Accessory anterior inferior tibio-fibular ligament (Bassetts ligament).

I-Anatomy:

Graphic illustration demonstrates the normal relationships of the anterior inferior tibiofibular ligament (AITFL), accessory anterior inferior tibiofibular ligament (Bassett's ligament), anterior talofibular ligament (ATFL), and calcaneofibular ligament (CFL).

1- The distal tibiofibular joint is composed of a ligamentous complex including the anterior inferior tibiofibular ligament (AITFL), the posterior inferior tibiofibular ligament (PITFL), and the interosseous ligament. 
2- A distal separate ligament or fascicle of the AITFL has been described, located just distal to the AITFL, the accessory anterior inferior tibiofibular ligament.
3-Thickened accessory anterior inferior tibiofibular ligament contribute to pain from antero-lateral impingement (less common cause).
4- Other causes contributed to pain from antero-lateral impingement are:
- Synovitis.
- Hyalinized scar tissue.
- Chondral injury of the talar dome.

5-The accessory anterior inferior tibiofibular ligament (also published in the radiology literature as “Bassett’s ligament”) runs parallel and distal to the AITFL, also attaching to the tibia and fibula. The distal attachment of Bassett’s ligament approximates the fibular attachment of the anterior talofibular ligament (ATFL). The length ranges from 17-22 mm, thickness from 1-2 mm, and width from 3-5 mm.

II-Pathology:
-Repetitive microtrauma may affects antero-lateral gutter result in pain contributed to antero-lateral impingement due to the upper mentioned causes.

Graphic illustration demonstrates hypertrophied synovial tissue and fibrosis within the anterolateral gutter, contributing to anterolateral impingement.

Graphic illustration demonstrates an abnormally thickened Bassett's ligament, surrounded by synovitis/inflammation, contributing to anterolateral impingement.

A coronal T2-weighted image demonstrates an anterolateral talar dome chondral lesion and subchondral bone edema (arrowhewad), in conjunction with a thickened Bassett's ligament (arrow).

III- Imaging:
1- Bassett’s ligament to be visible in all three standard MR imaging planes, seen most commonly (89%) with sequential axial images. Due to the anatomic orientation of Bassett’s ligament, coronal imaging is often easiest to visualize the low signal fibers paralleling the course of the AITFL, and separated by a band of higher signal (Figure 7). Axial images are useful to identify the fibular attachment located inferior and slightly medial to the AITFL fibular attachment (Figure 8). Sagittal images again demonstrate Bassett’s ligament inferior to the fibular attachment of the AITFL, at or below the apex of the anterior fibular contour (Figure 9). The tibial attachment of Bassett’s ligament may be less conspicuous due to blending of fibers with the AITFL.

Figure 8:

Axial fat-suppressed T1-weighted arthrographic images progressing from superior (left) to inferior (right) demonstrate Bassett's ligament (arrowhead) attaching to the fibula, medial and inferior to the AITFL (arrow).

Figure 9:

Sagittal T1 (Figure 9) and fat-suppressed proton density-weighted (Figure 9b) images in two different patients demonstrating the fibular attachment of Basset's ligament, located inferior to that of the AITFL, located at or inferior to the to the apex of the fibular contour (arrow). 

Figure 7: A coronal T2-weighted fat-suppressed image showing the oblique orientation of Bassett's ligament (arrow), paralleling the AITFL, separated by a thin band of increased signal.

Figure 10 also demonstrates an abnormally thickened ATFL (arrowhead).

Figure 10:

Axial T2-weighted fat-suppressed (Figure 10a) and axial T2-weighted non fat-suppressed (Figure 10b) images in different patients demonstrate ill-defined intermediate to low signal within the anterolateral gutter, consistent with synovitis and scarring (arrows).

Figure 10:

Axial T2-weighted fat-suppressed (Figure 10a) and axial T2-weighted non fat-suppressed (Figure 10b) images in different patients demonstrate ill-defined intermediate to low signal within the anterolateral gutter, consistent with synovitis and scarring (arrows).

Figure 11:

Osseous contributions to anterolateral impingement. An axial T2-weighted image (Figure 11a) demonstrates an ununited avulsion ossification in the anterolateral gutter (arrow). An axial T1-weighted image (Figure 11b) in a different patient demonstrates prominent osseous spurs along the anterior joint (arrows).

Figure 11:

Osseous contributions to anterolateral impingement. An axial T2-weighted image (Figure 11a) demonstrates an ununited avulsion ossification in the anterolateral gutter (arrow). An axial T1-weighted image (Figure 11b) in a different patient demonstrates prominent osseous spurs along the anterior joint (arrows).

Reference