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Anatomy of the Flexor Digitorum Profundus Insertion
Kyle J. Chepla, MD; Robert J. Goitz; John R. Fowler, MD
Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA

Introduction: Treatment of zone I flexor digitorum profundus (FDP) injuries requires reattachment of the tendon to the distal phalanx. Previous studies have evaluated the biomechanical strength of various repair techniques; however, none have described the anatomy of the FDP insertion or the proper location of an anatomic repair. We believe that correct placement of the tendon is essential to better restore native biomechanics and may improve clinical outcomes.

Methods: The FDP insertion to the index, middle, ring and little fingers were dissected in ten fresh-frozen cadavers. The FDP tendon was bluntly dissected off the volar plate, which was elevated from proximal to distal, before the distal phalanx was disarticulated. The distal phalanx was then inked and the FDP was sharply dissected off the bone (Figure 1). The insertion length, width, and distance from the joint of the insertion were measured and then the insertion surface area and centroid of the FDP insertion were calculated.

Results: The average insertion length and width were 6.2 mm (range 5.1-7.0) and 7.9 mm (range 6.9-8.4) respectively. The average surface area of the distal phalanx occupied by the FDP tendon, for all fingers, was 20.1% (range 15.0-26.5) (Table 1). The average distance from the most proximal insertion to the joint surface was 1.2 mm (range 0.4-2.1) with the intervening space occupied by the volar plate insertion, and the calculated distance of the centroid of the FDP insertion from the DIP joint was 3.6 mm (range 2.5-5.1) or approximately 20% of the phalangeal length (Tables 2 and 3).

Conclusions: The percentage of the distal phalanx occupied by the insertion of the FDP tendon into the distal phalanx, the distance of the most proximal FDP insertion from the joint, and the distance from the joint to the centroid of the insertion are fairly consistent in all fingers and not gender specific. Furthermore, the shape of the FDP insertion, widest proximally and tapering distally, was consistent amongst specimens. The findings of this study will allow for proper positioning of the FDP repair on the distal phalanx independent of the technique chosen. It remains to be seen whether this will restore the native biomechanics of the finger and improve patient outcomes.

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