Anatomical Spaces of the Pectoral Region
An anatomical space can be loosely classified as any space that is not completely occupied by tissue. There are several anatomical spaces in the pectoral girdle that act as passage ways for neurovascular structures to traverse the upper limb.
The suprascapular foramen is situated at the superior lateral border of the scapula. It is bordered superiorly by the superior transverse scapular ligament and inferiorly by the suprascapular notch. The foramen is the passage way for the suprascapular nerve (travelling under the ligament), originating from the upper trunk of the brachial plexus. The suprascapular artery travels adjacent to the nerve, above the ligament.
Located in the axilla, the quadrangular space is bordered superiorly by subscapularis muscle (by teres minor muscle when viewed posteriorly), inferiorly by teres major muscle, laterally by the surgical neck of the humerus and medially by the long head of triceps brachii muscle. The axillary nerve and the posterior circumflex humoral artery (PCHA) travel posteriorly through the quadrangular space to gain access to the posterior division of the pectoral girdle where they both supply the deltoid.
(Upper) Triangular Space
The (upper) triangular space acts as a conduit between the anterior axillary compartment and the posterior scapular segment. The superior border of teres major muscle forms the inferior border of the space. The inferior border of teres minor forms the superior border of the space when viewed posteriorly; but when viewed anteriorly, the superior border of the space is formed by the inferior border of subscapularis. Finally, the space is bounded laterally by the medial border of the long head of triceps brachii muscle. The circumflex scapular artery passes through this space to join the scapular anastomoses.
Triangular Interval (Lower Triangular Space)
In a technical sense, the triangular interval lies outside the axilla since it is situated below the inferior border of teres major muscle (the lowest boundary of the axilla). Therefore, this space acts as a pathway between the anterior and posterior divisions of the arm, as well as between the posterior part of the arm and the axilla. It is bordered laterally by the shaft of the humerus and medially by the lateral border of the long head of triceps brachii muscle. The Profunda brachii artery and the radial nerve pass through this space to enter the arm.
The most common pathologies associated with these spaces are a result of compression caused by trauma, hyperplasia or hypertrophy. Compression of the suprascapular nerve results in paralysis to both supraspinatus & infraspinatus muscles. Supraspinatus is also commonly damaged during birth along with the axillary & musculocutaneous nerves, producing a defect known as Erb’s Palsy.
Neurovascular compression in the quadrangular space can result in Quadrilateral [Quadrangular] Space Syndrome (QSS). It is an uncommon condition that affects athletes. There are four hallmark signs that are associated with QSS. They are:
- Shoulder pain that is poorly localized.
- Paresthesia not associated with the dermatomes.
- Positive arteriogram revealing an occluded PCHA while the affected shoulder is abducted or externally rotated.
- Discrete point tenderness in the area of the quadrangular space.