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Swan Neck Deformity

- See:
       - Phalangeal Injury
       - Thumb Swan Neck Deformity 
       - Transverse Retinacular Ligament

- Discussion:
    - deformity involves hyperextension of PIP Joint w/ flexion of DIP joint;
    - deformity may start at either the PIP or DIP;
    - at PIP joint, there is obligatory attunuation of the volar plate;
    - at DIP joint there is elongation or rupture of attachment of the extensor tendon to the base of the distal phalanx;
           - this results in mallet deformity of distal joint & in addition, an extensor tendon imbalance, which leading to hyperextension
                    deformity at PIP jont;
    - summation of pathology:
           - stretching of the volar plate at PIP joint;
           - intrinsic tightness;
           - collateral ligament contracture
           - DIP laxity;
    - inciting causes:
           - in contast to the boutonniere deformity, swan neck deformities may begin and the DIP, PIP, or MP joints, causing swan neck
                  deformities in the remaining joints;
           - MP joint pathology:
                  - intrinsic and central tendon tightness leads to MP joint subluxation;
                  - even before MPJ subluxation develops, the intrinsic tendon tightness may lead to PIP hyper-extension deformity;
                  - once the MPJ subluxation develops (w/ MPJ flexion deformity), there will be a secondary PIP hyperextension deformity as
                            a result of altered balance;
          - PIP joint pathology:
                  - PIP Joint hyperextension from lax volar capsule secondary to synovitis;
                  - FDS rupture (loss of dynamic PIP Joint stabilization)
                  - complete excision of the FDS;
          - DIP joint pathology:
                  - mallet deformity (common cause)
                       - in RA, there may be stretching or disruption of the distal extensor mechanism, resulting in mallet deformity;
                       - as a result of the mallet deformity, there will be eventual PIP hyperextension deformity (the DIP will therefore show
                                more advanced deformity than the PIP joint);
                  - terminal tendon ruptures w/ secondary hyperextension PIP Joint;
          - misc:
                  - swan neck following excision of FDS
                  - following tight repair of FDP or free tendon grafting;
                  - esp likely to occur in pts w/ hyperextensible PIP joints;
                  - intrinsic contracture:
                       - has the effect of causing PIP hyperextension which eventually causes volar plate attenuation;

- Non Operative Treatment:
    - extension block splint (Figure of eight or Murphy ring);

- Treatment Based on Classification

- Operative Techniques

    - splinting and synovectomy:
         - in swan neck deformity, flexor synovitis is treated first;
    - FDS sling: (Urbaniak)
         - FDS is transected in the palm and is brought over the A2 pulley and sutured back to itself;
         - this acts as a checkrein against PIP hyperextension;
    - hemitenodesis of FDS:
         - indicated if articular surfaces are OK;
         - hemitenodesis of FDS tendon to base of middle phalanx will limit hyper-extension deformity of the PIP joint;
         - one slip of the FDS is separated from the other and is divided about 1.5 to 2 cm proximal to the PIP joint;
                - the tendon slip can be sutured into the flexor tendon sheath with the finger held in slight flexion;
         - the joint should be held in 20 deg of flexion for 6 weeks;
    - extensor mechanism:
         - it is usually not necessary to lengthen central slip;
         - required releases include:
                - dorsal capsule;
                - collateral ligaments;
                - palmar plate;
    - dermadesis:
         - indications: mild flexible deformity in weak hands;
         - involves excision & closure of ellipse of loose skin over flexor aspect of PIP Joint;
         - preserve underlying vessels and nerves;
         - long term results are poor;
    - intrinsic tenodesis:
         - indicated for intrinsic tightness in RA (especially when ulnar drift is not present);
         - releases PIP extension contracture and improves DIP flexion contracture;
    - arthrodesis: (see phalangeal arthrodesis)
         - if joint surface is not OK, then fuse PIP Joint;
         - arthrodesis of index finger provides the greatest amount of f(x) w/ the least amount of morbidity;
         - note that arthrodesis of long & ring fingers can produce quadriga effect due to the tethering of the profundus tendons;
         - fusion of the DIP joint is performed only if swan neck deformity originates at this joint (ie the DIP deformity should be
                 more advanced than the PIP joint deformity);
                 - the joint should be fused in full extension;
         - technique:
                 - curvilinear incision over the dorsum of the DIP joint;
                 - divide the extensor apparatus transversely;
                 - currette out the articular cartilage;
                 - mold bony surfaces to allow good opposition;
                 - fixation is achieved w/ a longitudinal K wire;
                 - mark or predrill the surface of the middle phalanx before the K wire is driven retrograde out the distal phalanx and then
                           back into the middle phalanx;
                 - a second obliquely placed wire is inserted if necessary;
    - implant arthroplasty is rarely indicated;
         - MCP is adressed at same time (arthroplasty) to balance extensor mechanism;
         - there is a high incidence of recurrance;
         - note that dorsal skin is tight from hyper-extension contraction, and wound closure will be difficult if digit is placed in flexion;
                 - in necessary leave the distal portion of the wound open, in order to avoid skin tension;
    - littler procedure: (ORL reconstruction)
         - involves creation of an oblique retinacular ligament using a lateral band;
         - this procedure involves releasing a lateral band which may be necessary in any case due to when intrinsic tightness;
         - this procedure is better suited for primary PIP deformity (w/ secondary  DIP deformity);
                 - w/ primary DIP deformity, the PIP hyper-extension will be corrected, but the DIP deformity will not be corrected;
         - prior to any reconstructive procedure full passive motion of the PIP and DIP joints needs to be restored;  
         - to address abnormal arc of flexion, checkrein at PIP Joint needs to be recreated;
         - one lateral band is transected distally (distal to the transverse fibers);
         - ulnar lateral band is transected proximal to PIP joint but is left attached distally;
         - it is mobilized & transferred volar to Cleland's ligament, so that it is volar to the axis of motion at the PIP joint;
         - it sutured to a pulley at base of PIP w/ appropriate tension, ie there is sufficient DIP extension and correction of PIP hyper-extension;
                 - tranposed tendon should function similar to the oblique retinacular ligament, hence when the PIP joint extends the DIP will
                           extend as well;
         - place K wire across PIP Joint, which is held in sl flexion,
         - references:
                 - The spiral oblique retinacular ligament (SORL).

Superficialis Sling (Flexor Digitorum Superficialis Tenodesis) for Swan Neck Reconstruction

Correction of rheumatoid swan-neck deformity by lateral band mobilization.

The spiral oblique retinacular ligament (SORL).

Surgical Treatment of Swan Neck Deformity in Rheumatoid Arthritis

The rheumatoid swan-neck deformity.

Treatment of chronic, traumatic hyperextension deformities of the proximal interphalangeal joint with flexor digitorum superficialis tenodesis.

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