The subscapularis is a large triangular

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

which fills the subscapular fossa and inserts into the

lesser tubercle The lesser tubercle of the humerus, although smaller, is more prominent than the greater tubercle: it is situated in front, and is directed medially and anteriorly. The projection of the lesser tubercle is anterior from the junction that is found ...

of the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

and the front of the capsule of the

shoulder-joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial join ...

Structure

It arises from its medial two-thirds and Some fibers arise from tendinous laminae, which intersect the muscle and are attached to ridges on the bone; others from an

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...

, which separates the muscle from the

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meaning ...

and the long head of the

triceps brachii The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates. It consists of 3 parts: the medial, lateral, and long head. It is the muscle principally respon ...

. The fibers pass laterally and coalesce into a tendon that is inserted into the

of the

and the anterior part of the shoulder-joint capsule. Tendinous fibers extend to the greater tubercle with insertions into the bicipital groove.

Relations

The tendon of the muscle is separated from the neck of the scapula by a large

bursa ( grc-gre, Προῦσα, Proûsa, Latin: Prusa, ota, بورسه, Arabic:بورصة) is a city in northwestern Turkey and the administrative center of Bursa Province. The fourth-most populous city in Turkey and second-most populous in the ...

, which communicates with the cavity of the shoulder-joint through an aperture in the capsule. The subscapularis is separated from the

serratus anterior The serratus anterior is a muscle that originates on the surface of the 1st to 8th ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula. The serratus anterior acts to pull the scapula fo ...

books.google.com/books?id=AtC4BAAAQBAJ&lpg=PA549&vq=bursa%20subscapularis%20%22serratus%20anterior%22&pg=PA549#v=snippet&q=supraserratus&f=false Shoulder Arthroscopy: Principles and Practice] , Springer Science & Business Media, Dec 16, 2013. . Accessed 2016-11-07.

Nerve supply

The subscapularis is supplied by the upper subscapular nerve, upper and

lower subscapular nerve The lower subscapular nerve, also known as the inferior subscapular nerve, is the third branch of the posterior cord of the brachial plexus. It innervates the inferior portion of the subscapularis muscle and the teres major muscle. Structure T ...

s, branches of the

posterior cord The posterior cord is a part of the brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the ...

of the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

. (C5-C6)

Function

The subscapularis rotates the

head of the humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...

medially (internal rotation) and adducts it; when the arm is raised, it draws the

forward and downward. It is a powerful defense to the front of the

, preventing

displacement Displacement may refer to: Physical sciences Mathematics and Physics * Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...

of the head of the humerus.

Clinical significance

Examination

The Gerber Lift-off test is the established clinical test for examination of the subscapularis. The bear hug test (internal rotation while palm is held on opposite shoulder and elbow is held in a position of maximal anterior translation) for subscapularis muscle tears has high sensitivity. Positive bear-hug and belly press tests indicate significant tearing of subscapularis.

Imaging

There is no singularly imaging device or technique for a satisfying and complete subscapularis examination, but rather the combination of the sagittal oblique MRI / short-axis US and axial MRI / long-axis US planes seems to generate useful results. Additionally, lesser tuberosity bony changes have been associated with subscapularis tendon tears. Findings with cysts seem to be more specific and combined findings with cortical irregularities more sensitive. Another fact typically for the subscapularis muscle is the fatty infiltration of the superior portions, while sparing the inferior portions. Since the long

biceps The biceps or biceps brachii ( la, musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join ...

tendon absents itself from the shoulder joint through the rotator cuff interval, it is easily possible to distinguish between the supraspinatus and the subscapularis tendon. Those two tendons build the interval sling.

Ultrasonography

Mack et al. developed an ultrasonographic procedure with which it is possible to explore almost the complete rotator cuff within six steps. It unveils clearly the whole area from the subedge of the subscapularis tendon until the intersection between the infraspinatus tendon and musculus teres minor. One of six steps does focus on the subscapularis tendon. In the first instance the examinator guides the applicator to the proximal humerus as perpendicularly as possible to the sulcus intertubercularis. Gliding now medially shows the insertion of the subscapularis tendon.

Longitudinal plane of the musculus subscapularis and its tendon

The subscapularis tendon lies approximately 3 to 5 cm under the surface. Quite deep for ultrasonography, and therefore displaying through a highly penetrative 5 MHz linear applicator is worth a try. And it really turned out to ease a detailed examination of the muscle which just abuts to the scapula. However, the tendon of primary interest does not get mapped as closely as desired. As anatomical analysis showed, it is only by external rotation possible to see the ventral part of the joint socket and its labrum. While at the neutral position the tuberculum minus occludes the view. Summing up it is through an external arm rotation and a medially applied 5 MHz sector sonic head possible to display the ventral part of the joint socket and its labrum with notedly lower echogenicity. The following sectional planes are defined for the sonographic examination of the different shoulder joint structures:

Tissue harmonic imaging

Primarily in abdominal imaging, tissue harmonic imaging (THI) gets more and more valued and used additionally to conventional ultrasonography. THI involves the use of harmonic frequencies that originate within the tissue as a result of nonlinear wave front propagation and are not present in the incident beam. These harmonic signals may arise differently at anatomic sites with similar impedances and thus lead to higher contrast resolution.” Along with higher contrast resolution it has an elevated signal-to-noise ratio and significantly reduced inter- and intraobserver variability compared with conventional US. Additionally it is possible to nearly eliminate ordinary US artifacts, i.e. side-lobe, near-field artifacts, reverberation artifacts. As aforementioned THI has already led to enhanced abdominal, breast, vascular and cardiac sonography. For musculo-skeletal aspects THI has not been used that much, although this method features some useful potential. For example, for the still tricky discrimination between the presence of a hypoechoic defect and/or loss of the outer tendon convexity/non-visualization of the tendon, that is between partial- and full-thickness rotator cuff tears. In comparison to a checking MR Arthrography Strobel K. ''et al.'' has arrived at the conclusion that through THI it is possible to achieve a generally improved visibility of joint and tendon surfaces, especially superior for subscapularis tendon abnormalities.

Additional images

File:Subscapularis muscle animation3.gif, Subscapularis muscle (shown in red). Animation. File:Subscapularis muscle animation.gif, Same as the left, but the bones around the muscle are shown as semi-transparent. File:Thorax section 9.jpg, Transverse section of thorax featuring subscapularis muscle File:Shoulder joint.svg, Diagram of the human shoulder joint

References

External links

{{Authority control Muscles of the upper limb Rotator cuff Shoulder medial rotators