracic spinal nerves.¹

There is no electromyographic evidence supporting a role for either the SPS or SPI  in respiration. Thus, the main evidence  suggesting  such  a role is one the basis of their attachments. The clinical importance of these muscles is that both are implicated in chronic pain syndromes like idiopathic  myalgia  or painful  shoulder  syndrome and scapulocostal syndrome.

Figure 1- Serratus posterior superior (SPS) and serratus posterior inferior (SPI) muscles

MATERIALS AND METHODS

For the preparation of this paper we consulted scientific articles published in English and textbooks. The articles were accessed from a basic search in PubMed database (http://www.ncbi.nlm.nih.gov/pubmed), using terms like serratus posterior superior, serratus posterior inferior and scapulocostal syndrome. The data concerning anatomy, function and clinical significance of serratus posterior superior and inferior muscles was collected and analysed.

DISCUSSION

The standard textbook of Anatomy mentions conflicting views on function of these muscles.The British edition of Gray's Anatomy  indicates that  the  role of the  serratus  posterior  superior is  uncertain  in  man  whereas   the  American   edition   describes   a  specific function   for  this  muscle,  namely,   elevating  the  ribs during  deep  inspiration.  Similarly,  for the presumably related  muscle,  serratus  posterior   inferior ,  the British edition  indicates  that  the  muscle's action is to draw  the   lower  ribs  downward   and   backward,  although  possibly  not  in respiration.  In  contrast,  the American  edition of this text  states  that  the muscle  is active  during  forced  expiration.⁵ Hollinshead’s Anatomy mentions the serratus posterior muscles as inspiratory muscles which is similar to that stated in clinical anatomy by  Moore  and  Dalley .^6,7 But Snell anatomy  indicates  that  the  SPS is active  in inspiration  and  the  SPI  in expiration.⁸

Regarding the function of muscles other different views are present in previous literatures. Travell and Simons suggested  that  the  SPI  functions synergistically  with  the  ipsilateral  iliocostalis  and longissimus  for rotation  (unilateral)  and extension   (bilateral)  of  the  spine while in  respiration,   the  muscle  acts synergistically with  the quadratus lumborum.⁵

Vilensky et al suggested that  the  SPS and  SPI  have  reflex  connections  with   the   respiratory   muscles   such  that   overstretching   results    in    compensatory    movements. The muscles  may  function  to measure stress  levels  at the  superior  and  inferior  limits  of the  thoracic  spine.  Considering,   the  ambiguous   relationship   between    muscle   spindle   density   and   presumed   proprioceptive    function,   they  suggested  that  better electromyographic   recordings  and electroneurography of the motor and sensory nerves  of these  muscles, rather  than  further  histological  analysis, would  be the best  approach  to understanding   their  function. Authors further stated that  until  there  is supportive  evidence,  no respiratory  function  be attributed to  either   the  SPS  or  the  SPI,  and  that  the  possible clinical  importance   of these  muscles  as generators  of pain,  especially   shoulder   pain,  which  is  one  of  the frequent  locations  of myofascial  pain, should be  mentioned    in  gross  anatomy  courses and  textbooks.⁵

The scapulocostal syndrome, an insufficiently understood condition was clinically studied in 201 cases by Fourie   LJ in 1991. The pain was the presenting symptom in all cases and important cause was from an enthesopathy of the serratus posterior superior muscle. The operation of 'serratotomy' (severing the serratus posterior superior muscle) was performed with excellent results in 6 patients in whom conservative treatment failed. This study supports that SPS is one of the cause of  painful  shoulder  syndrome and scapulocostal syndrome.⁹

Recent study  by Loukas M et al supported that SPS and SPI have role in role in respiration based on their findings that no morphometric difference exists between the SPS and SPI of COPD patients versus controls.¹⁰

Further investigation need to be done on these muscles to confirm their functional and clinical importance.

CONCLUSION

We undertook this study with the aim of providing a more accurate report about the serratus posterior superior and inferior muscles, because of  interesting relationship with  chronic pain syndromes like idiopathic  myalgia  or painful  shoulder  syndrome and scapulocostal syndrome. Finally, this study shall be useful for  clinicians, surgeons and academics that manipulate and keep  particular interest for these mysterious muscles .

ACKNOWLEDGEMENT

Authors acknowledge the great help received from the scholars whose articles cited and included in references of this manuscript. The authors are also grateful to authors/ publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.

References:

1. Standring, S. (Ed). Gray's Anatomy: The Anatomical Basis of Clinical Practice 40th ed. New York: Churchill Livingstone.2008;2729-31.
2. Satoh  JI.  The serratus   posterior  superior  in  certain  catarrhine  monkeys and  man,  in particular  the  structure    of  the   muscular    digitations    and  their   nerve   supply.   Okajimas Folia  Anat  Jpn. 1969; 46:65-122.
3. Sinclair DC. Muscles and fasciae, In: Romanes GJ (ed) Cunningham’s textbook of anatomy. 12th eds. Oxford: Oxford University Press, 1981; 352.
4. Satoh  J I.  The   serratus   posterior    inferior   in monkey and man,   in particular the structure of the   digitations    of this muscle    and   their    nerve   supply.    Okajimas    Folia   Anat   jpn. 1970; 47:19-61.
5. Vilensky JA, Baltes M, Weikel L, Fortin JD, Fourie LJ. Serratus posterior muscles: anatomy, clinical relevance, and function. Clin Anat. 2001 ;14(4):237-41.
6. Hollinshead WH,Rosse C( eds). In: Textbook of anatomy. 4th ed. Philadelphia.1985;309-310
7. Moore   KL,  Dalley  AF  II. Clinically oriented  anatomy.   4th ed.  Baltimore: Lippincott     Williams and Wilkins. 1999; 80.
8. Snell   RS. Clinical anatomy    for  medical   students.  Baltimore: Lippincott   Williams and Wilkins. 2000; 58.
9. Fourie   LJ. The    scapulocostal     syndrome.    S  Afr  Med   J  1991; 79:721-724.
10. Loukas M, Louis RG Jr, Wartmann CT, Tubbs RS, Gupta AA, Apaydin N, Jordan R. An anatomic investigation of the serratus posterior superior and serratus posterior inferior muscles. Surg Radiol Anat. 2008;30(2):119-23.