SDF and DDF tendons work against which structure to prevent overextension?

• A. Suspensory ligament
• B. Carpal bones
• C. Extensor retinaculum
• D. Lacertus fibrosus

Answer: (D)

The key idea is how the stay apparatus keeps the limb from collapsing under weight by opposing the flexor tendons. The superficial and deep digital flexor tendons are powerful flexors of the fetlock and pastern. To prevent the limb from overflexing or bending too much (or, in this context, to prevent overextension when the limb is bearing weight), a fibrous band called the lacertus fibrosus acts as a check. This band runs from the biceps brachii tendon toward the extensor mechanisms and transmits tension that opposes the pull of the flexor tendons. In effect, it helps lock the limb in a more extended position and stabilizes the joints during weight bearing.

So, the lacertus fibrosus is the structure that the SDF and DDF tendons work against to prevent overextension.