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Using Lunula Size To Approximate The Location Of The Insertion Of The Terminal Tendon Of The Digital Extensor Mechanism.
Jeff Jett, DO; Marc Trzeciak, DO
Valley Consortium for Medical Education, Modesto, CA
Introduction: Identifying the junction of the terminal tendon (TT) of the digital extensor mechanism and proximal aspect of the germinal matrix can be challenging. We tested the hypothesis that doubling the lunula distance would give a good approximation of this transition zone.
Materials and Methods: Twenty phalanges from five fresh frozen cadaver specimens were dissected along the dorsal surface over the distal interphalangeal joint. The terminal tendon of the digital extensor mechanism was identified and the distance proximal to the lunula was recorded. The size of the lunula was then measured from proximal to distal.
Results: Twenty phalanges were dissected in total (5 index, 5 long, 5 ring, and 5 small fingers). The average distance from the proximal end of the lunula to TT insertion was 5.8 mm (Index = 5.6 mm, long = 5.8 mm, ring = 6 mm, small = 5.6 mm). Average size of the lunula was 2.65 mm (Index = 2.6 mm, long = 2.6 mm, ring = 2.6 mm, small = 2.8 mm). The average ratio of TT insertion to lunula size was 2.19 (Index = 2.15, long = 2.23, ring = 2.3, small = 2.0).
Conclusion: The size of the lunula may be used as a guide to the site of the insertion of the digital extensor TT. By doubling the size of the visible lunula, one may estimate the point of TT insertion.
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