Deep fascia is the dense fibrous connective tissue that interpenetrates and surrounds the muscles, bones, nerves and blood vessels of the body. It is in the form of a fibrous sheet which invests the body beneath the superficial fascia. It is devoid of fat, and is usually inelastic and tough.
Distribution of deep fascia:
- Deep fascia is best defined in the limbs where it forms tough and tight sleeves and in the neck where it forms a collar.
- It is ill-defined on the trunk and face
Important Features of Deep Fascia:
1. Extensions (prolongations) of the deep fascia form:
- The intermuscular septa which divide the limb into compartments.
- The fibroareolar sheaths for the muscles, vessels and nerves.
2. Thickenings of the deep fascia form:
- Retinacula (retention bands) around certain joints like wrist and ankle.
- The palmar and plantar aponeuroses for protection of nerves and blood vessels.
3. Deep fascia never crosses a subcutaneous hone. Instead it blends with its periosteum and is bound down to the bone.
Modifications of Deep Fascia:
1. Forms the intermuscular septa separating functionally different group of muscles into separate compartments.
2. Covers each muscle as epimysium which sends in the septa to enclose each muscle fasciculus known as perimysium. From the perimysium septa pass to enclose each Muscle fiber. These fine septa are the endomysium. Through all these connective tissue septa, e.g. epimysium, perimysium and endomysium, arterioles, capillaries, venules, lymphatics and nerves traverse to reach each muscle fibred.
3. Deep fascia covers each nerve as epineurium, each nerve fascicle as perineurium and individual nerve fibered as endoneurium. These connective tissue coverings support the nerve fibers and carry capillaries and lymphatics.
4. Forms sheaths around large arteries, e.g. carotid sheath, axillary sheath. The deep fascia is dense around the artery and rather loose around the vein to give an allowance for the vein to distend.
5. Modified to form the capsule, synovial membrane and bursae in relation to the joints.
6. Forms tendon sheaths wherever tendons cross over a joint. This mechanism prevents wear and tear of the tendon. In the region of palm and sole it is modified to form aponeuroses, e.g. palmar and plantar aponeuroses which afford protection to the underlying-structures. It also forms septa between various muscles. These septa are specially well developed in the calf muscles of lower limb. The contraction of calf muscles in the tight sleeve of deep fascia helps in pushing the venous blood and lymph towards the ‘heart. Thus the deep fascia helps in venous and lymphatic return from the lower limb.
7. In the forearm and leg, the deep fascia is modified to form the interosseous membrane, which keeps:
- The two bones at optimum distance.
- Increases surface area for attachment of muscles.
- Transmits weight from one bone to other.
Functions of Deep Fascia:
- Deep fascia keeps the underlying structures in position an preserves the characteristic surface contour of the limbs and neck.
- It provides extra surface for muscular attachment
- It helps in venous and lymphatic return.
- It assists muscles in their action by the degree of tension and pressure it exerts upon their surfaces.
- The retinacula act as pulleys and serve to prevent the loss of power. In such situations the friction is minimized by the synovial sheaths of tendons.