Subscapularis muscle
Encyclopedia
The subscapularis is a large triangular muscle which fills the subscapular fossa
and inserts into the lesser tubercle
of the humerus
and the front of the capsule of the shoulder-joint.
.
Some fibers arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis
, which separates the muscle from the teres major and the long head of the triceps brachii.
The fibers pass laterally and coalesce into a tendon which inserts into the lesser tubercle
of the humerus
and the anterior part of the shoulder joint capsule.
, which communicates with the cavity of the shoulder-joint through an aperture in the capsule.
and lower subscapular nerve
s, branches of the posterior cord of the brachial plexus
.
forward and downward. It is a powerful defense to the front of the shoulder-joint, preventing displacement
of the head of the humerus.
Although the subscapularis is the major and most powerful muscle of the rotator cuff and has an enormous meaning in the gleno-humeral stability and dynamic it is neglected in the clinical literature. Despite its importance and impact on conservative or surgical treatment, operative planning and approach or post-surgical prognosis. Lo and Burkhart even tagged the subscapularis tendon hypercritically as the „forgotten tendon“. That arises by the gap of the described tear prevalence in cadavers between 29 and 37% and in clinical studies around 27%. This is likely related to the difficulties in radiological, arthroscopic and even open surgical assessment of this particular muscle and its tendon, especially for inferior tears. For example can even full-thickness tears be mimicked by intact tendon fibers or overlying scars attached to the greater tuberosity. Since the strong stabilizing effect of the coraco-humeral ligament a possible muscle retraction can be expeditiously underestimated. Scar tissue can be adulterant for MR Arthrographic images, as it may prevent leakage of contrast material.
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 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.
Longitudinal plane of the musculus subscapularis and its tendon
The subscapularis tendon lies approximately 3 to 5 centimeter under the surface. Quite deep for ultrasonogaphy, 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 so primarily interested tendon 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:
THI - 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 presence of a hypo echoic defect and or loss of the outer tendon convexity / no visualization of the tendon, that is between partial- / 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.
Subscapular fossa
The costal or ventral surface of the scapula presents a broad concavity, the subscapular fossa.It provides an attachment for the subscapularis muscle.-External links: - "Scapular Region: Scapula "...
and inserts into the lesser tubercle
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....
of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and the front of the capsule of the shoulder-joint.
Origin and insertion
It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border (subscapular fossa) of the scapulaScapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
.
Some fibers arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis
Aponeurosis
Aponeuroses are layers of flat broad tendons. They have a shiny, whitish-silvery color, are histologically similar to tendons, and are very sparingly supplied with blood vessels and nerves. When dissected, aponeuroses are papery, and peel off by sections...
, which separates the muscle from the teres major and the long head of the triceps brachii.
The fibers pass laterally and coalesce into a tendon which inserts into the lesser tubercle
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....
of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and the anterior part of the shoulder joint capsule.
Relations
The tendon of the muscle is separated from the neck of the scapula by a large bursaBursa (anatomy)
A bursa is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of slimy fluid . It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement...
, which communicates with the cavity of the shoulder-joint through an aperture in the capsule.
Innervation
Innervation to subscapularis is supplied by the upperUpper subscapular nerve
The upper subscapular enters the upper part of the Subscapularis, and is frequently represented by two branches. It is derived from C5, C6 nerve fibers, and branches from the posterior cord of the brachial plexus....
and lower subscapular nerve
Lower subscapular nerve
The lower subscapular nerve is a nerve that supplies the lower part of the subscapularis muscle, and also supplies the teres major muscle....
s, branches of the posterior cord of the brachial plexus
Brachial plexus
The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
.
Actions
The subscapularis rotates the head of the humerus medially (internal rotation); when the arm is raised, it draws the humerusHumerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
forward and downward. It is a powerful defense to the front of the shoulder-joint, preventing displacement
Subluxation
A subluxation may have different meanings, depending on the medical specialty involved. It implies the presence of an incomplete or partial dislocation of a joint or organ. The World Health Organization defines both the medical subluxation and the chiropractic subluxation...
of the head of the humerus.
Injury diagnosis
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
Although the subscapularis is the major and most powerful muscle of the rotator cuff and has an enormous meaning in the gleno-humeral stability and dynamic it is neglected in the clinical literature. Despite its importance and impact on conservative or surgical treatment, operative planning and approach or post-surgical prognosis. Lo and Burkhart even tagged the subscapularis tendon hypercritically as the „forgotten tendon“. That arises by the gap of the described tear prevalence in cadavers between 29 and 37% and in clinical studies around 27%. This is likely related to the difficulties in radiological, arthroscopic and even open surgical assessment of this particular muscle and its tendon, especially for inferior tears. For example can even full-thickness tears be mimicked by intact tendon fibers or overlying scars attached to the greater tuberosity. Since the strong stabilizing effect of the coraco-humeral ligament a possible muscle retraction can be expeditiously underestimated. Scar tissue can be adulterant for MR Arthrographic images, as it may prevent leakage of contrast material.
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 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 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 centimeter under the surface. Quite deep for ultrasonogaphy, 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 so primarily interested tendon 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:
| ventral transversal | ventral sagittal medial | ventral sagittal lateral | lateral coronal | lateral transversal/sagittal: | dorsal transversal | dorsal sagittal |
|---|---|---|---|---|---|---|
| subscapularis muscle (longitudinal) | subscapularis muscle (transversal) | Intertub. sulcus with long head of biceps brachii (longitudinal) | supraspinatus muscle (longitudinal) | supraspinatus muscle (transversal) | infraspinatus muscle (longitudinal) | supraspinatus muscle (transversal) |
| Intertubercular sulcus with long head of biceps brachii (transversal) | Hill-Sachs-Lesio |
THI - 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 presence of a hypo echoic defect and or loss of the outer tendon convexity / no visualization of the tendon, that is between partial- / 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.