Minor Round Muscle: Anatomical Disposition, Function, Injury Mechanisms, Symptoms, Diagnosis and Treatment

Together with the infraspinatus, supraspinatus and subscapularis muscles, they are part of the rotator cuff muscles located in the shoulder area.

The smaller round muscle is a small, cylinder-shaped muscle: elongated, narrow, tapered and scalloped, which is located on the back of the shoulder.

The name of the smaller round muscle comes from the shape that shows the part that is visible, a rounded aspect is observed since the rest is sheltered by different muscles. The smaller round muscle is located in the upper extremities.

The rotator cuff is a set of organs that plays an important role in both internal and external rotation in the shoulder joint.

Anatomical disposition and origin

The smaller round muscle is located below the infraspinatus, major round and triceps brachii muscles. It is perceived as part of the infraspinatus muscle, but when you observe its fibers you can see that they are separated.

The fibers of the lesser round muscle extend biased upwards and to the sides, and originate from the scapula at its lateral edge.

The tendon of the minor round muscle crosses, and is first attached to the capsule of the shoulder joint in the posterior area, and then its fibers are traced and inserted into the lower face of the humerus, in the greater tubercle.

Function

The primary function of the smaller round muscle is to give the necessary stability to the glenoid cavity and keep the head of the humerus centered.

The joint of the rotator cuff, where the smaller round muscle is located, is one of the most flexible in the human body.

This group of muscles; Infraspinatus, supraspinatus, and subscapularly with the minor round, hold the joint to prevent injury during shoulder movement.

The movements of external rotation, lateral rotation of the arm and adduction of the arm are favored by the minor round muscle as secondary but not less important functions.

Innervation:  The innervation of the minor round muscle is performed by the axillary nerve ( circumflex ) which is a motor nerve branch of this muscle located in the space of the Velpeau quadrilateral, between the scapula and the humerus.

This axillary nerve originates at the level of the axilla where the posterior cord of the brachial plexus is located, originating from the spinal segments C5 and C6 through the posterior fascicle.

The damage of the branches that innervate the minor round muscle can be clinically very significant.

These injuries are injuries that are usually of traumatic origin and cause weakness in the abduction movement of the arm, causing a motor deficit in the external rotation of the arm.

Vascularization:  The vascularization of the minor round muscle is performed by the circumflex scapular artery.

This artery is responsible for carrying out the irrigation of the minor round muscle, piercing it reaching the infraspinatus fossa.

Mechanisms of injury

The pain of a lesion in the minor round muscle can be confused with shoulder bursitis.

Omalgia produces musculoskeletal pain and in most cases this pain is associated with pathologies that include the muscles and tendons that are part of the rotator cuff.

The pain present in the minor round muscle is produced by tearing and can be acute or chronic, caused by a sudden movement of the arm.

Because of the disposition of the minor round muscle, it is injured by the efforts made when the movement of throwing objects with the arm occurs or as a consequence of a trauma caused by a direct impact on the muscle.

These movements produce a compression with the bony structures of the arm on which the muscle is inserted.

symptom

The minor round muscle lesion leads to the appearance of pain in the back of the shoulder, this injury can occur in the fourth and fifth fingers, dysesthesia.

The movement of lengthening the arm upwards and backwards causes the pain to increase, which is a sign that helps the differential diagnosis.

Diagnosis

Because of its location, in the group formed by the muscles that make up the rotator cuff, it is not possible to isolate the function of the minor round muscle.

Physical exams include a hand test, where a slight restriction in movement will be revealed when external rotation is performed.

For diagnosis, the patient places the forearm of the shoulder where the pain is present, in a position parallel to the mammary line with the back facing upwards.

The hand and forearm should be moved keeping it parallel with the intermammary line.

This movement will cause an elongation of the minor round muscle that will produce a sensation of pain in the injured muscle fibers and in the tissue present around the hematoma.

Treatment

The treatment will depend on the degree and type of injury, as well as:

  • The prescription of a passive physiotherapy.
  • The prescription of non-steroidal anti-inflammatories.
  • Perform infiltrations with corticosteroids.
  • The use of an invasive treatment of trigger points.
  • Avoid mechanical stresses on the muscle.
  • Improve the position when sleeping.
  • Perform stretching exercises.
  • The use of prolonged-release skin patches.
  • Recommend the immobilization of the shoulder with the use of orthopedic devices.