Extensor Tendon Injuries Flashcards
Extensor Tendons in the Digits
- Extensor digitorum communis
- Extensor indicis proprius
- Extensor digiti minimi
Thumb
- Extensor pollicis longus- extends the tip
- Extensor pollicis brevis- extends the mp
*primary ones without the dorsal expansion piece
Extensor Digitorum Communis
Innervation
-Posterior interosseous nerve (a deep motor branch of the radial nerve)
Action
- Extends the MCP joints of the medial four digits
- In conjunction with the lumbricals, extends the IP joints.
- Weakly extend the wrist.
*Helps extend the IPs through the dorsal expansions with the lumbricals (primary job is to extend the IPs)
EDC
- Inserts at the base of the middle phalanx in extensor zone 3.
- this area is called the central slip- name of insertion point of the EDC on the middle phalanx just as it crosses the middle phalanx.
*Is a secondary mover of the wrist. Not a primary. Can be a problem after coming out of a cast because it thinks that it can lift the heavy wrist
Central Slip
Dorsal expansion- lateral bands are fibers that come from the lumbricals and the interossei and join together to insert on the dorsal phalanx
Extensor Hood Mechanism
- The “extensor hood”, Also called “extensor expansion mechanism” or “extensor aponeurosis” is made up of a combination of tendinous fibers coming from the palmer and dorsal interossei, the lumbricals and the EDC proximal to insertion.
- Job is too extend the DIP and PIP of the finger while the MCPs are flexed. They work together.
Extensor Hood Mechanism
- Lateral bands connect the middle phalanx and the distal phalanx.
- When the extensor muscle contracts it shortens and pulls on these attachments to straighten the finger.
-EDC doesn’t go past the DIP joint but through its fibrous connections it extends on up with help from the lumbricals and the interossei.
Terminal tendon
end of dorsal expansion mechanism
Lateral bands
- don’t have the EDC fibers in it.
- lumbricals only come up the radial side.
Tension on the lateral bands fully straightens the PIPJ and the terminal insertion is the only means by which the distal phalanx extends.
-this allows us to flex at the MCPJ and extend at the IPs
Extensor hood mechanism cont’d
-Keep the EDC on top of the metacarpal head on the back (kind of like a pulley) to help keep things in place/ a sheath- sagittal fibers. Keep the EDC staying on top..
(RA, lupus can effect its ability to stay on top)
Triangular ligament
- keeps terminal components of lateral bands from migrating downward. Injury to the triangular ligament can lead to a Boutonniere deformity.
- top distal portion of the dorsal expansion ligament
Transverse retinacular ligament.
Keeps the lateral bands from migrating up or dorsally. An injury in this area would result in swan neck deformity.
-keeps the lateral bands from moving.
Superior Oblique retinacular ligament (SORL)- ligament of landsmere
- gets tight with immobilization.
- It is located at the distal end of the middle phalanx and extends across the DIP and inserts on the distal phalanx. If tight it will limit DIP flexion.
-Also on the very top and goes over the entire expansion mechanism. Can get tight and prevent the system from expanding.
Sagittal bands
-at the MCP level and keep the EDC on a track over the dorsal MP joint. When a sagittal band is loose or ruptured the tendon can sublux. RA attacks the soft tissues and can affect all of these structures which results in hand deformity.
Extensor tendon zones
I- DIP joint II- Middle Phalanx III- PIP joint IV- Proximal Phalanx V- MCP joint VI- Metacarpal VII- Dorsal retinaculum VIII- Distal forearm
thumb I- IP joint II- Proximal Phalanx III- MCP joint IV- Metacarpal V- CMC joint/radial styloid
Treatment Goals
- Prevent tendon rupture
- Protect the tendon
- Promote tendon healing
- Encourage tendon gliding
- Prevent flexion contractures
- Control edema
- Restore PROM and AROM
- Maintain ROM of uninvolved joints
- Return to previous level of function
