Gross Anatomy Block 2 Practice Test

Lumbricals contribute to which combination of movements at the metacarpophalangeal and interphalangeal joints?

Flexion at the MCP joints and extension at the IP joints Flexion at the MCP joints and flexion at the IP joints Extension at the MCP joints and extension at the IP joints Extension at the MCP joints and flexion at the IP joints

Correct Answer:

Flexion at the MCP joints and extension at the IP joints

Explanation:

Lumbricals adjust finger posture by acting on the extensor mechanism to coordinate motion at the metacarpophalangeal and interphalangeal joints. They originate from the tendon of the flexor digitorum profundus and insert into the dorsal extensor expansions of the digits. When they contract, they pull on that extensor expansion toward the palm, which causes flexion at the MCP joints while, via the extensor mechanism, they produce extension at the IP joints. This combination—MCP flexion with IP extension—allows the finger to maintain a balanced, functional grip. If a choice suggested extension at the MCP joints or flexion at the IP joints, it would not reflect the lumbricals’ typical pull on the extensor mechanism.

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