How does navicular disease affect the stay apparatus function?

• A. It improves load transfer efficiency
• B. It compromises navicular apparatus and distal digital tendon mechanics, reducing load transfer efficiency and increasing pain
• C. It has no effect
• D. It only affects the hind limb

Answer: (B)

Stay apparatus relies on passive structures, including the navicular apparatus and the distal digital flexor tendon, to transfer and distribute load so the horse can stand with minimal muscular effort. When navicular disease affects these tissues, the mechanical function of the navicular apparatus and DDFT becomes disrupted and painful. This reduces the efficiency of load transfer along the digit, making it harder for the limb to bear weight passively and increasing pain and guarding. As a result, the stay apparatus is compromised because the very structures that help keep the limb standing without constant muscular work are impaired.