What is a typical function of sesamoid bones?

• A. Major site of muscle attachment
• B. Protect tendons and act as pulleys that improve the efficiency of a muscle's pull
• C. Form joint surfaces
• D. Provide structural support in the spine

Answer: (B)

Sesamoid bones serve to protect tendons where they pass over joints and to redirect and enhance the pull of a muscle. They’re small bones embedded within tendons in high-friction or high-load areas, and they act like pulleys. By increasing the angle at which the tendon pulls, they raise the effective lever arm, making the muscle’s force more efficient at moving the joint. A classic example is the patella in the quadriceps tendon, which sits in front of the knee and increases the quadriceps’ torque to straighten the leg while reducing tendon wear.

This isn’t about being major attachment sites for muscles, forming joint surfaces, or providing spinal support. Those roles belong to other bones and structures. The protective and pulley-like function of sesamoids is what helps tendons operate more smoothly and powerfully where they pass over joints.