MSK Individual Readiness Assurance Test (iRAT) Practice Test

The thing being tested is how a distal limb joint is controlled by a specific flexor tendon. In horses, the coffin joint is the distal interphalangeal joint, and the deep digital flexor tendon (together with its muscle) is the primary structure that flexes this joint by pulling on the distal phalanx. If a foal has involvement in this tendon–muscle unit, the coffin joint (the distal interphalangeal joint) is the one most affected, leading to changes in flexion of the toe. The superficial digital flexor tendon mainly influences the proximal interphalangeal joint and is less involved with the coffin joint; the carpus and flexor carpi ulnaris relate to the wrist area, and the stifle joint with the hind limb’s biceps femoris are not involved in the front‑limb distal flexor mechanism. So the combination of the distal interphalangeal joint and the deep digital flexor apparatus best fits the described situation.