Pectoral region

Pectoral region is a part of the anterior chest wall. FRCEM curriculum also includes trapezius & latissimus dorsi in this section, which are posterior chest wall muscles.

Pectoralis major

  • The most superficial of the pectoral muscles
  • Large, fan shaped
  • Origin – sternal half of the clavicle, upper half of sternum (superior 6 costal cartilages) and aponeurosis of external abdominal oblique muscle
  • Insertion – all 3 parts become a flat tendon that inserts into the intertubercular groove of humerus
  • Innervation – medial & lateral pectoral nerves (C5-C8 & T1)
  • Action – ADDucts & medially rotates upper arm; clavicular head flexes upper limb
Screenshot 2018-12-11 at 17.20.59.png
Fig 1. Pectoralis major

Pectoralis minor

  • Lies underneath pectoralis major
  • Origin – 3rd – 5th ribs
  • Insertion – coracoid process of the scapula
  • Innervation – Medial pectoral nerve (C8, T1)
  • Action – stabilises the scapula

Serratus anterior

  • Forms medial border of axilla
  • Origin – lateral aspect of upper 8 ribs
  • Insertion – medial border of scapula
  • Innervation – long thoracic nerve (C5-C7)
  • Action – rotates the scapula & pulls it towards the ribcage
Screenshot 2018-12-11 at 17.47.07.png
Fig 2. Pectoralis minor & Serratus anterior

Trapezius

  • Superficial extrinsic shoulder muscle (extrinsic means originating from the torso and attaching to the bones of the shoulder)
  • Broad, flat, triangular muscle
  • Origin – skull, nuchal ligament & spinal processes of C7-T12
  • Insertion – clavicle, acromion and the scapula spine
  • Innervation – accessory nerve (CN XI) & C3-C4
  • Action – elevation of scapula & rotates it during the abduction of the arm

Latissimus dorsi

  • Superficial extrinsic shoulder muscle
  • Origin – T6-T12 spinous processes, iliac crest, thoracolumbar fascia & inferior 3 ribs
  • Insertion – become a tendon that attaches to intertubercular sulcus of the humerus
  • Innervation – thoracodorsal nerve (C6-C8)
  • Action – extends, adducts & medially rotates the upper limb
Screenshot 2018-12-11 at 18.52.15.png
Fig 3. Trapezius & Latissimus dorsi

Sternoclavicular joint

  • Saddle joint – moves in two axes (but is actually pretty mobile and can move more like a a ball-and-socket type joint)
  • Sternal end of clavicle, manubrium of sternum & part of the 1st costal cartilage
  • Stability provided by the ligaments
    • Sternoclavicular ligaments (anterior & posterior)
    • Interclavicular ligament
    • Costoclavicular ligament
Screenshot 2018-12-11 at 18.30.05.png
Fig 4. Sternoclavicular joint
  • Innervation – medial supraclavicular nerve (C3 & C4) and nerve to subclavius (C5 & C6)
  • Large mobility
Screenshot 2018-12-11 at 18.53.56.png
Fig 5. Movements of sternoclavicular joint

Acromioclavicular joint

  • Plane type synovial joint
  • Lateral end of clavicle & acromion of the scapula
  • Stability provided by ligaments
    • Intrinsic
      • Acromioclavicular ligament – from acromion to lateral clavicle
    • Extrinsic
      • Conoid ligament – vertically from coracoid process of scapula to the conoid tubercle of the clavicle
      • Trapezoid ligament – from coracoid process of scapula to the trapezoid line of the clavicle
Screenshot 2018-12-11 at 18.41.11.png
Fig 6. Acromioclavicular joint ligaments
  • Innervation – suprascapular (C5) & lateral pectoral nerve (C5-C7)
  • Action – mainly passive movements, axial rotation, anteroposterior movement
  • Role in force transmission following a fall – in particular dislocation or possible ligamental tear

Extra nugget!

Screenshot 2018-12-12 at 08.02.06.png
Fig 7. Rockwood classification of acromioclavicular joint injuries

References

  • Teach Me Anatomy (teachmeanatomy.info/upper-limb)
  • Netter’s Anatomy Flashcards 3rd edition
  • Netter’s Anatomy Colouring book
  • instantanatomy.net
  • James et al. Acute Shoulder Injuries in Adults.  Am Fam Physician. 2016 Jul 15;94(2):119-127. (https://www.aafp.org/afp/2016/0715/p119.html)

 

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