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Exam of Boutoniere Injuries

- Chronic Injury:
    - flexion deformity of PIP & an extension deformity at DIP joint;
    - MCP hyperextension deformity;
    - after the central slip has been disrupted for some time, there will be volar migration of lateral bands, and contracture of oblique retaincular lig.
    - after the lateral bands have become contracted in a volar position, there will be limited flexion of the DIP joint when the finger is placed in MCP hyperextension and PIP hyperflexion (which puts lateral bands on maximum stretch);

- Acute Injury:
    - at initial presentation, PIP may appear to be a swollen & painful;
           - w/ time, manifestations of deformity (PIP flexion, DIP extension) appear;
    - w/ disrupted triangular ligament:
           - patients will not be able to actively extend PIP joint, but will be able to actively hold the PIP in extension, if it is first passively extended;
                 - this occurs because the lateral bands will relocate into their native position w/ PIP extension, allowing pt to hold finger in extension;
           - if it is unclear whether the central slip is disrupted, then test PIP joint extension w/ the wrist and MP joints held in flexion;
                        - this should relax the lateral bands;
    - w/ intact triangular ligament:
           - PIP joint may initially be capable of weak finger extension if the triangular ligament is intact;
           - active extension is possible because the triangular ligament holds the lateral bands in their native posiiton;
    - rupture of central slip must be differentiated from collateral ligament sprain;
           - pt will note tenderness on dorsum of finger rather than sides of joint;
           - loss of active PIP extension when MP is in extension and PIP is placed in 90 deg flexion;
           - weak extension against resistance = central slip injury;
           - extravasation of intra-articular dye dorsal and distal to PIP joint;
           - >15-20 deg loss of active extension at PIP joint w/ wrist & MCP flexed;
    - w/ acute injury the patient should at least be able to passively extend the PIP joint;
           - inability to extend the PIP joint passively, may indicated that the lateral bands have become trapped under the proximal phalanx condyles

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