A surgical instrument, comprising: a handle assembly including a first drive member; and an adapter assembly configured to selectively engage the handle assembly, the adapter assembly including: a knob housing; an outer tube extending distally from the knob housing and defining a longitudinal axis; an end effector extending distally from the outer tube, the end effector is movable from a first position where the end effector is aligned with the longitudinal axis, to a second position where the end effector is disposed at an angle relative to the longitudinal axis; an articulation link (86, 88) extending through at least a portion of the outer tube and disposed in mechanical cooperation with the end effector, wherein longitudinal translation of the articulation link relative to the outer tube causes the end effector to move from its first position to its second position; and a sensor assembly including a first portion disposed in mechanical cooperation with the articulation link, and a second portion disposed at least partially within the outer tube, the sensor assembly configured to determine an actual amount of articulation of the end effector based on a distance the articulation link moves longitudinally relative to the outer tube; and characterized in that the adapter assembly includes a ring gear disposed at least partially within the knob housing and in mechanical cooperation with the first drive member when the adapter assembly is engaged with the handle assembly, wherein rotation of the first drive member causes rotation of the ring gear about the longitudinal axis, which causes longitudinal translation of the articulation link. a handle assembly including a first drive member; and an adapter assembly configured to selectively engage the handle assembly, the adapter assembly including: a knob housing; an outer tube extending distally from the knob housing and defining a longitudinal axis; an end effector extending distally from the outer tube, the end effector is movable from a first position where the end effector is aligned with the longitudinal axis, to a second position where the end effector is disposed at an angle relative to the longitudinal axis; an articulation link (86, 88) extending through at least a portion of the outer tube and disposed in mechanical cooperation with the end effector, wherein longitudinal translation of the articulation link relative to the outer tube causes the end effector to move from its first position to its second position; and a sensor assembly including a first portion disposed in mechanical cooperation with the articulation link, and a second portion disposed at least partially within the outer tube, the sensor assembly configured to determine an actual amount of articulation of the end effector based on a distance the articulation link moves longitudinally relative to the outer tube; and characterized in that the adapter assembly includes a ring gear disposed at least partially within the knob housing and in mechanical cooperation with the first drive member when the adapter assembly is engaged with the handle assembly, wherein rotation of the first drive member causes rotation of the ring gear about the longitudinal axis, which causes longitudinal translation of the articulation link. a knob housing; an outer tube extending distally from the knob housing and defining a longitudinal axis; an end effector extending distally from the outer tube, the end effector is movable from a first position where the end effector is aligned with the longitudinal axis, to a second position where the end effector is disposed at an angle relative to the longitudinal axis; an articulation link (86, 88) extending through at least a portion of the outer tube and disposed in mechanical cooperation with the end effector, wherein longitudinal translation of the articulation link relative to the outer tube causes the end effector to move from its first position to its second position; and a sensor assembly including a first portion disposed in mechanical cooperation with the articulation link, and a second portion disposed at least partially within the outer tube, the sensor assembly configured to determine an actual amount of articulation of the end effector based on a distance the articulation link moves longitudinally relative to the outer tube; and characterized in that the adapter assembly includes a ring gear disposed at least partially within the knob housing and in mechanical cooperation with the first drive member when the adapter assembly is engaged with the handle assembly, wherein rotation of the first drive member causes rotation of the ring gear about the longitudinal axis, which causes longitudinal translation of the articulation link.