- See:
Forearm Extensors :
- Anatomy:
-
origin: 2 heads from lateral epicondyle & middle 1/3 of posterior ulna;
-
insertion:
- posterior surface of base of 5th metacarpal;
- ECU is the only wrist extensor that lies in its own fibro-osseus tunnel;
-
action: extends and adducts the hand at the wrist;
-
synergists: ECRL,
ECRB
-
nerve: deep radial -
C7 >
C6 >
C8;
- Tunnel VI:
- ECU passes thru groove on ulnar side of distal end of ulna & is covered by an annular ligament;
- tenosynovitis may occur at this point;
- synovial cyst may form in pt w/ RA as synovial sheath covering this tendon becomes irritated by constant ulnar deviation;
- tendon inserts into midportion of 5th metacarpal & can be used as tendon transfer both because of its length
& because it is more of ulnar deviator than dorsiflexor & can thus be readily spared;
- Dislocation of ECU Tendon:
- recurrent subluxation of ECU tendon is characterized by painful "snap" over ulnodorsal aspect of wrist,
particularly on forearm rotation;
- this condition may be confused w/ recurrent subluxation of
distal radioulnar joint;
- on supination w/ wrist-ulnar deviation, tendon displaces, often w/ audible snap, when moved in the ulnar and palmar directions;
- on pronation, it relocates into its normal sulcus;
- this condition as an acute injury has not been seen, but closed treatment by immobilization w/ forearm in pronation &
wrist in radial deviation may be appropriate;
-
dislocation of ECU from distal radius frx:
- see
Colles frx:
- in normal wrist ECU tendon crosses the extensor surface of distal ulna;
- ECU is more palpable when pt's wrist is extended & ulnarly deviated;
- w/ Colles frx w/ assoc frx of distal end of ulnar styloid process, dorsal carpal
ligament of tunnel VI may tear;
- as result, extensor tendon may dislocate over styloid process during pronation;
- in this instance there is perceptible, audible snap which may cause some attendant pain;
-
dislocation of ECU from RA:
- in RA, tendon may displace in an ulnar direction or rupture;
- in
RA wrist the tendon lies on volar surface of ulna as distal ulna begins to subluxate on the radius;
- thus tendon behaves as a flexor of the wrist rather than as extensor;
- this has the effect of causing an imbalance between the radial and ulnar extensors, and the radiocarpal joint
becomes pulled into radial deviation;
- as tendon slips from its position on back of ulna so it loses its role as stabiliser of the distal ulna, permitting more dislocation;
-
entrapment of ECU following
Galeazzi frx;
- extensor tendons can also occur at sites of frxs of distal part of radius w/ distal radio-ulnar joint involvement (Galeazzi frx types);
- x-rays show displaced frx of distal part of radius & widened distal radio-ulnar joint;
-
entrapment from ulnar styloid frx:
- see
ulnar styloid frx;
- ulnar styloid may sustain avulsion frx & displace into distal radio-ulnar joint w/ ECU is tendon;
- exam of distal ulna reveals vacant ECU sulcus (empty sulcus sign)
- distal radio-ulnar joint is irreducible even after internal fixation of radial frx, & dorsal exploration delineates interposed
ECU
tendon, with or without the avulsed ulnar styloid;
Excursion of prime wrist tendons.
Diagnosis and Anatomic Reconstruction of Extensor Carpi Ulnaris Subluxation
