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Perilunate Dislocations


- See:
       - Carpal Instability
       - Ligaments of the Wrist

- Discussion:
    - perilunate dislocation pattern provides a whole spectrum of wrist sprains, fractures, dislocations;
    - types of perilunate dislocations (in order of frequency):
            - transscaphoid-perilunate
            - perilunar
            - transscaphoid-trans-capitate-perilunar
            - transradial-styloid


- Mechanism:
    - carpal dislocations result from hyperdorsiflexion;
    - severe ligament injury is necessary to tear the distal row from the lunate to produce perilunate dislocation;
    - sequence of injury:
            - this injury pattern usually begins radially & destabilizes thru body of scaphoid (w/ frx) or thru scapholunate interval (w/ dissociation);
                   - scaphoid bridges the proximal and distal carpal rows;
                   - w/ dislocation between these rows, the scaphoid must either rotate or fracture
                   - this produces a perilunate dislocation, which may cause: trans-sccaphoid perilunate dislocation:
                   - distal half of scaphoid & remaining carpus dislocate around lunate;
            - force is transmitted ulnarly thru the space of Poirier (between lunate and capitate);
            - next force transmission disrupts the luno-triquetral articulation;
            - as a manifestation of the most severe form of the injury, the lunate may be dislocated into the carpal tunnel;
    - transradial styloid perilunate dislocation:
            - frx of radial styloid w/ dislocation of it & remaining carpus around lunate;
            - further destabilization passes distal to lunate, either thru space of Poirier or thru capitate (transcapitate frx), & then ulnar to lunate, either through hamate & triquetrum or thru lunotriquetral interval;


- Radiographs:
    - lateral radiographs will reveal loss of co-linearity between the capitate, lunate, and radius;
    - typically the captitate is located dorsal to the lunate and is aligned with the radius;

           


- Components of Perilunate Dislocation:
    - includes dorsal dislocation of distal row, scaphoid, and triquetrum;
    - lunate:
           - vascularity of the lunate
           - lunate is usually subluxated and angulated palmarly but still is located in the lunate fossa of the radius;
           - w/ more severe injury lunate may be dislocated into the carpal canal, or if strong, short radiolunate and ulnolunate ligamens are torn, it may be displaced free fragment;
           - lunate dislocation is considered the last stage of perilunate dislocation;
           - example of lunate dislocation: 

                   

    - capitate:
           - capitate fragment is frequently turned 180 deg so that its articular surface faces cancellous surface of major capitate fragment;
           - scaphoid & capitate fragments are devascularized by displacement;
           - space of poirier:
           - disruption occurs at scapholunate area & progresses into space of Poirier and then thru the lunotriquetral space;
           - rent develops during dorsal dislocations, and it is thru Space of Poirier interval that the lunate displaces into the carpal canal;
    - misc:
           - DISI:
                  - DISI collapse pattern, occurs because stabilizing influence of scaphoid is inital component of dislocation;
           - VISI:
                  - destabilization may begin ulnarly w/ a lunotriquetral dissociation;
                  - if lunate remains attached to scaphoid VISI will develop;


- Surgical Treatment:
    - delineate between those dislocations which easily reduce w/ close reduction & those that are irreducible or unstable;
           - in the later group, interposed capsule may be preventing the reduction;
    - palmar approach is typically needed to repair the rent in the volar capsule at the lunocapitate joint as well as carpal tunnel release;
    - dorsal approach is required for scaphoid fracture fixation or repair the torn scapholunate interosseous ligament;
    - note that one of the essential goals of treatment is to reduce the scapholunate gap (inaddition of volar ligament repair);
    - volar approach:
           - not all surgeons use a volar approach (unless a scaphoid fracture is present);
                   - in the case of a scaphoid fracture, the volar approach is devoted to fixing the fracture;
           - if there are neurovascular problems, a volar approach allows release of carpal tunnel;
           - combined w/ dorsal approach, this allows both intra articular & extra-articular damage to be assessed and treated adequately;
           - volar approach allows better reduction of the lunate and repair of the volar capsule;
           - may be opened, either along its attachments to radial rim or thru the constant rent in the space of poirier;
           - reference:
                   - The palmar radiocarpal ligaments:  A study of adult and fetal human wrist ligaments

