The deep fascia of the thigh is named, from its great extent, the fascia lata; it constitutes an investment for the whole of this region of the limb, but varies in thickness in different parts. Thus, it is thicker in the upper and lateral part of the thigh, where it receives a fibrous expansion from the Glutæus maximus, and where the Tensor fasciæ latæ is inserted between its layers; it is very thin behind and at the upper and medial part, where it covers the Adductor muscles, and again becomes stronger around the knee, receiving fibrous expansions from the tendon of the Biceps femoris laterally, from the Sartorius medially, and from the Quadriceps femoris in front.
The fascia lata is attached, above and behind, to the back of the sacrum and coccyx; laterally, to the iliac crest; in front, to the inguinal ligament, and to the superior ramus of the pubis; and medially, to the inferior ramus of the pubis, to the inferior ramus and tuberosity of the ischium, and to the lower border of the sacrotuberous ligament.
From its attachment to the iliac crest it passes down over the Glutæus medius to the upper border of the Glutæus maximus, where it splits into two layers, one passing superficial to and the other beneath this muscle; at the lower border of the muscle the two layers reunite.
Laterally, the fascia lata receives the greater part of the tendon of insertion of the Glutæus maximus, and becomes proportionately thickened.
The portion of the fascia lata attached to the front part of the iliac crest, and corresponding to the origin of the Tensor fasciæ latæ, extends down the lateral side of the thigh as two layers, one superficial to and the other beneath this muscle; at the lower end of the muscle these two layers unite and form a strong band, having first received the insertion of the muscle. This band is continued downward, under the name of the iliotibial tract (iliotibial band) and is attached to the lateral condyle of the tibia. The part of the iliotibial band which lies beneath the Tensor fasciæ latæ is prolonged upward to join the lateral part of the capsule of the hip-joint.
Below, the fasciæ lata is attached to all the prominent points around the knee-joint, viz., the condyles of the femur and tibia, and the head of the fibula. On either side of the patella it is strengthened by transverse fibers from the lower parts of the Vasti, which are attached to and support this bone. Of these the lateral are the stronger, and are continuous with the iliotibial band.
The deep surface of the fascia lata gives off two strong intermuscular septa, which are attached to the whole length of the linea aspera and its prolongations above and below; the lateral and stronger one, which extends from the insertion of the Glutæus maximus to the lateral condyle, separates the Vastus lateralis in front from the short head of the Biceps femoris behind, and gives partial origin to these muscles; the medial and thinner one separates the Vastus medialis from the Adductores and Pectineus. Besides these there are numerous smaller septa, separating the individual muscles, and enclosing each in a distinct sheath.