Rupture of Finger Annular Ligaments (A2/A4) in Climbers: Dynamic Ultrasound and Bowstring Assessment
Clinical Significance of A2 and A4
The A2 and A4 ligaments are located at the level of the proximal and middle phalanges, respectively, and are particularly significant in climbing injuries as they hold the flexor tendons and prevent them from bowstringing away from the bone. A2 injuries are common; additional involvement of A3 usually requires surgical repair (Jacobson, 2026).
Examination Technique
The dorsal hand lies flat on the table, the wrist in a neutral position, fingers extended. The finger is passively flexed and extended, observing the movement of the flexor tendons under the ligament. Normally, tendon movement is free, and the ligament should not 'lift' to allow tendons through (Griffith, 2025).
To assess bowstring, the finger is examined at rest in an extended position and during forced flexion: forced flexion of the interphalangeal joints with pressure on the fingertip while the metacarpophalangeal joint is extended. The distance between the flexor tendons and the phalangeal bodies should not increase during forced flexion (Griffith, 2025).
Quantitative Criteria for Bowstring
Volar displacement of the flexor tendons from the adjacent phalanx during active finger flexion against resistance is normally a maximum of 1 mm. Displacement at the distal A2 of more than 3 mm indicates a complete rupture of the A2 ligament (Jacobson, 2026).
| Parameter | Value | Interpretation |
|---|---|---|
| Volar displacement of tendons | ≤1 mm | Normal (active flexion against resistance) |
| Displacement at distal A2 | >3 mm | Complete A2 rupture |
Dynamic Assessment
Bowstring is assessed dynamically during active finger flexion — a static image is insufficient. Dynamic ultrasound is recognized as the imaging method for annular ligament injuries of the fingers (Klauser et al., Radiology 2002; Martinoli et al., Skeletal Radiol 2000).
Frequently asked questions
What is considered normal volar displacement of tendons?
No more than 1 mm from the adjacent phalanx during active finger flexion against resistance (Jacobson, 2026).
What threshold indicates a complete A2 rupture?
Volar displacement at the distal A2 of more than 3 mm indicates a complete rupture of the A2 ligament.
How is the bowstring test correctly performed?
The finger is examined at rest in extension and during forced flexion of the interphalangeal joints with pressure on the fingertip while the metacarpophalangeal joint is extended; the tendon-phalanx distance should not increase.
Why are A2 and A4 important for climbers?
They are located at the level of the proximal and middle phalanges and prevent bowstringing of the flexor tendons, making them particularly significant in climbing injuries.
When is surgical treatment required?
Additional involvement of the A3 ligament with A2 rupture usually requires surgical repair (Jacobson, 2026).