The deep digital flexor tendon inserts on which structure?

• A. Navicular bone
• B. Proximal phalanx
• C. Extensor process
• D. Semilunar crest of coffin

Answer: (D)

The deep digital flexor tendon attaches to the palmar/solar surface of the distal phalanx at the semilunar crest. This bony ridge on the coffin bone provides the anchor point for the tendon after it wraps around the navicular bone, allowing the digit to flex. The navicular bone acts as a pulley in this area, with a navicular bursa between the tendon and bone, so it isn’t the insertion site itself. The proximal phalanx is not where this tendon attaches, and the extensor process is the insertion point for the long digital extensor tendon on the dorsal side. So the semilunar crest of the coffin is the correct insertion site.