|<<Swan neck Deformity||Quadriga Effect>>|
A frequently missed injury to the ligaments and central slip of the PIP joint this injury most often leads to some long term compromise in the function of the finger regardless of how it is treated. When it typically presents a few weeks after injury, presumed at first to be a "jammed" finger, the distiguishing feature is the flexed resting posture of the PIP joint which will likely still be passively correctible (extension lag rather than flexion contracture). This is seen in conjunction with a hyperextended resting posture of the distal interphalangeal joint.
Closed treatment is by an alumafoam splint applied with coban to the PIP in full extension; then active flexion exercises of the DIP joint. The PIP is splinted full time for 5 weeks then full motion is allowed. A residual flexion contracture or extension lag at the PIP is typical, but if it can be limited to 20 degrees generally does not interfere with function if active DIP flexion is near normal. Swelling of the PIP persists for the better part of a year.
If there is fixed contracture therapy is directed at achieving full extension by static or dynamic splinting or serial casting to gain full passive extension at the pip joint.
Surgical treatments include efforts to reconstruct the central slip directly, or efforts to employ release of the terminal extensor tendon to diminish hyperextension at the DIP level and hopefully inprove the active extension at the PIP level as the extensor retracts and the slack pseudotendon over the PIP receives more tension via the confluent extensor hood.
Lacerations and crush injury to the dorsum of the PIP can include central slip injuries which can also go unrecognized with resultant deformity apparent at time of follow up. Usually exploration is pursued to obtain direct repair of the central slip. A 1.3 suture anchor or a transosseus suture tied over a button on the palmar surface with a 3-0 proline are two common methods.
In the case of crush injury there may be soft tissue defects to contend with, small defects are managable with random pattern flaps if a few millimeters of coverage over the repaired tendon is needed. Alternatively a more elaborate axial pattern flap can be used where applicable. Stable coverage is needed if tendon graft is used to reconstruct the central slip.
Pinning of the PIP in extension has the advantage of lessened concern for early failure due to lack of compliance or loss of position in the splint. Access to the hand to address or rehab other injuries may be enhanced. The concerns with a transarticular pin include the prospect for excessive stiffness or pin failure requiring the problematic retrieval of the broken pin from within the bone. It is helpful in such a case to have advanced the pin all the way through the bone on the opposit side of the joint so that if it should break a protruding end is available on both sides.
If a transosseus pin can be avoided well supervised rehab can be considered early allowing short arc active flexion with passive extension or a dynamic splint with a flexion stop. In any case any pin should be removed by 4 weeks and active motion initiated. Secondary capsulotomy and tenolysis after 4 months may be needed if the joint is very stiff in extension.
At times the patient will present with a laceration over the PIP which has been closed by the ER staff and the status of the central slip is uncertain. It may seem to be in tact clinically but then, within a week or two, extension lag and a tendency to hyperextension at the DIP will indicate the true diagnosis. Exploration within a four week interval from injury will usually allow for direct repair of the central slip which can then be managed as in the acutely recognized central slip injury.