The Four Rotator Muscles Explained

The Rotator Cuff (RC) is a common name for the group of 4 distinct muscles and their tendons, which provide strength and stability during motion to the shoulder complex. They are also referred to as the SITS muscle, with reference to the first letter of their names (Supraspinatus, Infraspinatus, Teres minor, and Subscapularis, respectively). The muscles arise from the scapula and connect to the head of the humerus, forming a cuff around the glenohumeral (GH) joint.  

 

   

  Origen on scapula Insertion on humerus Primary function
M. supraspinatus supraspinous fossa the superior facet of greater tuberosity abduction
M. infraspinatus infraspinous fossa the middle facet of greater tuberosity exorotation(lateral/external rotation)
M. teres minor lateral border of the scapula inferior facet of greater tuberosity exorotation(lateral/external rotation)
M. subscapularis subscapular fossa lesser tuberosity or humeral neck endorotation(medial/internal rotation)

 

Cranial to the rotator cuff, there is a bursa that covers and protects the muscles and tendons, as they are in close contact with the surrounding bones. https://youtu.be/zfrMhSebW2g?feature=shared The RC muscles are each used in a variety of upper extremity movements including flexion, abduction, internal rotation, and external rotation. They are essential players in almost every type of shoulder movement. Balanced strength and flexibility in each of the four muscles are vital to maintain the functioning of the entire shoulder girdle. As a group, the rotator cuff muscles are responsible for stabilizing the shoulder joint, by providing the “fine-tuning” movements of the head of the humerus within the glenoid fossa. They are deeper muscles and are very active in the neuromuscular control of the shoulder complex during upper extremity movements. They keep the head of the humerus within the small glenoid fossa of the scapula to enlarge the range of motion in the GH joint and avoid mechanical obstruction (i.e. a possible biomechanical impingement during elevation). It is well-documented that RC dysfunctions can lead to shoulder pain, impaired functional capacities, and a reduced quality of life. Image: Overview of the rotator cuff muscles – sagittal view RC injuries are common injuries that can occur at any age. In younger subjects, most injuries occur secondary to trauma or arise from overuse due to overhead activities (e.g. volleyball, tennis, pitching). The incidence of injuries increases with age, however, some individuals with rotator cuff pathology may be asymptomatic. The RC muscles can fall victim to muscle degeneration, impingement, and tearing with advancements in age. Poor biomechanics, such as postural dysfunctions (anterior posture of the GH in the glenoid cavity, for example) can prematurely affect the quality of the RC muscles and tendons due to repetitive strains and tissue encroachment. Most common injuries to the Rotator Cuff are often referred to as:

  • Rotator Cuff Tears (micro or macro tearing of the muscles or tendons);
  • Rotator Cuff Tendinitis (acute inflammation of the RC soft tissue);
  • Rotator Cuff Tendinopathy (chronic irritation or degeneration of the RC soft tissue);
  • Impingement syndrome (biomechanical dysfunction of the shoulder complex with causes abnormal wear and tear on the RC soft tissue).

It is important to note that RC tears or injuries are not always associated with pain or patient-reported loss of function. Moreover, it is worth noting that asymptomatic patients may develop symptoms in a relatively short period. The most common signs of rotator cuff injuries are:

  • Pain (may or may not be present). Can be localized to the anterior/lateral aspect of the shoulder, with referred pain down the upper arm (lateral aspect).
  • Painful range of motion
    • Painful arch (degrees vary – generally above shoulder height)
    • Painful external rotation / internal rotation / ABDuction
  • Muscle weakness in the shoulder joint (particularly ABDuction and ER)
  • Functional impairments (difficulty lifting, pushing, overhead movements, and movements with the hand behind the back (IR)).

These signs result mainly from a loss of the superior stability of the glenohumeral joint because of dysfunction of the rotator cuff muscles

  • Increase in age;
  • MRI tear characteristics;
  • Worker’s compensation status.

Factors, such as age, chronicity, and severity of muscle tendon unit impairments, have been repeatedly associated with higher retear rates and poorer clinical outcomes.

  • NSAIDs, Moderate strength (benefit exceeds the potential harm) for use in the absence of a full-thickness tear.
  • Activity modification, ice, heat, iontophoresis, TENS, PEMF, phonophoresis. Strength of recommendations: inconclusive.

 

  • Physiotherapy/exercise prescription/modalities. Inconclusive strength.
  • Conservative treatment is effective for many rotator cuff injuries and comprises injecting corticosteroid (or sodium hyaluronate) into the subacromial space and physical therapy to increase the strength of residual muscles and ameliorate shoulder stiffness.
  • Corticosteroid injections. Strength of recommendations: inconclusive.
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