The appearance of the ITB in a well-defined, surface anatomy model (22-year-old, elite male track and field athlete) at progressively increasing angles of knee flexion (a–c). The small skin blemish (arrow) is a convenient landmark for evaluating the changing appearance of the ITB at different angles of knee flexion. Note that at lesser knee flexion angles (a,b), the ‘ligamentous’ (lig) and ‘tendinous’ (ten) parts of the tract are both visible, proximal and distal to the lateral femoral epicondyle (E). The ligamentous part attaches to Gerdy's tubercle (G). As the knee is flexed, the tension in the ITB shifts from its anterior (A) to its posterior (P) fibres. This is aided by the increasing posterior ‘bowstringing’ of the biceps tendon (B). VL, vastus lateralis.

Gross and microscopic anatomy of the fibrous strands linking the ITB to the femur. All histological sections are stained with Masson's trichrome. (a) A gross anatomical view of the fascia lata (FL), which has been cut longitudinally and reflected laterally to reveal a strong fibrous band (arrow) that connects the ITB to the femur (F) immediately above the lateral epicondyle. Adipose tissue (A) fills the space between the two structures, but has been partly removed in order to display the fibrous strands. (b) A gross anatomical view of a thick fibrous strand (FS) extending from the ITB to the femur and attaching to the latter in the manner of a tendon enthesis, i.e. fanning out (arrows) as it reaches the bone. (c) A histological section through the attachment of a collection of fibrous strands (FS) that anchor the ITB to the femur adjacent to the lateral epicondyle (LE). Note how the strands do not stop at the surface of the thickened periosteum (P), but pass through it towards the bone (arrows). (d) A histological section cut in the coronal plane showing the attachment of the fibrous strands (arrows) to the thick periosteum on the femur. The fibrous strands splay out to attach both to the lateral epicondyle (LE) and to a region of the femur immediately proximal to it. Note the adipose tissue that lies deep to the strands and which contains conspicuous blood vessels (BV), and the anisotropy of the trabeculae at the lateral epicondyle. Scale bar, 500 µm. (e) A bundle of nerve fibres (arrows) typical of those traversing the adipose tissue deep to the ITB. Scale bar, 100 µm. (f) A Pacinian corpuscle (PC) and numerous blood vessels of various sizes surrounded by fat cells (FC) in the adipose tissue between the ITB and the femur. Scale bar, 100 µm. (g) A Pacinian corpuscle on the surface of the periosteum in the insertional angle deep to a fibrous band extending from the ITB to the femur. Scale bar, 500 µm.

Coronal plane MR scans (proton density weighted) of the iliotibial tract (ITB) showing the fibrous strands (arrows) linking the tract to the lateral epicondyle (LE) of the femur (F) in an asymptomatic volunteer. Note the presence of the lateral recess (LR) of the knee, which can be mistaken for a bursa. VL, vastus lateralis.

Coronal plane, T1-weighted MR scans of individuals with large (a) and small (b) quantities of subcutaneous adipose tissue (arrows) in the region of the knee. Note that the quantity of fat deep to the ITB does not differ between the two individuals.

Coronal plane, T1-weighted MR scans of the knee of a 61-year-old volunteer with the quadriceps muscles relaxed (a,b) and contracted (c,d). In ‘a’ and ‘c’, the knee is fully extended, whereas in ‘b’ and ‘d’ it is flexed to 30°. The images have been selected from a complete series of scans through the knee, so that the appearance of the femur is matched in ‘a’ and ‘b’ and in ‘c’ and ‘d’. In an extended knee (‘a’ and ‘c’), the iliotibial band (ITB) slopes laterally as it passes from the lateral epicondyle (LE) of the femur (F), to the lateral condyle (LC) of the tibia, but at 30° of flexion (‘b’ and ‘d’) it slopes medially. Consequently, the ITB is compressed against the lateral epicondyle at 30° of flexion. The more distal extension of vastus lateralis (VL) in a flexed knee reduces the space occupied by the fat deep to the ITB. This in turn compresses the fat. Note that in a fully extended knee, the ITB lies closer to the femur (i.e. acts as a brace) when the quadriceps muscles are contracted than when they are relaxed (compare ‘a’ and ‘c’).

Coronal (a) and axial (b) plane, fat-saturated T2-weighted MR scans of the knee of the 22-year-old male track and field athlete with ITB syndrome. A skin marker (M) has been placed adjacent to the symptomatic area, i.e. inferior to vastus lateralis (VL). Note the region of moderately high signal (arrowheads) in the adipose tissue deep to the iliotibial band (ITB) in both figures. Arrow, lateral recess; F, femur; LE, lateral epicondyle; P, patella; T, tibia.

Coronal (a) and axial (b) plane, fat-saturated T2-weighted MR scans of the knee of the 22-year-old female recreational marathon runner with ITB syndrome. Here, there is an extensive region of high signal (arrows) in the region occupied by adipose tissue deep to the ITB, indicative of oedema or inflammation in the region. F, femur; LE, lateral epicondyle; LR, lateral recess; P, patella; T, tibia.