Which of the following is true regarding the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of the digits two through five?

a. They are not true synovial joints.
b. They do not have any collateral ligaments to resist valgus and varus stresses.
c. The proximal articulating surface is larger than the distal articulating surface.
d. They are biaxial joints with two degrees of freedom.

ANS: C
The PIP and DIP joints are true synovial joints with only one degree of freedom. The articular surfaces are supported laterally by collateral ligaments. The volar plate adds to congruency of this joint by adding surface area to the base of the more distal phalanx, which is smaller in size than the head of the more proximal phalanx.