We present a method for tuning a photonic crystal microcavity by modulating the index of refraction of the lattice sites within and surrounding the microcavity. The index of refraction can be actively modulated after infiltrating anisotropic liquid crystals into a two-dimensional photonic crystal lattice of air cylinders in silicon. We analyze the Q-factors and resonance frequencies of a tunable photonic crystal microcavity by considering various methods of index modulation. These tunable cavities are incorporated in a channel drop filter to demonstrate their enhancement of wavelength division multiplexing photonic crystal applications.