The Fascia Lata
Fascia is defined as a sheet or band of fibrous tissue lying deep to the skin that lines, invests and separates structures within the body. There are three general classifications of fascia:
- Superficial fascia: blends with the reticular layer beneath the dermis.
- Deep fascia: envelopes muscles, bones and neurovascular structures.
- Visceral fascia: provides membranous investments that suspend organs within their cavities.
This article introduces the deep fascia of the thigh, the fascia lata. A detailed account of its structure, anatomical relations, function, attachments and clinical relevance will be outlined.
The fascia lata is a deep fascial investment of the whole thigh musculature and is analogous to a strong, extensible and elasticated stocking. It begins most proximally around the iliac crest and inguinal ligament and ends most distally to the bony prominences of the tibia; where it continues to become the deep fascia of the leg (the crural fascia).
The width of the fascia lata varies considerably at different regions of the thigh. It is thickest along the superolateral aspect of the thigh, originating from the fascial condensations from gluteus maximus and medius, and also from around the knee where the fascia receives reinforcing fibres from tendons. The fascial investment is thinnest where it covers the adductor muscles of the medial thigh.
The deepest aspect of fascia lata gives rise to three intermuscular septa that attach centrally to the femur. This divides the thigh musculature into three compartments; anterior, medial and lateral. The lateral intermuscular septum is the strongest of the three due to reinforcement from the iliotibial tract (see later), whereas the other two septa are proportionately weaker.
An ovoid hiatus is present in the fascia lata just inferior to the inguinal ligament known as the saphenous opening. This gap serves as an entry point for efferent lymphatic vessels and the great saphenous vein, draining into superficial inguinal lymph nodes and the femoral vein respectively. A covering of membranous tissue (the cribriform fascia) covers the hiatus which develops inferomedially from a sharp margin of the gap (the falciform margin).
Clinical Significance: Presentation of Femoral Hernias
Femoral hernias develop when an out-pouching of gastric viscera protrudes through the femoral canal. The protrusion becomes noticeable when it exits superficially through the saphenous opening within the fascia lata, producing a swelling inferior to the inguinal ligament.
In this clinical scenario, it is necessary to investigate promptly due to the high risk of incarceration with femoral hernias and to rule out other pathology such as lymphadenopathy.
The Iliotibial Tract (ITT)
The iliotibial tract is a longitudinal thickening of the fascia lata, which is strengthened posteriorly by fibres from the gluteus maximus. It is located laterally in the thigh, extending from the iliac tubercle to the lateral tibial condyle. The ITT has three main functions:
- Movement: acts as an extensor, abductor and lateral rotator of the hip, with an additional role in providing lateral stabilisation to the knee joint.
- Compartmentalisation: The deepest aspect of ITT extends centrally to form the lateral intermuscular septum of the thigh and attaches to the femur.
- Muscular sheath – forms a sheath for the tensor fascia lata muscle.
Tensor Fascia Lata (TFL)
The tensor fascia lata is a gluteal muscle that acts as a flexor, abductor and internal rotator of the hip. Its nomenclature however, is derived from its additional role in tensing the fascia lata.
The muscle originates from the iliac crest, and descends down the superolateral thigh. At the junction of the middle and upper thirds of the thigh, it inserts into the anterior aspect of the iliotibial tract. When stimulated, the tensor fasciae lata tautens the iliotibial band and braces the knee, especially when the opposite foot is lifted.
The property of TFL tightening the fascia lata is analogous to hoisting an elastic stocking up the thigh. When the fascia lata is pulled taut, it forces muscle groups closer together within their intermuscular septa towards the femur. This action centralises muscle weight and limits outward expansion, which in turn reduces the overall force required for movement at the hip joint.
An additional property of tensing the fascia lata is that it makes muscle contraction more efficient in compressing deep veins. This ensures adequate venous return to the heart from the lower limbs.
The fascia lata forms multiple superior attachments around the pelvis and hip region:
- Posterior: sacrum and coccyx
- Lateral: iliac crest
- Anterior: inguinal ligament, superior pubic rami
- Medial: inferior ischiopubic rami, ischial tuberosity, sacrotuberous ligament
The fascia lata is also continuous with regions of deep and superficial fascia at its superior aspect. The deep iliac fascia descends from the thoracic region at the diaphragm, covers the entire iliacus and psoas regions and blends with the fascia lata superiorly. Superficial fascia from the inferior abdominal wall (Scarpa’s fascia) and perineal region both blend with the fascia lata just below the inguinal ligament.
The lateral thickening of fascia lata forms the iliotibial tract and receives tendon insertions superiorly from gluteus maximus and tensor fascia lata. The widened band of fibres descends the lateral thigh and attaches to the lateral tibial condyle on the anterolateral (Gerdy) tubercle.
The fascia lata ends at the knee joint where it then becomes the deep fascia of the leg (the Crural fascia). Attachments are made at bony prominences around the knee including the femoral and tibial condyles, patella, head of fibula and the tibial tuberosity.
The deep aspect of fascia lata produces three intermuscular septa which attach centrally to the femur. The lateral septum joins to the lateral lip of the linea aspera and the medial and anterior septa attach to the medial lip. These attachments then continue along the whole length of the femur to include the supracondylar lines.
Clinical Significance: Transplantation
Dermatofasciotomy and debridement can leave large wound sites that require post-operative grafts to facilitate tissue regeneration and healing. The fascia lata graft is a popular choice as the iliotibial tract provides a particularly high concentration of connective tissue fibres, and can be surgically harvested whilst leaving the majority of fibres intact.
Novel developments in transplantation have also shown success with using fascia lata in reconstructive surgery. Advances have included:
- Heart valve replacements
- Eyelid reparations
- Dura mater repair
- Urinary incontinence treatment (fascia lata sling)
The main advantage of using fascia lata opposed to an artificial product (e.g. alloplastic silicone sheets) is that it is well vascularised upon transplantation, whereas the latter requires microvascular anastomosis.