The Infraspinatus, supraspinatus, and subscapularis muscles are part of the rotator cuff muscles in the shoulder area.
The minor round muscle is a small, cylinder-shaped muscle: elongated, narrow, tapered, and scalloped, located on the back of the shoulder.
The name of the minor round muscle comes from the shape that shows the visible part; a rounded aspect is observed since different forces shelter the rest. The little round muscle is located in the upper extremities.
The rotator cuff is a set of organs that plays a vital role in internal and external rotation in the shoulder joint.
Anatomical disposition and origin
The minor 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. Then its fibers are traced and inserted into the lower face of the humerus, in the greater tubercle.
The primary function of the minor 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 minor round muscle is located, is one of the most flexible in the human body.
This group of muscles, Infraspinatus, supraspinatus, and subscapular 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 peninsula are favored by the minor round muscle as secondary but not less essential functions.
Innervation: The innervation of the minor round muscle is performed by the axillary nerve ( circumflex ), a motor nerve branch of this muscle located in the space of the Velpeau quadrilateral, between the scapula the humerus.
This axillary nerve originates at the axilla level where the brachial plexus’s posterior cord is located, originating from the spinal segments C5 and C6 through the posterior fascicle.
The damage to the branches that innervate the minor round muscle can be clinically very significant.
These injuries 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 circumflex scapular artery performs the vascularization of the minor round muscle.
This artery is responsible for irrigating the minor round muscle, piercing it, and 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 arm movement.
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.
The minor round muscle lesion leads to 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 backward causes the pain to increase, which is a sign that helps the differential 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 to parallel them 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 the tissue present around the hematoma.
The treatment will depend on the degree and type of injury, as well as:
- The prescription of passive physiotherapy.
- The drug of non-steroidal anti-inflammatories.
- Perform infiltrations with corticosteroids.
- The use of 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 help of orthopedic devices.