ORIGIN: Supraspinous fossa of the scapula
INSERTION: It extends laterally, crossing over the shoulder joint to insert on the superior facet of the greater tubercle of humerus. Its fibers are oriented obliquely between multiple tendinous septa within the muscle, forming a multipennate fiber arrangement.
INNERVATION: Suprascapular nerve (C5-C6)
BLOOD SUPPLY: Suprascapular artery
ACTIONS: Initial 15 degrees of abduction of the arm, and stabilizes the shoulder joint by compressing the humeral head (pulls medially) into the glenoid fossa, counteracting the shearing superior force of the deltoid during arm elevation.
- It independently prevents the head of the humerus to slip inferiorly.
- The supraspinatus works as a synergist with the deltoid muscle to perform abduction, including when the arm is in adducted position.
- Beyond 15 degrees the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action.
- The transmission of signals of mechanical forces occurs with the help of fascial sheath. Along with that, fascia also communicates with the nervous system for effective muscular recruitment.
- This happens by controlling tone of muscles via reflex arcs.
- The distal station of Deep Back Arm Line (Myofascial lines) is the superior angle of the scapula, just above where the rhomboids join, but these fascial fibers link to the supraspinatus, which runs along the top of the scapula in the supraspinous fossa to the top of the ball of the humerus.
- The supraspinous fascia completes the osseofibrous case in which the supraspinatus muscle is contained and the deeper surface of the fascia is attached to some of the fibers of the muscle.
- It is thick medially, but thinner laterally under the coracoacromial ligament.
- Upper body posture significantly affects the recruitment of anterior and posterior musculature of shoulder region and may cause altered scapulo-humeral rhythm and biomechanical mal-alignment.
- When there are muscular imbalances in the upper body that either causes weakness or pain or reflex inhibition of supraspinatus, it will limit the effectiveness of the force couple formed with the middle deltoid to initiate humeral elevation and decrease the compressive force required to prevent excessive humeral head translation.
- As a result of this, the deltoid overshoots the lower rotator cuff muscles during overhead abduction and causes superior translation of humerus resulting into a compression on the bursal side of the supraspinatus thereby causing the “wringing out” effect.
- Excessive Scapular protraction, anterior tilting and downward rotation may cause anterior impingement either due to subacromial loading or rotator cuff overload and muscle imbalance resulting into reduced space in supraspinatus outlet leading to compression of supraspinatus. This causes inflammation of tendon and on long run wear and tear consequently leading to weakness.
- Damage in form of partial or full thickness tear also causes Supraspinatus weakness. This damage can be acute injury due to any trauma like fall or accident, or chronic overuse due to a combination of excessive overhead activities, and poor scapular position/stability associated with upper crossed syndrome or due to gradual degeneration of tendon and muscles that occurs with aging.
- The muscles that should be strengthen to correct biomechanics of the shoulder that cause supraspinatus tendonitis are external and internal rotators, deltoid, and scapular stabilizers (rhomboids, trapezius, serratus anterior, latissimus dorsi).
- Due to constant over-use of supraspinatus, repetitive overloading during shoulder elevation movements and impaired scapular kinematics, the muscle goes into spasmodic contraction for prolonged period of time resulting into development of fibrous nodules, taut bands in the muscle which when get irritated, triggers local pain as well as in the other areas of arm.
- Jain S, Shukla Y, Shah M. “To study the effect of empty can vs full can exercise in chronic supraspinatus tendonitis- a comparative study.” 2015; 3(1):15-19
- Thigpen CA et al. “Scapular Kinematics during supraspinatus rehab exercises. Comparision of Full Can Vs Empty Can techniques.” The American Journal of Sports Medicine. Nov 2005; 11.
- Myers T. “Anatomy Trains. Myofascial meridians for movement and manual therapists.” Churchill Livingston. Second edition.