Tensor Fascia Lata
| |
| Tensor Fascia Lata | |
|---|---|
| Muscle Type | |
| Origin | Anterior Superior Iliac Spine (ASIS) |
| Insertion | Iliotibial tract (via the greater trochanter) |
| Action | Hip – flexion, medial rotation, abduction; Knee – lateral rotation; Torso – stabilization |
| Synergists | |
| Antagonists | |
| Spinal innervation | L4, L5, S1 |
| Peripheral Innervation | Superior Gluteal Nerve |
| Vasculature | Primarily the lateral circumflex femoral artery and superior gluteal artery |
The tensor fasciae latae (TFL) is a small, fusiform muscle located on the lateral aspect of the thigh, just inferior to the anterior superior iliac spine (ASIS). Despite its name suggesting it acts as a tensor of the fascia, it functions as both a hip flexor and abductor and, via its attachment to the iliotibial tract (IT band), helps stabilize the knee. It is the most anterior of the superficial gluteal muscles and works in concert with the gluteus medius and minimus in many movements.
Structure
The tensor fasciae latae is a small, strap-like muscle encased in the fascia lata (deep fascia) of the thigh. Despite its size, its long distal attachment through the iliotibial band allows it to exert influence across both the hip and knee joints. It is a biarticular muscle, crossing the hip with its muscle belly and acting on the knee via the IT band.
Origin
The TFL originates from the anterior superior iliac spine (ASIS) and the adjacent anterior aspect of the iliac crest. This places it just lateral to the origin of the sartorius muscle at the ASIS. Together, these muscles form the anterior border of the iliac crest. The muscle belly then descends obliquely downward and slightly posteriorly over the lateral hip.
Insertion
The muscle fibers transition into a long tendon that merges into the iliotibial tract (IT band), a thick band of fascia running down the lateral thigh. The IT band attaches to Gerdy’s tubercle on the lateral aspect of the proximal tibia and also sends fibers to the lateral patella. Thus, the TFL indirectly influences knee stability via the IT band by maintaining tension that helps in knee extension and proper hip positioning.
Action
The TFL has several actions: it abducts the thigh and mildly flexes the hip, acting as a hip flexor—especially when the hip is already flexed, thereby assisting the iliopsoas. It also internally (medially) rotates the thigh due to its anterolateral pull on the femur. By tensioning the IT band, the TFL helps stabilize the pelvis and maintains knee extension by keeping lateral tension. When standing, it contracts to steady the pelvis and femur on the tibia. During gait, it is active in the early stance phase to stabilize the limb and in the swing phase to assist in limb positioning. Additionally, the tension provided by the TFL assists the gluteus maximus in stabilizing the extended knee.
Synergists
The TFL works closely with the gluteus medius and gluteus minimus in hip abduction and internal rotation. It also assists the iliopsoas and rectus femoris in hip flexion, particularly in initiating flexion from a neutral or extended position. The vastus lateralis, through its fascial connections, can be considered an indirect stabilizing synergist for the knee along with the TFL. Conversely, the upper fibers of the gluteus maximus also insert into the IT band, so the TFL and these fibers together help tension the fascia lata.
Antagonists
The posterior fibers of the gluteus maximus act as antagonists to the TFL’s internal rotation of the thigh by externally rotating it. Additionally, the hip adductors oppose the TFL’s abduction. Because the TFL contributes to hip flexion, the primary hip extensors (gluteus maximus and hamstrings) counteract its action. At the knee, since the TFL (via the IT band) helps maintain extension, the knee flexors (hamstrings) serve as antagonists in the context of knee stabilization.
Spinal Innervation
The spinal innervation originates from the L4, L5, and S1 nerve roots, which contribute to the formation of the superior gluteal nerve.
Peripheral Innervation
The superior gluteal nerve innervates the TFL, along with the gluteus medius and minimus. Its terminal branch continues anteriorly to pierce and supply the TFL near its deep surface. Weakness in the TFL is often associated with lesions of the superior gluteal nerve.
Vasculature
The TFL is primarily supplied by the ascending branch of the lateral circumflex femoral artery (LCFA), which wraps around the femur toward the ASIS region. The superior gluteal artery also contributes to its blood supply. The rich anastomoses around the hip ensure robust collateral circulation.
Clinical Application
– IT Band Syndrome: As the TFL tightens the IT band, overuse or hypertonicity can contribute to iliotibial band syndrome—a common cause of lateral knee pain, especially in runners. A tight or overactive TFL leads to excessive friction of the IT band over the lateral femoral condyle. Treatment involves stretching the TFL and IT band, foam rolling, and strengthening the hip abductors to balance muscle forces.
– Trochanteric Bursitis vs. Tendinopathy: TFL inflammation may mimic trochanteric bursitis. Because the TFL partially overlies the greater trochanter and inserts into the IT band, a very tight TFL can irritate the trochanteric bursa beneath the IT band. In injections for Greater Trochanteric Pain Syndrome (GTPS), the needle is sometimes placed near the TFL/IT band insertion to alleviate lateral hip pain. Chronic TFL strain can also contribute to anterolateral hip pain.
– Nerve Injury: In superior gluteal nerve palsy, in addition to gluteus medius and minimus involvement, loss of TFL function can reduce hip internal rotation strength and contribute to pelvic instability. However, because the TFL is relatively small, its loss is often overshadowed by deficits in the gluteus medius and minimus (resulting in a Trendelenburg gait). Interestingly, since the TFL also assists in hip flexion, patients with superior gluteal nerve palsy may experience slight difficulty initiating the swing phase of gait, although this is typically compensated by other hip flexors.
– Gait: The TFL contributes to the “lateral snap” in some people’s gait: when tight, it can cause the IT band to snap over the greater trochanter during hip flexion and extension. Although benign, this snapping (snapping hip syndrome) can be annoying. Stretching the hip abductors and external rotators to relax the TFL is usually recommended.
– Injection: The TFL muscle is a common site for trigger points that refer pain down the lateral thigh. Clinicians sometimes perform dry needling or trigger point injections into the TFL for myofascial pain. It can be palpated as a tense, tender spot just posterior to the ASIS when the patient alternately flexes and relaxes the hip.
– Surgical Note: The TFL and IT band together form part of the approach in certain surgeries (such as the anterolateral approach to the hip or during ORIF of femoral neck fractures). The TFL may be retracted anteriorly to expose deeper structures. In rare cases, an avulsion of the ASIS (the TFL’s origin) can occur—especially in adolescents during sports—leading to pain and requiring rest or fixation.
