A fascia is a fibrous connective tissue that can be found throughout the body. They wrap around neurovascular structures, organs and muscles in order to reduce friction between adjacent structures as well as to protect them from abrasions. Fascia throughout the body can be divided into three groups:
The fascia converges in the axilla, where it acts as a protective structure over the neurovascular structure of the axilla.
Although it is a single continuous fibrous sheath, the clavipectoral fascia has been subdivided into different segments. At the most superficial part, where it is attached to the coracoid process laterally and blends with the upper two external intercostal membranes medially, it is referred to as the costocoracoid membrane. At this level, the fascia splits and encompasses subclavius muscle (sometimes called the fascia of subclavius) and is attached to the borders of the subclavian groove.
The sheath reunites at the inferior border of subclavius muscle and forms a well-defined thickening called the costocoracoid ligament – spanning the distance between the coracoid process and the first costochondral joint.
The fascia continues loosely downward until it divides again at the superior border of pectoralis minor and encloses the muscle. At the inferior level of pectoralis minor muscle, the fibers again reunite. As seen with the costocoracoid ligament, the fascia thickens to become the suspensory ligament of the axilla. Here, the suspensory ligament of the axilla is attached to the axillary fascia that forms floor of the axilla.
The main role of any fascia is to allow smooth movement of adjacent structures over each other. The clavipectoral fascia is no different, in that it permits the gliding of pectoralis major muscle over pectoralis minor muscle. Furthermore, the suspensory ligaments of the axillae exert tension on the floor of the axillae, resulting in the trademark concavity commonly called the “arm pits”, seen most when the arm is abducted.
Located inferior to the costocoracoid ligament, medial to the coracoid process and superior to pectoralis minor (in the substance of the costocoracoid membrane) is an opening through which two structures enter and two structures leave the deep compartment of the pectoral girdle. The cephalic vein enters from the arm to join the axillary vein and lymphatic vessels from the infraclavicular nodes pass through the hiatus to join the apical nodes of the axilla.
The lateral pectoral nerve (branch of the lateral chord of the brachial plexus) and the thoracoacromial artery (or its branches – acromial, deltoid, pectoral and clavicular; branch of the first part of the axillary artery) exit the deep compartment of the pectoral girdle to their respective muscles.
The clavipectoral fascia is commonly resected or excised during shoulder arthroplasty (the process of replacing the shoulder joint. A common complication of this procedure is joint immobility. One attributing factor is that the true clavipectoral fascia has been replaced by fibrotic tissue. Removal of this and other scar tissue is integral to managing this complication.