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Subscapularis pathologies

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Subscapularis lesion

Definition

  • 5 muscles perform medial rotation of the shoulder:
    • Anterior deltoideus
    • Pectoralis major
    • Latissimus dorsi
    • Teres major
    • Subscapularis
  • By also testing adduction, 3 of these can be excluded if negative as they also perform adduction, this leaves the subscapularis and anterior deltoid as possible culprits
    • Anterior deltoid might also be excluded by doing resisted flexion

Occurrence

  • Rotator cuff tendinopathy of the shoulder affects more than 80% of people over eighty years of age

Localization

  • The lesion of the tendon is either located superficially or deep
    • If superficial, the tendon is impinged under the coracoacromial arch while lifting the arm and a painful arc is present
    • If deep, the tendon is impinged between the lesser tubercle and the processus coracoideus during passive horizontal adduction

Examination

  • Resisted medial rotation – painful
  • Resisted adduction – not affected
  • Painful arc
    • If superficial aspect of tendon is affected
  • Passive horizontal adduction
    • If deep aspect of tendon is affected
  • Active elevation – full range of motion
    • May be painful
  • Passive lateral rotation – may be full, might be limited due to pain
    • May be painful
    • If possible and the patients allows it, try to see if it is possible to get full range of motion to exclude a possible arthritis
  • Slow active de-elevation – painful
    • Indicates rotator cuff pathology 1

Additional functions

  • The subscapularis acts together with infraspinatus, latissimus dorsi and teres major as a depressor of the humeral head during abduction so that there is more space for the movement avoiding subacromial impingement2 3

Rupture of the subscapularis tendon

Definition

  • Might occur together with a supraspinatus tear or in isolation
  • Might also cause loosening of the restraint of the long head of biceps tendon in the bicipital groove causing a potential subluxation, dislocation and/or tearing of this tendon as well
  • The lower part of the distal tendon at the humerus is barely existent as the muscle goes almost directly from muscle to bone
    • Upper 60% of the insertion is tendinous and lower 40% is muscle

Causes

  • Hyperextension-external rotation trauma
  • As a result of an anterior dislocation of the shoulder

Localization

  • The tendon is divided into its upper and lower parts clinically
    • Lower: close to the bone insertion distally, while affecting the lower part of the muscle
    • Upper: At the lesser tubercle
      • Distal part of tendon is unaffected

Examination

  • Passive lateral rotation – excessive range of motion
  • ‘Lift-off’ sign
    • The patient places back of the hand on the posterior aspect of the pelvis, if the patient is unable to further internally rotate the arm away from the pelvis then the test is considered positive
  • ‘Belly-press’ test
    • The patient presses the hands in towards their belly
      • The test is considered positive when the arm is not able to be maintained abducted while medially rotating the hand in towards the belly

Considerations

  • A study which reviewed 435 rotator cuff repairs showed that 27,4% of rotator cuff tears had subscapularis tendon tears 4
  • A rupture of the subscapularis may lead to dislocation of the long head of biceps, this may again cause an additional reason for shoulder instability as the long head of biceps is not able to depress the head of the humerus during lifting of the arm.

References

  1. https://pubmed.ncbi.nlm.nih.gov/23306597/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652754/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3867080/
  4. https://pubmed.ncbi.nlm.nih.gov/18760206/