ORIGIN:

Upper 2/3, dorsal surfaces of the lateral border of the scapula, & to the aponeurosis separating this muscle from the teres major & infraspinatus

INSERTION:

Lowest facet of the greater tuberosity of the humerus and shoulder joint posterior capsule.

INNERVATION: Axillary nerve via pseudo ganglion (C5 & C6)

BLOOD SUPPLY: Suprascapular artery & circumflex scapular artery

 

ACTIONS: 

Teres minor laterally rotates the humerus with arm in any position along with the infraspinatus, stabilizes the humeral head in glenoid fossa & assists in adduction of the arm.

  • EMG analysis have suggested that during initial 70° elevation both these muscles have increased activity as they assist in downward sliding of humeral head and between 70° to 115° they produce humeral lateral rotation. After 115° there activity decreases.
  • Downward sliding & humeral lateral rotation results in smooth shoulder abduction and avoid jamming of humeral head against acromion process during overhead abduction.
  • Both these muscles eccentrically decelerate the shoulder internal rotation.

Synergists:

  • Teres minor works synergistically with Latissimus Dorsi, Pectoralis Major, Teres Major to adduct the shoulder.
  • The teres minor & infraspinatus work synergistically with posterior fibers of deltoid to laterally rotate the shoulder.
  • The teres minor & infraspinatus as part of rotator cuff work synergistically with supraspinatus & subscapularis to dynamically stabilize the glenohumeral joint.

 

Fascial integration:

    • Teres minor is a fairly superficial muscle, although it is hidden under complex network of fascia, muscles, arteries & nerves of the axilla.
    • The fascia covering the teres minor is called as the infraspinatus fascia, which separates the muscle from the teres major.
    • The medial border of the teres minor blends with the infraspinatus & inferior & lateral border is joined by teres major.
    • The infraspinatus fascia is a strong sheet of connective tissue that covers the infraspinatus fossa of the scapula. Six characteristic features of the infraspinatus fascia were noted: a medial band, an inferior-lateral band, and superior-lateral band of fascia, insertion of the posterior deltoid into the infraspinatus fascia, a transverse connection from the posterior deltoid muscle to the infraspinatus fascia, and a retinacular sheet deep to the deltoid and superficial to the infraspinatus and teres minor muscles.

 

  • The Myofascial line- Deep Back Arm Line which originates from upper thoracic & 7th cervical vertebra passes down and out with the rhomboid muscles to the vertebral border of the scapula & continues around the scapula with the rotator cuff, specifically infraspinatus & teres minor.

 

Postural dysfunction:

  • Poor body posture significantly affects the recruitment of anterior and posterior musculature of shoulder region causing some muscles to undergo tightness and some to undergo lengthening resulting into altered scapulo-humeral rhythm and biomechanical mal-alignment.
  • The tightness in posterior capsule of the shoulder may cause anterior translation of the humeral head. The infraspinatus & teres minor may contribute to tautness in the posterior capsule. But as they are placed posteriorly on the humerus and attached to greater tuberosity they may impart posterior translatory force.
  • According to Lawerence et al. & Scovazzo et al., pain & dysfunction did not result in superior glide but an increase in anterior glide during flexion and inferior glide during abduction. This can be thought of due to excessive activity of infraspinatus and teres minor muscles that contribute to the excess anterior translation & inferior glide.
  • Although the chances of other structures surrounding the shoulder are more commonly injured, the infraspinatus fascia is involved in compartment syndromes and the fascial bundles of this structure are certain to impact the biomechanical function of the muscles of the posterior shoulder.
  • The teres minor tendon can be damaged due to trauma, wear & tear from overuse, or among the individuals who are doing excessive overhead arm movements.
  • There can be teres minor tendonitis or rupture of tendon leading to muscle weakness or inhibition, which will consequently affect the glenohumeral joint stability and may lead to various shoulder pathologies.
  • Repetitive strain and overloading on teres minor may result into prolonged contraction of muscle causing development of trigger points within it.
  • These activities as a part of routine life or sports require over head arm movements for long periods, reaching back repeatedly for retrieving wallet or fasten a bra or zip a dress, typing on a computer without elbow support, etc.
  • Teres minor trigger points cause pain at the side of shoulder and cause referral pain over the region of posterior deltoid.

 

References:

  1. Norkins C, Levangie P. “Joint structure & function.” 4th ed.
  2. Myers T. “Anatomy Trains. Myofascial meridians for movement and manual therapists.” Churchill Livingston. Second edition.
  3. Fascial bundles of the infraspinatus fascia: anatomy, function, and clinical considerations- journal of anatomy-Onlinelibrarywilley-David Moccia, Andrew A. Nackashi, Rebecca Schilling and Peter J. Ward.
  4. Lawrence, R.L., Braman, J.P., Staker, J.L., Laprade, R.F., Ludewig, P.M. (2014) Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, JOSPT, 44(9). 646-B3
  5. Teres Minor- Wikipedia
  6. King of the gym.com- teres minor