The distal biceps tendon insertion onto the radial tubercle is best appreciated with dedicated MR sequences achieved by placing the arm in the Flexion ABduction Supination (FABS) position. This achieves a similar imaging plane to the Cobra position used during dynamic MSK ultrasonography of the insertion.
The FABS MR must not be done in the absence of other sequences because FABS-MR does not study the entire biceps tendon unit, especially the lacertus fibrosus. This is an important factor in tendon unit retraction. Hence the study is described as standard elbow with FABS sequences.
Useful to assess:
- Distal biceps tendon injury
- Injury to other tendons around the elbow
- Joint cartilages
- Ligaments
Positioning
- Standard Elbow: Forearm supinated and placed in well padded coil
- FABS: “Lying on the beach” position, elbow flexed and supinated, shoulder abducted, hand behind back of head
Scan
- Knee or flex coil for standard elbow
- Flex coil required for FABS
Standard Elbow
| Sequence | Slice / Gap |
| PD coronal | 3mm / 0.3mm |
| PDFS coronal | 3mm / 0.3mm |
| PDFS sagittal | 3mm / 0.3mm |
| T2FS axial | 3mm / 0.3mm |
FABS
| Sequence | Slice / Gap |
| T1 axial | 3mm / 0.3mm |
| PDFS axial | 3mm / 0.3mm |
Pitfalls to watch out for
Ensure radiographers understand anatomy of radial tubercle. This is especially important to understand the “true axial” plane of scanning in the FABS position in spite of the position of the shoulder and elbow. The point of this exercise is to bring the area of interest into the best plane for the field isocentre.