The supraspinatus is an important intrinsic muscle of the shoulder region, a part of the four-member rotator cuff muscle group. It is located in the upper region of the shoulder blade and connects to the greater tubercle of the humerus.
The main attachments for the supraspinatus are origination from the supraspinous fossa of the scapula and attachment to the greater tubercle of the humerus.
The primary action of the supraspinatus is abduction of the upper limb at the shoulder. Specifically, it performs the first 0-15o of shoulder abduction, and then assists the deltoid muscle in the additional 15-90o.
In addition to its main action of shoulder abduction, the supraspinatus also provides stability to the shoulder joint, along with the other rotator cuff muscles. It is innervated by the suprascapular nerve and is supplied with blood via the suprascapular artery.
Fig 1 - The rotator cuff muscles, which act to stabilise the shoulder joint.
The supraspinatus muscle is a critical component of the rotator cuff musculature and it plays an important role in shoulder abduction and stability.
The main biomechanical role of the supraspinatus is to provide stability to the shoulder joint by stabilising the humeral head in the glenoid fossa. This stability is provided by tension developed in the supraspinatus muscle when the humeral head is externally rotated.
During abduction of the shoulder, the supraspinatus provides a majority of the force that rotates the humerus into abduction. This force is further augmented by deltoid, supraspinatus and trapezius muscles. All these muscles together create an abductor force to initiate shoulder abduction.
The supraspinatus muscle is also involved in forward elevation of the shoulder, as it works in synergistic fashion with the anterior and middle deltoid muscles to elevate the humerus to 180 degrees, or to a completely overhead position.
The supraspinatus has an important role in rotational stability of the shoulder joint. It prevents the humeral head from being depressed or translated anteriorly and inferiorly. It also provides dynamic stability when the arm is abducted, allowing for the full range of motion of the shoulder joint.
In addition, the supraspinatus is a critical component in the maintenance of joint homeostasis, with its involvement in preventing undue pressure on the joint and maintaining healthy joint surface environment.
The supraspinatus also plays a role in dynamic shoulder stability. During shoulder abduction, it is responsible for maintaining the head of the humerus in the glenoid fossa, while the corresponding force is generated by the deltoid muscle and transferred to the humeral head. Similarly, during internal and external rotation of the shoulder, the supraspinatus works with the other rotator cuff muscles to provide stability to the joint.
The supraspinatus muscle is also involved in shoulder proprioception. It contributes to the joint’s sense of position in the same way as other rotator cuff muscles. This allows the shoulder joint to adjust itself appropriately during daily activities like reaching, throwing and lifting.
Lastly, the supraspinatus plays a role in force transmission through the shoulder joint. It assists in transferring the force from the upper extremity to the lower extremity, thus allowing for greater control and stability of the shoulder joint.
In conclusion, the supraspinatus is an important component of the rotator cuff musculature, playing an important role in shoulder stability, abduction, proprioception and force transmission.
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