- Discussion:
- may occur from frx (Galeazzi fracture or Colles frx), from radial head frx (as a part of an Essex Lopresti injury) or as an islated injury;
- injury to the TFCC is a necessary part of this injury;
- dorsal subluxation:
- dorsal dislocations are most common and result from fall on pronated hand;
- manifested by prominece of ulnar head and loss of supination;
- reduced by forearm supination;
- RU joints which cannot be closed reduced may have entrapment of the extensor tendons (ECU) - see below;
- volar subluxation:
- occurs less often and result from forced supination;
- diff diagnosis:
- ECU subluxation: elicited when wrist is held in ulnar deviation and wrist is supinated;
- anatomy and stabilizing structures:
- triangular fibrocartilage complex:
- major contributor to the stability of the RU joint;
- it is difficult to imagine RU joint instability with having TFCC tear;
- ligamentous attachements: (see ligament of the wrist)
- dorsal and palmar radioulnar ligaments are lax except in the extremes or pronation and supination;
- palmar radioulnar ligaments (ulnolunate and ulnotriquetral) resist dorsal displacement;
- effect of pronation:
- ulna assumes a small relative negaive varience position;
- ulnar head moves dorsally;
- in pronation, the dorsal radioulnar ligament is most important in maintaining joint stability;
- effect of supination:
- ulna assumes a small relative positive varience position;
- ulnar head moves volarly;
- in supination, the palmar radioulnar ligament is most important in maintaining stability;
- Exam:
- subluxation of RU joint should be differentiated from generalized laxity by examing the contralateral wrist;
- limited & painful rotation;
- supination is block by dorsal dislocation;
- pronation is block by palmar dislocation;
- ECU subluxation:
- is elicited when wrist is held in ulnar deviation and wrist is supinated;
- references:
- The “Ulnar Fovea Sign” for Defining Ulnar Wrist Pain: An Analysis of Sensitivity and Specificity.
- Radiographic Diagnosis:
- suggestive features of instability:
- widening of RU joint on AP view;
- fracture (or non union) at base of ulnar styloid;
- significant shortening of the radius;
- obvious dislocation on the lateral view;
- dislocation should not be diagnosed from a sinlge lateral view, since
rotation will affect the relative position of the ulnar head;
- it is essential that the lateral view be taken w/ proper technique so that the radial styloid process overlies the proximal pole of the scaphoid, lunate, and triquetrum;
- when proper positioning is ensured, dorsal or volar subluxation is noted by the relative position of the ulna above or below the radius;
- CT scan:
- the study of choice for instability;
- w/ suspected dorsal dislocation CT is taken w/ arm in supination;
- w/ suspected volar dislocation CT is taken w/ arm in pronation;
- CT will also reveal RU joint incongruity;
- Treatment of Dorsal Instability:
- acute instability:
- reduction is achieved w/ supination and direct pressure;
- percutaneous pin fixation: helps maintain the reduction;
- above elbow cast for 4-6 weeks;
- ref: An anatomic reconstruction of the distal radioulnar ligaments for posttraumatic distal radioulnar joint instability
- chronic instability:
- non operative treatment includes forearm and elbow immobilization which limits pronation and supination;
- dorsal capsulodesis w/ either local tissue or tendon graft (using palmaris longus)
- a radio-ulnar sling using a tendon graft is also effective;
- alternatively consider use of a distally based FCU strip or a proximally based ECU strip;
- the forearm should be held in supination for one month postop;
- ref: Functional bracing for distal radioulnar joint instability.
- Management of Entrapped Extensor Tendons:
- entrapment of extensor tendons can occur at sites of frxs of frx of distal part of radius w/ distal RU joint involvement (Galeazzi fracture);
- w/ entrapped extensor tendons, distal RU joint is irreducible even after internal fixation of radial frx, & dorsal exploration delineates interposed ECU tendon, w/ or w/o avulsed styloid;
- at time of injury, ECU may displace in an ulnar direction around ulnar head or directly radially into the distal radio-ulnar joint;
- open reduction of distal RU joint, suture repair of ECU fibro- osseous canal, & internal fixation of ulnar styloid fracture are necessary;
- references:
Irreducible fracture dislocation of the distal radioulnar joint secondary to entrapment of the ECU tendon.
Acute dislocations of the distal radioulnar joint.
Surgical correction of recurrent volar dislocation of the distal radioulnar joint. A case report.
Extensor carpi ulnaris and flexor carpi ulnaris tenodesis of the unstable distal ulna.
Radio-ulnar dissociation. A review of twenty cases.
Stabilization of the distal ulna by transfer of the pronator quadratus origin.
Tenodesis of the chronically unstable distal ulna.
Fractures and dislocations of the distal radioulnar joint.
Stabilizing mechanism of the distal radioulnar joint during pronation and supination.