Which of the following muscles act as strong interphalangeal (proximal interphalangeal [PIP] and distal interphalangeal [DIP]) extensors and weak metacarpophalangeal (MCP) flexors?
a. Interossei
b. Extensor indicis
c. Lumbricales
d. Oblique retinacular ligaments
ANS: C
Both the interossei and lumbricales provide flexion at the MCP joint. However, due to the greater moment arm of the interossei at this joint, they are better at providing flexion force at the MCP joint. The lumbricales have a more distal insertion on the lateral band to the profundus tendon and therefore exert a great force at the PIP and DIP joints.
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Fill in the blank(s) with the appropriate word(s).