| Fascia | |
| Latin: | fascia |
| Precursor: | Mesenchyme |
A fascia (; : fasciae or fascias;[1] adjective fascial; from Latin: "band") is a generic term for macroscopic membranous bodily structures.[2] Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location.
The knowledge of fascial structures is essential in surgery, as they create borders for infectious processes (for example Psoas abscess) and haematoma. An increase in pressure may result in a compartment syndrome, where a prompt fasciotomy may be necessary. For this reason, profound descriptions of fascial structures are available in anatomical literature from the 19th century.
Fasciae were traditionally thought of as passive structures that transmit mechanical tension generated by muscular activities or external forces throughout the body. An important function of muscle fasciae is to reduce friction of muscular force. In doing so, fasciae provide a supportive and movable wrapping for nerves and blood vessels as they pass through and between muscles.[3]
Fascial tissues are frequently innervated by sensory nerve endings. These include myelinated as well as unmyelinated nerves. Research indicates that fascia has proprioceptive (the ability to determine the body's orientation with respect to itself) as well as interoceptive (the ability to discern sensations within the body like the heartbeat) capabilities.[4]
Fascial tissues - particularly those with tendinous or aponeurotic properties - are also able to store and release elastic potential energy.
See main article: Fascial compartment. A fascial compartment is a section within the body that contains muscles and nerves and is surrounded by fascia. In the human body, the limbs can each be divided into two segments: The upper limb can be divided into the arm and the forearm and the sectional compartments of both of these – the fascial compartments of the arm and the fascial compartments of the forearm contain an anterior and a posterior compartment. The lower limbs can be divided into two segments – the leg and the thigh – and these contain the fascial compartments of the leg and the fascial compartments of the thigh.
Fascia itself becomes clinically important when it loses stiffness, becomes too stiff, or has decreased shearing ability.[5] When inflammatory fasciitis or trauma causes fibrosis and adhesions, fascial tissue fails to differentiate the adjacent structures effectively. This can happen after surgery, where the fascia has been incised and healing includes a scar that traverses the surrounding structures.
There exists some controversy about what structures are considered "fascia" and how they should be classified.[6] [7]
The current version of the International Federation of Associations of Anatomists divides into:
Two former, rather commonly used systems are:
| NA 1983 | TA 1997 | Description | Example | |
|---|---|---|---|---|
| Superficial fascia | (not considered fascia in this system) | This is found in the subcutis in most regions of the body, blending with the reticular layer of the dermis.[8] | Fascia of Scarpa | |
| Deep fascia | Fascia of muscles | This is the dense fibrous connective tissue that interpenetrates and surrounds the muscles, bones, nerves and blood vessels of the body. | Transverse fascia | |
| Visceral fascia | Visceral fascia, parietal fascia | This suspends the organs within their cavities and wraps them in layers of connective tissue membranes. | Pericardium |
Superficial fascia is the lowermost layer of the skin in nearly all of the regions of the body, that blends with the reticular dermis layer.[9] It is present on the face, over the upper portion of the sternocleidomastoid, at the nape of the neck and overlying the breastbone.[10] It consists mainly of loose areolar and fatty adipose connective tissue and is the layer that primarily determines the shape of a body. In addition to its subcutaneous presence, superficial fascia surrounds organs, glands and neurovascular bundles, and fills otherwise empty space at many other locations. It serves as a storage medium of fat and water; as a passageway for lymph, nerve and blood vessels; and as a protective padding to cushion and insulate.[11]
Superficial fascia is present, but does not contain fat, in the eyelid, ear, scrotum, penis and clitoris.[12]
Due to its viscoelastic properties, superficial fascia can stretch to accommodate the deposition of adipose that accompanies both ordinary and prenatal weight gain. After pregnancy and weight loss, the superficial fascia slowly reverts to its original level of tension.
Visceral fascia (also called subserous fascia) suspends the organs within their cavities and wraps them in layers of connective tissue membranes. Each of the organs is covered in a double layer of fascia; these layers are separated by a thin serous membrane.
Visceral fascia is less extensible than superficial fascia. Due to its suspensory role for the organs, it needs to maintain its tone rather consistently. If it is too lax, it contributes to organ prolapse, yet if it is hypertonic, it restricts proper organ motility.[14]
See main article: Deep fascia.
Deep fascia is a layer of dense fibrous connective tissue which surrounds individual muscles and divides groups of muscles into fascial compartments.This fascia has a high density of elastin fibre that determines its extensibility or resilience.[15] Deep fascia was originally considered to be essentially avascular but later investigations have confirmed a rich presence of thin blood vessels.[16] Deep fascia is also richly supplied with sensory receptors.[17] Examples of deep fascia are fascia lata, fascia cruris, brachial fascia, plantar fascia, thoracolumbar fascia and Buck's fascia.