What is the common action of lumbricals and interossei on the fingers?

What is the common action of lumbricals and interossei on the fingers?

• A. Lumbricals flex MP joints and extend IP joints; interossei abduct/adduct fingers
• B. Lumbricals extend MP joints and flex IP joints; interossei move the thumb
• C. Lumbricals abduct digits; interossei flex DIP
• D. Lumbricals and interossei extend the elbow

Answer: (A)

The shared effect of these intrinsic hand muscles is to control the fingers by coordinating movement at the metacarpophalangeal (MCP) and interphalangeal (IP) joints through the extensor mechanism. The lumbricals cause flexion at the MCP joints while extending the IP joints. The interossei primarily abduct or adduct the fingers, but they also contribute to MCP flexion and IP extension via the same extensor mechanism. Therefore, describing lumbricals as flexing the MCP joints and extending the IP joints, while noting that interossei abduct/adduct the digits, best captures their combined actions. Other options describe movements (like thumb motion or elbow extension) or incorrect IP joint actions that aren’t shared by these muscles.

The shared effect of these intrinsic hand muscles is to control the fingers by coordinating movement at the metacarpophalangeal (MCP) and interphalangeal (IP) joints through the extensor mechanism. The lumbricals cause flexion at the MCP joints while extending the IP joints. The interossei primarily abduct or adduct the fingers, but they also contribute to MCP flexion and IP extension via the same extensor mechanism. Therefore, describing lumbricals as flexing the MCP joints and extending the IP joints, while noting that interossei abduct/adduct the digits, best captures their combined actions. Other options describe movements (like thumb motion or elbow extension) or incorrect IP joint actions that aren’t shared by these muscles.