There are a whole lot of wrist/finger extensors trying to fit in the wrist and anatomically these are divided into 6 compartments.
- First compartment – it’s this that is affected in de Quervain tenosynovitis
- APL (abductor pollicis longus): attaches to 1st MC
- EPB (extensor pollicis brevis): attaches to base of proximal phalanx
- Second compartment
- ECRB (extensor carpi radialis brevis): attaches to 3rd MC
- ECRL (extensor carpis radialis longus): attaches to 2nd MC
- Third compartment
- EPL (extensor pollicis longus): passes around Lister’s tubercle of radius and inserts on distal phalanx of thumb (extends thumb IPJ)
- Fourth compartment – the posterior interosseus nerve lies on the floor of this compartment
- EDC (extensor digitorum communis): no direct attachment to phalanx, attaches to the extensor expansions
- EIP (extensor indicis proprius): lies ulnar to 1st EDC tendon)
- Fifth compartment
- EDM (extensor digiti minimi): attaches to extensor expansion of little finger
- Sixth compartment
- ECU (extensor carpi ulnaris): attaches to base of 5th MC
- Zone I: over the DIP (this is where mallet finger injuries occur)
- Zone II: middle phalanx
- Zone III: over the PIP
- Zone IV: proximal phalanx
- Zone V: over the MCP
- Zone VI: dorsum of hand/metacarpals
- Zone VII: over the extensor retinaculum/carpals
- Zone VIII: proximal wrist
- This is the connections of fascia between the EDC tendons and why you can’t stick your ring finger up alone, as it prevents independent movement.
- It can also lead to confusion about whether an extensor tendon has been cut as the juncture tendinum transmits MCP joint extension even if a tendon is cut (as long as it’s cut distal to the JT)
- But it’s also helpful as it prevents the cut tendon from retracting up into the forearm
great site. on this page i believe you mixed up insertions of ECRB and ECRL.
Thank you! A little bit of a dyslexic moment, but it’s now been corrected.
happy to have come across this site. Good work.
I will keep in touch.
Thank you very much for such a great site! :)
Greatly appreciative of this. It’s a great resource for novices having to find their way around the compartments of the wrist.
Wish there’s more detail on thumb extensor zones