                     

    - dorsal approach:
           - some surgeons rely on the dorsal approach alone for surgical fixation of perilunate dislocations;
                  - in the study by Cooney, et al (1987), 18 of 21 patients who underwent a dorsal approach had a satisfactory outcome;
           - patient is supine w/ wrist slightly flexed & placed on arm board;
           - perform a provisional reduction before the incision is made;
           - incision:
                  - Z or S shaped incision from base of second metacarpal over wrist to distal forearm is suggested for good healthy skin;
                  - alternatively, make a straight midline longitudinal one in line w/ third metacarpal and into the distal forearm;
                        - the incision will be made thru the 3rd compartment;
                        - this passes safely between the dorsal sensory branches of the ulnar nerve medially, and ofthe radial nerve laterally; 
                  - ref: Difficult wrist fractures. Perilunate fracture-dislocations of the wrist
           - extensor retinaculum:
                 - extensor retinaculum between the 3rd and 4th extensor compartments is reflected off of wrist capsule w/ care to avoid any damage to capsule itself;
                 - EPL is mobilized out of its sheath and is reflected radially;
                 - subperiosteally elevate the fourth compartment, w/o violating the tendon sheath;
                 - place Homan retractors on either side of the radius;
           - capsular incision:
                 - longitudinally incise thru the dorsal capsule in line w/ Lister's tubercle, and then elevate the wrist capsule off of the dorsal rim of the distal radius including the dorsal radiotriquetral ligament;
                        - preserve radiotriquetral ligament;
           - need to remove loose fragments
           - dorsal capsule is usually opened along its origins from dorsal rim, & longitudianlly in space between 2nd & 4th extensor compartments;
           - it is easier to examine cartilage surfaces & intra articular fragments thru the dorsal approach;
           - note that some surgeons elect to fix the scaphoid fracture (if one is present) through the dorsal incision;
    - K wire fixation:
           - following either open or closed reduction, K wire fixation will be required;
           - the usual statedgy includes:
                   - ORIF of scaphoid fracture, if one is present (see trans-scaphoid perilunate dislocation);
                   - temporary lunate fixation to the radius (w/ care to take the lunate out of dorsiflexion);
                         - alternatively insert a K wire into the lunate which then can be used as a joystick;
                   - capitolunate angle should be held at neutral or slight flexion;
                   - scapholunate fixation;
                         - before the scapho-lunate joint is pinned, pass the ligamentous repair sutures, but do not tie them together until all of the pins have been inserted and the reduction is optimal;
                         - once K wire fixation has been achieved, consider repairing the scapholunate interosseous ligament with a bone anchor, and then augmenting the repair with a dorsal capsulodesis;
                   - scapho-capitate fixation;
                         - w/ an optimal reduction, the lunate should cover the head of the capitate;
                   - triquetral-lunate fixation;

                     

- Post Op:
    - patients should understand clinical improvement takes upto one year;

- Complications:
    - secondary carpal collapse;
    - scapholunate dissociation;
    - lunotriquetral dissociation;



- Case Example:
    - 50-year-old male who was assaulted, sustaining a lunate dislocation; 

           



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Late Treatment of a Dorsal Transscaphoid, Transtriquetral Perilunate Wrist Dislocation With Avascular Changes of the Lunate.

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Chronic capitolunate instability

Dislocations of the lunate with and without fracture of the scaphoid.

Carpometacarpal dislocations. Long-term follow-up.

Open reduction of carpal dislocations: indications and operative techniques.

Transient vascular compromise of the lunate after fracture-dislocation or dislocation of the carpus.

Difficult wrist fractures. Perilunate fracture-dislocations of the wrist.

Late treatment of a dorsal transscaphoid, transtriquetral perilunate wrist dislocation with avascular changes of the lunate.

Median-nerve neuropathy associated with chronic anterior dislocation of the lunate.

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