A chair assembly includes a four-bar linkage assembly including a first linkage member and a second linkage member each having a U-shaped cross-sectional configuration that cooperate to form an interior space, a third linkage member and a fourth linkage member, wherein the linkage members are pivotably coupled to on another such that an upper end of the four-bar linkage is vertically adjustable between a raised and lowered positions, an arm rest assembly supported on the upper end of the four-bar linkage assembly, and a locking assembly including a first locking link having a first surface and a second locking link having plurality of teeth corresponding to a plurality of vertical positions of the four-bar link located between the raised and lowered positions, wherein the locking links are movable between locked and unlocked positions, and wherein the first and second locking links are located within the interior space.