What is the key difference in tendon routing between Flexor Digitorum Superficialis (FDS) and Flexor Digitorum Profundus (FDP)?

What is the key difference in tendon routing between Flexor Digitorum Superficialis (FDS) and Flexor Digitorum Profundus (FDP)?

• A. FDS splits and stops at the PIP; FDP passes through to the DIP
• B. FDS passes through to the DIP; FDP stops at the PIP
• C. FDS and FDP do not interact
• D. FDS passes under the FDP to the DIP

Answer: (A)

The main idea is how the two tendons navigate around each other. The FDS tendon splits into two slips that attach to the sides of the middle phalanx and effectively stops at the proximal interphalangeal joint. The FDP tendon runs deeper and passes through the split in the FDS, continuing to insert on the distal phalanx and crossing the distal interphalangeal joint. This routing lets the FDS flex the PIP while the FDP flexes the DIP, with the FDP threading through the FDS split to reach the fingertip.

The main idea is how the two tendons navigate around each other. The FDS tendon splits into two slips that attach to the sides of the middle phalanx and effectively stops at the proximal interphalangeal joint. The FDP tendon runs deeper and passes through the split in the FDS, continuing to insert on the distal phalanx and crossing the distal interphalangeal joint. This routing lets the FDS flex the PIP while the FDP flexes the DIP, with the FDP threading through the FDS split to reach the fingertip.