To correctly isolate and clinically test the integrity of the Flexor Digitorum Superficialis (FDS) tendon of the ring finger in the presence of an intact Flexor Digitorum Profundus (FDP), the examiner must perform which specific maneuver?

Explanation:
The correct option is c. The FDP tendons of the middle, ring, and small fingers share a common muscle belly in the forearm, making their action highly dependent on one another (the 'quadriga' effect). Conversely, the FDS tendons have independent muscle bellies. By holding the non-tested fingers in forced, rigid extension, the examiner mechanically blocks the entire FDP muscle from firing. This isolates the flexion of the tested digit entirely to its independent FDS tendon. If the FDS is lacerated, the patient will be completely unable to flex the PIP joint during this specific maneuver. Reference: Green's Operative Hand Surgery.