Subscapularis Write a complete description of the features of this muscle that a

Question

Subscapularis

Write a complete description of the features of this muscle that affect how it performs its main actions in the body, using the following template. Answer each prompt in the template.

Muscle topography or location: it fills the subscapular fossa

Principal attachments:

Origin:

Subscapular fossa (scapula)

Insertion:

Lesser tubercle (humerus)

Muscle shape: triangular shape

Joint moved (for each joint that is located between the principal attachments): shoulder joint

Functional characteristics of joint (plane, pivot, gliding, etc):

(synovial, ball- and –socket, diarthrosis_movement in all planes)

Type of movements allowed by joint: Be specific; all synovial joints are freely movable; it is the type or movement that we want to know

Planes of movements allowed by joint: all planes.

Relative positions of or directions between proximal and distal attachments

with respect to joint; for example, inferolateral to superomedial, etc.????

Muscle's “Line of Pull (orientation of main axis of muscle action relative to the segments connected by the joints); for example diagonal, orthogonal, in-line, etc.????

The muscle orientation combined with the movement allowed at the joints, causes

this change in position: ______side to side and up to down__________________

of this segment of the body: arm/humerus

in this (these) plane(s):_ plane not for either of these movements that you named, Use standard terms---flexion, adduction, rotation , etc. .________________

Explanation / Answer

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.

It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border (subscapular fossa) of the scapula.

ATTACHMENT

Some fibres 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 fibres 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. Tendinous fibres extend to the greater tubercle with insertions into the bicipital groove.

ORIGIN

Subscapularis originates from (a) medial 2/3rd of the costal surface of the scapula and (b) tendinous intermuscular septa connected to the ridges on the bone.

INSERTION

The fibres converge laterally into a broad tendon, which enters in front of the capsule of glenohumeral joint to be inserted on to the lesser tubercle of the humerus. The tendon is divided from the neck of the scapula by a large subscapular bursae, which usually interacts with all the synovial cavity of the shoulder joint.

MOVEMENTS

STANDARD MOVER ACTIONS

The subscapularis crosses the glenohumeral joint anteriorly from medial to lateral (with its fibres running horizontally in the transverse plane). However, it does not attach onto the first aspect of the humerus that it reaches, but rather wraps around the humerus to attach onto the lesser tubercle. Therefore when the subscapularis contracts and the humeral attachment is pulled toward the scapular attachment, the anterior side of the humerus moves medially. This movement is called medial rotation of the arm at the glenohumeral joint because the anterior side of the humerus rotates medially. Note the similarity of the direction of fibres of the subscapularis to the direction of fibres of the latissimus dorsi and teres major.

REVERSE MOVER ACTION

If the subscapularis contracts and the humerus is fixed, the subscapularis pulls the medial border of the scapula against the rib cage wall. This is called medial tilt of the scapula and occurs relative to the humerus at the glenohumeral joint. When the scapula moves relative to the arm at the glenohumeral joint, it also moves relative to the rib cage at the scapulocostal joint.

ADDITIONAL ACTIONS

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