Although considered by many to be a minor injury requiring only simple treatment, this image illustrates how a mallet finger deformity affects the delicate balance of forces in the dorsal apparatus. The limited excursion of the terminal tendon insertion (1-4 mm) offers little tolerance for change of tendon length. Mallet finger complication rate has been documented as high as 45%! (1)
When the terminal tendon insertion lacks continuity or is too long, the remaining central slip insertion receives all of the dorsal apparatus tension created by active finger extension. In hypermobile individuals, this results early in an associated swan neck deformity. Even in those not prone to hyperextension of the PIP joint, the prolonged imbalance of extension forces over time can lead to the associated swan neck deformity.
Knowing a mallet finger injury is a major disruption to the balance of finger motion should lead us to precise DIP immobilization (more than neutral extension in many individuals), blocking of PIP joint hyperextension during DIP immobilization, and a reticence to working too vigorously to regain flexion after immobilization.
- Stern PJ, Kastrup JJ. Complications and prognosis of treatment of mallet finger. J Hand Surg [Am.] 1988;13:329-34.
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